[RISC-V][ISel] Remove redundant czero.eqz like 'czero.eqz a0, a0, a0'

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

Author: zengdage

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -7503,6 +7503,17 @@ SDValue RISCVTargetLowering::lowerSELECT(SDValue Op, SelectionDAG &DAG) const {
       return DAG.getNode(ISD::ADD, DL, VT, CMOV, RHSVal);
     }
 
+    // c = setcc f, 0, seteq
+    // (select c, t, f) -> (or f, (czero_nez t, f))
+    if (CondV.getOpcode() == ISD::SETCC &&
+        ISD::SETEQ == cast<CondCodeSDNode>(CondV.getOperand(2))->get()) {
+      SDValue LHS = CondV.getOperand(0);
+      SDValue RHS = CondV.getOperand(1);
+      if (isNullConstant(RHS) && LHS == FalseV)
+        return DAG.getNode(
+            ISD::OR, DL, VT, FalseV,
+            DAG.getNode(RISCVISD::CZERO_NEZ, DL, VT, TrueV, LHS));
+    }
     // (select c, t, f) -> (or (czero_eqz t, c), (czero_nez f, c))
     // Unless we have the short forward branch optimization.
     if (!Subtarget.hasConditionalMoveFusion())

llvm/test/CodeGen/RISCV/select.ll

@@ -1887,8 +1887,7 @@ define void @select_redundant_czero_eqz(ptr %0, ptr %1) {
 ; 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:    vt.maskc a0, a0, a0
-; RV64IMXVTCONDOPS-NEXT:    or a0, a2, a0
+; RV64IMXVTCONDOPS-NEXT:    or a0, a0, a2
 ; RV64IMXVTCONDOPS-NEXT:    sd a0, 0(a1)
 ; RV64IMXVTCONDOPS-NEXT:    ret
 ;
@@ -1897,8 +1896,7 @@ define void @select_redundant_czero_eqz(ptr %0, ptr %1) {
 ; 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:    czero.eqz a0, a0, a0
-; RV32IMZICOND-NEXT:    or a0, a2, a0
+; RV32IMZICOND-NEXT:    or a0, a0, a2
 ; RV32IMZICOND-NEXT:    sw a0, 0(a1)
 ; RV32IMZICOND-NEXT:    ret
 ;
@@ -1907,8 +1905,7 @@ define void @select_redundant_czero_eqz(ptr %0, ptr %1) {
 ; 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:    czero.eqz a0, a0, a0
-; RV64IMZICOND-NEXT:    or a0, a2, a0
+; RV64IMZICOND-NEXT:    or a0, a0, a2
 ; RV64IMZICOND-NEXT:    sd a0, 0(a1)
 ; RV64IMZICOND-NEXT:    ret
 entry: