[llvm] 9bea770 - [InstCombine] Only requite not-undef in select equiv fold

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2024-06-06T09:38:08+02:00
New Revision: 9bea770b63861250c8bbec46f68df73da4f09508

URL: https://github.com/llvm/llvm-project/commit/9bea770b63861250c8bbec46f68df73da4f09508
DIFF: https://github.com/llvm/llvm-project/commit/9bea770b63861250c8bbec46f68df73da4f09508.diff

LOG: [InstCombine] Only requite not-undef in select equiv fold

As the comment already indicates, only replacement with undef
is problematic, as it introduces an additional use of undef.
Use the correct ValueTracking helper.

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
    llvm/test/Transforms/InstCombine/select.ll

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 313beb7b6407a..d2aaa5e230545 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -1294,8 +1294,7 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
   // X == Y ? X : Z with X == Y ? Y : Z, as that would lead to an infinite
   // replacement cycle.
   Value *CmpLHS = Cmp.getOperand(0), *CmpRHS = Cmp.getOperand(1);
-  if (TrueVal != CmpLHS &&
-      isGuaranteedNotToBeUndefOrPoison(CmpRHS, SQ.AC, &Sel, &DT)) {
+  if (TrueVal != CmpLHS && isGuaranteedNotToBeUndef(CmpRHS, SQ.AC, &Sel, &DT)) {
     if (Value *V = simplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, SQ,
                                           /* AllowRefinement */ true))
       // Require either the replacement or the simplification result to be a
@@ -1316,8 +1315,7 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
       if (replaceInInstruction(TrueVal, CmpLHS, CmpRHS))
         return &Sel;
   }
-  if (TrueVal != CmpRHS &&
-      isGuaranteedNotToBeUndefOrPoison(CmpLHS, SQ.AC, &Sel, &DT))
+  if (TrueVal != CmpRHS && isGuaranteedNotToBeUndef(CmpLHS, SQ.AC, &Sel, &DT))
     if (Value *V = simplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, SQ,
                                           /* AllowRefinement */ true))
       if (isa<Constant>(CmpLHS) || isa<Constant>(V))

diff  --git a/llvm/test/Transforms/InstCombine/select.ll b/llvm/test/Transforms/InstCombine/select.ll
index d110cc9f9eb4e..29b4d602ffa02 100644
--- a/llvm/test/Transforms/InstCombine/select.ll
+++ b/llvm/test/Transforms/InstCombine/select.ll
@@ -2852,8 +2852,7 @@ define i8 @select_replacement_sub_noundef_but_may_be_poison(i8 %x, i8 noundef %y
 ; CHECK-LABEL: @select_replacement_sub_noundef_but_may_be_poison(
 ; CHECK-NEXT:    [[Y:%.*]] = shl nuw i8 [[YY:%.*]], 1
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[Y]], [[X:%.*]]
-; CHECK-NEXT:    [[SUB:%.*]] = sub i8 [[X]], [[Y]]
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i8 [[SUB]], i8 [[Z:%.*]]
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i8 0, i8 [[Z:%.*]]
 ; CHECK-NEXT:    ret i8 [[SEL]]
 ;
   %y = shl nuw i8 %yy, 1