[llvm] [RISCV][SDAG] Improve codegen of select with constants if zicond is available (PR #82456)
via llvm-commits
llvm-commits at lists.llvm.org
Tue Feb 20 19:06:25 PST 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-backend-risc-v
Author: Yingwei Zheng (dtcxzyw)
<details>
<summary>Changes</summary>
This patch uses `add + czero.eqz/nez` to lower select with constants if zicond is available.
```
(select c, c1, c2) -> (add (czero_nez c2 - c1, c), c1)
(select c, c1, c2) -> (add (czero_eqz c1 - c2, c), c2)
```
The above code sequence is suggested by [RISCV Optimization Guide](https://riscv-optimization-guide-riseproject-c94355ae3e6872252baa952524.gitlab.io/riscv-optimization-guide.html#_avoid_branches_using_conditional_moves).
---
Full diff: https://github.com/llvm/llvm-project/pull/82456.diff
2 Files Affected:
- (modified) llvm/lib/Target/RISCV/RISCVISelLowering.cpp (+20)
- (modified) llvm/test/CodeGen/RISCV/select.ll (+274)
``````````diff
diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 9ab6895aed521e..f0de990779f02a 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -7355,6 +7355,26 @@ SDValue RISCVTargetLowering::lowerSELECT(SDValue Op, SelectionDAG &DAG) const {
if (isNullConstant(TrueV))
return DAG.getNode(RISCVISD::CZERO_NEZ, DL, VT, FalseV, CondV);
+ // (select c, c1, c2) -> (add (czero_nez c2 - c1, c), c1)
+ // (select c, c1, c2) -> (add (czero_eqz c1 - c2, c), c2)
+ if (isa<ConstantSDNode>(TrueV) && isa<ConstantSDNode>(FalseV)) {
+ const APInt &TrueVal = TrueV->getAsAPIntVal();
+ const APInt &FalseVal = FalseV->getAsAPIntVal();
+ const int TrueValCost = RISCVMatInt::getIntMatCost(
+ TrueVal, Subtarget.getXLen(), Subtarget, /*CompressionCost=*/true);
+ const int FalseValCost = RISCVMatInt::getIntMatCost(
+ FalseVal, Subtarget.getXLen(), Subtarget, /*CompressionCost=*/true);
+ bool IsCZERO_NEZ = TrueValCost <= FalseValCost;
+ SDValue LHSVal = DAG.getConstant(
+ IsCZERO_NEZ ? FalseVal - TrueVal : TrueVal - FalseVal, DL, VT);
+ SDValue RHSVal =
+ DAG.getConstant(IsCZERO_NEZ ? TrueVal : FalseVal, DL, VT);
+ SDValue CMOV =
+ DAG.getNode(IsCZERO_NEZ ? RISCVISD::CZERO_NEZ : RISCVISD::CZERO_EQZ,
+ DL, VT, LHSVal, CondV);
+ return DAG.getNode(ISD::ADD, DL, VT, CMOV, RHSVal);
+ }
+
// (select c, (and f, x), f) -> (or (and f, x), (czero_nez f, c))
if (TrueV.getOpcode() == ISD::AND &&
(TrueV.getOperand(0) == FalseV || TrueV.getOperand(1) == FalseV))
diff --git a/llvm/test/CodeGen/RISCV/select.ll b/llvm/test/CodeGen/RISCV/select.ll
index 7dd223df5e557e..d3cff41a4f247d 100644
--- a/llvm/test/CodeGen/RISCV/select.ll
+++ b/llvm/test/CodeGen/RISCV/select.ll
