diff --git a/llvm/test/CodeGen/X86/GlobalISel/legalize-leading-zeros-32.mir b/llvm/test/CodeGen/X86/GlobalISel/legalize-leading-zeros-32.mir
deleted file mode 100644
index 47438f3261157..0000000000000
--- a/llvm/test/CodeGen/X86/GlobalISel/legalize-leading-zeros-32.mir
+++ /dev/null
@@ -1,72 +0,0 @@
-# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 2
-# RUN: llc -mtriple=i386-linux-gnu -mattr=+lzcnt -run-pass=legalizer %s -o - | FileCheck %s
-
-# test count leading zeros for s8, s16, and s32
-
----
-name:            test_ctlz8
-alignment:       16
-legalized:       false
-regBankSelected: false
-registers:
-  - { id: 0, class: _, preferred-register: '' }
-  - { id: 1, class: _, preferred-register: '' }
-body:             |
-  bb.1:
-    ; CHECK-LABEL: name: test_ctlz8
-    ; CHECK: [[DEF:%[0-9]+]]:_(s8) = IMPLICIT_DEF
-    ; CHECK-NEXT: [[ZEXT:%[0-9]+]]:_(s16) = G_ZEXT [[DEF]](s8)
-    ; CHECK-NEXT: [[CTLZ:%[0-9]+]]:_(s16) = G_CTLZ [[ZEXT]](s16)
-    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s16) = G_CONSTANT i16 8
-    ; CHECK-NEXT: [[SUB:%[0-9]+]]:_(s16) = G_SUB [[CTLZ]], [[C]]
-    ; CHECK-NEXT: [[TRUNC:%[0-9]+]]:_(s8) = G_TRUNC [[SUB]](s16)
-    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s8) = COPY [[TRUNC]](s8)
-    ; CHECK-NEXT: RET 0, implicit [[COPY]](s8)
-    %0:_(s8) = IMPLICIT_DEF
-    %1:_(s8) = G_CTLZ %0
-    %2:_(s8) = COPY %1(s8)
-    RET 0, implicit %2
-
-...
----
-name:            test_ctlz32
-alignment:       16
-legalized:       false
-regBankSelected: false
-registers:
-  - { id: 0, class: _, preferred-register: '' }
-  - { id: 1, class: _, preferred-register: '' }
-body:             |
-  bb.1:
-    ; CHECK-LABEL: name: test_ctlz32
-    ; CHECK: [[DEF:%[0-9]+]]:_(s32) = IMPLICIT_DEF
-    ; CHECK-NEXT: [[CTLZ:%[0-9]+]]:_(s32) = G_CTLZ [[DEF]](s32)
-    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s32) = COPY [[CTLZ]](s32)
-    ; CHECK-NEXT: RET 0, implicit [[COPY]](s32)
-    %0:_(s32) = IMPLICIT_DEF
-    %1:_(s32) = G_CTLZ %0
-    %2:_(s32) = COPY %1(s32)
-    RET 0, implicit %2
-
-...
----
-name:            test_ctlz16
-alignment:       16
-legalized:       false
-regBankSelected: false
-registers:
-  - { id: 0, class: _, preferred-register: '' }
-  - { id: 1, class: _, preferred-register: '' }
-body:             |
-  bb.1:
-    ; CHECK-LABEL: name: test_ctlz16
-    ; CHECK: [[DEF:%[0-9]+]]:_(s16) = IMPLICIT_DEF
-    ; CHECK-NEXT: [[CTLZ:%[0-9]+]]:_(s16) = G_CTLZ [[DEF]](s16)
-    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s16) = COPY [[CTLZ]](s16)
-    ; CHECK-NEXT: RET 0, implicit [[COPY]](s16)
-    %0:_(s16) = IMPLICIT_DEF
-    %1:_(s16) = G_CTLZ %0
-    %2:_(s16) = COPY %1(s16)
-    RET 0, implicit %2
-
-...
