Reapply "[InstCombine] Preserve profile after folding select instructions with conditionals" (#161885) #161890

alanzhao1 · 2025-10-03T18:29:41Z

This reverts commit 572b579.

This is a reland of #159666 but with a fix moving the extern declaration of the flag under the LLVM namespace, which is needed to fix a linker error caused by #161240.

…ions with conditionals" (llvm#161885) This reverts commit 572b579. This is a reland of llvm#159666 but with a fix moving the `extern` declaration of the flag under the LLVM namespace, which is needed to fix a linker error caused by llvm#161240.

llvmbot · 2025-10-03T18:30:18Z

@llvm/pr-subscribers-llvm-transforms

Author: Alan Zhao (alanzhao1)

Changes

This reverts commit 572b579.

This is a reland of #159666 but with a fix moving the extern declaration of the flag under the LLVM namespace, which is needed to fix a linker error caused by #161240.

Full diff: https://github.com/llvm/llvm-project/pull/161890.diff

3 Files Affected:

(modified) llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp (+18-2)
(modified) llvm/test/Transforms/InstCombine/select-and-cmp.ll (+26-18)
(modified) llvm/test/Transforms/InstCombine/select-or-cmp.ll (+29-21)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 87000a1c36eef..3df448ddde99c 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -50,6 +50,9 @@
 using namespace llvm;
 using namespace PatternMatch;
 
+namespace llvm {
+extern cl::opt<bool> ProfcheckDisableMetadataFixes;
+}
 
 /// Replace a select operand based on an equality comparison with the identity
 /// constant of a binop.
@@ -4492,8 +4495,21 @@ Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {
   auto FoldSelectWithAndOrCond = [&](bool IsAnd, Value *A,
                                      Value *B) -> Instruction * {
     if (Value *V = simplifySelectInst(B, TrueVal, FalseVal,
-                                      SQ.getWithInstruction(&SI)))
-      return SelectInst::Create(A, IsAnd ? V : TrueVal, IsAnd ? FalseVal : V);
+                                      SQ.getWithInstruction(&SI))) {
+      Value *NewTrueVal = IsAnd ? V : TrueVal;
+      Value *NewFalseVal = IsAnd ? FalseVal : V;
+
+      // If the True and False values don't change, then preserve the branch
+      // metadata of the original select as the net effect of this change is to
+      // simplify the conditional.
+      Instruction *MDFrom = nullptr;
+      if (NewTrueVal == TrueVal && NewFalseVal == FalseVal &&
+          !ProfcheckDisableMetadataFixes) {
+        MDFrom = &SI;
+      }
+      return SelectInst::Create(A, NewTrueVal, NewFalseVal, "", nullptr,
+                                MDFrom);
+    }
 
     // Is (select B, T, F) a SPF?
     if (CondVal->hasOneUse() && SelType->isIntOrIntVectorTy()) {
diff --git a/llvm/test/Transforms/InstCombine/select-and-cmp.ll b/llvm/test/Transforms/InstCombine/select-and-cmp.ll
index 50e1493cad5c7..26c04ad412445 100644
--- a/llvm/test/Transforms/InstCombine/select-and-cmp.ll
+++ b/llvm/test/Transforms/InstCombine/select-and-cmp.ll
@@ -1,4 +1,4 @@
-; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals
 ; RUN: opt < %s -passes=instcombine -S | FileCheck %s
 
 define i32 @select_and_icmp(i32 %x, i32 %y, i32 %z) {
@@ -114,34 +114,34 @@ define i32 @select_and_icmp_inv(i32 %x, i32 %y, i32 %z) {
 
 ; Below used to be negative tests in InstSimplify, but are no more negative cases here
 
-define i32 @select_and_icmp_pred_bad_1(i32 %x, i32 %y, i32 %z) {
+define i32 @select_and_icmp_pred_bad_1(i32 %x, i32 %y, i32 %z) !prof !0 {
 ; CHECK-LABEL: @select_and_icmp_pred_bad_1(
-; CHECK-NEXT:    ret i32 [[X]]
+; CHECK-NEXT:    ret i32 [[X:%.*]]
 ;
   %A = icmp eq i32 %x, %z
   %B = icmp ne i32 %y, %z
   %C = and i1 %A, %B
-  %D = select i1 %C, i32 %z, i32 %x
+  %D = select i1 %C, i32 %z, i32 %x, !prof !1
   ret i32 %D
 }
 