@@ -1449,3 +1449,277 @@ entry:
%res = select i1 %cond, i32 %a, i32 %c
ret i32 %res
}
+
+define i32 @select_cst1(i1 zeroext %cond) {
+; RV32IM-LABEL: select_cst1:
+; RV32IM: # %bb.0:
+; RV32IM-NEXT: mv a1, a0
+; RV32IM-NEXT: li a0, 10
+; RV32IM-NEXT: bnez a1, .LBB37_2
+; RV32IM-NEXT: # %bb.1:
+; RV32IM-NEXT: li a0, 20
+; RV32IM-NEXT: .LBB37_2:
+; RV32IM-NEXT: ret
+;
+; RV64IM-LABEL: select_cst1:
+; RV64IM: # %bb.0:
+; RV64IM-NEXT: mv a1, a0
+; RV64IM-NEXT: li a0, 10
+; RV64IM-NEXT: bnez a1, .LBB37_2
+; RV64IM-NEXT: # %bb.1:
+; RV64IM-NEXT: li a0, 20
+; RV64IM-NEXT: .LBB37_2:
+; RV64IM-NEXT: ret
+;
+; RV64IMXVTCONDOPS-LABEL: select_cst1:
+; RV64IMXVTCONDOPS: # %bb.0:
+; RV64IMXVTCONDOPS-NEXT: li a1, 10
+; RV64IMXVTCONDOPS-NEXT: vt.maskcn a0, a1, a0
+; RV64IMXVTCONDOPS-NEXT: addi a0, a0, 10
+; RV64IMXVTCONDOPS-NEXT: ret
+;
+; CHECKZICOND-LABEL: select_cst1:
+; CHECKZICOND: # %bb.0:
+; CHECKZICOND-NEXT: li a1, 10
+; CHECKZICOND-NEXT: czero.nez a0, a1, a0
+; CHECKZICOND-NEXT: addi a0, a0, 10
+; CHECKZICOND-NEXT: ret
+ %ret = select i1 %cond, i32 10, i32 20
+ ret i32 %ret
+}
+
+define i32 @select_cst2(i1 zeroext %cond) {
+; RV32IM-LABEL: select_cst2:
+; RV32IM: # %bb.0:
+; RV32IM-NEXT: mv a1, a0
+; RV32IM-NEXT: li a0, 10
+; RV32IM-NEXT: bnez a1, .LBB38_2
+; RV32IM-NEXT: # %bb.1:
+; RV32IM-NEXT: lui a0, 5
+; RV32IM-NEXT: addi a0, a0, -480
+; RV32IM-NEXT: .LBB38_2:
+; RV32IM-NEXT: ret
+;
+; RV64IM-LABEL: select_cst2:
+; RV64IM: # %bb.0:
+; RV64IM-NEXT: mv a1, a0
+; RV64IM-NEXT: li a0, 10
+; RV64IM-NEXT: bnez a1, .LBB38_2
+; RV64IM-NEXT: # %bb.1:
+; RV64IM-NEXT: lui a0, 5
+; RV64IM-NEXT: addiw a0, a0, -480
+; RV64IM-NEXT: .LBB38_2:
+; RV64IM-NEXT: ret
+;
+; RV64IMXVTCONDOPS-LABEL: select_cst2:
+; RV64IMXVTCONDOPS: # %bb.0:
+; RV64IMXVTCONDOPS-NEXT: lui a1, 5
+; RV64IMXVTCONDOPS-NEXT: addiw a1, a1, -490
+; RV64IMXVTCONDOPS-NEXT: vt.maskcn a0, a1, a0
+; RV64IMXVTCONDOPS-NEXT: addi a0, a0, 10
+; RV64IMXVTCONDOPS-NEXT: ret
+;
+; RV32IMZICOND-LABEL: select_cst2:
+; RV32IMZICOND: # %bb.0:
+; RV32IMZICOND-NEXT: lui a1, 5
+; RV32IMZICOND-NEXT: addi a1, a1, -490
+; RV32IMZICOND-NEXT: czero.nez a0, a1, a0
+; RV32IMZICOND-NEXT: addi a0, a0, 10
+; RV32IMZICOND-NEXT: ret
+;
+; RV64IMZICOND-LABEL: select_cst2:
+; RV64IMZICOND: # %bb.0:
+; RV64IMZICOND-NEXT: lui a1, 5
+; RV64IMZICOND-NEXT: addiw a1, a1, -490
+; RV64IMZICOND-NEXT: czero.nez a0, a1, a0
+; RV64IMZICOND-NEXT: addi a0, a0, 10
+; RV64IMZICOND-NEXT: ret
+ %ret = select i1 %cond, i32 10, i32 20000
+ ret i32 %ret
+}
+
+define i32 @select_cst3(i1 zeroext %cond) {
+; RV32IM-LABEL: select_cst3:
+; RV32IM: # %bb.0:
+; RV32IM-NEXT: bnez a0, .LBB39_2
+; RV32IM-NEXT: # %bb.1:
+; RV32IM-NEXT: lui a0, 5
+; RV32IM-NEXT: addi a0, a0, -480
+; RV32IM-NEXT: ret
+; RV32IM-NEXT: .LBB39_2:
+; RV32IM-NEXT: lui a0, 7
+; RV32IM-NEXT: addi a0, a0, 1328
+; RV32IM-NEXT: ret
+;
+; RV64IM-LABEL: select_cst3:
+; RV64IM: # %bb.0:
+; RV64IM-NEXT: bnez a0, .LBB39_2
+; RV64IM-NEXT: # %bb.1:
+; RV64IM-NEXT: lui a0, 5
+; RV64IM-NEXT: addiw a0, a0, -480
+; RV64IM-NEXT: ret
+; RV64IM-NEXT: .LBB39_2:
+; RV64IM-NEXT: lui a0, 7
+; RV64IM-NEXT: addiw a0, a0, 1328
+; RV64IM-NEXT: ret
+;
+; RV64IMXVTCONDOPS-LABEL: select_cst3:
+; RV64IMXVTCONDOPS: # %bb.0:
+; RV64IMXVTCONDOPS-NEXT: lui a1, 1048574
+; RV64IMXVTCONDOPS-NEXT: addiw a1, a1, -1808
+; RV64IMXVTCONDOPS-NEXT: vt.maskcn a0, a1, a0
+; RV64IMXVTCONDOPS-NEXT: lui a1, 7
+; RV64IMXVTCONDOPS-NEXT: addiw a1, a1, 1328
+; RV64IMXVTCONDOPS-NEXT: add a0, a0, a1
+; RV64IMXVTCONDOPS-NEXT: ret
+;
+; RV32IMZICOND-LABEL: select_cst3:
+; RV32IMZICOND: # %bb.0:
+; RV32IMZICOND-NEXT: lui a1, 1048574
+; RV32IMZICOND-NEXT: addi a1, a1, -1808
+; RV32IMZICOND-NEXT: czero.nez a0, a1, a0
+; RV32IMZICOND-NEXT: lui a1, 7
+; RV32IMZICOND-NEXT: addi a1, a1, 1328
+; RV32IMZICOND-NEXT: add a0, a0, a1
+; RV32IMZICOND-NEXT: ret
+;
+; RV64IMZICOND-LABEL: select_cst3:
+; RV64IMZICOND: # %bb.0:
+; RV64IMZICOND-NEXT: lui a1, 1048574
+; RV64IMZICOND-NEXT: addiw a1, a1, -1808
+; RV64IMZICOND-NEXT: czero.nez a0, a1, a0
+; RV64IMZICOND-NEXT: lui a1, 7
+; RV64IMZICOND-NEXT: addiw a1, a1, 1328
+; RV64IMZICOND-NEXT: add a0, a0, a1
+; RV64IMZICOND-NEXT: ret
+ %ret = select i1 %cond, i32 30000, i32 20000
+ ret i32 %ret
+}
+
+define i32 @select_cst4(i1 zeroext %cond) {
+; RV32IM-LABEL: select_cst4:
+; RV32IM: # %bb.0:
+; RV32IM-NEXT: mv a1, a0
+; RV32IM-NEXT: li a0, -2048
+; RV32IM-NEXT: bnez a1, .LBB40_2
+; RV32IM-NEXT: # %bb.1:
+; RV32IM-NEXT: li a0, 2047
+; RV32IM-NEXT: .LBB40_2:
+; RV32IM-NEXT: ret
+;
+; RV64IM-LABEL: select_cst4:
+; RV64IM: # %bb.0:
+; RV64IM-NEXT: mv a1, a0
+; RV64IM-NEXT: li a0, -2048
+; RV64IM-NEXT: bnez a1, .LBB40_2
+; RV64IM-NEXT: # %bb.1:
+; RV64IM-NEXT: li a0, 2047
+; RV64IM-NEXT: .LBB40_2:
+; RV64IM-NEXT: ret
+;
+; RV64IMXVTCONDOPS-LABEL: select_cst4:
+; RV64IMXVTCONDOPS: # %bb.0:
+; RV64IMXVTCONDOPS-NEXT: lui a1, 1
+; RV64IMXVTCONDOPS-NEXT: addiw a1, a1, -1
+; RV64IMXVTCONDOPS-NEXT: vt.maskcn a0, a1, a0
+; RV64IMXVTCONDOPS-NEXT: addi a0, a0, -2048
+; RV64IMXVTCONDOPS-NEXT: ret
+;
+; RV32IMZICOND-LABEL: select_cst4:
+; RV32IMZICOND: # %bb.0:
+; RV32IMZICOND-NEXT: lui a1, 1
+; RV32IMZICOND-NEXT: addi a1, a1, -1
+; RV32IMZICOND-NEXT: czero.nez a0, a1, a0
+; RV32IMZICOND-NEXT: addi a0, a0, -2048
