diff --git a/clang/test/ClangScanDeps/cas-fs-prefix-mapping.c b/clang/test/ClangScanDeps/cas-fs-prefix-mapping.c
index 3f3c6dfbe6857..134032e050271 100644
--- a/clang/test/ClangScanDeps/cas-fs-prefix-mapping.c
+++ b/clang/test/ClangScanDeps/cas-fs-prefix-mapping.c
@@ -4,21 +4,21 @@
 // REQUIRES: ondisk_cas
 // RUN: rm -rf %t
 // RUN: split-file %s %t
-// RUN: sed -e "s|DIR|%t|g" -e "s|CLANG|%clang|g" -e "s|SDK|%S/Inputs/SDK|g" %t/cdb.json.template > %t/cdb.json
+// RUN: sed -e "s|DIR|%/t|g" -e "s|CLANG|%/ncclang|g" -e "s|SDK|%/S/Inputs/SDK|g" %t/cdb.json.template > %t/cdb.json
 
 // == Tree
 // Ensure the filesystem has the mapped paths.
 
 // RUN: clang-scan-deps -compilation-database %t/cdb.json -format experimental-tree -cas-path %t/cas \
-// RUN:    -prefix-map=%t=/^src -prefix-map-sdk=/^sdk -prefix-map-toolchain=/^tc \
+// RUN:    -prefix-map=%t=%/root^src -prefix-map-sdk=%/root^sdk -prefix-map-toolchain=%/root^tc \
 // RUN:  | sed -E 's/tree ([^ ]+) for.*/\1/' > %t/tree_id.txt
 // RUN: llvm-cas -cas %t/cas -ls-tree-recursive @%t/tree_id.txt > %t/tree_result.txt
-// RUN: FileCheck %s -input-file %t/tree_result.txt -check-prefix=FILES
+// RUN: FileCheck %s -input-file %t/tree_result.txt -DROOT=%{/roott} -check-prefix=FILES
 
-// FILES: file llvmcas://{{.*}} /^sdk/usr/include/stdlib.h
-// FILES: file llvmcas://{{.*}} /^src/t.c
-// FILES: file llvmcas://{{.*}} /^src/top.h
-// FILES: file llvmcas://{{.*}} /^tc/lib/clang/{{.*}}/include/stdarg.h
+// FILES: file llvmcas://{{.*}} [[ROOT]]^sdk/usr/include/stdlib.h
+// FILES: file llvmcas://{{.*}} [[ROOT]]^src/t.c
+// FILES: file llvmcas://{{.*}} [[ROOT]]^src/top.h
+// FILES: file llvmcas://{{.*}} [[ROOT]]^tc/lib/clang/{{.*}}/include/stdarg.h
 
 // == Full Tree
 // This should have the same filesystem as above, and we also check the command-
@@ -26,18 +26,18 @@
 
 // RUN: cat %t/tree_id.txt > %t/full_tree_result.txt
 // RUN: clang-scan-deps -compilation-database %t/cdb.json -format experimental-tree-full -cas-path %t/cas \
-// RUN:    -prefix-map=%t=/^src -prefix-map-sdk=/^sdk -prefix-map-toolchain=/^tc \
+// RUN:    -prefix-map=%t=%/root^src -prefix-map-sdk=%/root^sdk -prefix-map-toolchain=%/root^tc \
 // RUN:  >> %t/full_tree_result.txt
-// RUN: FileCheck %s -input-file %t/full_tree_result.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK
+// RUN: cat %t/full_tree_result.txt | %PathSanitizingFileCheck --sanitize PREFIX=%/t --sanitize SDK_PREFIX=%/S/Inputs/SDK --sanitize ROOT^=%/root^ --enable-yaml-compatibility %s
 
 // == Full
 // Same as full tree.
 
 // RUN: cat %t/tree_id.txt > %t/full_result.txt
 // RUN: clang-scan-deps -compilation-database %t/cdb.json -format experimental-full -cas-path %t/cas \
-// RUN:    -prefix-map=%t=/^src -prefix-map-sdk=/^sdk -prefix-map-toolchain=/^tc \
+// RUN:    -prefix-map=%t=%/root^src -prefix-map-sdk=%/root^sdk -prefix-map-toolchain=%/root^tc \
 // RUN:  >> %t/full_result.txt
-// RUN: FileCheck %s -input-file %t/full_result.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK
+// RUN: cat %t/full_result.txt | %PathSanitizingFileCheck --sanitize PREFIX=%/t --sanitize SDK_PREFIX=%/S/Inputs/SDK --sanitize ROOT^=%/root^ --enable-yaml-compatibility %s
 
 // CHECK: [[MAPPED_FS_ID:llvmcas://[[:xdigit:]]+]]
 // CHECK:      "modules": []
@@ -49,36 +49,36 @@
 // CHECK:              "clang-module-deps": []
 // CHECK:              "command-line": [
 // CHECK:                "-fcas-path"
-// CHECK-NEXT:           "[[PREFIX]]/cas"
+// CHECK-NEXT:           "PREFIX{{/|\\\\}}cas"
 // CHECK:                "-fcas-fs"
 // CHECK-NEXT:           "[[MAPPED_FS_ID]]"
 // CHECK:                "-fcas-fs-working-directory"
-// CHECK-NEXT:           "/^src"
+// CHECK-NEXT:           "ROOT^src"
 // CHECK:                "-x"
 // CHECK-NEXT:           "c"
-// CHECK-NEXT:           "/^src/t.c"
+// CHECK-NEXT:           "ROOT^src{{/|\\\\}}t.c"
 // CHECK:                "-isysroot"
-// CHECK-NEXT:           "/^sdk"
+// CHECK-NEXT:           "ROOT^sdk"
 // CHECK:                "-resource-dir"
-// CHECK-NEXT:           "/^tc/lib/clang/{{.*}}"
+// CHECK-NEXT:           "ROOT^tc{{/|\\\\}}lib{{/|\\\\}}clang{{/|\\\\}}{{.*}}"
 // CHECK:                "-isystem"
-// CHECK-NEXT:           "/^sdk/usr/local/include
+// CHECK-NEXT:           "ROOT^sdk{{/|\\\\}}usr{{/|\\\\}}local{{/|\\\\}}include
 // CHECK:                "-isystem"
-// CHECK-NEXT:           "/^tc/lib/clang/{{.*}}/include"
+// CHECK-NEXT:           "ROOT^tc{{/|\\\\}}lib{{/|\\\\}}clang{{/|\\\\}}{{.*}}{{/|\\\\}}include"
 // CHECK:                "-internal-externc-isystem"
-// CHECK-NEXT:           "/^sdk/usr/include"
-// CHECK:                "-fdebug-compilation-dir=/^src"
-// CHECK:                "-fcoverage-compilation-dir=/^src"
-// CHECK-NOT: [[PREFIX]]
-// CHECK-NOT: [[SDK_PREFIX]]
+// CHECK-NEXT:           "ROOT^sdk{{/|\\\\}}usr{{/|\\\\}}include"
+// CHECK:                "-fdebug-compilation-dir=ROOT^src"
+// CHECK:                "-fcoverage-compilation-dir=ROOT^src"
+// CHECK-NOT: PREFIX
+// CHECK-NOT: SDK_PREFIX
 // CHECK:              ]
 // CHECK:              "file-deps": [
-// CHECK:                "[[PREFIX]]/t.c"
-// CHECK:                "[[PREFIX]]/top.h"
-// CHECK:                "{{.*}}include/stdarg.h"
-// CHECK:                "[[SDK_PREFIX]]/usr/include/stdlib.h"
+// CHECK:                "PREFIX{{/|\\\\}}t.c"
+// CHECK:                "PREFIX{{/|\\\\}}top.h"
+// CHECK:                "{{.*}}include{{/|\\\\}}stdarg.h"
+// CHECK:                "SDK_PREFIX{{/|\\\\}}usr{{/|\\\\}}include{{/|\\\\}}stdlib.h"
 // CHECK:              ]
-// CHECK:              "input-file": "[[PREFIX]]/t.c"
+// CHECK:              "input-file": "PREFIX{{/|\\\\}}t.c"
 
 //--- cdb.json.template
 [
diff --git a/clang/test/ClangScanDeps/include-tree-prefix-mapping-pch-remap.c b/clang/test/ClangScanDeps/include-tree-prefix-mapping-pch-remap.c
index 8c379ef60014d..d117fa5ffadf2 100644
--- a/clang/test/ClangScanDeps/include-tree-prefix-mapping-pch-remap.c
+++ b/clang/test/ClangScanDeps/include-tree-prefix-mapping-pch-remap.c
@@ -1,11 +1,11 @@
 // REQUIRES: ondisk_cas
 // RUN: rm -rf %t
 // RUN: split-file %s %t
-// RUN: sed -e "s|DIR|%t|g" %t/cdb.json.template > %t/cdb.json
+// RUN: sed -e "s|DIR|%/t|g" %t/cdb.json.template > %t/cdb.json
 
 // RUN: clang-scan-deps -compilation-database %t/cdb.json \
 // RUN:   -format experimental-include-tree-full -cas-path %t/cas \
-// RUN:   -prefix-map=%t=/^src -prefix-map-sdk=/^sdk -prefix-map-toolchain=/^tc > %t/deps.json
+// RUN:   -prefix-map=%t=%/root^src -prefix-map-sdk=%/root^sdk -prefix-map-toolchain=%/root^tc > %t/deps.json
 
 //--- cdb.json.template
 [{
diff --git a/clang/test/ClangScanDeps/include-tree-prefix-mapping.c b/clang/test/ClangScanDeps/include-tree-prefix-mapping.c
index e0842a7be6b98..a61c9e00b94be 100644
--- a/clang/test/ClangScanDeps/include-tree-prefix-mapping.c
+++ b/clang/test/ClangScanDeps/include-tree-prefix-mapping.c
@@ -1,33 +1,33 @@
 // REQUIRES: ondisk_cas
 // RUN: rm -rf %t
 // RUN: split-file %s %t
-// RUN: sed -e "s|DIR|%t|g" -e "s|CLANG|%clang|g" -e "s|SDK|%S/Inputs/SDK|g" %t/cdb.json.template > %t/cdb.json
+// RUN: sed -e "s|DIR|%/t|g" -e "s|CLANG|%/ncclang|g" -e "s|SDK|%/S/Inputs/SDK|g" %t/cdb.json.template > %t/cdb.json
 
 // RUN: clang-scan-deps -compilation-database %t/cdb.json -format experimental-include-tree -cas-path %t/cas \
-// RUN:   -prefix-map=%t=/^src -prefix-map-sdk=/^sdk -prefix-map-toolchain=/^tc > %t/result.txt
-// RUN: FileCheck %s -input-file %t/result.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK
+// RUN:   -prefix-map=%t=%/root^src -prefix-map-sdk=%/root^sdk -prefix-map-toolchain=%/root^tc > %t/result.txt
+// RUN: cat %t/result.txt | %PathSanitizingFileCheck --sanitize PREFIX=%/t --sanitize SDK_PREFIX=%/S/Inputs/SDK --sanitize ROOT^=%/root^ %s
 
-// CHECK:      {{.*}} - [[PREFIX]]/t.c
-// CHECK-NOT: [[PREFIX]]
-// CHECK-NOT: [[SDK_PREFIX]]
-// CHECK: /^src{{[/\\]}}t.c
-// CHECK: /^src{{[/\\]}}top.h
-// CHECK: /^tc{{[/\\]}}lib{{[/\\]}}clang{{[/\\]}}{{.*}}{{[/\\]}}include{{[/\\]}}stdarg.h
-// CHECK: /^sdk{{[/\\]}}usr{{[/\\]}}include{{[/\\]}}stdlib.h
+// CHECK:      {{.*}} - PREFIX{{/|\\}}t.c
+// CHECK-NOT: PREFIX
+// CHECK-NOT: SDK_PREFIX
+// CHECK: ROOT^src{{[/\\]}}t.c
+// CHECK: ROOT^src{{[/\\]}}top.h
+// CHECK: ROOT^tc{{[/\\]}}lib{{[/\\]}}clang{{[/\\]}}{{.*}}{{[/\\]}}include{{[/\\]}}stdarg.h
+// CHECK: ROOT^sdk{{[/\\]}}usr{{[/\\]}}include{{[/\\]}}stdlib.h
 
 // RUN: clang-scan-deps -compilation-database %t/cdb.json \
 // RUN:   -format experimental-include-tree-full -cas-path %t/cas \
-// RUN:   -prefix-map=%t=/^src -prefix-map-sdk=/^sdk -prefix-map-toolchain=/^tc > %t/deps.json
+// RUN:   -prefix-map=%t=%/root^src -prefix-map-sdk=%/root^sdk -prefix-map-toolchain=%/root^tc > %t/deps.json
 
 // RUN: cat %t/result.txt > %t/full.txt
 // RUN: echo "FULL DEPS START" >> %t/full.txt
-// RUN: cat %t/deps.json | sed 's:\\\\\?:/:g' >> %t/full.txt
+// RUN: cat %t/deps.json >> %t/full.txt
 
-// RUN: FileCheck %s -DPREFIX=%/t -DSDK_PREFIX=%S/Inputs/SDK -check-prefix=FULL -input-file %t/full.txt
+// RUN: cat %t/full.txt | %PathSanitizingFileCheck --sanitize PREFIX=%/t --sanitize SDK_PREFIX=%/S/Inputs/SDK --sanitize ROOT^=%/root^ --enable-yaml-compatibility %s -check-prefix=FULL
 
 // Capture the tree id from experimental-include-tree ; ensure that it matches
 // the result from experimental-full.
-// FULL: [[TREE_ID:llvmcas://[[:xdigit:]]+]] - [[PREFIX]]/t.c
+// FULL: [[TREE_ID:llvmcas://[[:xdigit:]]+]] - PREFIX{{/|\\}}t.c
 // FULL: FULL DEPS START
 
