[InstCombine] Guard noundef for transformation from xor to or disjoint

[vfdff]

Fix #96857

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Allen (vfdff)

Changes

Fix #96857

---

Full diff: https://github.com/llvm/llvm-project/pull/96905.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (+6-2)
• (modified) llvm/test/Transforms/InstCombine/xor.ll (+32)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index d767fa3930e2f..a8547b40eb6b0 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -4593,8 +4593,12 @@ Instruction *InstCombinerImpl::visitXor(BinaryOperator &I) {
   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
   Value *M;
   if (match(&I, m_c_Xor(m_c_And(m_Not(m_Value(M)), m_Value()),
-                        m_c_And(m_Deferred(M), m_Value()))))
-    return BinaryOperator::CreateDisjointOr(Op0, Op1);
+                        m_c_And(m_Deferred(M), m_Value())))) {
+    if (isGuaranteedNotToBeUndefOrPoison(M))
+      return BinaryOperator::CreateDisjointOr(Op0, Op1);
+    else
+      return BinaryOperator::CreateOr(Op0, Op1);
+  }
 
   if (Instruction *Xor = visitMaskedMerge(I, Builder))
     return Xor;
diff --git a/llvm/test/Transforms/InstCombine/xor.ll b/llvm/test/Transforms/InstCombine/xor.ll
index 9a59db40ef8b1..2ff95821f4e00 100644
--- a/llvm/test/Transforms/InstCombine/xor.ll
+++ b/llvm/test/Transforms/InstCombine/xor.ll
@@ -1453,3 +1453,35 @@ define i32 @tryFactorization_xor_ashr_ashr(i32 %a) {
   %xor = xor i32 %not, %shr1
   ret i32 %xor
 }
+
+; https://alive2.llvm.org/ce/z/SOxv-e
+define i4 @PR96857_xor_with_noundef(i4  %val0, i4  %val1, i4 noundef %val2) {
+; CHECK-LABEL: @PR96857_xor_with_noundef(
+; CHECK-NEXT:    [[VAL4:%.*]] = and i4 [[VAL2:%.*]], [[VAL0:%.*]]
+; CHECK-NEXT:    [[VAL5:%.*]] = xor i4 [[VAL2]], -1
+; CHECK-NEXT:    [[VAL6:%.*]] = and i4 [[VAL5]], [[VAL1:%.*]]
+; CHECK-NEXT:    [[VAL7:%.*]] = or disjoint i4 [[VAL4]], [[VAL6]]
+; CHECK-NEXT:    ret i4 [[VAL7]]
+;
+  %val4 = and i4 %val2, %val0
+  %val5 = xor i4 %val2, -1
+  %val6 = and i4 %val5, %val1
+  %val7 = xor i4 %val4, %val6
+  ret i4 %val7
+}
+
+; https://alive2.llvm.org/ce/z/whLTaJ
+define i4 @PR96857_xor_without_noundef(i4  %val0, i4  %val1, i4 %val2) {
+; CHECK-LABEL: @PR96857_xor_without_noundef(
+; CHECK-NEXT:    [[VAL4:%.*]] = and i4 [[VAL2:%.*]], [[VAL0:%.*]]
+; CHECK-NEXT:    [[VAL5:%.*]] = xor i4 [[VAL2]], -1
+; CHECK-NEXT:    [[VAL6:%.*]] = and i4 [[VAL5]], [[VAL1:%.*]]
+; CHECK-NEXT:    [[VAL7:%.*]] = or i4 [[VAL4]], [[VAL6]]
+; CHECK-NEXT:    ret i4 [[VAL7]]
+;
+  %val4 = and i4 %val2, %val0
+  %val5 = xor i4 %val2, -1
+  %val6 = and i4 %val5, %val1
+  %val7 = xor i4 %val4, %val6
+  ret i4 %val7
+}

[dtcxzyw]

Suggested change

	if (isGuaranteedNotToBeUndefOrPoison(M))
	if (isGuaranteedNotToBeUndef(M))

It is safe if M is a poison value.

[vfdff]

Update, thanks @dtcxzyw

[nikic]

LGTM

[vfdff]

Thanks for your review