diff --git a/llvm/test/CodeGen/X86/GlobalISel/legalize-leading-zeros.mir b/llvm/test/CodeGen/X86/GlobalISel/legalize-leading-zeros.mir
index cb4bae122329c..931a31ff3a2d2 100644
--- a/llvm/test/CodeGen/X86/GlobalISel/legalize-leading-zeros.mir
+++ b/llvm/test/CodeGen/X86/GlobalISel/legalize-leading-zeros.mir
@@ -1,5 +1,10 @@
 # NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 2
-# RUN: llc -mtriple=x86_64-linux-gnu -mattr=+lzcnt -run-pass=legalizer %s -o - | FileCheck %s
+# RUN: llc -mtriple=x86_64-linux-gnu -mattr=+lzcnt -run-pass=legalizer %s -o - | FileCheck %s --check-prefixes=CHECK,X64
+# RUN: llc -mtriple=i386-linux-gnu -mattr=+lzcnt -run-pass=legalizer -global-isel-abort=2 -pass-remarks-missed='gisel*'  %s 2>%t -o - | FileCheck %s --check-prefixes=CHECK,X86
+# RUN: FileCheck -check-prefix=ERR32  %s < %t
+
+# ERR32: remark: <unknown>:0:0: unable to legalize instruction: %13:_(s32), %14:_(s1) = G_USUBE %8:_, %10:_, %12:_ (in function: test_ctlz35)
+# ERR32: remark: <unknown>:0:0: unable to legalize instruction: %1:_(s64) = G_SELECT %6:_(s1), %9:_, %10:_ (in function: test_ctlz64)
 
 # test count leading zeros for s16, s32, and s64
 
@@ -13,20 +18,32 @@ registers:
   - { id: 1, class: _, preferred-register: '' }
 body:             |
   bb.1:
-    ; CHECK-LABEL: name: test_ctlz35
-    ; CHECK: [[DEF:%[0-9]+]]:_(s35) = IMPLICIT_DEF
-    ; CHECK-NEXT: [[ZEXT:%[0-9]+]]:_(s64) = G_ZEXT [[DEF]](s35)
-    ; CHECK-NEXT: [[CTLZ:%[0-9]+]]:_(s64) = G_CTLZ [[ZEXT]](s64)
-    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s64) = G_CONSTANT i64 29
-    ; CHECK-NEXT: [[SUB:%[0-9]+]]:_(s64) = G_SUB [[CTLZ]], [[C]]
-    ; CHECK-NEXT: [[TRUNC:%[0-9]+]]:_(s35) = G_TRUNC [[SUB]](s64)
-    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s35) = COPY [[TRUNC]](s35)
-    ; CHECK-NEXT: RET 0, implicit [[COPY]](s35)
+    ; X64-LABEL: name: test_ctlz35
+    ; X64: [[DEF:%[0-9]+]]:_(s35) = IMPLICIT_DEF
+    ; X64-NEXT: [[ZEXT:%[0-9]+]]:_(s64) = G_ZEXT [[DEF]](s35)
+    ; X64-NEXT: [[CTLZ:%[0-9]+]]:_(s64) = G_CTLZ [[ZEXT]](s64)
+    ; X64-NEXT: [[C:%[0-9]+]]:_(s64) = G_CONSTANT i64 29
+    ; X64-NEXT: [[SUB:%[0-9]+]]:_(s64) = G_SUB [[CTLZ]], [[C]]
+    ; X64-NEXT: [[TRUNC:%[0-9]+]]:_(s35) = G_TRUNC [[SUB]](s64)
+    ; X64-NEXT: [[COPY:%[0-9]+]]:_(s35) = COPY [[TRUNC]](s35)
+    ; X64-NEXT: RET 0, implicit [[COPY]](s35)
+    ; X86-LABEL: name: test_ctlz35
+    ; X86: [[DEF:%[0-9]+]]:_(s35) = IMPLICIT_DEF
+    ; X86-NEXT: [[ZEXT:%[0-9]+]]:_(s64) = G_ZEXT [[DEF]](s35)
+    ; X86-NEXT: [[CTLZ:%[0-9]+]]:_(s64) = G_CTLZ [[ZEXT]](s64)
+    ; X86-NEXT: [[C:%[0-9]+]]:_(s64) = G_CONSTANT i64 29
+    ; X86-NEXT: [[UV:%[0-9]+]]:_(s32), [[UV1:%[0-9]+]]:_(s32) = G_UNMERGE_VALUES [[CTLZ]](s64)
+    ; X86-NEXT: [[UV2:%[0-9]+]]:_(s32), [[UV3:%[0-9]+]]:_(s32) = G_UNMERGE_VALUES [[C]](s64)
+    ; X86-NEXT: [[USUBO:%[0-9]+]]:_(s32), [[USUBO1:%[0-9]+]]:_(s1) = G_USUBO [[UV]], [[UV2]]
+    ; X86-NEXT: [[USUBE:%[0-9]+]]:_(s32), [[USUBE1:%[0-9]+]]:_(s1) = G_USUBE [[UV1]], [[UV3]], [[USUBO1]]
+    ; X86-NEXT: [[MV:%[0-9]+]]:_(s64) = G_MERGE_VALUES [[USUBO]](s32), [[USUBE]](s32)
+    ; X86-NEXT: [[TRUNC:%[0-9]+]]:_(s35) = G_TRUNC [[MV]](s64)
+    ; X86-NEXT: [[COPY:%[0-9]+]]:_(s35) = COPY [[TRUNC]](s35)
+    ; X86-NEXT: RET 0, implicit [[COPY]](s35)
     %0:_(s35) = IMPLICIT_DEF
     %1:_(s35) = G_CTLZ %0
     %2:_(s35) = COPY %1(s35)
     RET 0, implicit %2
-
 ...
