[CVP] Flip signedness icmp predicate in use level

[XChy]

Resolve #69928.
Alive2 Proof.

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: XChy (XChy)

Changes

Resolve #69928.
Alive2 Proof.

---

Full diff: https://github.com/llvm/llvm-project/pull/69948.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp (+3-2)
• (modified) llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll (+75)

diff --git a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
index 523196e5e6eab71..9043c434313fedc 100644
--- a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
+++ b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
@@ -294,8 +294,9 @@ static bool processICmp(ICmpInst *Cmp, LazyValueInfo *LVI) {
 
   ICmpInst::Predicate UnsignedPred =
       ConstantRange::getEquivalentPredWithFlippedSignedness(
-          Cmp->getPredicate(), LVI->getConstantRange(Cmp->getOperand(0), Cmp),
-          LVI->getConstantRange(Cmp->getOperand(1), Cmp));
+          Cmp->getPredicate(),
+          LVI->getConstantRangeAtUse(Cmp->getOperandUse(0)),
+          LVI->getConstantRangeAtUse(Cmp->getOperandUse(1)));
 
   if (UnsignedPred == ICmpInst::Predicate::BAD_ICMP_PREDICATE)
     return false;
diff --git a/llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll b/llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll
index c4f0ade39942a76..24acd528e6dcde5 100644
--- a/llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll
@@ -1246,3 +1246,78 @@ declare <2 x i8> @llvm.umin.v2i8(<2 x i8>, <2 x i8>)
 declare <2 x i8> @llvm.umax.v2i8(<2 x i8>, <2 x i8>)
 
 attributes #4 = { noreturn }
+
+define i64 @test_select_flip(i64 noundef %arg) {
+; CHECK-LABEL: @test_select_flip(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp ult i64 [[ARG:%.*]], 1000
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp ult i64 [[ARG]], 100
+; CHECK-NEXT:    [[SELECT:%.*]] = select i1 [[CMP1]], i1 [[CMP2]], i1 false
+; CHECK-NEXT:    br i1 [[SELECT]], label [[GOOD:%.*]], label [[BAD:%.*]]
+; CHECK:       bad:
+; CHECK-NEXT:    ret i64 1
+; CHECK:       good:
+; CHECK-NEXT:    ret i64 0
+;
+entry:
+  %cmp1 = icmp ult i64 %arg, 1000
+  %cmp2 = icmp slt i64 %arg, 100
+  %select = select i1 %cmp1, i1 %cmp2, i1 false
+  br i1 %select, label %good, label %bad
+
+bad:
+  ret i64 1
+
+good:
+  ret i64 0
+}
+
+define i64 @test_select_flip_fail1(i64 noundef %arg) {
+; CHECK-LABEL: @test_select_flip_fail1(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp slt i64 [[ARG:%.*]], 1000
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp slt i64 [[ARG]], 100
+; CHECK-NEXT:    [[SELECT:%.*]] = select i1 [[CMP1]], i1 [[CMP2]], i1 false
+; CHECK-NEXT:    br i1 [[SELECT]], label [[GOOD:%.*]], label [[BAD:%.*]]
+; CHECK:       bad:
+; CHECK-NEXT:    ret i64 1
+; CHECK:       good:
+; CHECK-NEXT:    ret i64 0
+;
+entry:
+  %cmp1 = icmp slt i64 %arg, 1000
+  %cmp2 = icmp slt i64 %arg, 100
+  %select = select i1 %cmp1, i1 %cmp2, i1 false
+  br i1 %select, label %good, label %bad
+
+bad:
+  ret i64 1
+
+good:
+  ret i64 0
+}
+
+define i64 @test_select_flip_fail2(i64 noundef %arg) {
+; CHECK-LABEL: @test_select_flip_fail2(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp ult i64 [[ARG:%.*]], 1000
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp slt i64 [[ARG]], 100
+; CHECK-NEXT:    [[SELECT:%.*]] = select i1 [[CMP1]], i1 false, i1 [[CMP2]]
+; CHECK-NEXT:    br i1 [[SELECT]], label [[GOOD:%.*]], label [[BAD:%.*]]
+; CHECK:       bad:
+; CHECK-NEXT:    ret i64 1
+; CHECK:       good:
+; CHECK-NEXT:    ret i64 0
+;
+entry:
+  %cmp1 = icmp ult i64 %arg, 1000
+  %cmp2 = icmp slt i64 %arg, 100
+  %select = select i1 %cmp1, i1 false, i1 %cmp2
+  br i1 %select, label %good, label %bad
+
+bad:
+  ret i64 1
+
+good:
+  ret i64 0
+}

[nikic]

The change looks good to me, but can you please adjust the test coverage so the second condition is not implied (i.e. folds to true) by the first? In that case the transform isn't really meaningful.

As you mark #69928 as fixed, you should also add the test case from there.

[nikic]

The br is unnecessary.

[nikic]

You've removed it everywhere but here?

[XChy]

It is a copy from the original issue, so it contains br.

[nikic]

We don't need a literal copy, just the relevant part.

[nikic]

LGTM apart from test nits.