[RISC-V][ISel] Remove redundant czero.eqz like 'czero.eqz a0, a0, a0' (#90208)

In RISC-V ISel, the instruction `czero.eqz a0, a0, a0` is meaningless.
This patch does the following folds in ISel:
```
czero_eqz x, (setcc x, 0, ne) -> x
czero_nez x, (setcc x, 0, eq) -> x
```

---------

Signed-off-by: Zhijin Zeng <[email protected]>

Author: zengdage

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -16164,23 +16164,31 @@ SDValue RISCVTargetLowering::PerformDAGCombine(SDNode *N,
   case ISD::SELECT:
     return performSELECTCombine(N, DAG, Subtarget);
   case RISCVISD::CZERO_EQZ:
-  case RISCVISD::CZERO_NEZ:
+  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 (N->getOperand(1).getOpcode() == ISD::XOR &&
-        isOneConstant(N->getOperand(1).getOperand(1))) {
-      SDValue Cond = N->getOperand(1).getOperand(0);
+    if (RHS.getOpcode() == ISD::XOR && isOneConstant(RHS.getOperand(1))) {
+      SDValue Cond = RHS.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),
-                           N->getOperand(0), Cond);
+        return DAG.getNode(NewOpc, SDLoc(N), N->getValueType(0), LHS, Cond);
       }
     }
+    // czero_eqz x, (setcc x, 0, ne) -> x
+    // czero_nez x, (setcc x, 0, eq) -> x
+    if (RHS.getOpcode() == ISD::SETCC && isNullConstant(RHS.getOperand(1)) &&
+        cast<CondCodeSDNode>(RHS.getOperand(2))->get() ==
+            (N->getOpcode() == RISCVISD::CZERO_EQZ ? ISD::CondCode::SETNE
+                                                   : ISD::CondCode::SETEQ) &&
+        LHS == RHS.getOperand(0))
+      return LHS;
     return SDValue();
-
+  }
   case RISCVISD::SELECT_CC: {
     // Transform
     SDValue LHS = N->getOperand(0);