 // FULL-NEXT: {
@@ -40,7 +40,7 @@
 // FULL:                "command-line": [
 // FULL-NEXT:             "-cc1"
 // FULL:                  "-fcas-path"
-// FULL-NEXT:             "[[PREFIX]]/cas"
+// FULL-NEXT:             "PREFIX{{/|\\\\}}cas"
 // FULL:                  "-disable-free"
 // FULL:                  "-fcas-include-tree"
 // FULL-NEXT:             "[[TREE_ID]]"
@@ -49,15 +49,15 @@
 // FULL:                  "-x"
 // FULL-NEXT:             "c"
 // FULL:                  "-isysroot"
-// FULL-NEXT:             "/^sdk"
+// FULL-NEXT:             "ROOT^sdk"
 // FULL:                ]
 // FULL:                "file-deps": [
-// FULL-DAG:              "[[PREFIX]]/t.c"
-// FULL-DAG:              "[[PREFIX]]/top.h"
-// FULL-DAG:              "{{.*}}/stdarg.h"
-// FULL-DAG:              "[[SDK_PREFIX]]/usr/include/stdlib.h"
+// FULL-DAG:              "PREFIX{{/|\\\\}}t.c"
+// FULL-DAG:              "PREFIX{{/|\\\\}}top.h"
+// FULL-DAG:              "{{.*}}{{/|\\\\}}stdarg.h"
+// FULL-DAG:              "SDK_PREFIX{{/|\\\\}}usr{{/|\\\\}}include{{/|\\\\}}stdlib.h"
 // FULL:                ]
-// FULL:                "input-file": "[[PREFIX]]/t.c"
+// FULL:                "input-file": "PREFIX{{/|\\\\}}t.c"
 // FULL:              }
 // FULL:            ]
 // FULL:          }
diff --git a/clang/test/ClangScanDeps/modules-cas-fs-prefix-mapping-caching.c b/clang/test/ClangScanDeps/modules-cas-fs-prefix-mapping-caching.c
index 230b21b83fae7..064d9f0d20783 100644
--- a/clang/test/ClangScanDeps/modules-cas-fs-prefix-mapping-caching.c
+++ b/clang/test/ClangScanDeps/modules-cas-fs-prefix-mapping-caching.c
@@ -5,19 +5,19 @@
 // RUN: rm -rf %t
 // RUN: split-file %s %t
 // RUN: cp -r %t/dir1 %t/dir2
-// RUN: sed -e "s|DIR|%t/dir1|g" -e "s|CLANG|%clang|g" -e "s|SDK|%S/Inputs/SDK|g" %t/cdb.json.template > %t/dir1/cdb.json
-// RUN: sed -e "s|DIR|%t/dir2|g" -e "s|CLANG|%clang|g" -e "s|SDK|%S/Inputs/SDK|g" %t/cdb.json.template > %t/dir2/cdb.json
+// RUN: sed -e "s|DIR|%/t/dir1|g" -e "s|CLANG|%/ncclang|g" -e "s|SDK|%/S/Inputs/SDK|g" %t/cdb.json.template > %t/dir1/cdb.json
+// RUN: sed -e "s|DIR|%/t/dir2|g" -e "s|CLANG|%/ncclang|g" -e "s|SDK|%/S/Inputs/SDK|g" %t/cdb.json.template > %t/dir2/cdb.json
 
 // RUN: clang-scan-deps -compilation-database %t/dir1/cdb.json -format experimental-full \
 // RUN:    -cas-path %t/cas -module-files-dir %t/dir1/modules \
-// RUN:    -prefix-map-sdk=/^sdk -prefix-map-toolchain=/^tc \
-// RUN:    -prefix-map=%t/dir1/modules=/^modules -prefix-map=%t/dir1=/^src -optimize-args=none \
+// RUN:    -prefix-map-sdk=%/root^sdk -prefix-map-toolchain=%/root^tc \
+// RUN:    -prefix-map=%t/dir1/modules=%/root^modules -prefix-map=%t/dir1=%/root^src -optimize-args=none \
 // RUN:  > %t/dir1.txt
 
 // RUN: clang-scan-deps -compilation-database %t/dir2/cdb.json -format experimental-full \
 // RUN:    -cas-path %t/cas -module-files-dir %t/dir2/modules \
-// RUN:    -prefix-map-sdk=/^sdk -prefix-map-toolchain=/^tc \
-// RUN:    -prefix-map=%t/dir2/modules=/^modules -prefix-map=%t/dir2=/^src -optimize-args=none \
+// RUN:    -prefix-map-sdk=%/root^sdk -prefix-map-toolchain=%/root^tc \
+// RUN:    -prefix-map=%t/dir2/modules=%/root^modules -prefix-map=%t/dir2=%/root^src -optimize-args=none \
 // RUN:  > %t/dir2.txt
 
 // Extract individual commands.
@@ -29,15 +29,21 @@
 // RUN: %deps-to-rsp %t/dir2.txt --module-name=A > %t/dir2/A.cc1.rsp
 // RUN: %deps-to-rsp %t/dir2.txt --tu-index 0 > %t/dir2/tu.cc1.rsp
 
-// RUN: (cd %t/dir1; %clang @B.cc1.rsp) 2>&1 | FileCheck %s -check-prefix=CACHE-MISS
-// RUN: (cd %t/dir1; %clang @A.cc1.rsp) 2>&1 | FileCheck %s -check-prefix=CACHE-MISS
-// RUN: (cd %t/dir1; %clang @tu.cc1.rsp) 2>&1 | FileCheck %s -check-prefix=CACHE-MISS
+// RUN: cd %t/dir1 && %clang @B.cc1.rsp > %t/miss-B.txt 2>&1
+// RUN: cat %t/miss-B.txt | FileCheck %s -check-prefix=CACHE-MISS
+// RUN: cd %t/dir1 && %clang @A.cc1.rsp > %t/miss-A.txt 2>&1
+// RUN: cat %t/miss-A.txt | FileCheck %s -check-prefix=CACHE-MISS
+// RUN: cd %t/dir1 && %clang @tu.cc1.rsp > %t/miss-tu.txt 2>&1
+// RUN: cat %t/miss-tu.txt | FileCheck %s -check-prefix=CACHE-MISS
 
 // CACHE-MISS: compile job cache miss
 
-// RUN: (cd %t/dir2; %clang @B.cc1.rsp) 2>&1 | FileCheck %s -check-prefix=CACHE-HIT
-// RUN: (cd %t/dir2; %clang @A.cc1.rsp) 2>&1 | FileCheck %s -check-prefix=CACHE-HIT
-// RUN: (cd %t/dir2; %clang @tu.cc1.rsp) 2>&1 | FileCheck %s -check-prefix=CACHE-HIT
+// RUN: cd %t/dir2 && %clang @B.cc1.rsp > %t/hit-B.txt 2>&1
+// RUN: cat %t/hit-B.txt | FileCheck %s -check-prefix=CACHE-HIT
+// RUN: cd %t/dir2 && %clang @A.cc1.rsp > %t/hit-A.txt 2>&1
+// RUN: cat %t/hit-B.txt | FileCheck %s -check-prefix=CACHE-HIT
+// RUN: cd %t/dir2 && %clang @tu.cc1.rsp > %t/hit-tu.txt 2>&1
+// RUN: cat %t/hit-tu.txt | FileCheck %s -check-prefix=CACHE-HIT
 
 // CACHE-HIT: compile job cache hit
 
diff --git a/clang/test/ClangScanDeps/modules-cas-fs-prefix-mapping.c b/clang/test/ClangScanDeps/modules-cas-fs-prefix-mapping.c
index 24190438079f4..63892d1a87595 100644
--- a/clang/test/ClangScanDeps/modules-cas-fs-prefix-mapping.c
+++ b/clang/test/ClangScanDeps/modules-cas-fs-prefix-mapping.c
@@ -5,15 +5,15 @@
 
 // RUN: rm -rf %t
 // RUN: split-file %s %t
-// RUN: sed -e "s|DIR|%t|g" -e "s|CLANG|%clang|g" -e "s|SDK|%S/Inputs/SDK|g" %t/cdb.json.template > %t/cdb.json
+// RUN: sed -e "s|DIR|%/t|g" -e "s|CLANG|%/ncclang|g" -e "s|SDK|%/S/Inputs/SDK|g" %t/cdb.json.template > %t/cdb.json
 
 // RUN: clang-scan-deps -compilation-database %t/cdb.json -format experimental-full \
 // RUN:    -cas-path %t/cas -module-files-dir %t/modules \
-// RUN:    -prefix-map=%t/modules=/^modules -prefix-map=%t=/^src -prefix-map-sdk=/^sdk -prefix-map-toolchain=/^tc \
+// RUN:    -prefix-map=%t/modules=%/root^modules -prefix-map=%t=%/root^src -prefix-map-sdk=%/root^sdk -prefix-map-toolchain=%/root^tc \
 // RUN:  > %t/full_result.txt
 
 // Check the command-lines.
-// RUN: FileCheck %s -input-file %t/full_result.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK
+// RUN: cat %t/full_result.txt | %PathSanitizingFileCheck --sanitize PREFIX=%/t --sanitize SDK_PREFIX=%/S/Inputs/SDK --sanitize ROOT^=%/root^ --enable-yaml-compatibility %s
 
 // Extract individual commands.
 // RUN: %deps-to-rsp %t/full_result.txt --module-name=B > %t/B.cc1.rsp
@@ -27,18 +27,18 @@
 // RUN: llvm-cas -cas %t/cas -ls-tree-recursive @%t/B_id.txt > %t/B_fs.txt
 // RUN: llvm-cas -cas %t/cas -ls-tree-recursive @%t/A_id.txt > %t/A_fs.txt
 // RUN: llvm-cas -cas %t/cas -ls-tree-recursive @%t/tu_id.txt > %t/tu_fs.txt
-// RUN: FileCheck %s -input-file %t/A_fs.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK -check-prefixes=FS_NEG,FS
-// RUN: FileCheck %s -input-file %t/B_fs.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK -check-prefixes=FS_NEG,FS
-// RUN: FileCheck %s -input-file %t/tu_fs.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK -check-prefixes=FS_NEG,FS
+// RUN: FileCheck %s -input-file %t/A_fs.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK -DROOT=%{/roott} -check-prefixes=FS_NEG,FS
+// RUN: FileCheck %s -input-file %t/B_fs.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK -DROOT=%{/roott} -check-prefixes=FS_NEG,FS
+// RUN: FileCheck %s -input-file %t/tu_fs.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK -DROOT=%{/roott} -check-prefixes=FS_NEG,FS
 
 // FS_NEG-NOT: [[PREFIX]]
 // FS_NEG-NOT: [[SDK_PREFIX]]
 // FS_NEG-NOT: .pcm{{$}}
-// FS: file llvmcas://{{.*}} /^sdk/usr/include/stdlib.h
-// FS: file llvmcas://{{.*}} /^src/a.h
-// FS: file llvmcas://{{.*}} /^src/b.h
-// FS: file llvmcas://{{.*}} /^src/module.modulemap
-// FS: file llvmcas://{{.*}} /^tc/lib/clang/{{.*}}/include/stdarg.h
+// FS: file llvmcas://{{.*}} [[ROOT]]^sdk/usr/include/stdlib.h
+// FS: file llvmcas://{{.*}} [[ROOT]]^src/a.h
+// FS: file llvmcas://{{.*}} [[ROOT]]^src/b.h
+// FS: file llvmcas://{{.*}} [[ROOT]]^src/module.modulemap
+// FS: file llvmcas://{{.*}} [[ROOT]]^tc/lib/clang/{{.*}}/include/stdarg.h
 
