Instcombine: Fix pattern where the sext did not dominate the icmp using it
llvm-svn: 123121
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 71a286e..ff41ab8 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -281,8 +281,8 @@
Value *FalseVal = SI.getFalseValue();
// Check cases where the comparison is with a constant that
- // can be adjusted to fit the min/max idiom. We may edit ICI in
- // place here, so make sure the select is the only user.
+ // can be adjusted to fit the min/max idiom. We may move or edit ICI
+ // here, so make sure the select is the only user.
if (ICI->hasOneUse())
if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) {
// X < MIN ? T : F --> F
@@ -364,6 +364,11 @@
ICI->setOperand(1, CmpRHS);
SI.setOperand(1, TrueVal);
SI.setOperand(2, FalseVal);
+
+ // Move ICI instruction right before the select instruction. Otherwise
+ // the sext/zext value may be defined after the ICI instruction uses it.
+ ICI->moveBefore(&SI);
+
Changed = true;
break;
}
diff --git a/llvm/test/Transforms/InstCombine/select.ll b/llvm/test/Transforms/InstCombine/select.ll
index c9b880d..6633564 100644
--- a/llvm/test/Transforms/InstCombine/select.ll
+++ b/llvm/test/Transforms/InstCombine/select.ll
@@ -678,3 +678,14 @@
; CHECK-NEXT: %min = select i1 %is_a_nonpositive, i64 %a_ext, i64 2
; CHECK-NEXT: ret i64 %min
}
+define i64 @test50(i32 %a) nounwind {
+ %is_a_nonpositive = icmp ult i32 %a, 3
+ %a_ext = sext i32 %a to i64
+ %min = select i1 %is_a_nonpositive, i64 2, i64 %a_ext
+ ret i64 %min
+; CHECK: @test50
+; CHECK-NEXT: %a_ext = sext i32 %a to i64
+; CHECK-NEXT: %is_a_nonpositive = icmp ugt i64 %a_ext, 2
+; CHECK-NEXT: %min = select i1 %is_a_nonpositive, i64 %a_ext, i64 2
+; CHECK-NEXT: ret i64 %min
+}