[llvm-branch-commits] [llvm] 9c49dcc - [ConstantFold] Don't fold and/or i1 poison to poison (NFC)

[Juneyoung Lee via llvm-branch-commits]

Author: Juneyoung Lee
Date: 2020-11-30T22:58:31+09:00
New Revision: 9c49dcc356eb4c59fc1353bbbaae6d3a56a656c1

URL: https://github.com/llvm/llvm-project/commit/9c49dcc356eb4c59fc1353bbbaae6d3a56a656c1
DIFF: https://github.com/llvm/llvm-project/commit/9c49dcc356eb4c59fc1353bbbaae6d3a56a656c1.diff

LOG: [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

Added: 
    

Modified: 
    llvm/lib/IR/ConstantFold.cpp
    llvm/test/Transforms/InstSimplify/ConstProp/poison.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index 3243ddd604ee..d9564a31b5de 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

diff  --git a/llvm/test/Transforms/InstSimplify/ConstProp/poison.ll b/llvm/test/Transforms/InstSimplify/ConstProp/poison.ll
index 542823a44e2f..f3fe29ff57ba 100644
--- a/llvm/test/Transforms/InstSimplify/ConstProp/poison.ll
+++ b/llvm/test/Transforms/InstSimplify/ConstProp/poison.ll
@@ -114,3 +114,15 @@ define void @other_ops(i8 %x) {
   call void (...) @use(i1 %i1, i1 %i2, i8 %i3, i8 %i4, i8* getelementptr (i8, i8* poison, i64 1), i8* getelementptr inbounds (i8, i8* undef, i64 1))
   ret void
 }
+
+; TODO: these must be folded into poison; D92270
+define void @logicalops_i1(i1 %x) {
+; CHECK-LABEL: @logicalops_i1(
+; CHECK-NEXT:    call void (...) @use(i1 true, i1 false)
+; CHECK-NEXT:    ret void
+;
+  %i1 = or i1 %x, poison
+  %i2 = and i1 %x, poison
+  call void (...) @use(i1 %i1, i1 %i2)
+  ret void
+}