[llvm] d085b42 - [InstSimplify] Do not simplify freeze in `simplifyWithOpReplaced` (#91215)

[via llvm-commits]

Author: Yingwei Zheng
Date: 2024-05-08T10:04:09+08:00
New Revision: d085b42cbbefe79a41113abcd2b1e1f2a203acef

URL: https://github.com/llvm/llvm-project/commit/d085b42cbbefe79a41113abcd2b1e1f2a203acef
DIFF: https://github.com/llvm/llvm-project/commit/d085b42cbbefe79a41113abcd2b1e1f2a203acef.diff

LOG: [InstSimplify] Do not simplify freeze in `simplifyWithOpReplaced` (#91215)

See the LangRef:
> All uses of a value returned by the same ‘freeze’ instruction are
guaranteed to always observe the same value, while different ‘freeze’
instructions may yield different values.

It is incorrect to replace freezes with the simplified value.

Proof:
https://alive2.llvm.org/ce/z/3Dn9Cd
https://alive2.llvm.org/ce/z/Qyh5h6

Fixes https://github.com/llvm/llvm-project/issues/91178

Added: 
    

Modified: 
    llvm/lib/Analysis/InstructionSimplify.cpp
    llvm/test/Transforms/InstCombine/icmp.ll
    llvm/test/Transforms/InstCombine/select.ll
    llvm/test/Transforms/PGOProfile/chr.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 4061dae83c10f..37a7259a5cd02 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4312,6 +4312,10 @@ static Value *simplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp,
   if (match(I, m_Intrinsic<Intrinsic::is_constant>()))
     return nullptr;
 
+  // Don't simplify freeze.
+  if (isa<FreezeInst>(I))
+    return nullptr;
+
   // Replace Op with RepOp in instruction operands.
   SmallVector<Value *, 8> NewOps;
   bool AnyReplaced = false;

diff  --git a/llvm/test/Transforms/InstCombine/icmp.ll b/llvm/test/Transforms/InstCombine/icmp.ll
index 31093c7ca1036..2d786c8f48833 100644
--- a/llvm/test/Transforms/InstCombine/icmp.ll
+++ b/llvm/test/Transforms/InstCombine/icmp.ll
@@ -5183,3 +5183,18 @@ entry:
   %cmp = icmp eq i8 %add2, %add1
   ret i1 %cmp
 }
+
+define i1 @icmp_freeze_sext(i16 %x, i16 %y) {
+; CHECK-LABEL: @icmp_freeze_sext(
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp uge i16 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    [[CMP1_FR:%.*]] = freeze i1 [[CMP1]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i16 [[Y]], 0
+; CHECK-NEXT:    [[CMP2:%.*]] = or i1 [[TMP1]], [[CMP1_FR]]
+; CHECK-NEXT:    ret i1 [[CMP2]]
+;
+  %cmp1 = icmp uge i16 %x, %y
+  %ext = sext i1 %cmp1 to i16
+  %ext.fr = freeze i16 %ext
+  %cmp2 = icmp uge i16 %ext.fr, %y
+  ret i1 %cmp2
+}

diff  --git a/llvm/test/Transforms/InstCombine/select.ll b/llvm/test/Transforms/InstCombine/select.ll
index 2efe2742ca491..2ade6faa99be3 100644
--- a/llvm/test/Transforms/InstCombine/select.ll
+++ b/llvm/test/Transforms/InstCombine/select.ll
@@ -4580,3 +4580,35 @@ define i32 @sequence_select_with_same_cond_extra_use(i1 %c1, i1 %c2){
   %s3 = select i1 %c1, i32 789, i32 %s2
   ret i32 %s3
 }
+
+define i8 @test_replace_freeze_multiuse(i1 %x, i8 %y) {
+; CHECK-LABEL: @test_replace_freeze_multiuse(
+; CHECK-NEXT:    [[EXT:%.*]] = zext i1 [[X:%.*]] to i8
+; CHECK-NEXT:    [[SHL:%.*]] = shl nuw i8 [[EXT]], [[Y:%.*]]
+; CHECK-NEXT:    [[SHL_FR:%.*]] = freeze i8 [[SHL]]
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[X]], i8 0, i8 [[SHL_FR]]
+; CHECK-NEXT:    [[ADD:%.*]] = add i8 [[SHL_FR]], [[SEL]]
+; CHECK-NEXT:    ret i8 [[ADD]]
+;
+  %ext = zext i1 %x to i8
+  %shl = shl nuw i8 %ext, %y
+  %shl.fr = freeze i8 %shl
+  %sel = select i1 %x, i8 0, i8 %shl.fr
+  %add = add i8 %shl.fr, %sel
+  ret i8 %add
+}
+
+define i8 @test_replace_freeze_oneuse(i1 %x, i8 %y) {
+; CHECK-LABEL: @test_replace_freeze_oneuse(
+; CHECK-NEXT:    [[EXT:%.*]] = zext i1 [[X:%.*]] to i8
+; CHECK-NEXT:    [[SHL:%.*]] = shl nuw i8 [[EXT]], [[Y:%.*]]
+; CHECK-NEXT:    [[SHL_FR:%.*]] = freeze i8 [[SHL]]
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[X]], i8 0, i8 [[SHL_FR]]
+; CHECK-NEXT:    ret i8 [[SEL]]
+;
+  %ext = zext i1 %x to i8
+  %shl = shl nuw i8 %ext, %y
+  %shl.fr = freeze i8 %shl
+  %sel = select i1 %x, i8 0, i8 %shl.fr
+  ret i8 %sel
+}

diff  --git a/llvm/test/Transforms/PGOProfile/chr.ll b/llvm/test/Transforms/PGOProfile/chr.ll
index 0551a171091ca..38e8f8536a19c 100644
--- a/llvm/test/Transforms/PGOProfile/chr.ll
+++ b/llvm/test/Transforms/PGOProfile/chr.ll
@@ -1298,11 +1298,12 @@ define i32 @test_chr_14(ptr %i, ptr %j, i32 %sum0, i1 %pred, i32 %z) !prof !14 {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[Z_FR:%.*]] = freeze i32 [[Z:%.*]]
 ; CHECK-NEXT:    [[I0:%.*]] = load i32, ptr [[I:%.*]], align 4
-; CHECK-NEXT:    [[V1:%.*]] = icmp eq i32 [[Z_FR]], 1
-; CHECK-NEXT:    br i1 [[V1]], label [[BB1:%.*]], label [[ENTRY_SPLIT_NONCHR:%.*]], !prof [[PROF15]]
+; CHECK-NEXT:    [[V1_NOT:%.*]] = icmp eq i32 [[Z_FR]], 1
+; CHECK-NEXT:    br i1 [[V1_NOT]], label [[BB1:%.*]], label [[ENTRY_SPLIT_NONCHR:%.*]], !prof [[PROF15]]
 ; CHECK:       entry.split.nonchr:
+; CHECK-NEXT:    [[PRED_FR:%.*]] = freeze i1 [[PRED:%.*]]
 ; CHECK-NEXT:    [[V0:%.*]] = icmp eq i32 [[Z_FR]], 0
-; CHECK-NEXT:    [[V3_NONCHR:%.*]] = and i1 [[V0]], [[PRED:%.*]]
+; CHECK-NEXT:    [[V3_NONCHR:%.*]] = and i1 [[V0]], [[PRED_FR]]
 ; CHECK-NEXT:    br i1 [[V3_NONCHR]], label [[BB0_NONCHR:%.*]], label [[BB1]], !prof [[PROF16]]
 ; CHECK:       bb0.nonchr:
 ; CHECK-NEXT:    call void @foo()