llvm/test/CodeGen/RISCV/select.ll

@@ -1858,3 +1858,113 @@ define i32 @select_cst6(i1 zeroext %cond) {
   %ret = select i1 %cond, i32 2049, i32 2047
   ret i32 %ret
 }
+
+@select_redundant_czero_eqz_data = global i32 0, align 4
+
+define void @select_redundant_czero_eqz1(ptr %0, ptr %1) {
+; RV32IM-LABEL: select_redundant_czero_eqz1:
+; RV32IM:       # %bb.0: # %entry
+; RV32IM-NEXT:    bnez a0, .LBB49_2
+; RV32IM-NEXT:  # %bb.1:
+; RV32IM-NEXT:    lui a0, %hi(select_redundant_czero_eqz_data)
+; RV32IM-NEXT:    addi a0, a0, %lo(select_redundant_czero_eqz_data)
+; RV32IM-NEXT:  .LBB49_2: # %entry
+; RV32IM-NEXT:    sw a0, 0(a1)
+; RV32IM-NEXT:    ret
+;
+; RV64IM-LABEL: select_redundant_czero_eqz1:
+; RV64IM:       # %bb.0: # %entry
+; RV64IM-NEXT:    bnez a0, .LBB49_2
+; RV64IM-NEXT:  # %bb.1:
+; RV64IM-NEXT:    lui a0, %hi(select_redundant_czero_eqz_data)
+; RV64IM-NEXT:    addi a0, a0, %lo(select_redundant_czero_eqz_data)
+; RV64IM-NEXT:  .LBB49_2: # %entry
+; RV64IM-NEXT:    sd a0, 0(a1)
+; RV64IM-NEXT:    ret
+;
+; RV64IMXVTCONDOPS-LABEL: select_redundant_czero_eqz1:
+; RV64IMXVTCONDOPS:       # %bb.0: # %entry
+; RV64IMXVTCONDOPS-NEXT:    lui a2, %hi(select_redundant_czero_eqz_data)
+; RV64IMXVTCONDOPS-NEXT:    addi a2, a2, %lo(select_redundant_czero_eqz_data)
+; RV64IMXVTCONDOPS-NEXT:    vt.maskcn a2, a2, a0
+; RV64IMXVTCONDOPS-NEXT:    or a0, a2, a0
+; RV64IMXVTCONDOPS-NEXT:    sd a0, 0(a1)
+; RV64IMXVTCONDOPS-NEXT:    ret
+;
+; RV32IMZICOND-LABEL: select_redundant_czero_eqz1:
+; RV32IMZICOND:       # %bb.0: # %entry
+; RV32IMZICOND-NEXT:    lui a2, %hi(select_redundant_czero_eqz_data)
+; RV32IMZICOND-NEXT:    addi a2, a2, %lo(select_redundant_czero_eqz_data)
+; RV32IMZICOND-NEXT:    czero.nez a2, a2, a0
+; RV32IMZICOND-NEXT:    or a0, a2, a0
+; RV32IMZICOND-NEXT:    sw a0, 0(a1)
+; RV32IMZICOND-NEXT:    ret
+;
+; RV64IMZICOND-LABEL: select_redundant_czero_eqz1:
+; RV64IMZICOND:       # %bb.0: # %entry
+; RV64IMZICOND-NEXT:    lui a2, %hi(select_redundant_czero_eqz_data)
+; RV64IMZICOND-NEXT:    addi a2, a2, %lo(select_redundant_czero_eqz_data)
+; RV64IMZICOND-NEXT:    czero.nez a2, a2, a0
+; RV64IMZICOND-NEXT:    or a0, a2, a0
+; RV64IMZICOND-NEXT:    sd a0, 0(a1)
+; RV64IMZICOND-NEXT:    ret
+entry:
+  %3 = icmp eq ptr %0, null
+  %4 = select i1 %3, ptr @select_redundant_czero_eqz_data, ptr %0
+  store ptr %4, ptr %1, align 8
+  ret void
+}
+
+define void @select_redundant_czero_eqz2(ptr %0, ptr %1) {
+; RV32IM-LABEL: select_redundant_czero_eqz2:
+; RV32IM:       # %bb.0: # %entry
+; RV32IM-NEXT:    bnez a0, .LBB50_2
+; RV32IM-NEXT:  # %bb.1: # %entry
+; RV32IM-NEXT:    lui a0, %hi(select_redundant_czero_eqz_data)
+; RV32IM-NEXT:    addi a0, a0, %lo(select_redundant_czero_eqz_data)
+; RV32IM-NEXT:  .LBB50_2: # %entry
+; RV32IM-NEXT:    sw a0, 0(a1)
+; RV32IM-NEXT:    ret
+;
+; RV64IM-LABEL: select_redundant_czero_eqz2:
+; RV64IM:       # %bb.0: # %entry
+; RV64IM-NEXT:    bnez a0, .LBB50_2
+; RV64IM-NEXT:  # %bb.1: # %entry
+; RV64IM-NEXT:    lui a0, %hi(select_redundant_czero_eqz_data)
+; RV64IM-NEXT:    addi a0, a0, %lo(select_redundant_czero_eqz_data)
+; RV64IM-NEXT:  .LBB50_2: # %entry
+; RV64IM-NEXT:    sd a0, 0(a1)
+; RV64IM-NEXT:    ret
+;
+; RV64IMXVTCONDOPS-LABEL: select_redundant_czero_eqz2:
+; RV64IMXVTCONDOPS:       # %bb.0: # %entry
+; RV64IMXVTCONDOPS-NEXT:    lui a2, %hi(select_redundant_czero_eqz_data)
+; RV64IMXVTCONDOPS-NEXT:    addi a2, a2, %lo(select_redundant_czero_eqz_data)
+; RV64IMXVTCONDOPS-NEXT:    vt.maskcn a2, a2, a0
+; RV64IMXVTCONDOPS-NEXT:    or a0, a0, a2
+; RV64IMXVTCONDOPS-NEXT:    sd a0, 0(a1)
+; RV64IMXVTCONDOPS-NEXT:    ret
+;
+; RV32IMZICOND-LABEL: select_redundant_czero_eqz2:
+; RV32IMZICOND:       # %bb.0: # %entry
+; RV32IMZICOND-NEXT:    lui a2, %hi(select_redundant_czero_eqz_data)
+; RV32IMZICOND-NEXT:    addi a2, a2, %lo(select_redundant_czero_eqz_data)
+; RV32IMZICOND-NEXT:    czero.nez a2, a2, a0
+; RV32IMZICOND-NEXT:    or a0, a0, a2
+; RV32IMZICOND-NEXT:    sw a0, 0(a1)
+; RV32IMZICOND-NEXT:    ret
+;
+; RV64IMZICOND-LABEL: select_redundant_czero_eqz2:
+; RV64IMZICOND:       # %bb.0: # %entry
+; RV64IMZICOND-NEXT:    lui a2, %hi(select_redundant_czero_eqz_data)
+; RV64IMZICOND-NEXT:    addi a2, a2, %lo(select_redundant_czero_eqz_data)
+; RV64IMZICOND-NEXT:    czero.nez a2, a2, a0
+; RV64IMZICOND-NEXT:    or a0, a0, a2
+; RV64IMZICOND-NEXT:    sd a0, 0(a1)
+; RV64IMZICOND-NEXT:    ret
+entry:
+  %3 = icmp ne ptr %0, null
+  %4 = select i1 %3, ptr %0, ptr @select_redundant_czero_eqz_data
+  store ptr %4, ptr %1, align 8
+  ret void
+}