 // Check that it builds.
 // RUN: %clang @%t/B.cc1.rsp
@@ -54,71 +54,71 @@
 // CHECK:                "module-name": "B"
 // CHECK:              }
 // CHECK:            ]
-// CHECK:            "clang-modulemap-file": "[[PREFIX]]/module.modulemap"
+// CHECK:            "clang-modulemap-file": "PREFIX{{/|\\\\}}module.modulemap"
 // CHECK:            "command-line": [
 // CHECK:              "-fcas-path"
-// CHECK:              "[[PREFIX]]/cas"
+// CHECK:              "PREFIX{{/|\\\\}}cas"
 // CHECK:              "-fcas-fs"
 // CHECK:              "[[A_ROOT_ID]]"
 // CHECK:              "-fcas-fs-working-directory"
-// CHECK:              "/^src"
-// CHECK:              "-fmodule-map-file=/^src/module.modulemap"
+// CHECK:              "ROOT^src"
+// CHECK:              "-fmodule-map-file=ROOT^src{{/|\\\\}}module.modulemap"
 // CHECK:              "-o"
-// CHECK:              "[[PREFIX]]/modules/{{.*}}/A-{{.*}}.pcm"
+// CHECK:              "PREFIX{{/|\\\\}}modules{{/|\\\\}}{{.*}}{{/|\\\\}}A-{{.*}}.pcm"
 // CHECK:              "-fmodule-file-cache-key"
-// CHECK:              "/^modules/{{.*}}/B-[[B_CONTEXT_HASH:[^.]+]].pcm"
+// CHECK:              "ROOT^modules{{/|\\\\}}{{.*}}{{/|\\\\}}B-[[B_CONTEXT_HASH:[^.]+]].pcm"
 // CHECK:              "llvmcas://{{.*}}"
 // CHECK:              "-x"
 // CHECK:              "c"
-// CHECK:              "/^src/module.modulemap"
+// CHECK:              "ROOT^src{{/|\\\\}}module.modulemap"
 // CHECK:              "-isysroot"
-// CHECK:              "/^sdk"
+// CHECK:              "ROOT^sdk"
 // CHECK:              "-resource-dir"
-// CHECK:              "/^tc/lib/clang/{{.*}}"
-// CHECK:              "-fmodule-file=B=/^modules/{{.*}}/B-[[B_CONTEXT_HASH]].pcm"
+// CHECK:              "ROOT^tc{{/|\\\\}}lib{{/|\\\\}}clang{{/|\\\\}}{{.*}}"
+// CHECK:              "-fmodule-file=B=ROOT^modules{{/|\\\\}}{{.*}}{{/|\\\\}}B-[[B_CONTEXT_HASH]].pcm"
 // CHECK:              "-isystem"
-// CHECK:              "/^tc/lib/clang/{{.*}}/include"
+// CHECK:              "ROOT^tc{{/|\\\\}}lib{{/|\\\\}}clang{{/|\\\\}}{{.*}}{{/|\\\\}}include"
 // CHECK:              "-internal-externc-isystem"
-// CHECK:              "/^sdk/usr/include"
+// CHECK:              "ROOT^sdk{{/|\\\\}}usr{{/|\\\\}}include"
 // CHECK:            ]
 // CHECK:            "file-deps": [
-// CHECK:              "[[PREFIX]]/module.modulemap"
-// CHECK:              "[[PREFIX]]/a.h"
+// CHECK:              "PREFIX{{/|\\\\}}module.modulemap"
+// CHECK:              "PREFIX{{/|\\\\}}a.h"
 // CHECK:            ]
 // CHECK:            "name": "A"
 // CHECK:          }
 // CHECK:          {
 // CHECK:            "casfs-root-id": "[[B_ROOT_ID:llvmcas://[[:xdigit:]]+]]"
 // CHECK:            "clang-module-deps": [],
-// CHECK:            "clang-modulemap-file": "[[PREFIX]]/module.modulemap"
+// CHECK:            "clang-modulemap-file": "PREFIX{{/|\\\\}}module.modulemap"
 // CHECK:            "command-line": [
 // CHECK:              "-fcas-path"
-// CHECK:              "[[PREFIX]]/cas"
+// CHECK:              "PREFIX{{/|\\\\}}cas"
 // CHECK:              "-fcas-fs"
 // CHECK:              "[[B_ROOT_ID]]"
 // CHECK:              "-fcas-fs-working-directory"
-// CHECK:              "/^src"
+// CHECK:              "ROOT^src"
 // CHECK:              "-o"
-// CHECK:              "[[PREFIX]]/modules/{{.*}}/B-[[B_CONTEXT_HASH]].pcm"
+// CHECK:              "PREFIX{{/|\\\\}}modules{{/|\\\\}}{{.*}}{{/|\\\\}}B-[[B_CONTEXT_HASH]].pcm"
 // CHECK:              "-x"
 // CHECK:              "c"
-// CHECK:              "/^src/module.modulemap"
+// CHECK:              "ROOT^src{{/|\\\\}}module.modulemap"
 // CHECK:              "-isysroot"
-// CHECK:              "/^sdk"
+// CHECK:              "ROOT^sdk"
 // CHECK:              "-resource-dir"
-// CHECK:              "/^tc/lib/clang/{{.*}}"
+// CHECK:              "ROOT^tc{{/|\\\\}}lib{{/|\\\\}}clang{{/|\\\\}}{{.*}}"
 // CHECK:              "-isystem"
-// CHECK:              "/^tc/lib/clang/{{.*}}/include"
+// CHECK:              "ROOT^tc{{/|\\\\}}lib{{/|\\\\}}clang{{/|\\\\}}{{.*}}{{/|\\\\}}include"
 // CHECK:              "-internal-externc-isystem"
-// CHECK:              "/^sdk/usr/include"
+// CHECK:              "ROOT^sdk{{/|\\\\}}usr{{/|\\\\}}include"
 // CHECK:            ]
 // CHECK:            "context-hash": "[[B_CONTEXT_HASH]]"
 // CHECK:            "file-deps": [
 // Note: PREFIX, SDK_PREFIX and toolchain path are unordered
-// CHECK-DAG:          "[[PREFIX]]/module.modulemap"
-// CHECK-DAG:          "[[PREFIX]]/b.h"
-// CHECK-DAG:          "{{.*}}/include/stdarg.h"
-// CHECK-DAG:          "[[SDK_PREFIX]]/usr/include/stdlib.h"
+// CHECK-DAG:          "PREFIX{{/|\\\\}}module.modulemap"
+// CHECK-DAG:          "PREFIX{{/|\\\\}}b.h"
+// CHECK-DAG:          "{{.*}}{{/|\\\\}}include{{/|\\\\}}stdarg.h"
+// CHECK-DAG:          "SDK_PREFIX{{/|\\\\}}usr{{/|\\\\}}include{{/|\\\\}}stdlib.h"
 // CHECK:            ]
 // CHECK:            "name": "B"
 // CHECK:          }
@@ -135,32 +135,32 @@
 // CHECK:                ]
 // CHECK:                "command-line": [
 // CHECK:                  "-fcas-path"
-// CHECK:                  "[[PREFIX]]/cas"
+// CHECK:                  "PREFIX{{/|\\\\}}cas"
 // CHECK:                  "-fcas-fs"
 // CHECK:                  "[[TU_ROOT_ID]]"
 // CHECK:                  "-fcas-fs-working-directory"
-// CHECK:                  "/^src"
-// CHECK:                  "-fmodule-map-file=/^src/module.modulemap"
+// CHECK:                  "ROOT^src"
+// CHECK:                  "-fmodule-map-file=ROOT^src{{/|\\\\}}module.modulemap"
 // CHECK:                  "-fmodule-file-cache-key"
-// CHECK:                  "/^modules/{{.*}}A-{{.*}}.pcm"
+// CHECK:                  "ROOT^modules{{/|\\\\}}{{.*}}A-{{.*}}.pcm"
 // CHECK:                  "llvmcas://{{.*}}"
 // CHECK:                  "-x"
 // CHECK:                  "c"
-// CHECK:                  "/^src/t.c"
+// CHECK:                  "ROOT^src{{/|\\\\}}t.c"
 // CHECK:                  "-isysroot"
-// CHECK:                  "/^sdk"
+// CHECK:                  "ROOT^sdk"
 // CHECK:                  "-resource-dir"
-// CHECK:                  "/^tc/lib/clang/{{.*}}"
-// CHECK:                  "-fmodule-file=A=/^modules/{{.*}}/A-{{.*}}.pcm"
+// CHECK:                  "ROOT^tc{{/|\\\\}}lib{{/|\\\\}}clang{{/|\\\\}}{{.*}}"
+// CHECK:                  "-fmodule-file=A=ROOT^modules{{/|\\\\}}{{.*}}{{/|\\\\}}A-{{.*}}.pcm"
 // CHECK:                  "-isystem"
-// CHECK:                  "/^tc/lib/clang/{{.*}}/include"
+// CHECK:                  "ROOT^tc{{/|\\\\}}lib{{/|\\\\}}clang{{/|\\\\}}{{.*}}{{/|\\\\}}include"
 // CHECK:                  "-internal-externc-isystem"
-// CHECK:                  "/^sdk/usr/include"
+// CHECK:                  "ROOT^sdk{{/|\\\\}}usr{{/|\\\\}}include"
 // CHECK:                ],
 // CHECK:                "file-deps": [
-// CHECK:                  "[[PREFIX]]/t.c"
+// CHECK:                  "PREFIX{{/|\\\\}}t.c"
 // CHECK:                ]
-// CHECK:                "input-file": "[[PREFIX]]/t.c"
+// CHECK:                "input-file": "PREFIX{{/|\\\\}}t.c"
 // CHECK:              }
 
 
diff --git a/clang/test/ClangScanDeps/modules-include-tree-prefix-map.c b/clang/test/ClangScanDeps/modules-include-tree-prefix-map.c
index 8eb7da7be4bea..cde604544d5fc 100644
--- a/clang/test/ClangScanDeps/modules-include-tree-prefix-map.c
+++ b/clang/test/ClangScanDeps/modules-include-tree-prefix-map.c
@@ -4,12 +4,13 @@
 // RUN: rm -rf %t
 // RUN: split-file %s %t/dir1
 // RUN: cp -r %t/dir1 %t/dir2
-// RUN: sed -e "s|DIR|%/t/dir1|g" -e "s|CLANG|%clang|g" %t/dir1/cdb.json.template > %t/cdb1.json
-// RUN: sed -e "s|DIR|%/t/dir2|g" -e "s|CLANG|%clang|g" %t/dir1/cdb.json.template > %t/cdb2.json
+// RUN: sed -e "s|DIR|%/t/dir1|g" -e "s|CLANG|%/ncclang|g" %t/dir1/cdb.json.template > %t/cdb1.json
+// RUN: sed -e "s|DIR|%/t/dir2|g" -e "s|CLANG|%/ncclang|g" %t/dir1/cdb.json.template > %t/cdb2.json
 
 // RUN: clang-scan-deps -compilation-database %t/cdb1.json \
 // RUN:   -cas-path %t/cas -module-files-dir %t/dir1/outputs \
-// RUN:   -prefix-map=%t/dir1/outputs=/^modules -prefix-map=%t/dir1=/^src -prefix-map-sdk=/^sdk -prefix-map-toolchain=/^tc \
+// RUN:   -prefix-map=%t/dir1/outputs=%/root^modules -prefix-map=%t/dir1=%/root^src \
+// RUN:   -prefix-map-sdk=%/root^sdk -prefix-map-toolchain=%/root^tc \
 // RUN:   -format experimental-include-tree-full -mode preprocess-dependency-directives -optimize-args=none \
 // RUN:   > %t/deps.json
 
@@ -45,50 +46,50 @@
 
 // RUN: cat %t/deps.json >> %t/result.txt
 
-// RUN: FileCheck %s -input-file %t/result.txt -DPREFIX=%/t
+// RUN: cat %t/result.txt | %PathSanitizingFileCheck --sanitize PREFIX=%/t --sanitize ROOT^=%/root^ --enable-yaml-compatibility %s
 
 // CHECK-LABEL: MODULE Top
 // CHECK: <module-includes> llvmcas://{{[[:xdigit:]]+}}
 // CHECK: 1:1 <built-in> llvmcas://{{[[:xdigit:]]+}}
-// CHECK: 2:1 /^src/Top.h llvmcas://{{[[:xdigit:]]+}}
+// CHECK: 2:1 ROOT^src{{/|\\}}Top.h llvmcas://{{[[:xdigit:]]+}}
 // CHECK: Module Map:
 // CHECK: Top
 // CHECK:   export *
 // CHECK: Files:
 // CHECK-NOT: module.modulemap
-// CHECK: /^src/Top.h llvmcas://{{[[:xdigit:]]+}}
+// CHECK: ROOT^src{{/|\\}}Top.h llvmcas://{{[[:xdigit:]]+}}
 // CHECK-NOT: module.modulemap
 
 // CHECK-LABEL: MODULE Left
 // CHECK: <module-includes> llvmcas://{{[[:xdigit:]]+}}
 // CHECK: 1:1 <built-in> llvmcas://{{[[:xdigit:]]+}}
-// CHECK: 2:1 /^src/Left.h llvmcas://{{[[:xdigit:]]+}}
+// CHECK: 2:1 ROOT^src{{/|\\}}Left.h llvmcas://{{[[:xdigit:]]+}}
 // CHECK:   2:1 (Module) Top
 // CHECK: Module Map:
 // CHECK: Left
 // CHECK:   export *
 // CHECK: Files:
 // CHECK-NOT: module.modulemap
-// CHECK: /^src/Left.h llvmcas://{{[[:xdigit:]]+}}
+// CHECK: ROOT^src{{/|\\}}Left.h llvmcas://{{[[:xdigit:]]+}}
 // CHECK-NOT: module.modulemap
-// CHECK: /^src/Top.h llvmcas://{{[[:xdigit:]]+}}
+// CHECK: ROOT^src{{/|\\}}Top.h llvmcas://{{[[:xdigit:]]+}}
 
 // CHECK-LABEL: MODULE Right
 // CHECK: <module-includes> llvmcas://{{[[:xdigit:]]+}}
 // CHECK: 1:1 <built-in> llvmcas://{{[[:xdigit:]]+}}
-// CHECK: 2:1 /^src/Right.h llvmcas://{{[[:xdigit:]]+}}
+// CHECK: 2:1 ROOT^src{{/|\\}}Right.h llvmcas://{{[[:xdigit:]]+}}
 // CHECK:   2:1 (Module) Top
 // CHECK: Module Map:
 // CHECK: Right
 // CHECK:   export *
 // CHECK: Files:
 // CHECK-NOT: module.modulemap
-// CHECK: /^src/Right.h llvmcas://{{[[:xdigit:]]+}}
+// CHECK: ROOT^src{{/|\\}}Right.h llvmcas://{{[[:xdigit:]]+}}
 // CHECK-NOT: module.modulemap
-// CHECK: /^src/Top.h llvmcas://{{[[:xdigit:]]+}}
+// CHECK: ROOT^src{{/|\\}}Top.h llvmcas://{{[[:xdigit:]]+}}
 
 // CHECK-LABEL: TRANSLATION UNIT
-// CHECK: /^src/tu.m llvmcas://{{[[:xdigit:]]+}}
+// CHECK: ROOT^src{{/|\\}}tu.m llvmcas://{{[[:xdigit:]]+}}
 // CHECK: 1:1 <built-in> llvmcas://{{[[:xdigit:]]+}}
 // CHECK: 2:1 (Module) Left
 // CHECK: 3:1 (Module) Right
@@ -100,9 +101,9 @@
 // CHECK-NOT: Module Map
 // CHECK: Files:
 // CHECK-NOT: module.modulemap
-// CHECK: /^src/Left.h llvmcas://{{[[:xdigit:]]+}}
-// CHECK: /^src/Top.h llvmcas://{{[[:xdigit:]]+}}
-// CHECK: /^src/Right.h llvmcas://{{[[:xdigit:]]+}}
+// CHECK: ROOT^src{{/|\\}}Left.h llvmcas://{{[[:xdigit:]]+}}
+// CHECK: ROOT^src{{/|\\}}Top.h llvmcas://{{[[:xdigit:]]+}}
+// CHECK: ROOT^src{{/|\\}}Right.h llvmcas://{{[[:xdigit:]]+}}
 