 ---
 name:            test_ctlz8
@@ -51,7 +68,6 @@ body:             |
     %1:_(s8) = G_CTLZ %0
     %2:_(s8) = COPY %1(s8)
     RET 0, implicit %2
-
 ...
 ---
 name:            test_ctlz64
@@ -63,16 +79,27 @@ registers:
   - { id: 1, class: _, preferred-register: '' }
 body:             |
   bb.1:
-    ; CHECK-LABEL: name: test_ctlz64
-    ; CHECK: [[DEF:%[0-9]+]]:_(s64) = IMPLICIT_DEF
-    ; CHECK-NEXT: [[CTLZ:%[0-9]+]]:_(s64) = G_CTLZ [[DEF]](s64)
-    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s64) = COPY [[CTLZ]](s64)
-    ; CHECK-NEXT: RET 0, implicit [[COPY]](s64)
+    ; X64-LABEL: name: test_ctlz64
+    ; X64: [[DEF:%[0-9]+]]:_(s64) = IMPLICIT_DEF
+    ; X64-NEXT: [[CTLZ:%[0-9]+]]:_(s64) = G_CTLZ [[DEF]](s64)
+    ; X64-NEXT: [[COPY:%[0-9]+]]:_(s64) = COPY [[CTLZ]](s64)
+    ; X64-NEXT: RET 0, implicit [[COPY]](s64)
+    ; X86-LABEL: name: test_ctlz64
+    ; X86: [[DEF:%[0-9]+]]:_(s64) = IMPLICIT_DEF
+    ; X86-NEXT: [[UV:%[0-9]+]]:_(s32), [[UV1:%[0-9]+]]:_(s32) = G_UNMERGE_VALUES [[DEF]](s64)
+    ; X86-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+    ; X86-NEXT: [[ICMP:%[0-9]+]]:_(s1) = G_ICMP intpred(eq), [[UV1]](s32), [[C]]
+    ; X86-NEXT: [[CTLZ:%[0-9]+]]:_(s64) = G_CTLZ [[UV]](s32)
+    ; X86-NEXT: [[C1:%[0-9]+]]:_(s64) = G_CONSTANT i64 32
+    ; X86-NEXT: [[ADD:%[0-9]+]]:_(s64) = G_ADD [[CTLZ]], [[C1]]
+    ; X86-NEXT: [[CTLZ_ZERO_UNDEF:%[0-9]+]]:_(s64) = G_CTLZ_ZERO_UNDEF [[UV1]](s32)
+    ; X86-NEXT: [[SELECT:%[0-9]+]]:_(s64) = G_SELECT [[ICMP]](s1), [[ADD]], [[CTLZ_ZERO_UNDEF]]
+    ; X86-NEXT: [[COPY:%[0-9]+]]:_(s64) = COPY [[SELECT]](s64)
+    ; X86-NEXT: RET 0, implicit [[COPY]](s64)
     %0:_(s64) = IMPLICIT_DEF
     %1:_(s64) = G_CTLZ %0
     %2:_(s64) = COPY %1(s64)
     RET 0, implicit %2
-
 ...
 ---
 name:            test_ctlz32
@@ -93,7 +120,6 @@ body:             |
     %1:_(s32) = G_CTLZ %0
     %2:_(s32) = COPY %1(s32)
     RET 0, implicit %2
-
 ...
 ---
 name:            test_ctlz16
@@ -114,5 +140,4 @@ body:             |
     %1:_(s16) = G_CTLZ %0
     %2:_(s16) = COPY %1(s16)
     RET 0, implicit %2
-
 ...