[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

@@ -1858,3 +1858,62 @@ 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_eqz(ptr %0, ptr %1) {
+; RV32IM-LABEL: select_redundant_czero_eqz:
+; 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_eqz:
+; 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_eqz:
+; 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:    vt.maskc a0, a0, a0
+; RV64IMXVTCONDOPS-NEXT:    or a0, a2, a0
+; RV64IMXVTCONDOPS-NEXT:    sd a0, 0(a1)
+; RV64IMXVTCONDOPS-NEXT:    ret
+;
+; RV32IMZICOND-LABEL: select_redundant_czero_eqz:
+; 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:    czero.eqz a0, a0, a0
+; RV32IMZICOND-NEXT:    or a0, a2, a0
+; RV32IMZICOND-NEXT:    sw a0, 0(a1)
+; RV32IMZICOND-NEXT:    ret
+;
+; RV64IMZICOND-LABEL: select_redundant_czero_eqz:
+; 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:    czero.eqz a0, a0, 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
+}