+; RV32IMZICOND-NEXT: ret
+;
+; RV64IMZICOND-LABEL: select_cst4:
+; RV64IMZICOND: # %bb.0:
+; RV64IMZICOND-NEXT: lui a1, 1
+; RV64IMZICOND-NEXT: addiw a1, a1, -1
+; RV64IMZICOND-NEXT: czero.nez a0, a1, a0
+; RV64IMZICOND-NEXT: addi a0, a0, -2048
+; RV64IMZICOND-NEXT: ret
+ %ret = select i1 %cond, i32 -2048, i32 2047
+ ret i32 %ret
+}
+
+define i32 @select_cst5(i1 zeroext %cond) {
+; RV32IM-LABEL: select_cst5:
+; RV32IM: # %bb.0:
+; RV32IM-NEXT: mv a1, a0
+; RV32IM-NEXT: li a0, 2047
+; RV32IM-NEXT: bnez a1, .LBB41_2
+; RV32IM-NEXT: # %bb.1:
+; RV32IM-NEXT: lui a0, 1
+; RV32IM-NEXT: addi a0, a0, -2047
+; RV32IM-NEXT: .LBB41_2:
+; RV32IM-NEXT: ret
+;
+; RV64IM-LABEL: select_cst5:
+; RV64IM: # %bb.0:
+; RV64IM-NEXT: mv a1, a0
+; RV64IM-NEXT: li a0, 2047
+; RV64IM-NEXT: bnez a1, .LBB41_2
+; RV64IM-NEXT: # %bb.1:
+; RV64IM-NEXT: lui a0, 1
+; RV64IM-NEXT: addiw a0, a0, -2047
+; RV64IM-NEXT: .LBB41_2:
+; RV64IM-NEXT: ret
+;
+; RV64IMXVTCONDOPS-LABEL: select_cst5:
+; RV64IMXVTCONDOPS: # %bb.0:
+; RV64IMXVTCONDOPS-NEXT: li a1, 2
+; RV64IMXVTCONDOPS-NEXT: vt.maskcn a0, a1, a0
+; RV64IMXVTCONDOPS-NEXT: addi a0, a0, 2047
+; RV64IMXVTCONDOPS-NEXT: ret
+;
+; CHECKZICOND-LABEL: select_cst5:
+; CHECKZICOND: # %bb.0:
+; CHECKZICOND-NEXT: li a1, 2
+; CHECKZICOND-NEXT: czero.nez a0, a1, a0
+; CHECKZICOND-NEXT: addi a0, a0, 2047
+; CHECKZICOND-NEXT: ret
+ %ret = select i1 %cond, i32 2047, i32 2049
+ ret i32 %ret
+}
+
+define i32 @select_cst6(i1 zeroext %cond) {
+; RV32IM-LABEL: select_cst6:
+; RV32IM: # %bb.0:
+; RV32IM-NEXT: bnez a0, .LBB42_2
+; RV32IM-NEXT: # %bb.1:
+; RV32IM-NEXT: li a0, 2047
+; RV32IM-NEXT: ret
+; RV32IM-NEXT: .LBB42_2:
+; RV32IM-NEXT: lui a0, 1
+; RV32IM-NEXT: addi a0, a0, -2047
+; RV32IM-NEXT: ret
+;
+; RV64IM-LABEL: select_cst6:
+; RV64IM: # %bb.0:
+; RV64IM-NEXT: bnez a0, .LBB42_2
+; RV64IM-NEXT: # %bb.1:
+; RV64IM-NEXT: li a0, 2047
+; RV64IM-NEXT: ret
+; RV64IM-NEXT: .LBB42_2:
+; RV64IM-NEXT: lui a0, 1
+; RV64IM-NEXT: addiw a0, a0, -2047
+; RV64IM-NEXT: ret
+;
+; RV64IMXVTCONDOPS-LABEL: select_cst6:
+; RV64IMXVTCONDOPS: # %bb.0:
+; RV64IMXVTCONDOPS-NEXT: li a1, 2
+; RV64IMXVTCONDOPS-NEXT: vt.maskc a0, a1, a0
+; RV64IMXVTCONDOPS-NEXT: addi a0, a0, 2047
+; RV64IMXVTCONDOPS-NEXT: ret
+;
+; CHECKZICOND-LABEL: select_cst6:
+; CHECKZICOND: # %bb.0:
+; CHECKZICOND-NEXT: li a1, 2
+; CHECKZICOND-NEXT: czero.eqz a0, a1, a0
+; CHECKZICOND-NEXT: addi a0, a0, 2047
+; CHECKZICOND-NEXT: ret
+ %ret = select i1 %cond, i32 2049, i32 2047
+ ret i32 %ret
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/82456
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