[llvm] [RISCV] Break the (czero_eqz x, (setne x, 0)) -> x combine into 2 combines. (PR #90428)

[Yingwei Zheng via llvm-commits]

================
@@ -16165,28 +16165,36 @@ SDValue RISCVTargetLowering::PerformDAGCombine(SDNode *N,
     return performSELECTCombine(N, DAG, Subtarget);
   case RISCVISD::CZERO_EQZ:
   case RISCVISD::CZERO_NEZ: {
-    SDValue LHS = N->getOperand(0);
-    SDValue RHS = N->getOperand(1);
-    // czero_eq X, (xor Y, 1) -> czero_ne X, Y if Y is 0 or 1.
-    // czero_ne X, (xor Y, 1) -> czero_eq X, Y if Y is 0 or 1.
-    if (RHS.getOpcode() == ISD::XOR && isOneConstant(RHS.getOperand(1))) {
-      SDValue Cond = RHS.getOperand(0);
+    SDValue Val = N->getOperand(0);
+    SDValue Cond = N->getOperand(1);
+
+    unsigned Opc = N->getOpcode();
+
+    // czero_eqz x, x -> x
+    if (Opc && Val == Cond)
+      return Val;
+
+    unsigned InvOpc =
+        Opc == RISCVISD::CZERO_EQZ ? RISCVISD::CZERO_NEZ : RISCVISD::CZERO_EQZ;
+
+    // czero_eqz X, (xor Y, 1) -> czero_nez X, Y if Y is 0 or 1.
+    // czero_nez X, (xor Y, 1) -> czero_eqz X, Y if Y is 0 or 1.
+    if (Cond.getOpcode() == ISD::XOR && isOneConstant(Cond.getOperand(1))) {
+      Cond = Cond.getOperand(0);
       APInt Mask = APInt::getBitsSetFrom(Cond.getValueSizeInBits(), 1);
-      if (DAG.MaskedValueIsZero(Cond, Mask)) {
-        unsigned NewOpc = N->getOpcode() == RISCVISD::CZERO_EQZ
-                              ? RISCVISD::CZERO_NEZ
-                              : RISCVISD::CZERO_EQZ;
-        return DAG.getNode(NewOpc, SDLoc(N), N->getValueType(0), LHS, Cond);
-      }
+      if (DAG.MaskedValueIsZero(Cond, Mask))
+        return DAG.getNode(InvOpc, SDLoc(N), N->getValueType(0), Val, Cond);
+    }
----------------
dtcxzyw wrote:

At least we can use a new variable instead of overwriting Cond.


https://github.com/llvm/llvm-project/pull/90428