[InstCombine] fix undef propagation for vector urem transform (PR44186)

As described here:
https://bugs.llvm.org/show_bug.cgi?id=44186

The match() code safely allows undef values, but we can't safely
propagate a vector constant that contains an undef to the new
compare instruction.

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 0b9128a..f7b39d9 100644 (file)
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -1368,8 +1368,10 @@ Instruction *InstCombiner::visitURem(BinaryOperator &I) {
   }
 
   // 1 urem X -> zext(X != 1)
-  if (match(Op0, m_One()))
-    return CastInst::CreateZExtOrBitCast(Builder.CreateICmpNE(Op1, Op0), Ty);
+  if (match(Op0, m_One())) {
+    Value *Cmp = Builder.CreateICmpNE(Op1, ConstantInt::get(Ty, 1));
+    return CastInst::CreateZExtOrBitCast(Cmp, Ty);
+  }
 
   // X urem C -> X < C ? X : X - C, where C >= signbit.
   if (match(Op1, m_Negative())) {

diff --git a/llvm/test/Transforms/InstCombine/vector-urem.ll b/llvm/test/Transforms/InstCombine/vector-urem.ll
index 113451f..c9b79b2 100644 (file)
--- a/llvm/test/Transforms/InstCombine/vector-urem.ll
+++ b/llvm/test/Transforms/InstCombine/vector-urem.ll
@@ -39,7 +39,7 @@ define <4 x i32> @test_v4i32_one(<4 x i32> %a0) {
 
 define <4 x i32> @test_v4i32_one_undef(<4 x i32> %a0) {
 ; CHECK-LABEL: @test_v4i32_one_undef(
-; CHECK-NEXT:    [[TMP1:%.*]] = icmp ne <4 x i32> [[A0:%.*]], <i32 1, i32 1, i32 1, i32 undef>
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ne <4 x i32> [[A0:%.*]], <i32 1, i32 1, i32 1, i32 1>
 ; CHECK-NEXT:    [[TMP2:%.*]] = zext <4 x i1> [[TMP1]] to <4 x i32>
 ; CHECK-NEXT:    ret <4 x i32> [[TMP2]]
 ;