-define i32 @select_and_icmp_pred_bad_2(i32 %x, i32 %y, i32 %z) {
+define i32 @select_and_icmp_pred_bad_2(i32 %x, i32 %y, i32 %z) !prof !0 {
 ; CHECK-LABEL: @select_and_icmp_pred_bad_2(
 ; CHECK-NEXT:    [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]]
-; CHECK-NEXT:    [[D:%.*]] = select i1 [[B]], i32 [[Z]], i32 [[X]]
+; CHECK-NEXT:    [[D:%.*]] = select i1 [[B]], i32 [[Z]], i32 [[X:%.*]], !prof [[PROF1:![0-9]+]]
 ; CHECK-NEXT:    ret i32 [[D]]
 ;
   %A = icmp ne i32 %x, %z
   %B = icmp eq i32 %y, %z
   %C = and i1 %A, %B
-  %D = select i1 %C, i32 %z, i32 %x
+  %D = select i1 %C, i32 %z, i32 %x, !prof !1
   ret i32 %D
 }
 
 define i32 @select_and_icmp_pred_bad_3(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @select_and_icmp_pred_bad_3(
-; CHECK-NEXT:    [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]]
-; CHECK-NEXT:    [[D:%.*]] = select i1 [[B_NOT]], i32 [[X]], i32 [[Z]]
+; CHECK-NEXT:    [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]]
+; CHECK-NEXT:    [[D:%.*]] = select i1 [[B_NOT]], i32 [[X:%.*]], i32 [[Z]]
 ; CHECK-NEXT:    ret i32 [[D]]
 ;
   %A = icmp ne i32 %x, %z
@@ -153,8 +153,8 @@ define i32 @select_and_icmp_pred_bad_3(i32 %x, i32 %y, i32 %z) {
 
 define i32 @select_and_icmp_pred_bad_4(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @select_and_icmp_pred_bad_4(
-; CHECK-NEXT:    [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]]
-; CHECK-NEXT:    [[D:%.*]] = select i1 [[B]], i32 [[Z]], i32 [[X]]
+; CHECK-NEXT:    [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]]
+; CHECK-NEXT:    [[D:%.*]] = select i1 [[B]], i32 [[Z]], i32 [[X:%.*]]
 ; CHECK-NEXT:    ret i32 [[D]]
 ;
   %A = icmp eq i32 %x, %z
@@ -166,7 +166,7 @@ define i32 @select_and_icmp_pred_bad_4(i32 %x, i32 %y, i32 %z) {
 
 define i32 @select_and_icmp_alt_bad_1(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @select_and_icmp_alt_bad_1(
-; CHECK-NEXT:    ret i32 [[Z]]
+; CHECK-NEXT:    ret i32 [[Z:%.*]]
 ;
   %A = icmp eq i32 %x, %z
   %B = icmp ne i32 %y, %z
@@ -177,8 +177,8 @@ define i32 @select_and_icmp_alt_bad_1(i32 %x, i32 %y, i32 %z) {
 
 define i32 @select_and_icmp_alt_bad_2(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @select_and_icmp_alt_bad_2(
-; CHECK-NEXT:    [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]]
-; CHECK-NEXT:    [[D:%.*]] = select i1 [[B]], i32 [[X]], i32 [[Z]]
+; CHECK-NEXT:    [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]]
+; CHECK-NEXT:    [[D:%.*]] = select i1 [[B]], i32 [[X:%.*]], i32 [[Z]]
 ; CHECK-NEXT:    ret i32 [[D]]
 ;
   %A = icmp ne i32 %x, %z
@@ -191,8 +191,8 @@ define i32 @select_and_icmp_alt_bad_2(i32 %x, i32 %y, i32 %z) {
 
 define i32 @select_and_icmp_alt_bad_3(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @select_and_icmp_alt_bad_3(
-; CHECK-NEXT:    [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]]
-; CHECK-NEXT:    [[D:%.*]] = select i1 [[B_NOT]], i32 [[Z]], i32 [[X]]
+; CHECK-NEXT:    [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]]
+; CHECK-NEXT:    [[D:%.*]] = select i1 [[B_NOT]], i32 [[Z]], i32 [[X:%.*]]
 ; CHECK-NEXT:    ret i32 [[D]]
 ;
   %A = icmp ne i32 %x, %z
@@ -204,8 +204,8 @@ define i32 @select_and_icmp_alt_bad_3(i32 %x, i32 %y, i32 %z) {
 
