[ConstantFold] Don't fold and/or i1 poison to poison (NFC)

.. because it causes miscompilation when combined with select i1 -> and/or.

It is the select fold which is incorrect; but it is costly to disable the fold, so hack this one.

D92270

1 files changed, 8 insertions, 1 deletions

diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index 3243ddd..d9564a3 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -1105,7 +1105,14 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode, Constant *C1,
   }
 
   // Binary operations propagate poison.
-  if (isa<PoisonValue>(C1) || isa<PoisonValue>(C2))
+  // FIXME: Currently, or/and i1 poison aren't folded into poison because
+  // it causes miscompilation when combined with another optimization in
+  // InstCombine (select i1 -> and/or). The select fold is wrong, but
+  // fixing it requires an effort, so temporarily disable this until it is
+  // fixed.
+  bool PoisonFold = !C1->getType()->isIntegerTy(1) ||
+                    (Opcode != Instruction::Or && Opcode != Instruction::And);
+  if (PoisonFold && (isa<PoisonValue>(C1) || isa<PoisonValue>(C2)))
     return PoisonValue::get(C1->getType());
 
   // Handle scalar UndefValue and scalable vector UndefValue. Fixed-length