ConstantFoldInstOperands doesn't like compares, hand it off to instsimplify instead.

Fixes PR10040.

llvm-svn: 132254

2 files changed, 20 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 2a451ce5f12..aeb3c3e880f 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -298,6 +298,16 @@ static Value *SimplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp,
       return SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, TD);
   }
 
+  // Same for CmpInsts.
+  if (CmpInst *C = dyn_cast<CmpInst>(I)) {
+    if (C->getOperand(0) == Op)
+      return SimplifyCmpInst(C->getPredicate(), RepOp, C->getOperand(1), TD);
+    if (C->getOperand(1) == Op)
+      return SimplifyCmpInst(C->getPredicate(), C->getOperand(0), RepOp, TD);
+  }
+
+  // TODO: We could hand off more cases to instsimplify here.
+
   // If all operands are constant after substituting Op for RepOp then we can
   // constant fold the instruction.
   if (Constant *CRepOp = dyn_cast<Constant>(RepOp)) {
diff --git a/llvm/test/Transforms/InstCombine/select.ll b/llvm/test/Transforms/InstCombine/select.ll
index 379228512cd..4ca9bd2c07c 100644
--- a/llvm/test/Transforms/InstCombine/select.ll
+++ b/llvm/test/Transforms/InstCombine/select.ll
@@ -789,3 +789,13 @@ define i32 @test59(i32 %x, i32 %y) nounwind {
 ; CHECK-NEXT: and i32 %x, %y
 ; CHECK-NEXT: ret
 }
+
+define i1 @test60(i32 %x, i1* %y) nounwind {
+  %cmp = icmp eq i32 %x, 0
+  %load = load i1* %y, align 1
+  %cmp1 = icmp slt i32 %x, 1
+  %sel = select i1 %cmp, i1 %load, i1 %cmp1
+  ret i1 %sel
+; CHECK: @test60
+; CHECK: select
+}