 define i32 @select_and_icmp_alt_bad_4(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @select_and_icmp_alt_bad_4(
-; CHECK-NEXT:    [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]]
-; CHECK-NEXT:    [[D:%.*]] = select i1 [[B]], i32 [[X]], i32 [[Z]]
+; CHECK-NEXT:    [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]]
+; CHECK-NEXT:    [[D:%.*]] = select i1 [[B]], i32 [[X:%.*]], i32 [[Z]]
 ; CHECK-NEXT:    ret i32 [[D]]
 ;
   %A = icmp eq i32 %x, %z
@@ -322,3 +322,11 @@ define i32 @select_and_icmp_alt_bad_false_val(i32 %x, i32 %y, i32 %z, i32 %k) {
   %D = select i1 %C, i32 %x, i32 %k
   ret i32 %D
 }
+
+!0 = !{!"function_entry_count", i64 1000}
+!1 = !{!"branch_weights", i32 2, i32 3}
+
+;.
+; CHECK: [[META0:![0-9]+]] = !{!"function_entry_count", i64 1000}
+; CHECK: [[PROF1]] = !{!"branch_weights", i32 2, i32 3}
+;.
diff --git a/llvm/test/Transforms/InstCombine/select-or-cmp.ll b/llvm/test/Transforms/InstCombine/select-or-cmp.ll
index 72a3747c5e405..82b069bc91e88 100644
--- a/llvm/test/Transforms/InstCombine/select-or-cmp.ll
+++ b/llvm/test/Transforms/InstCombine/select-or-cmp.ll
@@ -1,4 +1,4 @@
-; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals
 ; RUN: opt < %s -passes=instcombine -S | FileCheck %s
 
 define i32 @select_or_icmp(i32 %x, i32 %y, i32 %z) {
@@ -114,47 +114,47 @@ define i32 @select_or_icmp_inv(i32 %x, i32 %y, i32 %z) {
 
 ; Below used to be negative tests in InstSimplify, but are no more negative cases here
 
-define i32 @select_and_icmp_pred_bad_1(i32 %x, i32 %y, i32 %z) {
+define i32 @select_and_icmp_pred_bad_1(i32 %x, i32 %y, i32 %z) !prof !0 {
 ; CHECK-LABEL: @select_and_icmp_pred_bad_1(
-; CHECK-NEXT:    [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]]
-; CHECK-NEXT:    [[D:%.*]] = select i1 [[B_NOT]], i32 [[X]], i32 [[Z]]
+; CHECK-NEXT:    [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]]
+; CHECK-NEXT:    [[D:%.*]] = select i1 [[B_NOT]], i32 [[X:%.*]], i32 [[Z]], !prof [[PROF1:![0-9]+]]
 ; CHECK-NEXT:    ret i32 [[D]]
 ;
   %A = icmp eq i32 %x, %z
   %B = icmp ne i32 %y, %z
   %C = or i1 %A, %B
-  %D = select i1 %C, i32 %z, i32 %x
+  %D = select i1 %C, i32 %z, i32 %x, !prof !1
   ret i32 %D
 }
 
-define i32 @select_and_icmp_pred_bad_2(i32 %x, i32 %y, i32 %z) {
+define i32 @select_and_icmp_pred_bad_2(i32 %x, i32 %y, i32 %z) !prof !0 {
 ; CHECK-LABEL: @select_and_icmp_pred_bad_2(
-; CHECK-NEXT:    ret i32 [[Z]]
+; CHECK-NEXT:    ret i32 [[Z:%.*]]
 ;
   %A = icmp ne i32 %x, %z
   %B = icmp eq i32 %y, %z
   %C = or i1 %A, %B
-  %D = select i1 %C, i32 %z, i32 %x
+  %D = select i1 %C, i32 %z, i32 %x, !prof !1
   ret i32 %D
 }
 
-define i32 @select_and_icmp_pred_bad_3(i32 %x, i32 %y, i32 %z) {
+define i32 @select_and_icmp_pred_bad_3(i32 %x, i32 %y, i32 %z) !prof !0 {
 ; CHECK-LABEL: @select_and_icmp_pred_bad_3(
-; CHECK-NEXT:    [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]]
-; CHECK-NEXT:    [[D:%.*]] = select i1 [[B]], i32 [[Z]], i32 [[X]]
+; CHECK-NEXT:    [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]]
+; CHECK-NEXT:    [[D:%.*]] = select i1 [[B]], i32 [[Z]], i32 [[X:%.*]], !prof [[PROF2:![0-9]+]]
 ; CHECK-NEXT:    ret i32 [[D]]
 ;
   %A = icmp eq i32 %x, %z
   %B = icmp eq i32 %y, %z
   %C = or i1 %A, %B
-  %D = select i1 %C, i32 %z, i32 %x
+  %D = select i1 %C, i32 %z, i32 %x, !prof !1
   ret i32 %D
 }
 
 define i32 @select_and_icmp_pred_bad_4(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @select_and_icmp_pred_bad_4(
-; CHECK-NEXT:    [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]]
-; CHECK-NEXT:    [[D:%.*]] = select i1 [[B_NOT]], i32 [[X]], i32 [[Z]]
+; CHECK-NEXT:    [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]]
+; CHECK-NEXT:    [[D:%.*]] = select i1 [[B_NOT]], i32 [[X:%.*]], i32 [[Z]]
 ; CHECK-NEXT:    ret i32 [[D]]
 ;
   %A = icmp ne i32 %x, %z
@@ -166,8 +166,8 @@ define i32 @select_and_icmp_pred_bad_4(i32 %x, i32 %y, i32 %z) {
 