 // CHECK-LABEL: System module-includes
 // CHECK-NEXT: #import "sys.h"
@@ -117,14 +118,14 @@
 // CHECK:                "module-name": "Top"
 // CHECK:              }
 // CHECK-NEXT:       ]
-// CHECK:            "clang-modulemap-file": "[[PREFIX]]/dir1/module.modulemap"
+// CHECK:            "clang-modulemap-file": "PREFIX{{/|\\\\}}dir1{{/|\\\\}}module.modulemap"
 // CHECK:            "command-line": [
 // CHECK-NEXT:         "-cc1"
 // CHECK:              "-fcas-path"
-// CHECK-NEXT:         "[[PREFIX]]/cas"
+// CHECK-NEXT:         "PREFIX{{/|\\\\}}cas"
 // CHECK-NOT: -fmodule-map-file
 // CHECK:              "-o"
-// CHECK-NEXT:         "[[PREFIX]]/dir1/outputs/{{.*}}/Left-{{.*}}.pcm"
+// CHECK-NEXT:         "PREFIX{{/|\\\\}}dir1{{/|\\\\}}outputs{{/|\\\\}}{{.*}}{{/|\\\\}}Left-{{.*}}.pcm"
 // CHECK:              "-disable-free"
 // CHECK:              "-fno-pch-timestamp"
 // CHECK:              "-fcas-include-tree"
@@ -132,16 +133,16 @@
 // CHECK:              "-fcache-compile-job"
 // CHECK:              "-emit-module"
 // CHECK:              "-fmodule-file-cache-key"
-// CHECK-NEXT:         "/^modules/{{.*}}/Top-{{.*}}.pcm"
+// CHECK-NEXT:         "ROOT^modules{{/|\\\\}}{{.*}}{{/|\\\\}}Top-{{.*}}.pcm"
 // CHECK-NEXT:         "llvmcas://{{[[:xdigit:]]+}}"
-// CHECK:              "-fmodule-file=Top=/^modules/{{.*}}/Top-{{.*}}.pcm"
+// CHECK:              "-fmodule-file=Top=ROOT^modules{{/|\\\\}}{{.*}}{{/|\\\\}}Top-{{.*}}.pcm"
 // CHECK:              "-fmodules"
 // CHECK:              "-fmodule-name=Left"
 // CHECK:              "-fno-implicit-modules"
 // CHECK:            ]
 // CHECK:            "file-deps": [
-// CHECK-NEXT:         "[[PREFIX]]/dir1/module.modulemap"
-// CHECK-NEXT:         "[[PREFIX]]/dir1/Left.h"
+// CHECK-NEXT:         "PREFIX{{/|\\\\}}dir1{{/|\\\\}}module.modulemap"
+// CHECK-NEXT:         "PREFIX{{/|\\\\}}dir1{{/|\\\\}}Left.h"
 // CHECK:            ]
 // CHECK:            "name": "Left"
 // CHECK:          }
@@ -152,14 +153,14 @@
 // CHECK:                "module-name": "Top"
 // CHECK:              }
 // CHECK-NEXT:       ]
-// CHECK:            "clang-modulemap-file": "[[PREFIX]]/dir1/module.modulemap"
+// CHECK:            "clang-modulemap-file": "PREFIX{{/|\\\\}}dir1{{/|\\\\}}module.modulemap"
 // CHECK:            "command-line": [
 // CHECK-NEXT:         "-cc1"
 // CHECK:              "-fcas-path"
-// CHECK-NEXT:         "[[PREFIX]]/cas"
+// CHECK-NEXT:         "PREFIX{{/|\\\\}}cas"
 // CHECK-NOT: -fmodule-map-file
 // CHECK:              "-o"
-// CHECK-NEXT:         "[[PREFIX]]/dir1/outputs/{{.*}}/Right-{{.*}}.pcm"
+// CHECK-NEXT:         "PREFIX{{/|\\\\}}dir1{{/|\\\\}}outputs{{/|\\\\}}{{.*}}{{/|\\\\}}Right-{{.*}}.pcm"
 // CHECK:              "-disable-free"
 // CHECK:              "-fno-pch-timestamp"
 // CHECK:              "-fcas-include-tree"
@@ -167,29 +168,29 @@
 // CHECK:              "-fcache-compile-job"
 // CHECK:              "-emit-module"
 // CHECK:              "-fmodule-file-cache-key
-// CHECK-NEXT:         "/^modules/{{.*}}/Top-{{.*}}.pcm"
+// CHECK-NEXT:         "ROOT^modules{{/|\\\\}}{{.*}}{{/|\\\\}}Top-{{.*}}.pcm"
 // CHECK-NEXT:         "llvmcas://{{[[:xdigit:]]+}}"
-// CHECK:              "-fmodule-file=Top=/^modules/{{.*}}/Top-{{.*}}.pcm"
+// CHECK:              "-fmodule-file=Top=ROOT^modules{{/|\\\\}}{{.*}}{{/|\\\\}}Top-{{.*}}.pcm"
 // CHECK:              "-fmodules"
 // CHECK:              "-fmodule-name=Right"
 // CHECK:              "-fno-implicit-modules"
 // CHECK:            ]
 // CHECK:            "file-deps": [
-// CHECK-NEXT:         "[[PREFIX]]/dir1/module.modulemap"
-// CHECK-NEXT:         "[[PREFIX]]/dir1/Right.h"
+// CHECK-NEXT:         "PREFIX{{/|\\\\}}dir1{{/|\\\\}}module.modulemap"
+// CHECK-NEXT:         "PREFIX{{/|\\\\}}dir1{{/|\\\\}}Right.h"
 // CHECK-NEXT:       ]
 // CHECK:            "name": "Right"
 // CHECK:          }
 // CHECK-NEXT:     {
 // CHECK:            "cas-include-tree-id": "[[SYS_TREE:llvmcas://[[:xdigit:]]+]]"
 // CHECK:            "clang-module-deps": []
-// CHECK:            "clang-modulemap-file": "[[PREFIX]]/dir1/System/module.modulemap"
+// CHECK:            "clang-modulemap-file": "PREFIX{{/|\\\\}}dir1{{/|\\\\}}System{{/|\\\\}}module.modulemap"
 // CHECK:            "command-line": [
 // CHECK-NEXT:         "-cc1"
 // CHECK:              "-fcas-path"
-// CHECK-NEXT:         "[[PREFIX]]/cas"
+// CHECK-NEXT:         "PREFIX{{/|\\\\}}cas"
 // CHECK:              "-o"
-// CHECK-NEXT:         "[[PREFIX]]/dir1/outputs/{{.*}}/System-{{.*}}.pcm"
+// CHECK-NEXT:         "PREFIX{{/|\\\\}}dir1{{/|\\\\}}outputs{{/|\\\\}}{{.*}}{{/|\\\\}}System-{{.*}}.pcm"
 // CHECK:              "-disable-free"
 // CHECK:              "-fno-pch-timestamp"
 // CHECK:              "-fcas-include-tree"
@@ -201,22 +202,22 @@
 // CHECK:              "-fno-implicit-modules"
 // CHECK:            ]
 // CHECK:            "file-deps": [
-// CHECK-DAG:         "[[PREFIX]]/dir1/System/module.modulemap"
-// CHECK-DAG:         "[[PREFIX]]/dir1/System/sys.h"
-// CHECK-DAG:         "{{.*}}/stdbool.h"
+// CHECK-DAG:         "PREFIX{{/|\\\\}}dir1{{/|\\\\}}System{{/|\\\\}}module.modulemap"
+// CHECK-DAG:         "PREFIX{{/|\\\\}}dir1{{/|\\\\}}System{{/|\\\\}}sys.h"
+// CHECK-DAG:         "{{.*}}{{/|\\\\}}stdbool.h"
 // CHECK:            ]
 // CHECK:            "name": "System"
 // CHECK:          }
 // CHECK-NEXT:     {
 // CHECK:            "cas-include-tree-id": "[[TOP_TREE:llvmcas://[[:xdigit:]]+]]"
 // CHECK:            "clang-module-deps": []
-// CHECK:            "clang-modulemap-file": "[[PREFIX]]/dir1/module.modulemap"
+// CHECK:            "clang-modulemap-file": "PREFIX{{/|\\\\}}dir1{{/|\\\\}}module.modulemap"
 // CHECK:            "command-line": [
 // CHECK-NEXT:         "-cc1"
 // CHECK:              "-fcas-path"
-// CHECK-NEXT:         "[[PREFIX]]/cas"
+// CHECK-NEXT:         "PREFIX{{/|\\\\}}cas"
 // CHECK:              "-o"
-// CHECK-NEXT:         "[[PREFIX]]/dir1/outputs/{{.*}}/Top-{{.*}}.pcm"
+// CHECK-NEXT:         "PREFIX{{/|\\\\}}dir1{{/|\\\\}}outputs{{/|\\\\}}{{.*}}{{/|\\\\}}Top-{{.*}}.pcm"
 // CHECK:              "-disable-free"
 // CHECK:              "-fno-pch-timestamp"
 // CHECK:              "-fcas-include-tree"
@@ -228,8 +229,8 @@
 // CHECK:              "-fno-implicit-modules"
 // CHECK:            ]
 // CHECK:            "file-deps": [
-// CHECK-NEXT:         "[[PREFIX]]/dir1/module.modulemap"
-// CHECK-NEXT:         "[[PREFIX]]/dir1/Top.h"
+// CHECK-NEXT:         "PREFIX{{/|\\\\}}dir1{{/|\\\\}}module.modulemap"
+// CHECK-NEXT:         "PREFIX{{/|\\\\}}dir1{{/|\\\\}}Top.h"
 // CHECK-NEXT:       ]
 // CHECK:            "name": "Top"
 // CHECK:          }
@@ -253,7 +254,7 @@
 // CHECK:                "command-line": [
 // CHECK-NEXT:             "-cc1"
 // CHECK:                  "-fcas-path"
-// CHECK-NEXT:             "[[PREFIX]]/cas"
+// CHECK-NEXT:             "PREFIX{{/|\\\\}}cas"
 // CHECK-NOT: -fmodule-map-file
 // CHECK:                  "-disable-free"
 // CHECK:                  "-fcas-include-tree"
@@ -261,20 +262,20 @@
 // CHECK:                  "-fcache-compile-job"
 // CHECK:                  "-fsyntax-only"
 // CHECK:                  "-fmodule-file-cache-key"
-// CHECK-NEXT:             "/^modules/{{.*}}/Left-{{.*}}.pcm"
+// CHECK-NEXT:             "ROOT^modules{{/|\\\\}}{{.*}}{{/|\\\\}}Left-{{.*}}.pcm"
 // CHECK-NEXT:             "llvmcas://{{[[:xdigit:]]+}}"
 // CHECK:                  "-fmodule-file-cache-key"
-// CHECK-NEXT:             "/^modules/{{.*}}/Right-{{.*}}.pcm"
+// CHECK-NEXT:             "ROOT^modules{{/|\\\\}}{{.*}}{{/|\\\\}}Right-{{.*}}.pcm"
 // CHECK-NEXT:             "llvmcas://{{[[:xdigit:]]+}}"
-// CHECK:                  "-fmodule-file=Left=/^modules/{{.*}}/Left-{{.*}}.pcm"
-// CHECK:                  "-fmodule-file=Right=/^modules/{{.*}}/Right-{{.*}}.pcm"
+// CHECK:                  "-fmodule-file=Left=ROOT^modules{{/|\\\\}}{{.*}}{{/|\\\\}}Left-{{.*}}.pcm"
+// CHECK:                  "-fmodule-file=Right=ROOT^modules{{/|\\\\}}{{.*}}{{/|\\\\}}Right-{{.*}}.pcm"
 // CHECK:                  "-fmodules"
 // CHECK:                  "-fno-implicit-modules"
 // CHECK:                ]
 // CHECK:                "file-deps": [
-// CHECK-NEXT:             "[[PREFIX]]/dir1/tu.m"
+// CHECK-NEXT:             "PREFIX{{/|\\\\}}dir1{{/|\\\\}}tu.m"
 // CHECK-NEXT:           ]
-// CHECK:                "input-file": "[[PREFIX]]/dir1/tu.m"
+// CHECK:                "input-file": "PREFIX{{/|\\\\}}dir1{{/|\\\\}}tu.m"
 // CHECK:              }
 // CHECK-NEXT:       ]
 // CHECK-NEXT:     }
@@ -291,7 +292,8 @@
 // Scan in a different directory
 // RUN: clang-scan-deps -compilation-database %t/cdb2.json \
 // RUN:   -cas-path %t/cas -module-files-dir %t/dir2/outputs \
-// RUN:   -prefix-map=%t/dir2/outputs=/^modules -prefix-map=%t/dir2=/^src -prefix-map-sdk=/^sdk -prefix-map-toolchain=/^tc \
+// RUN:   -prefix-map=%t/dir2/outputs=%/root^modules -prefix-map=%t/dir2=%/root^src \
+// RUN:   -prefix-map-sdk=%/root^sdk -prefix-map-toolchain=%/root^tc \
 // RUN:   -format experimental-include-tree-full -mode preprocess-dependency-directives -optimize-args=none \
 // RUN:   > %t/deps2.json
 
diff --git a/clang/test/ClangScanDeps/modules-pch-cas-fs-prefix-mapping-caching.c b/clang/test/ClangScanDeps/modules-pch-cas-fs-prefix-mapping-caching.c
index 3341c048b87ee..b68a623fe3774 100644
--- a/clang/test/ClangScanDeps/modules-pch-cas-fs-prefix-mapping-caching.c
+++ b/clang/test/ClangScanDeps/modules-pch-cas-fs-prefix-mapping-caching.c
@@ -5,62 +5,72 @@
 // RUN: rm -rf %t
 // RUN: split-file %s %t
 // RUN: cp -r %t/dir1 %t/dir2
-// RUN: sed -e "s|DIR|%t/dir1|g" -e "s|CLANG|%clang|g" -e "s|SDK|%S/Inputs/SDK|g" %t/cdb.json.template > %t/dir1/cdb.json
-// RUN: sed -e "s|DIR|%t/dir1|g" -e "s|CLANG|%clang|g" -e "s|SDK|%S/Inputs/SDK|g" %t/cdb_pch.json.template > %t/dir1/cdb_pch.json
-// RUN: sed -e "s|DIR|%t/dir2|g" -e "s|CLANG|%clang|g" -e "s|SDK|%S/Inputs/SDK|g" %t/cdb.json.template > %t/dir2/cdb.json
-// RUN: sed -e "s|DIR|%t/dir2|g" -e "s|CLANG|%clang|g" -e "s|SDK|%S/Inputs/SDK|g" %t/cdb_pch.json.template > %t/dir2/cdb_pch.json
+// RUN: sed -e "s|DIR|%/t/dir1|g" -e "s|CLANG|%/ncclang|g" -e "s|SDK|%/S/Inputs/SDK|g" %t/cdb.json.template > %t/dir1/cdb.json
+// RUN: sed -e "s|DIR|%/t/dir1|g" -e "s|CLANG|%/ncclang|g" -e "s|SDK|%/S/Inputs/SDK|g" %t/cdb_pch.json.template > %t/dir1/cdb_pch.json
+// RUN: sed -e "s|DIR|%/t/dir2|g" -e "s|CLANG|%/ncclang|g" -e "s|SDK|%/S/Inputs/SDK|g" %t/cdb.json.template > %t/dir2/cdb.json
+// RUN: sed -e "s|DIR|%/t/dir2|g" -e "s|CLANG|%/ncclang|g" -e "s|SDK|%/S/Inputs/SDK|g" %t/cdb_pch.json.template > %t/dir2/cdb_pch.json
 
 // == Scan PCH
 // RUN: clang-scan-deps -compilation-database %t/dir1/cdb_pch.json -format experimental-full -optimize-args=none \
 // RUN:    -cas-path %t/cas -module-files-dir %t/dir1/modules \
-// RUN:    -prefix-map=%t/dir1/modules=/^modules -prefix-map=%t/dir1=/^src -prefix-map-sdk=/^sdk -prefix-map-toolchain=/^tc \
+// RUN:    -prefix-map=%t/dir1/modules=%/root^modules -prefix-map=%t/dir1=%/root^src -prefix-map-sdk=%/root^sdk -prefix-map-toolchain=%/root^tc \
 // RUN:  > %t/pch_dir1.txt
 
