[llvm] [PatternMatch] Add `m_c_XorLike` matcher; NFC (PR #122642)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-ir

Author: None (goldsteinn)

<details>
<summary>Changes</summary>

`m_c_XorLike` matches either:
    `(xor L, R)`, `(xor R, L)`, or `(sub nuw R, L)` iff `R.isMask()`.

This is in preperation for dropping the fold from:
    `(sub C_Mask, X)` -> `(xor X, C_Mask)`


---
Full diff: https://github.com/llvm/llvm-project/pull/122642.diff


2 Files Affected:

- (modified) llvm/include/llvm/IR/PatternMatch.h (+28) 
- (modified) llvm/unittests/IR/PatternMatch.cpp (+66) 


``````````diff
diff --git a/llvm/include/llvm/IR/PatternMatch.h b/llvm/include/llvm/IR/PatternMatch.h
index cd9a36029e6dbd..e50459716fe0eb 100644
--- a/llvm/include/llvm/IR/PatternMatch.h
+++ b/llvm/include/llvm/IR/PatternMatch.h
@@ -1430,6 +1430,34 @@ m_NUWAddLike(const LHS &L, const RHS &R) {
   return m_CombineOr(m_NUWAdd(L, R), m_DisjointOr(L, R));
 }
 
+template <typename LHS, typename RHS>
+struct XorLike_match {
+  LHS L;
+  RHS R;
+
+  XorLike_match(const LHS &L, const RHS &R) : L(L), R(R) {}
+
+  template <typename OpTy> bool match(OpTy *V) {
+    if (auto *Op = dyn_cast<BinaryOperator>(V)) {
+      if (Op->getOpcode() == Instruction::Sub && Op->hasNoUnsignedWrap() &&
+          PatternMatch::match(Op->getOperand(0), m_LowBitMask()))
+		  ; // Pass
+      else if (Op->getOpcode() != Instruction::Xor)
+        return false;
+      return (L.match(Op->getOperand(0)) && R.match(Op->getOperand(1))) ||
+             (L.match(Op->getOperand(1)) && R.match(Op->getOperand(0)));
+    }
+    return false;
+  }
+};
+
+// Match either `(xor L, R)`, `(xor R, L)` or `(sub nuw R, L)` iff `R.isMask()`
+// Only commutative matcher as the `sub` will need to swap the L and R.
+template <typename LHS, typename RHS>
+inline auto m_c_XorLike(const LHS &L, const RHS &R) {
+  return XorLike_match<LHS, RHS>(L, R);
+}
+
 //===----------------------------------------------------------------------===//
 // Class that matches a group of binary opcodes.
 //
diff --git a/llvm/unittests/IR/PatternMatch.cpp b/llvm/unittests/IR/PatternMatch.cpp
index 47fde5782a13bc..da2c09ea199290 100644
--- a/llvm/unittests/IR/PatternMatch.cpp
+++ b/llvm/unittests/IR/PatternMatch.cpp
@@ -533,6 +533,72 @@ TEST_F(PatternMatchTest, BitWise) {
   EXPECT_FALSE(m_c_BitwiseLogic(m_Zero(), m_Zero()).match(Xor));
 }
 
+TEST_F(PatternMatchTest, XorLike) {
+  Value *AllocaX = IRB.CreateAlloca(IRB.getInt32Ty());
+  Value *X = IRB.CreateLoad(IRB.getInt32Ty(), AllocaX);
+  Value *AllocaY = IRB.CreateAlloca(IRB.getInt32Ty());
+  Value *Y = IRB.CreateLoad(IRB.getInt32Ty(), AllocaY);
+  Value *MaskC = IRB.getInt32(31);
+  Value *NonMaskC = IRB.getInt32(32);
+
+  Value *OpA, *OpB;
+  {
+    Value *Xor = IRB.CreateXor(X, Y);
+    Value *Sub = IRB.CreateNUWSub(X, Y);
+    OpA = nullptr;
+    OpB = nullptr;
+    EXPECT_TRUE(m_c_XorLike(m_Value(OpA), m_Value(OpB)).match(Xor));
+    EXPECT_TRUE(OpA != OpB && (OpA == X || OpB == X) && (OpA == Y || OpB == Y));
+    OpA = nullptr;
+    OpB = nullptr;
+    EXPECT_FALSE(m_c_XorLike(m_Value(OpA), m_Value(OpB)).match(Sub));
+  }
+  {
+    Value *Xor = IRB.CreateXor(X, MaskC);
+    Value *Sub = IRB.CreateNUWSub(MaskC, X);
+    OpA = nullptr;
+    OpB = nullptr;	
+    EXPECT_TRUE(m_c_XorLike(m_Value(OpA), m_Value(OpB)).match(Xor));
+    EXPECT_TRUE(OpA != OpB && (OpA == X || OpB == X) &&
+                (OpA == MaskC || OpB == MaskC));
+    OpA = nullptr;
+    OpB = nullptr;
+    EXPECT_TRUE(m_c_XorLike(m_Value(OpA), m_Value(OpB)).match(Sub));
+    EXPECT_TRUE(OpA != OpB && (OpA == X || OpB == X) &&
+                (OpA == MaskC || OpB == MaskC));
+  }
+  {
+    Value *Xor = IRB.CreateXor(X, MaskC);
+    Value *Sub = IRB.CreateNSWSub(MaskC, X);
+    OpA = nullptr;
+    OpB = nullptr;	
+    EXPECT_TRUE(m_c_XorLike(m_Value(OpA), m_Value(OpB)).match(Xor));
+    EXPECT_TRUE(OpA != OpB && (OpA == X || OpB == X) &&
+                (OpA == MaskC || OpB == MaskC));
+    OpA = nullptr;
+    OpB = nullptr;
+    EXPECT_FALSE(m_c_XorLike(m_Value(OpA), m_Value(OpB)).match(Sub));
+  }
+  {
+    Value *Sub = IRB.CreateNUWSub(X, MaskC);
+    OpA = nullptr;
+    OpB = nullptr;
+    EXPECT_FALSE(m_c_XorLike(m_Value(OpA), m_Value(OpB)).match(Sub));
+  }
+  {
+    Value *Xor = IRB.CreateXor(X, NonMaskC);
+    Value *Sub = IRB.CreateNUWSub(NonMaskC, X);
+    OpA = nullptr;
+    OpB = nullptr;	
+    EXPECT_TRUE(m_c_XorLike(m_Value(OpA), m_Value(OpB)).match(Xor));
+    EXPECT_TRUE(OpA != OpB && (OpA == X || OpB == X) &&
+                (OpA == NonMaskC || OpB == NonMaskC));
+    OpA = nullptr;
+    OpB = nullptr;
+    EXPECT_FALSE(m_c_XorLike(m_Value(OpA), m_Value(OpB)).match(Sub));
+  }  
+}
+
 TEST_F(PatternMatchTest, ZExtSExtSelf) {
   LLVMContext &Ctx = IRB.getContext();
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/122642