[llvm] [InstSimpify] Simplifying `(xor (sub C_Mask, X), C_Mask)` -> `X` (PR #122552)

[Nikita Popov via llvm-commits]

================
@@ -2540,6 +2548,14 @@ static Value *simplifyXorInst(Value *Op0, Value *Op1, const SimplifyQuery &Q,
   if (Value *V = simplifyByDomEq(Instruction::Xor, Op0, Op1, Q, MaxRecurse))
     return V;
 
+  // (xor (sub nuw C_Mask, X), C_Mask) -> X
+  {
+    Value *X;
+    if (match(Op0, m_NUWSub(m_Specific(Op1), m_Value(X))) &&
+        match(Op1, m_CheckedInt([](const APInt &C) { return C.isMask(); })))
----------------
nikic wrote:

```suggestion
        match(Op1, m_LowBitMask())
```

https://github.com/llvm/llvm-project/pull/122552