[llvm] 0dc20e3 - [InstSimplify] fold 'xor X, poison' and 'div/rem X, poison' to poison

[Nuno Lopes via llvm-commits]

Author: Nuno Lopes
Date: 2022-01-30T10:46:54Z
New Revision: 0dc20e321cb58946cf14e59aa028ab6287bfe687

URL: https://github.com/llvm/llvm-project/commit/0dc20e321cb58946cf14e59aa028ab6287bfe687
DIFF: https://github.com/llvm/llvm-project/commit/0dc20e321cb58946cf14e59aa028ab6287bfe687.diff

LOG: [InstSimplify] fold 'xor X, poison' and 'div/rem X, poison' to poison

Added: 
    

Modified: 
    llvm/lib/Analysis/InstructionSimplify.cpp
    llvm/test/Transforms/NewGVN/basic.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index b71b39334ace7..4775340b34386 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -951,7 +951,7 @@ static Value *simplifyDivRem(Instruction::BinaryOps Opcode, Value *Op0,
 
   // X / undef -> poison
   // X % undef -> poison
-  if (Q.isUndefValue(Op1))
+  if (Q.isUndefValue(Op1) || isa<PoisonValue>(Op1))
     return PoisonValue::get(Ty);
 
   // X / 0 -> poison
@@ -2418,6 +2418,10 @@ static Value *SimplifyXorInst(Value *Op0, Value *Op1, const SimplifyQuery &Q,
   if (Constant *C = foldOrCommuteConstant(Instruction::Xor, Op0, Op1, Q))
     return C;
 
+  // X ^ poison -> poison
+  if (isa<PoisonValue>(Op1))
+    return Op1;
+
   // A ^ undef -> undef
   if (Q.isUndefValue(Op1))
     return Op1;

diff  --git a/llvm/test/Transforms/NewGVN/basic.ll b/llvm/test/Transforms/NewGVN/basic.ll
index fb167ebd0fac5..970ec81d00544 100644
--- a/llvm/test/Transforms/NewGVN/basic.ll
+++ b/llvm/test/Transforms/NewGVN/basic.ll
@@ -44,8 +44,7 @@ define i8 @simplify_add_poison(i8 %x) {
 
 define i8 @simplify_xor_poison(i8 %x) {
 ; CHECK-LABEL: @simplify_xor_poison(
-; CHECK-NEXT:    [[R:%.*]] = xor i8 poison, [[X:%.*]]
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 poison
 ;
   %r = xor i8 poison, %x
   ret i8 %r
@@ -61,8 +60,7 @@ define i8 @simplify_sdiv_poison(i8 %x) {
 
 define i8 @simplify_urem_poison(i8 %x) {
 ; CHECK-LABEL: @simplify_urem_poison(
-; CHECK-NEXT:    [[R:%.*]] = urem i8 [[X:%.*]], poison
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 poison
 ;
   %r = urem i8 %x, poison
   ret i8 %r