[ValueTracking] Respect `samesign` flag in `isKnownInversion` (#112390)

In https://github.com/llvm/llvm-project/pull/93591 we introduced
`isKnownInversion` and assumes `X` is poison implies `Y` is poison
because they share common operands. But after introducing `samesign`
this assumption no longer hold if `X` is an icmp has `samesign` flag.

Alive2 link: https://alive2.llvm.org/ce/z/rj3EwQ (Please run it locally
with this patch and https://github.com/AliveToolkit/alive2/pull/1098).

This approach is the most conservative way in my mind to address this
problem. If `X` has `samesign` flag, it will check if `Y` also has this
flag and make sure constant RHS operands have the same sign.

Fixes https://github.com/llvm/llvm-project/issues/112350.

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index eb8d170..e9ed8b3 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -8522,6 +8522,10 @@ bool llvm::isKnownInversion(const Value *X, const Value *Y) {
       !match(Y, m_c_ICmp(Pred2, m_Specific(A), m_Value(C))))
     return false;
 
+  // They must both have samesign flag or not.
+  if (cast<ICmpInst>(X)->hasSameSign() != cast<ICmpInst>(Y)->hasSameSign())
+    return false;
+
   if (B == C)
     return Pred1 == ICmpInst::getInversePredicate(Pred2);
 
@@ -8530,6 +8534,11 @@ bool llvm::isKnownInversion(const Value *X, const Value *Y) {
   if (!match(B, m_APInt(RHSC1)) || !match(C, m_APInt(RHSC2)))
     return false;
 
+  // Sign bits of two RHSCs should match.
+  if (cast<ICmpInst>(X)->hasSameSign() &&
+      RHSC1->isNonNegative() != RHSC2->isNonNegative())
+    return false;
+
   const auto CR1 = ConstantRange::makeExactICmpRegion(Pred1, *RHSC1);
   const auto CR2 = ConstantRange::makeExactICmpRegion(Pred2, *RHSC2);