 // RUN: clang-scan-deps -compilation-database %t/dir2/cdb_pch.json -format experimental-full -optimize-args=none \
 // RUN:    -cas-path %t/cas -module-files-dir %t/dir2/modules \
-// RUN:    -prefix-map=%t/dir2/modules=/^modules -prefix-map=%t/dir2=/^src -prefix-map-sdk=/^sdk -prefix-map-toolchain=/^tc \
+// RUN:    -prefix-map=%t/dir2/modules=%/root^modules -prefix-map=%t/dir2=%/root^src -prefix-map-sdk=%/root^sdk -prefix-map-toolchain=%/root^tc \
 // RUN:  > %t/pch_dir2.txt
 
 // == Build PCH
 // RUN: %deps-to-rsp %t/pch_dir1.txt --module-name=B > %t/dir1/B.cc1.rsp
 // RUN: %deps-to-rsp %t/pch_dir1.txt --module-name=A > %t/dir1/A.cc1.rsp
 // RUN: %deps-to-rsp %t/pch_dir1.txt --tu-index 0 > %t/dir1/pch.cc1.rsp
-// RUN: (cd %t/dir1; %clang @B.cc1.rsp) 2>&1 | FileCheck %s -check-prefix=CACHE-MISS
-// RUN: (cd %t/dir1; %clang @A.cc1.rsp) 2>&1 | FileCheck %s -check-prefix=CACHE-MISS
-// RUN: (cd %t/dir1; %clang @pch.cc1.rsp) 2>&1 | FileCheck %s -check-prefix=CACHE-MISS
+// RUN: cd %t/dir1 && %clang @B.cc1.rsp > %t/miss-B.txt 2>&1
+// RUN: cat %t/miss-B.txt | FileCheck %s -check-prefix=CACHE-MISS
+// RUN: cd %t/dir1 && %clang @A.cc1.rsp > %t/miss-A.txt 2>&1
+// RUN: cat %t/miss-A.txt | FileCheck %s -check-prefix=CACHE-MISS
+// RUN: cd %t/dir1 && %clang @pch.cc1.rsp > %t/miss-pch.txt 2>&1
+// RUN: cat %t/miss-pch.txt | FileCheck %s -check-prefix=CACHE-MISS
 
 // CACHE-MISS: compile job cache miss
 
 // RUN: %deps-to-rsp %t/pch_dir2.txt --module-name=B > %t/dir2/B.cc1.rsp
 // RUN: %deps-to-rsp %t/pch_dir2.txt --module-name=A > %t/dir2/A.cc1.rsp
 // RUN: %deps-to-rsp %t/pch_dir2.txt --tu-index 0 > %t/dir2/pch.cc1.rsp
-// RUN: (cd %t/dir2; %clang @B.cc1.rsp) 2>&1 | FileCheck %s -check-prefix=CACHE-HIT
-// RUN: (cd %t/dir2; %clang @A.cc1.rsp) 2>&1 | FileCheck %s -check-prefix=CACHE-HIT
-// RUN: (cd %t/dir2; %clang @pch.cc1.rsp) 2>&1 | FileCheck %s -check-prefix=CACHE-HIT
+// RUN: cd %t/dir2 && %clang @B.cc1.rsp > %t/hit-B.txt 2>&1
+// RUN: cat %t/hit-B.txt | FileCheck %s -check-prefix=CACHE-HIT
+// RUN: cd %t/dir2 && %clang @A.cc1.rsp > %t/hit-A.txt 2>&1
+// RUN: cat %t/hit-B.txt | FileCheck %s -check-prefix=CACHE-HIT
+// RUN: cd %t/dir2 && %clang @pch.cc1.rsp > %t/hit-pch.txt 2>&1
+// RUN: cat %t/hit-pch.txt | FileCheck %s -check-prefix=CACHE-HIT
 
 // CACHE-HIT: compile job cache hit
 
 // == Scan TU, including PCH
 // RUN: clang-scan-deps -compilation-database %t/dir1/cdb.json -format experimental-full -optimize-args=none \
 // RUN:    -cas-path %t/cas -module-files-dir %t/dir1/modules \
-// RUN:    -prefix-map=%t/dir1/modules=/^modules -prefix-map=%t/dir1=/^src -prefix-map-sdk=/^sdk -prefix-map-toolchain=/^tc \
+// RUN:    -prefix-map=%t/dir1/modules=%/root^modules -prefix-map=%t/dir1=%/root^src -prefix-map-sdk=%/root^sdk -prefix-map-toolchain=%/root^tc \
 // RUN:  > %t/dir1.txt
 
 // RUN: clang-scan-deps -compilation-database %t/dir2/cdb.json -format experimental-full -optimize-args=none \
 // RUN:    -cas-path %t/cas -module-files-dir %t/dir2/modules \
-// RUN:    -prefix-map=%t/dir2/modules=/^modules -prefix-map=%t/dir2=/^src -prefix-map-sdk=/^sdk -prefix-map-toolchain=/^tc \
+// RUN:    -prefix-map=%t/dir2/modules=%/root^modules -prefix-map=%t/dir2=%/root^src -prefix-map-sdk=%/root^sdk -prefix-map-toolchain=%/root^tc \
 // RUN:  > %t/dir2.txt
 
 // == Build TU
 // RUN: %deps-to-rsp %t/dir1.txt --module-name=C > %t/dir1/C.cc1.rsp
 // RUN: %deps-to-rsp %t/dir1.txt --tu-index 0 > %t/dir1/tu.cc1.rsp
-// RUN: (cd %t/dir1; %clang @C.cc1.rsp) 2>&1 | FileCheck %s -check-prefix=CACHE-MISS
-// RUN: (cd %t/dir1; %clang @tu.cc1.rsp) 2>&1 | FileCheck %s -check-prefix=CACHE-MISS
+// RUN: cd %t/dir1 && %clang @C.cc1.rsp > %t/c-miss.txt 2>&1
+// RUN: cat %t/c-miss.txt | FileCheck %s -check-prefix=CACHE-MISS
+// RUN: cd %t/dir1 && %clang @tu.cc1.rsp > %t/tu-miss.txt 2>&1
+// RUN: cat %t/tu-miss.txt | FileCheck %s -check-prefix=CACHE-MISS
 
 // RUN: %deps-to-rsp %t/dir2.txt --module-name=C > %t/dir2/C.cc1.rsp
 // RUN: %deps-to-rsp %t/dir2.txt --tu-index 0 > %t/dir2/tu.cc1.rsp
-// RUN: (cd %t/dir2; %clang @C.cc1.rsp) 2>&1 | FileCheck %s -check-prefix=CACHE-HIT
-// RUN: (cd %t/dir2; %clang @tu.cc1.rsp) 2>&1 | FileCheck %s -check-prefix=CACHE-HIT
+// RUN: cd %t/dir2 && %clang @C.cc1.rsp > %t/c-hit.txt 2>&1
+// RUN: cat %t/c-hit.txt | FileCheck %s -check-prefix=CACHE-HIT
+// RUN: cd %t/dir2 && %clang @tu.cc1.rsp > %t/tu-hit.txt  2>&1
+// RUN: cat %t/tu-hit.txt | FileCheck %s -check-prefix=CACHE-HIT
 
 // RUN: diff -u %t/dir1/prefix.h.pch %t/dir2/prefix.h.pch
 // RUN: diff -r -u %t/dir1/modules %t/dir2/modules
diff --git a/clang/test/ClangScanDeps/modules-pch-cas-fs-prefix-mapping.c b/clang/test/ClangScanDeps/modules-pch-cas-fs-prefix-mapping.c
index aee657ce58e3d..8dad299143de9 100644
--- a/clang/test/ClangScanDeps/modules-pch-cas-fs-prefix-mapping.c
+++ b/clang/test/ClangScanDeps/modules-pch-cas-fs-prefix-mapping.c
@@ -5,17 +5,17 @@
 
 // RUN: rm -rf %t
 // RUN: split-file %s %t
-// RUN: sed -e "s|DIR|%t|g" -e "s|CLANG|%clang|g" -e "s|SDK|%S/Inputs/SDK|g" %t/cdb.json.template > %t/cdb.json
-// RUN: sed -e "s|DIR|%t|g" -e "s|CLANG|%clang|g" -e "s|SDK|%S/Inputs/SDK|g" %t/cdb_pch.json.template > %t/cdb_pch.json
+// RUN: sed -e "s|DIR|%/t|g" -e "s|CLANG|%/ncclang|g" -e "s|SDK|%/S/Inputs/SDK|g" %t/cdb.json.template > %t/cdb.json
+// RUN: sed -e "s|DIR|%/t|g" -e "s|CLANG|%/ncclang|g" -e "s|SDK|%/S/Inputs/SDK|g" %t/cdb_pch.json.template > %t/cdb_pch.json
 
 // == Scan PCH
 // RUN: clang-scan-deps -compilation-database %t/cdb_pch.json -format experimental-full \
 // RUN:    -cas-path %t/cas -module-files-dir %t/modules \
-// RUN:    -prefix-map=%t/modules=/^modules -prefix-map=%t=/^src -prefix-map-sdk=/^sdk -prefix-map-toolchain=/^tc \
+// RUN:    -prefix-map=%t/modules=%/root^modules -prefix-map=%t=%/root^src -prefix-map-sdk=%/root^sdk -prefix-map-toolchain=%/root^tc \
 // RUN:  > %t/pch_result.txt
 
 // == Check specifics of the PCH command-line
-// RUN: FileCheck %s -input-file %t/pch_result.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK -check-prefix=PCH
+// RUN: cat %t/pch_result.txt | %PathSanitizingFileCheck --sanitize PREFIX=%/t --sanitize SDK_PREFIX=%/S/Inputs/SDK --sanitize ROOT^=%/root^ --enable-yaml-compatibility %s -check-prefix=PCH
 
 // == Build PCH
 // RUN: %deps-to-rsp %t/pch_result.txt --module-name=B > %t/B.cc1.rsp
@@ -30,11 +30,11 @@
 // == Scan TU, including PCH
 // RUN: clang-scan-deps -compilation-database %t/cdb.json -format experimental-full \
 // RUN:    -cas-path %t/cas -module-files-dir %t/modules \
-// RUN:    -prefix-map=%t/modules=/^modules -prefix-map=%t=/^src -prefix-map-sdk=/^sdk -prefix-map-toolchain=/^tc \
+// RUN:    -prefix-map=%t/modules=%/root^modules -prefix-map=%t=%/root^src -prefix-map-sdk=%/root^sdk -prefix-map-toolchain=%/root^tc \
 // RUN:  > %t/result.txt
 
 // == Check specifics of the TU command-line
-// RUN: FileCheck %s -input-file %t/result.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK
+// RUN: cat %t/result.txt | %PathSanitizingFileCheck --sanitize PREFIX=%/t --sanitize SDK_PREFIX=%/S/Inputs/SDK --sanitize ROOT^=%/root^ --enable-yaml-compatibility %s
 
 // == Build TU
 // RUN: %deps-to-rsp %t/result.txt --module-name=C > %t/C.cc1.rsp
@@ -55,20 +55,20 @@
 // RUN: llvm-cas -cas %t/cas -ls-tree-recursive @%t/pch_id.txt > %t/pch_fs.txt
 // RUN: llvm-cas -cas %t/cas -ls-tree-recursive @%t/tu_id.txt > %t/tu_fs.txt
 
-// RUN: FileCheck %s -input-file %t/A_fs.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK -check-prefixes=FS_NEG,FS
-// RUN: FileCheck %s -input-file %t/B_fs.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK -check-prefixes=FS_NEG,FS
-// RUN: FileCheck %s -input-file %t/C_fs.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK -check-prefixes=FS_NEG,FS
-// RUN: FileCheck %s -input-file %t/pch_fs.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK -check-prefixes=FS_NEG,FS
-// RUN: FileCheck %s -input-file %t/tu_fs.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK -check-prefixes=FS_NEG,FS
+// RUN: FileCheck %s -input-file %t/A_fs.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK -DROOT=%{/roott} -check-prefixes=FS_NEG,FS
+// RUN: FileCheck %s -input-file %t/B_fs.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK -DROOT=%{/roott} -check-prefixes=FS_NEG,FS
+// RUN: FileCheck %s -input-file %t/C_fs.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK -DROOT=%{/roott} -check-prefixes=FS_NEG,FS
+// RUN: FileCheck %s -input-file %t/pch_fs.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK -DROOT=%{/roott} -check-prefixes=FS_NEG,FS
+// RUN: FileCheck %s -input-file %t/tu_fs.txt -DPREFIX=%t -DSDK_PREFIX=%S/Inputs/SDK -DROOT=%{/roott} -check-prefixes=FS_NEG,FS
 
 // FS_NEG-NOT: [[PREFIX]]
 // FS_NEG-NOT: [[SDK_PREFIX]]
 // FS_NEG-NOT: .pcm{{$}}
-// FS: file llvmcas://{{.*}} /^sdk/usr/include/stdlib.h
-// FS: file llvmcas://{{.*}} /^src/a.h
-// FS: file llvmcas://{{.*}} /^src/b.h
-// FS: file llvmcas://{{.*}} /^src/module.modulemap
-// FS: file llvmcas://{{.*}} /^tc/lib/clang/{{.*}}/include/stdarg.h
+// FS: file llvmcas://{{.*}} [[ROOT]]^sdk/usr/include/stdlib.h
+// FS: file llvmcas://{{.*}} [[ROOT]]^src/a.h
+// FS: file llvmcas://{{.*}} [[ROOT]]^src/b.h
+// FS: file llvmcas://{{.*}} [[ROOT]]^src/module.modulemap
+// FS: file llvmcas://{{.*}} [[ROOT]]^tc/lib/clang/{{.*}}/include/stdarg.h
 
