[llvm] Combine (X ^ Y) and (X == Y) where appropriate (PR #130922)

[Craig Topper via llvm-commits]

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@@ -17194,8 +17194,47 @@ static bool combine_CC(SDValue &LHS, SDValue &RHS, SDValue &CC, const SDLoc &DL,
     return true;
   }
 
+  // If XOR is reused and has an immediate that will fit in XORI,
+  // do not fold
+  auto Is12BitConstant = [](const SDValue &Op) -> bool {
+    if (Op.getOpcode() == ISD::Constant) {
+      const int64_t RiscvAluImmBits = 12;
+      const int64_t RiscvAluImmUpperBound = (1 << RiscvAluImmBits) - 1;
+      const int64_t RiscvAluImmLowerBound = -(1 << RiscvAluImmBits);
+      const int64_t XorCnst =
+          llvm::dyn_cast<llvm::ConstantSDNode>(Op)->getSExtValue();
+      return (XorCnst >= RiscvAluImmLowerBound) &&
+             (XorCnst <= RiscvAluImmUpperBound);
+    }
+    return false;
+  };
+  // Fold (X(i1) ^ 1) == 0 -> X != 0
+  auto SingleBitOp = [&DAG](const SDValue &VarOp,
+                            const SDValue &ConstOp) -> bool {
+    if (ConstOp.getOpcode() == ISD::Constant) {
+      const int64_t XorCnst =
+          llvm::dyn_cast<llvm::ConstantSDNode>(ConstOp)->getSExtValue();
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topperc wrote:

The `llvm::` is unnecessary. Move the dyn_cast into the `if` instead of checking the opcode.

https://github.com/llvm/llvm-project/pull/130922