 define i32 @select_or_icmp_alt_bad_1(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @select_or_icmp_alt_bad_1(
-; CHECK-NEXT:    [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]]
-; CHECK-NEXT:    [[D:%.*]] = select i1 [[B_NOT]], i32 [[Z]], i32 [[X]]
+; CHECK-NEXT:    [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]]
+; CHECK-NEXT:    [[D:%.*]] = select i1 [[B_NOT]], i32 [[Z]], i32 [[X:%.*]]
 ; CHECK-NEXT:    ret i32 [[D]]
 ;
   %A = icmp eq i32 %x, %z
@@ -179,7 +179,7 @@ define i32 @select_or_icmp_alt_bad_1(i32 %x, i32 %y, i32 %z) {
 
 define i32 @select_or_icmp_alt_bad_2(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @select_or_icmp_alt_bad_2(
-; CHECK-NEXT:    ret i32 [[X]]
+; CHECK-NEXT:    ret i32 [[X:%.*]]
 ;
   %A = icmp ne i32 %x, %z
   %B = icmp eq i32 %y, %z
@@ -190,8 +190,8 @@ define i32 @select_or_icmp_alt_bad_2(i32 %x, i32 %y, i32 %z) {
 
 define i32 @select_or_icmp_alt_bad_3(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @select_or_icmp_alt_bad_3(
-; CHECK-NEXT:    [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]]
-; CHECK-NEXT:    [[D:%.*]] = select i1 [[B]], i32 [[X]], i32 [[Z]]
+; CHECK-NEXT:    [[B:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]]
+; CHECK-NEXT:    [[D:%.*]] = select i1 [[B]], i32 [[X:%.*]], i32 [[Z]]
 ; CHECK-NEXT:    ret i32 [[D]]
 ;
   %A = icmp eq i32 %x, %z
@@ -203,8 +203,8 @@ define i32 @select_or_icmp_alt_bad_3(i32 %x, i32 %y, i32 %z) {
 
 define i32 @select_or_icmp_alt_bad_4(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @select_or_icmp_alt_bad_4(
-; CHECK-NEXT:    [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z]]
-; CHECK-NEXT:    [[D:%.*]] = select i1 [[B_NOT]], i32 [[Z]], i32 [[X]]
+; CHECK-NEXT:    [[B_NOT:%.*]] = icmp eq i32 [[Y:%.*]], [[Z:%.*]]
+; CHECK-NEXT:    [[D:%.*]] = select i1 [[B_NOT]], i32 [[Z]], i32 [[X:%.*]]
 ; CHECK-NEXT:    ret i32 [[D]]
 ;
   %A = icmp ne i32 %x, %z
@@ -321,3 +321,11 @@ define i32 @select_or_icmp_alt_bad_false_val(i32 %x, i32 %y, i32 %z, i32 %k) {
   %D = select i1 %C, i32 %x, i32 %k
   ret i32 %D
 }
+
+!0 = !{!"function_entry_count", i64 1000}
+!1 = !{!"branch_weights", i32 2, i32 3}
+;.
+; CHECK: [[META0:![0-9]+]] = !{!"function_entry_count", i64 1000}
+; CHECK: [[PROF1]] = !{!"branch_weights", i32 3, i32 2}
+; CHECK: [[PROF2]] = !{!"branch_weights", i32 2, i32 3}
+;.

alanzhao1 requested review from joker-eph and mtrofin October 3, 2025 18:29

alanzhao1 requested a review from nikic as a code owner October 3, 2025 18:29

llvmbot added llvm:instcombine Covers the InstCombine, InstSimplify and AggressiveInstCombine passes llvm:transforms labels Oct 3, 2025

alanzhao1 mentioned this pull request Oct 3, 2025

[InstCombine] Preserve profile after folding select instructions with conditionals #159666

Merged

alanzhao1 merged commit 3b38314 into llvm:main Oct 3, 2025
12 checks passed

alanzhao1 deleted the bugfix/reland-instcombine-fix branch October 3, 2025 22:17

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Reapply "[InstCombine] Preserve profile after folding select instructions with conditionals" (#161885) #161890

Reapply "[InstCombine] Preserve profile after folding select instructions with conditionals" (#161885) #161890

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Reapply "[InstCombine] Preserve profile after folding select instructions with conditionals" (#161885) #161890

Reapply "[InstCombine] Preserve profile after folding select instructions with conditionals" (#161885) #161890

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