 // Check that it builds.
 // RUN: %clang @%t/B.cc1.rsp
@@ -84,71 +84,71 @@
 // PCH:                "module-name": "B"
 // PCH:              }
 // PCH:            ]
-// PCH:            "clang-modulemap-file": "[[PREFIX]]/module.modulemap"
+// PCH:            "clang-modulemap-file": "PREFIX{{/|\\\\}}module.modulemap"
 // PCH:            "command-line": [
 // PCH:              "-fcas-path"
-// PCH:              "[[PREFIX]]/cas"
+// PCH:              "PREFIX{{/|\\\\}}cas"
 // PCH:              "-fcas-fs"
 // PCH:              "[[A_ROOT_ID]]"
 // PCH:              "-fcas-fs-working-directory"
-// PCH:              "/^src"
-// PCH:              "-fmodule-map-file=/^src/module.modulemap"
+// PCH:              "ROOT^src"
+// PCH:              "-fmodule-map-file=ROOT^src{{/|\\\\}}module.modulemap"
 // PCH:              "-o"
-// PCH:              "[[PREFIX]]/modules/{{.*}}/A-{{.*}}.pcm"
+// PCH:              "PREFIX{{/|\\\\}}modules{{/|\\\\}}{{.*}}{{/|\\\\}}A-{{.*}}.pcm"
 // PCH:              "-fmodule-file-cache-key"
-// PCH:              "/^modules/{{.*}}/B-[[B_CONTEXT_HASH:[^.]+]].pcm"
+// PCH:              "ROOT^modules{{/|\\\\}}{{.*}}{{/|\\\\}}B-[[B_CONTEXT_HASH:[^.]+]].pcm"
 // PCH:              "llvmcas://{{.*}}"
 // PCH:              "-x"
 // PCH:              "c"
-// PCH:              "/^src/module.modulemap"
+// PCH:              "ROOT^src{{/|\\\\}}module.modulemap"
 // PCH:              "-isysroot"
-// PCH:              "/^sdk"
+// PCH:              "ROOT^sdk"
 // PCH:              "-resource-dir"
-// PCH:              "/^tc/lib/clang/{{.*}}"
-// PCH:              "-fmodule-file=B=/^modules/{{.*}}/B-[[B_CONTEXT_HASH]].pcm"
+// PCH:              "ROOT^tc{{/|\\\\}}lib{{/|\\\\}}clang{{/|\\\\}}{{.*}}"
+// PCH:              "-fmodule-file=B=ROOT^modules{{/|\\\\}}{{.*}}{{/|\\\\}}B-[[B_CONTEXT_HASH]].pcm"
 // PCH:              "-isystem"
-// PCH:              "/^tc/lib/clang/{{.*}}/include"
+// PCH:              "ROOT^tc{{/|\\\\}}lib{{/|\\\\}}clang{{/|\\\\}}{{.*}}{{/|\\\\}}include"
 // PCH:              "-internal-externc-isystem"
-// PCH:              "/^sdk/usr/include"
+// PCH:              "ROOT^sdk{{/|\\\\}}usr{{/|\\\\}}include"
 // PCH:            ]
 // PCH:            "file-deps": [
-// PCH:              "[[PREFIX]]/module.modulemap"
-// PCH:              "[[PREFIX]]/a.h"
+// PCH:              "PREFIX{{/|\\\\}}module.modulemap"
+// PCH:              "PREFIX{{/|\\\\}}a.h"
 // PCH:            ]
 // PCH:            "name": "A"
 // PCH:          }
 // PCH:          {
 // PCH:            "casfs-root-id": "[[B_ROOT_ID:llvmcas://[[:xdigit:]]+]]"
 // PCH:            "clang-module-deps": [],
-// PCH:            "clang-modulemap-file": "[[PREFIX]]/module.modulemap"
+// PCH:            "clang-modulemap-file": "PREFIX{{/|\\\\}}module.modulemap"
 // PCH:            "command-line": [
 // PCH:              "-fcas-path"
-// PCH:              "[[PREFIX]]/cas"
+// PCH:              "PREFIX{{/|\\\\}}cas"
 // PCH:              "-fcas-fs"
 // PCH:              "[[B_ROOT_ID]]"
 // PCH:              "-fcas-fs-working-directory"
-// PCH:              "/^src"
+// PCH:              "ROOT^src"
 // PCH:              "-o"
-// PCH:              "[[PREFIX]]/modules/{{.*}}/B-[[B_CONTEXT_HASH]].pcm"
+// PCH:              "PREFIX{{/|\\\\}}modules{{/|\\\\}}{{.*}}{{/|\\\\}}B-[[B_CONTEXT_HASH]].pcm"
 // PCH:              "-x"
 // PCH:              "c"
-// PCH:              "/^src/module.modulemap"
+// PCH:              "ROOT^src{{/|\\\\}}module.modulemap"
 // PCH:              "-isysroot"
-// PCH:              "/^sdk"
+// PCH:              "ROOT^sdk"
 // PCH:              "-resource-dir"
-// PCH:              "/^tc/lib/clang/{{.*}}"
+// PCH:              "ROOT^tc{{/|\\\\}}lib{{/|\\\\}}clang{{/|\\\\}}{{.*}}"
 // PCH:              "-isystem"
-// PCH:              "/^tc/lib/clang/{{.*}}/include"
+// PCH:              "ROOT^tc{{/|\\\\}}lib{{/|\\\\}}clang{{/|\\\\}}{{.*}}{{/|\\\\}}include"
 // PCH:              "-internal-externc-isystem"
-// PCH:              "/^sdk/usr/include"
+// PCH:              "ROOT^sdk{{/|\\\\}}usr{{/|\\\\}}include"
 // PCH:            ]
 // PCH:            "context-hash": "[[B_CONTEXT_HASH]]"
 // PCH:            "file-deps": [
 // Note: PREFIX, SDK_PREFIX and toolchain path are unordered
-// PCH-DAG:          "[[PREFIX]]/module.modulemap"
-// PCH-DAG:          "[[PREFIX]]/b.h"
-// PCH-DAG:          "[[SDK_PREFIX]]/usr/include/stdlib.h"
-// PCH-DAG:          "{{.*}}/include/stdarg.h"
+// PCH-DAG:          "PREFIX{{/|\\\\}}module.modulemap"
+// PCH-DAG:          "PREFIX{{/|\\\\}}b.h"
+// PCH-DAG:          "SDK_PREFIX{{/|\\\\}}usr{{/|\\\\}}include{{/|\\\\}}stdlib.h"
+// PCH-DAG:          "{{.*}}{{/|\\\\}}include{{/|\\\\}}stdarg.h"
 // PCH:            ]
 // PCH:            "name": "B"
 // PCH:          }
@@ -165,32 +165,32 @@
 // PCH:                ]
 // PCH:                "command-line": [
 // PCH:                  "-fcas-path"
-// PCH:                  "[[PREFIX]]/cas"
+// PCH:                  "PREFIX{{/|\\\\}}cas"
 // PCH:                  "-fcas-fs"
 // PCH:                  "[[TU_ROOT_ID]]"
 // PCH:                  "-fcas-fs-working-directory"
-// PCH:                  "/^src"
-// PCH:                  "-fmodule-map-file=/^src/module.modulemap"
+// PCH:                  "ROOT^src"
+// PCH:                  "-fmodule-map-file=ROOT^src{{/|\\\\}}module.modulemap"
 // PCH:                  "-fmodule-file-cache-key"
-// PCH:                  "/^modules/{{.*}}A-{{.*}}.pcm"
+// PCH:                  "ROOT^modules{{/|\\\\}}{{.*}}A-{{.*}}.pcm"
 // PCH:                  "llvmcas://{{.*}}"
 // PCH:                  "-x"
 // PCH:                  "c-header"
-// PCH:                  "/^src/prefix.h"
+// PCH:                  "ROOT^src{{/|\\\\}}prefix.h"
 // PCH:                  "-isysroot"
-// PCH:                  "/^sdk"
+// PCH:                  "ROOT^sdk"
 // PCH:                  "-resource-dir"
-// PCH:                  "/^tc/lib/clang/{{.*}}"
-// PCH:                  "-fmodule-file=A=/^modules/{{.*}}/A-{{.*}}.pcm"
+// PCH:                  "ROOT^tc{{/|\\\\}}lib{{/|\\\\}}clang{{/|\\\\}}{{.*}}"
+// PCH:                  "-fmodule-file=A=ROOT^modules{{/|\\\\}}{{.*}}{{/|\\\\}}A-{{.*}}.pcm"
 // PCH:                  "-isystem"
-// PCH:                  "/^tc/lib/clang/{{.*}}/include"
+// PCH:                  "ROOT^tc{{/|\\\\}}lib{{/|\\\\}}clang{{/|\\\\}}{{.*}}{{/|\\\\}}include"
 // PCH:                  "-internal-externc-isystem"
-// PCH:                  "/^sdk/usr/include"
+// PCH:                  "ROOT^sdk{{/|\\\\}}usr{{/|\\\\}}include"
 // PCH:                ],
 // PCH:                "file-deps": [
-// PCH:                  "[[PREFIX]]/prefix.h"
+// PCH:                  "PREFIX{{/|\\\\}}prefix.h"
 // PCH:                ]
-// PCH:                "input-file": "[[PREFIX]]/prefix.h"
+// PCH:                "input-file": "PREFIX{{/|\\\\}}prefix.h"
 // PCH:              }
 
 // CHECK:      {
@@ -201,26 +201,26 @@
 // CHECK:            "command-line": [
 // CHECK-NEXT:         "-cc1"
 // CHECK:              "-fcas-path"
-// CHECK-NEXT:         "[[PREFIX]]{{.}}cas"
+// CHECK-NEXT:         "PREFIX{{.}}cas"
 // CHECK:              "-fcas-fs"
 // CHECK-NEXT:         "[[C_ROOT_ID]]"
 // CHECK:              "-fcas-fs-working-directory"
-// CHECK-NEXT:         "/^src"
+// CHECK-NEXT:         "ROOT^src"
 // CHECK:              "-fcache-compile-job"
 // CHECK:              "-emit-module"
-// CHECK:              "-fmodule-file=/^modules/{{.*}}/B-{{.*}}.pcm"
+// CHECK:              "-fmodule-file=ROOT^modules{{/|\\\\}}{{.*}}{{/|\\\\}}B-{{.*}}.pcm"
 // CHECK:              "-fmodule-file-cache-key"
-// CHECK:              "/^modules/{{.*}}/B-{{.*}}.pcm"
+// CHECK:              "ROOT^modules{{/|\\\\}}{{.*}}{{/|\\\\}}B-{{.*}}.pcm"
 // CHECK:              "llvmcas://{{.*}}"
 // CHECK:              "-x"
 // CHECK-NEXT:         "c"
-// CHECK-NEXT:         "/^src/module.modulemap"
+// CHECK-NEXT:         "ROOT^src{{/|\\\\}}module.modulemap"
 // CHECK:              "-isysroot"
-// CHECK-NEXT:         "/^sdk"
+// CHECK-NEXT:         "ROOT^sdk"
 // CHECK:              "-resource-dir"
-// CHECK-NEXT:         "/^tc/lib/clang/{{.*}}"
-// CHECK-NOT: [[PREFIX]]
-// CHECK-NOT: [[SDK_PREFIX]]
+// CHECK-NEXT:         "ROOT^tc{{/|\\\\}}lib{{/|\\\\}}clang{{/|\\\\}}{{.*}}"
+// CHECK-NOT: PREFIX
+// CHECK-NOT: SDK_PREFIX
 // CHECK:            ]
 // CHECK:            "name": "C"
 // CHECK:          }
@@ -237,37 +237,37 @@
 // CHECK:                ]
 // CHECK:                "command-line": [
 // CHECK:                  "-fcas-path"
-// CHECK-NEXT:             "[[PREFIX]]/cas"
+// CHECK-NEXT:             "PREFIX{{/|\\\\}}cas"
 // CHECK:                  "-fcas-fs"
 // CHECK-NEXT:             "[[TU_ROOT_ID]]"
 // CHECK:                  "-fcas-fs-working-directory"
-// CHECK-NEXT:             "/^src"
-// CHECK:                  "-fmodule-map-file=/^src/module.modulemap"
+// CHECK-NEXT:             "ROOT^src"
+// CHECK:                  "-fmodule-map-file=ROOT^src{{/|\\\\}}module.modulemap"
 // CHECK:                  "-fmodule-file-cache-key"
-// CHECK:                  "/^modules/{{.*}}C-{{.*}}.pcm"
+// CHECK:                  "ROOT^modules{{/|\\\\}}{{.*}}C-{{.*}}.pcm"
 // CHECK:                  "llvmcas://{{.*}}"
 // CHECK:                  "-x"
 // CHECK-NEXT:             "c"
-// CHECK-NEXT:             "/^src/t.c"
+// CHECK-NEXT:             "ROOT^src{{/|\\\\}}t.c"
 // CHECK:                  "-isysroot"
-// CHECK-NEXT:             "/^sdk"
+// CHECK-NEXT:             "ROOT^sdk"
 // CHECK:                  "-resource-dir"
-// CHECK-NEXT:             "/^tc/lib/clang/{{.*}}"
-// CHECK:                  "-fmodule-file=C=/^modules/{{.*}}/C-{{.*}}.pcm"
+// CHECK-NEXT:             "ROOT^tc{{/|\\\\}}lib{{/|\\\\}}clang{{/|\\\\}}{{.*}}"
+// CHECK:                  "-fmodule-file=C=ROOT^modules{{/|\\\\}}{{.*}}{{/|\\\\}}C-{{.*}}.pcm"
 // CHECK:                  "-isystem"
-// CHECK-NEXT:             "/^sdk/usr/local/include"
+// CHECK-NEXT:             "ROOT^sdk{{/|\\\\}}usr{{/|\\\\}}local{{/|\\\\}}include"
 // CHECK:                  "-isystem"
-// CHECK-NEXT:             "/^tc/lib/clang/{{.*}}/include"
+// CHECK-NEXT:             "ROOT^tc{{/|\\\\}}lib{{/|\\\\}}clang{{/|\\\\}}{{.*}}{{/|\\\\}}include"
 // CHECK:                  "-internal-externc-isystem"
-// CHECK-NEXT:             "/^sdk/usr/include"
+// CHECK-NEXT:             "ROOT^sdk{{/|\\\\}}usr{{/|\\\\}}include"
 // CHECK:                  "-include-pch"
-// CHECK-NEXT:             "/^src/prefix.h.pch"
+// CHECK-NEXT:             "ROOT^src{{/|\\\\}}prefix.h.pch"
 // CHECK:                ],
 // CHECK:                "file-deps": [
-// CHECK:                  "[[PREFIX]]/t.c"
-// CHECK:                  "[[PREFIX]]/prefix.h.pch"
+// CHECK:                  "PREFIX{{/|\\\\}}t.c"
+// CHECK:                  "PREFIX{{/|\\\\}}prefix.h.pch"
 // CHECK:                ]
-// CHECK:                "input-file": "[[PREFIX]]/t.c"
+// CHECK:                "input-file": "PREFIX{{/|\\\\}}t.c"
 // CHECK:              }
 
