[llvm] [InstCombine] Fix type mismatch between cond and value in `foldSelectToCopysign` (PR #76343)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Yingwei Zheng (dtcxzyw)

<details>
<summary>Changes</summary>

This patch fixes the miscompilation when we try to bitcast a floating point vector into an integer scalar.


---
Full diff: https://github.com/llvm/llvm-project/pull/76343.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp (+3) 
- (modified) llvm/test/Transforms/InstCombine/select.ll (+15) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 20bf00344b144b..3c6ce450c5bcfa 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -2363,6 +2363,9 @@ static Instruction *foldSelectToCopysign(SelectInst &Sel,
   Value *FVal = Sel.getFalseValue();
   Type *SelType = Sel.getType();
 
+  if (ICmpInst::makeCmpResultType(TVal->getType()) != Cond->getType())
+    return nullptr;
+
   // Match select ?, TC, FC where the constants are equal but negated.
   // TODO: Generalize to handle a negated variable operand?
   const APFloat *TC, *FC;
diff --git a/llvm/test/Transforms/InstCombine/select.ll b/llvm/test/Transforms/InstCombine/select.ll
index 7583a75385a769..94aa012f868015 100644
--- a/llvm/test/Transforms/InstCombine/select.ll
+++ b/llvm/test/Transforms/InstCombine/select.ll
@@ -1735,6 +1735,21 @@ define float @copysign_type_mismatch(double %x) {
 
 ; Negative test
 
+define <2 x float> @copysign_type_mismatch2(<2 x float> %x) {
+; CHECK-LABEL: @copysign_type_mismatch2(
+; CHECK-NEXT:    [[I:%.*]] = bitcast <2 x float> [[X:%.*]] to i64
+; CHECK-NEXT:    [[ISPOS:%.*]] = icmp sgt i64 [[I]], -1
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[ISPOS]], <2 x float> <float 1.000000e+00, float 1.000000e+00>, <2 x float> <float -1.000000e+00, float -1.000000e+00>
+; CHECK-NEXT:    ret <2 x float> [[R]]
+;
+  %i = bitcast <2 x float> %x to i64
+  %ispos = icmp sgt i64 %i, -1
+  %r = select i1 %ispos, <2 x float> <float 1.0, float 1.0>, <2 x float> <float -1.0, float -1.0>
+  ret <2 x float> %r
+}
+
+; Negative test
+
 define float @copysign_wrong_cmp(float %x) {
 ; CHECK-LABEL: @copysign_wrong_cmp(
 ; CHECK-NEXT:    [[I:%.*]] = bitcast float [[X:%.*]] to i32

``````````

</details>


https://github.com/llvm/llvm-project/pull/76343