[llvm] 2fd3037 - [ConstantFold] Allow propagation of poison for and/or i1

[Juneyoung Lee via llvm-commits]

Author: Juneyoung Lee
Date: 2021-06-24T02:03:09+09:00
New Revision: 2fd3037ac615643fe8058292d2b89bb19a49cb2f

URL: https://github.com/llvm/llvm-project/commit/2fd3037ac615643fe8058292d2b89bb19a49cb2f
DIFF: https://github.com/llvm/llvm-project/commit/2fd3037ac615643fe8058292d2b89bb19a49cb2f.diff

LOG: [ConstantFold] Allow propagation of poison for and/or i1

They were disallowed due to its bad interaction with select i1 -> and/or i1.
The transformation is now disabled by D101191, so let's revive this.

Added: 
    

Modified: 
    llvm/lib/IR/ConstantFold.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index 652ccd3efb31..e2925784953b 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -1124,14 +1124,7 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode, Constant *C1,
   }
 
   // Binary operations propagate poison.
-  // 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)))
+  if (isa<PoisonValue>(C1) || isa<PoisonValue>(C2))
     return PoisonValue::get(C1->getType());
 
   // Handle scalar UndefValue and scalable vector UndefValue. Fixed-length