 //--- cdb.json.template
diff --git a/clang/utils/PathSanitizingFileCheck b/clang/utils/PathSanitizingFileCheck
index eaf8a67a18c06..cb717299a3a5c 100644
--- a/clang/utils/PathSanitizingFileCheck
+++ b/clang/utils/PathSanitizingFileCheck
@@ -70,7 +70,9 @@ constants.""")
 
     if args.enable_windows_compatibility:
         if args.enable_yaml_compatibility:
-            slashes_re = r'(/|\\\\|\\\\\\\\)'
+            # Put the double escaped backslahes before the single
+            # escaped to ensure longest match
+            slashes_re = r'(/|\\\\\\\\|\\\\)'
         else:
             slashes_re = r'(/|\\\\)'
     else:
diff --git a/llvm/include/llvm/CAS/TreePath.h b/llvm/include/llvm/CAS/TreePath.h
new file mode 100644
index 0000000000000..054f0e94fb72c
--- /dev/null
+++ b/llvm/include/llvm/CAS/TreePath.h
@@ -0,0 +1,45 @@
+//===- llvm/CAS/TreePath.h - Tree path utility ------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CAS_TREEPATH_H
+#define LLVM_CAS_TREEPATH_H
+
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Path.h"
+#include <string>
+
+namespace llvm::cas {
+
+// On Windows, prepend a dummy root backslash to tree paths internally
+// (\C:\foo) and distinguish them from normal file paths (C:\foo) that
+// come from and return to clients and are passed to sys::fs
+// functions. This is so that we can have a single root and CAS ID
+// representing the root of the filesystem (that may otherwise spread
+// across multiple trees / drives) and the path handling to be more
+// uniform with the Posix systems. These convert paths between them.
+// TODO: Reassess this way of handling multiple roots for Windows later.
+inline std::string getTreePath(StringRef FilePath, sys::path::Style PathStyle) {
+  if (sys::path::is_style_windows(PathStyle)) {
+    assert(FilePath[0] != '\\');
+    std::string TreePath = "\\" + std::string(FilePath);
+    return TreePath;
+  }
+  return FilePath.str();
+}
+
+inline StringRef getFilePath(StringRef TreePath, sys::path::Style PathStyle) {
+  if (sys::path::is_style_windows(PathStyle)) {
+    assert(TreePath[0] == '\\');
+    return TreePath.drop_front(1);
+  }
+  return TreePath;
+}
+
+} // namespace llvm::cas
+
+#endif // LLVM_CAS_TREEPATH_H
diff --git a/llvm/include/llvm/Support/PrefixMapper.h b/llvm/include/llvm/Support/PrefixMapper.h
index 69782e4e35ea4..8c483c5694892 100644
--- a/llvm/include/llvm/Support/PrefixMapper.h
+++ b/llvm/include/llvm/Support/PrefixMapper.h
@@ -170,8 +170,8 @@ class TreePathPrefixMapper : public PrefixMapper {
   /// Find the tree path for \p Path, getting the real path for its parent
   /// directory but not following symlinks in \a sys::path::filename().
   ///
-  /// \returns The tree path, or the original path if there are any errors.
-  StringRef getTreePath(StringRef Path);
+  /// \returns The tree path, or none if there are any errors.
+  std::optional<StringRef> getTreePath(StringRef Path);
 
 public:
   void add(const MappedPrefix &Mapping) override;
diff --git a/llvm/lib/CAS/CachingOnDiskFileSystem.cpp b/llvm/lib/CAS/CachingOnDiskFileSystem.cpp
index 9c2ce9325a64a..3b9c6089fcbb3 100644
--- a/llvm/lib/CAS/CachingOnDiskFileSystem.cpp
+++ b/llvm/lib/CAS/CachingOnDiskFileSystem.cpp
@@ -12,6 +12,7 @@
 #include "llvm/CAS/FileSystemCache.h"
 #include "llvm/CAS/HierarchicalTreeBuilder.h"
 #include "llvm/CAS/ObjectStore.h"
+#include "llvm/CAS/TreePath.h"
 #include "llvm/Config/config.h"
 #include "llvm/Support/FileSystem.h"
 #include <mutex>
@@ -24,31 +25,6 @@ void CachingOnDiskFileSystem::anchor() {}
 
 namespace {
 
-// On Windows, prepend a dummy root backslash to tree paths internally
-// (\C:\foo) and distinguish them from normal file paths (C:\foo) that
-// come from and return to clients and are passed to sys::fs
-// functions. This is so that we can have a single root and CAS ID
-// representing the root of the filesystem (that may otherwise spread
-// across multiple trees / drives) and the path handling to be more
-// uniform with the Posix systems. These convert paths between them.
-// TODO: Reassess this way of handling multiple roots for Windows later.
-static std::string getTreePath(StringRef FilePath, sys::path::Style PathStyle) {
-  if (sys::path::is_style_windows(PathStyle)) {
-    assert(FilePath[0] != '\\');
-    std::string TreePath = "\\" + std::string(FilePath);
-    return TreePath;
-  }
-  return FilePath.str();
-}
-
-static StringRef getFilePath(StringRef TreePath, sys::path::Style PathStyle) {
-  if (sys::path::is_style_windows(PathStyle)) {
-    assert(TreePath[0] == '\\');
-    return TreePath.drop_front(1);
-  }
-  return TreePath;
-}
-
 class CachingOnDiskFileSystemImpl final : public CachingOnDiskFileSystem {
   struct WorkingDirectoryType {
     FileSystemCache::DirectoryEntry *Entry;
@@ -338,7 +314,8 @@ CachingOnDiskFileSystemImpl::makeSymlink(DirectoryEntry &Parent,
   PathStorage TreePathStorage(TreePath);
   SmallString<128> Target;
   if (auto Err = readLink(
-          getFilePath(TreePathStorage.Path, Cache->getPathStyle()), Target))
+          llvm::cas::getFilePath(TreePathStorage.Path, Cache->getPathStyle()),
+          Target))
     return std::move(Err);
   return makeSymlinkTo(Parent, TreePathStorage.Path, Target);
 }
@@ -364,7 +341,7 @@ static bool is_executable(StringRef TreePath, sys::fs::file_status Status,
   // This isn't the most reliable way but does better than just
   // checking owner_exe because most owned files have all_all
   // permission regardless of they are executable files.
-  StringRef FilePath = getFilePath(TreePath, PathStyle);
+  StringRef FilePath = llvm::cas::getFilePath(TreePath, PathStyle);
   return (Status.permissions() & sys::fs::perms::owner_exe) &&
       (FilePath.ends_with_insensitive(".exe") ||
        sys::fs::exists(FilePath + ".exe"));
@@ -396,7 +373,8 @@ CachingOnDiskFileSystemImpl::makeEntry(
     std::optional<sys::fs::file_status> KnownStatus) {
   assert(Parent.isDirectory() && "Expected a directory");
   PathStorage TreePathStorage(TreePath);
-  StringRef FilePath = getFilePath(TreePathStorage.Path, Cache->getPathStyle());
+  StringRef FilePath = llvm::cas::getFilePath(TreePathStorage.Path,
+      Cache->getPathStyle());
 
   // lstat is extremely slow...
   sys::fs::file_status Status;
@@ -467,7 +445,7 @@ CachingOnDiskFileSystemImpl::getRealPath(const Twine &Path,
           getDirectoryEntry(Path, /*FollowSymlinks=*/true).moveInto(Entry))
     return errorToErrorCode(std::move(E));
 
-  StringRef RealFilePath = getFilePath(Entry->getTreePath(),
+  StringRef RealFilePath = llvm::cas::getFilePath(Entry->getTreePath(),
       Cache->getPathStyle());
   Output.resize(RealFilePath.size());
   llvm::copy(RealFilePath, Output.begin());
@@ -525,11 +503,12 @@ CachingOnDiskFileSystemImpl::getDirectoryIterator(const Twine &Path) {
   // Walk the directory on-disk to discover entries.
   std::error_code EC;
   SmallVector<std::string> TreePaths;
-  StringRef EntryFilePath = getFilePath(Entry->getTreePath(),
+  StringRef EntryFilePath = llvm::cas::getFilePath(Entry->getTreePath(),
       Cache->getPathStyle());
   for (sys::fs::directory_iterator I(EntryFilePath, EC), E;
        !EC && I != E; I.increment(EC)) {
-    TreePaths.emplace_back(getTreePath(I->path(), Cache->getPathStyle()));
+    TreePaths.emplace_back(llvm::cas::getTreePath(I->path(),
+        Cache->getPathStyle()));
   }
   if (EC)
     return EC;
@@ -565,8 +544,8 @@ CachingOnDiskFileSystemImpl::preloadRealPath(DirectoryEntry &From,
   SmallString<256> ExpectedRealTreePath;
   ExpectedRealTreePath = From.getTreePath();
   sys::path::append(ExpectedRealTreePath, RemainingStorage.Path);
-  SmallString<256> ExpectedRealPath = getFilePath(ExpectedRealTreePath.str(),
-                                                  Cache->getPathStyle());
+  SmallString<256> ExpectedRealPath = llvm::cas::getFilePath(
+      ExpectedRealTreePath.str(), Cache->getPathStyle());
 
   // Most paths don't exist. Start with a stat. Profiling says this is faster
   // on Darwin when running clang-scan-deps (looks like allocation traffic in
@@ -588,7 +567,7 @@ CachingOnDiskFileSystemImpl::preloadRealPath(DirectoryEntry &From,
       /* expand_tilde */false))
     return errorCodeToError(EC);
 
-  SmallString<256> RealTreePath = StringRef(getTreePath(RealPath,
+  SmallString<256> RealTreePath = StringRef(llvm::cas::getTreePath(RealPath,
       Cache->getPathStyle()));
   FileSystemCache::LookupPathState State(Cache->getPathStyle(),
       Cache->getRoot(get_separator(Cache->getPathStyle())), RealTreePath);
@@ -803,7 +782,7 @@ DiscoveryInstanceImpl::requestDirectoryEntry(DirectoryEntry &Parent,
   assert(Parent.isDirectory() && "Expected a directory");
   SmallString<256> Path(Parent.getTreePath());
   sys::path::append(Path, Name);
-  StringRef FilePath = getFilePath(Path.str(), FS.getPathStyle());
+  StringRef FilePath = llvm::cas::getFilePath(Path.str(), FS.getPathStyle());
 
   // lstat is extremely slow...
   sys::fs::file_status Status;
@@ -832,7 +811,7 @@ DiscoveryInstanceImpl::requestDirectoryEntry(DirectoryEntry &Parent,
     if (Name.equals_insensitive(NextName) || !isASCII(Name)) {
       // Might be a case-insensitive match, check if it's the same entity.
       // FIXME: put this unique id in the cache.
-      StringRef NextFilePath = getFilePath(Next->getTreePath(),
+      StringRef NextFilePath = llvm::cas::getFilePath(Next->getTreePath(),
           FS.getPathStyle());
       sys::fs::file_status StatNext;
       if (std::error_code EC =
diff --git a/llvm/lib/Support/PrefixMapper.cpp b/llvm/lib/Support/PrefixMapper.cpp
index 7105301e539a3..2f06e1512c7cc 100644
--- a/llvm/lib/Support/PrefixMapper.cpp
+++ b/llvm/lib/Support/PrefixMapper.cpp
@@ -9,6 +9,8 @@
 #include "llvm/Support/PrefixMapper.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringExtras.h"
+#include "llvm/ADT/StringMap.h"
+#include "llvm/CAS/TreePath.h"
 #include "llvm/Support/StringSaver.h"
 #include "llvm/Support/VirtualFileSystem.h"
 
@@ -102,6 +104,30 @@ static bool startsWith(StringRef Path, StringRef Prefix,
   return true;
 }
 
+static bool equals(StringRef Prefix1, StringRef Prefix2,
+                   sys::path::Style PathStyle) {
+  if (PathStyle == sys::path::Style::posix ||
+      (PathStyle == sys::path::Style::native &&
+       sys::path::is_style_posix(sys::path::Style::native)))
+    return Prefix1 == Prefix2;
+
+  if (Prefix1.size() != Prefix2.size())
+    return false;
+
+  // Windows prefix matching : case and separator insensitive
+  for (size_t I = 0, E = Prefix1.size(); I != E; ++I) {
+    bool Sep1 = sys::path::is_separator(Prefix1[I], PathStyle);
+    bool Sep2 = sys::path::is_separator(Prefix2[I], PathStyle);
+    if (Sep1 != Sep2)
+      return false;
+    if (Sep1)
+      continue;
+    if (toLower(Prefix1[I]) != toLower(Prefix2[I]))
+      return false;
+  }
+  return true;
+}
+
 std::optional<StringRef> PrefixMapper::mapImpl(StringRef Path,
                                           SmallVectorImpl<char> &Storage) {
   for (const MappedPrefix &Map : Mappings) {
@@ -189,22 +215,24 @@ TreePathPrefixMapper::~TreePathPrefixMapper() = default;
 
 std::optional<StringRef>
 TreePathPrefixMapper::mapImpl(StringRef Path, SmallVectorImpl<char> &Storage) {
-  StringRef TreePath = getTreePath(Path);
-  std::optional<StringRef> Mapped = PrefixMapper::mapImpl(TreePath, Storage);
+  std::optional<StringRef> TreePath = getTreePath(Path);
+  StringRef FilePath = TreePath ?
+      llvm::cas::getFilePath(TreePath.value(), getPathStyle()) : Path;
+  std::optional<StringRef> Mapped = PrefixMapper::mapImpl(FilePath, Storage);
   if (Mapped)
     return *Mapped;
-  if (TreePath != Path)
-    return TreePath;
+  if (FilePath != Path)
+    return FilePath;
   return std::nullopt;
 }
 
-StringRef TreePathPrefixMapper::getTreePath(StringRef Path) {
+std::optional<StringRef> TreePathPrefixMapper::getTreePath(StringRef Path) {
   if (Path.empty())
-    return Path;
+    return std::nullopt;
   auto Entry = FS->getDirectoryEntry(Path, /*FollowSymlinks=*/false);
   if (!Entry) {
     consumeError(Entry.takeError());
-    return Path;
+    return std::nullopt;
   }
   return (*Entry)->getTreePath();
 }
@@ -214,10 +242,12 @@ void TreePathPrefixMapper::add(const MappedPrefix &Mapping) {
   // only affect the behaviour when later mapping a path that cannot be
   // canonicalized, since a non-canonical prefix cannot match a canonical path.
   PrefixMapper::add(Mapping);
-  StringRef Old = getTreePath(Mapping.Old);
+  std::optional<StringRef> OldTreePath = getTreePath(Mapping.Old);
+  if (!OldTreePath) return;
+  StringRef Old = llvm::cas::getFilePath(OldTreePath.value(), getPathStyle());
   StringRef New = Mapping.New;
   // Add the canonical prefix mapping, if different.
-  if (Old != Mapping.Old)
+  if (!equals(Old, Mapping.Old, getPathStyle()))
     PrefixMapper::add(MappedPrefix{Old, New});
 }
 
@@ -225,6 +255,13 @@ StringRef
 TreePathPrefixMapper::mapDirEntry(const vfs::CachedDirectoryEntry &Entry,
                                   SmallVectorImpl<char> &Storage) {
   StringRef TreePath = Entry.getTreePath();
-  std::optional<StringRef> Mapped = PrefixMapper::mapImpl(TreePath, Storage);
-  return Mapped ? *Mapped : TreePath;
+  StringRef FilePath = llvm::cas::getFilePath(TreePath, getPathStyle());
+  std::optional<StringRef> Mapped = PrefixMapper::mapImpl(FilePath, Storage);
+  if (Mapped) {
+    std::string MappedTreePath =
+        llvm::cas::getTreePath(*Mapped, getPathStyle());
+    Storage.assign(MappedTreePath.begin(), MappedTreePath.end());
+    return StringRef(Storage.begin(), Storage.size());
+  }
+  return TreePath;
 }
diff --git a/llvm/unittests/CAS/CachingOnDiskFileSystemTest.cpp b/llvm/unittests/CAS/CachingOnDiskFileSystemTest.cpp
index b6f0d0469eb8b..bb10ad25e3742 100644
--- a/llvm/unittests/CAS/CachingOnDiskFileSystemTest.cpp
+++ b/llvm/unittests/CAS/CachingOnDiskFileSystemTest.cpp
@@ -402,6 +402,15 @@ TEST(CachingOnDiskFileSystemTest, TrackNewAccesses) {
     ASSERT_THAT_ERROR(Schema.load(Tree->getRef()).moveInto(TreeNode),
                       Succeeded());
 
+#ifdef _WIN32
+    ASSERT_NE(TreeNode, std::nullopt);
+    EXPECT_EQ(TreeNode->size(), 1u);
+    auto DriveNode = TreeNode->lookup(sys::path::root_name(TestDirectory.path()));
+    ASSERT_TRUE(DriveNode);
+    ASSERT_THAT_ERROR(Schema.load(DriveNode->getRef()).moveInto(TreeNode),
+                      Succeeded());
+#endif
+
     // Check that all the files are found.
     EXPECT_EQ(Files.size(), TreeNode->size());
     for (const auto &F : Files)
@@ -451,6 +460,14 @@ TEST(CachingOnDiskFileSystemTest, TrackNewAccessesStack) {
     std::optional<llvm::cas::TreeProxy> TreeNode;
     ASSERT_THAT_ERROR(Schema.load(Tree->getRef()).moveInto(TreeNode),
                       Succeeded());
+#ifdef _WIN32
+    ASSERT_NE(TreeNode, std::nullopt);
+    EXPECT_EQ(TreeNode->size(), 1u);
+    auto DriveNode = TreeNode->lookup(sys::path::root_name(TestDirectory.path()));
+    ASSERT_TRUE(DriveNode);
+    ASSERT_THAT_ERROR(Schema.load(DriveNode->getRef()).moveInto(TreeNode),
+                      Succeeded());
+#endif
     ASSERT_EQ(TreeNode->size(), 2u);
     EXPECT_TRUE(TreeNode->lookup(sys::path::filename(Temps[2].path())));
     EXPECT_TRUE(TreeNode->lookup(sys::path::filename(Temps[3].path())));
@@ -472,6 +489,14 @@ TEST(CachingOnDiskFileSystemTest, TrackNewAccessesStack) {
     std::optional<llvm::cas::TreeProxy> TreeNode;
     ASSERT_THAT_ERROR(Schema.load(Tree->getRef()).moveInto(TreeNode),
                       Succeeded());
+#ifdef _WIN32
+    ASSERT_NE(TreeNode, std::nullopt);
+    EXPECT_EQ(TreeNode->size(), 1u);
+    auto DriveNode = TreeNode->lookup(sys::path::root_name(TestDirectory.path()));
+    ASSERT_TRUE(DriveNode);
+    ASSERT_THAT_ERROR(Schema.load(DriveNode->getRef()).moveInto(TreeNode),
+                      Succeeded());
+#endif
     ASSERT_EQ(TreeNode->size(), 2u);
     EXPECT_TRUE(TreeNode->lookup(sys::path::filename(Temps[0].path())));
     EXPECT_TRUE(TreeNode->lookup(sys::path::filename(Temps[1].path())));
@@ -534,6 +559,14 @@ TEST(CachingOnDiskFileSystemTest, TrackNewAccessesExists) {
     std::optional<llvm::cas::TreeProxy> TreeNode;
     ASSERT_THAT_ERROR(Schema.load(Tree->getRef()).moveInto(TreeNode),
                       Succeeded());
+#ifdef _WIN32
+    ASSERT_NE(TreeNode, std::nullopt);
+    EXPECT_EQ(TreeNode->size(), 1u);
+    auto DriveNode = TreeNode->lookup(sys::path::root_name(TestDirectory.path()));
+    ASSERT_TRUE(DriveNode);
+    ASSERT_THAT_ERROR(Schema.load(DriveNode->getRef()).moveInto(TreeNode),
+                      Succeeded());
+#endif
     auto Node0 = TreeNode->lookup(sys::path::filename(Temps[0].path()));
     auto Node1 = TreeNode->lookup(sys::path::filename(Temps[1].path()));
     ASSERT_TRUE(Node0);
@@ -558,6 +591,14 @@ TEST(CachingOnDiskFileSystemTest, TrackNewAccessesExists) {
     std::optional<llvm::cas::TreeProxy> TreeNode;
     ASSERT_THAT_ERROR(Schema.load(Tree->getRef()).moveInto(TreeNode),
                       Succeeded());
+#ifdef _WIN32
+    ASSERT_NE(TreeNode, std::nullopt);
+    EXPECT_EQ(TreeNode->size(), 1u);
+    auto DriveNode = TreeNode->lookup(sys::path::root_name(TestDirectory.path()));
+    ASSERT_TRUE(DriveNode);
+    ASSERT_THAT_ERROR(Schema.load(DriveNode->getRef()).moveInto(TreeNode),
+                      Succeeded());
+#endif
     auto Node0 = TreeNode->lookup(sys::path::filename(Temps[0].path()));
     auto Node1 = TreeNode->lookup(sys::path::filename(Temps[1].path()));
     ASSERT_TRUE(Node0);
@@ -582,6 +623,14 @@ TEST(CachingOnDiskFileSystemTest, TrackNewAccessesExists) {
     std::optional<llvm::cas::TreeProxy> TreeNode;
     ASSERT_THAT_ERROR(Schema.load(Tree->getRef()).moveInto(TreeNode),
                       Succeeded());
+#ifdef _WIN32
+    ASSERT_NE(TreeNode, std::nullopt);
+    EXPECT_EQ(TreeNode->size(), 1u);
+    auto DriveNode = TreeNode->lookup(sys::path::root_name(TestDirectory.path()));
+    ASSERT_TRUE(DriveNode);
+    ASSERT_THAT_ERROR(Schema.load(DriveNode->getRef()).moveInto(TreeNode),
+                      Succeeded());
+#endif
     auto Node0 = TreeNode->lookup(sys::path::filename(Temps[0].path()));
     auto Node1 = TreeNode->lookup(sys::path::filename(Temps[1].path()));
     ASSERT_TRUE(Node0);
@@ -684,6 +733,15 @@ TEST(CachingOnDiskFileSystemTest, ExcludeFromTacking) {
     EXPECT_EQ(FS->excludeFromTracking(F21.path()), std::error_code());
     AccessAllFiles();
     auto Tree = CreateTreeFromNewAccesses();
+#ifdef _WIN32
+    ASSERT_NE(Tree, std::nullopt);
+    EXPECT_EQ(Tree->size(), 1u);
+    auto DriveNode = Tree->lookup(sys::path::root_name(TestDirectory.path()));
+    ASSERT_TRUE(DriveNode);
+    auto DriveDir = Schema.load(DriveNode->getRef());
+    ASSERT_THAT_EXPECTED(DriveDir, Succeeded());
+    Tree = *DriveDir;
+#endif
     ASSERT_NE(Tree, std::nullopt);
     EXPECT_EQ(Tree->size(), 1u);
     EXPECT_FALSE(Tree->lookup("d1"));
@@ -702,6 +760,15 @@ TEST(CachingOnDiskFileSystemTest, ExcludeFromTacking) {
     EXPECT_EQ(FS->excludeFromTracking(D1.path()), std::error_code());
     EXPECT_EQ(FS->excludeFromTracking(F21.path()), std::error_code());
     auto Tree = CreateTreeFromNewAccesses();
+#ifdef _WIN32
+    ASSERT_NE(Tree, std::nullopt);
+    EXPECT_EQ(Tree->size(), 1u);
+    auto DriveNode = Tree->lookup(sys::path::root_name(TestDirectory.path()));
+    ASSERT_TRUE(DriveNode);
+    auto DriveDir = Schema.load(DriveNode->getRef());
+    ASSERT_THAT_EXPECTED(DriveDir, Succeeded());
+    Tree = *DriveDir;
+#endif
     ASSERT_NE(Tree, std::nullopt);
     EXPECT_EQ(Tree->size(), 1u);
     EXPECT_FALSE(Tree->lookup("d1"));
@@ -720,6 +787,15 @@ TEST(CachingOnDiskFileSystemTest, ExcludeFromTacking) {
     EXPECT_EQ(FS->excludeFromTracking(D1Sub.path()), std::error_code());
     EXPECT_EQ(FS->excludeFromTracking(D2.path()), std::error_code());
     auto Tree = CreateTreeFromNewAccesses();
+#ifdef _WIN32
+    ASSERT_NE(Tree, std::nullopt);
+    EXPECT_EQ(Tree->size(), 1u);
+    auto DriveNode = Tree->lookup(sys::path::root_name(TestDirectory.path()));
+    ASSERT_TRUE(DriveNode);
+    auto DriveDir = Schema.load(DriveNode->getRef());
+    ASSERT_THAT_EXPECTED(DriveDir, Succeeded());
+    Tree = *DriveDir;
+#endif
     ASSERT_NE(Tree, std::nullopt);
     EXPECT_EQ(Tree->size(), 1u);
     EXPECT_FALSE(Tree->lookup("d2"));
diff --git a/llvm/unittests/Support/PrefixMapperTest.cpp b/llvm/unittests/Support/PrefixMapperTest.cpp
index ce6630e04759a..4f364e4ceef86 100644
--- a/llvm/unittests/Support/PrefixMapperTest.cpp
+++ b/llvm/unittests/Support/PrefixMapperTest.cpp
@@ -416,7 +416,7 @@ TEST(TreePathPrefixMapperTest, construct) {
 
 TEST(TreePathPrefixMapperTest, add) {
   auto FS = makeIntrusiveRefCnt<GetDirectoryEntryFileSystem>();
-  TreePathPrefixMapper PM(FS);
+  TreePathPrefixMapper PM(FS, sys::path::Style::posix);
 
   // Non-canonical paths create two map entries: one for the canonical and one
   // for the non-canonical path.
@@ -440,7 +440,7 @@ TEST(TreePathPrefixMapperTest, add) {
 
 TEST(TreePathPrefixMapperTest, addRange) {
   auto FS = makeIntrusiveRefCnt<GetDirectoryEntryFileSystem>();
-  TreePathPrefixMapper PM(FS);
+  TreePathPrefixMapper PM(FS, sys::path::Style::posix);
 
   MappedPrefix MissingMapping[] = {
       {"missing", "/new"},
@@ -465,7 +465,7 @@ TEST(TreePathPrefixMapperTest, addRange) {
 
 TEST(TreePathPrefixMapperTest, addInverseRange) {
   auto FS = makeIntrusiveRefCnt<GetDirectoryEntryFileSystem>();
-  TreePathPrefixMapper PM(FS);
+  TreePathPrefixMapper PM(FS, sys::path::Style::posix);
 
   MappedPrefix MissingMapping[] = {
       {"/new", "missing"},
diff --git a/llvm/utils/lit/lit/TestRunner.py b/llvm/utils/lit/lit/TestRunner.py
index bf3444fa9319c..f37d769013d05 100644
--- a/llvm/utils/lit/lit/TestRunner.py
+++ b/llvm/utils/lit/lit/TestRunner.py
@@ -1553,6 +1553,17 @@ def regex_escape(s):
         ]
     )
 
+    substitutions.extend(
+        [
+            # The filesystem root and their tree path forms for
+            # Windows for CAS prefix mapping. The t suffix stands for
+            # tree path. Those with suffixes need to use {} because
+            # lit macro names cannot be a prefix of another macro.
+            ("%/root", os.environ.get('SystemDrive') + "/" if kIsWindows else "/"),
+            ("%{/roott}", "/" + os.environ.get('SystemDrive') + "/" if kIsWindows else "/"),
+        ]
+    )
+
     return substitutions
 
 
diff --git a/llvm/utils/lit/lit/llvm/config.py b/llvm/utils/lit/lit/llvm/config.py
index e47fa93a7beb8..b59348be09f8c 100644
--- a/llvm/utils/lit/lit/llvm/config.py
+++ b/llvm/utils/lit/lit/llvm/config.py
@@ -1,5 +1,6 @@
 import itertools
 import os
+import pathlib
 import platform
 import re
 import subprocess
@@ -756,6 +757,17 @@ def use_clang(
                     command=self.config.clang,
                     extra_args=["--driver-mode=g++"] + additional_flags,
                 ),
+                # A clang path with natural casing on Windows. Same as
+                # %/clang on non-Windows.
+                ToolSubst(
+                    "%/ncclang",
+                    command = (
+                        str(pathlib.Path(self.config.clang).resolve(strict=False)).replace("\\", "/")
+                        if platform.system() == "Windows"
+                        else self.config.clang.replace("\\", "/")
+                    ),
+                    extra_args=additional_flags
+                ),
             ]
             self.add_tool_substitutions(tool_substitutions)
             self.config.substitutions.append(("%resource_dir", builtin_include_dir))