[llvm] [RISCV] Add DAG combine to turn (sub (shl X, 8), X) into orc.b (PR #96680)
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Tue Jun 25 12:04:17 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-backend-risc-v
Author: Craig Topper (topperc)
<details>
<summary>Changes</summary>
If only bits 8, 16, 24, 32, etc. can be non-zero.
This is what (mul X, 255) is decomposed to. This decomposition happens early before RISC-V DAG combine runs.
This patch does not support types larger than XLen so i64 on i32 fails to generate 2 orc.b instructions. It might have worked if the mul hadn't been decomposed before it was expanded.
Partial fix for #<!-- -->96595.
---
Full diff: https://github.com/llvm/llvm-project/pull/96680.diff
3 Files Affected:
- (modified) llvm/lib/Target/RISCV/RISCVISelLowering.cpp (+36-2)
- (modified) llvm/test/CodeGen/RISCV/rv32zbb.ll (+61)
- (modified) llvm/test/CodeGen/RISCV/rv64zbb.ll (+66)
``````````diff
diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 7c7f167821234d..9e988783e2eb6c 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -12502,12 +12502,15 @@ void RISCVTargetLowering::ReplaceNodeResults(SDNode *N,
}
break;
}
- case RISCVISD::BREV8: {
+ case RISCVISD::BREV8:
+ case RISCVISD::ORC_B: {
MVT VT = N->getSimpleValueType(0);
MVT XLenVT = Subtarget.getXLenVT();
assert((VT == MVT::i16 || (VT == MVT::i32 && Subtarget.is64Bit())) &&
"Unexpected custom legalisation");
- assert(Subtarget.hasStdExtZbkb() && "Unexpected extension");
+ assert(((N->getOpcode() == RISCVISD::BREV8 && Subtarget.hasStdExtZbkb()) ||
+ (N->getOpcode() == RISCVISD::ORC_B && Subtarget.hasStdExtZbb())) &&
+ "Unexpected extension");
SDValue NewOp = DAG.getNode(ISD::ANY_EXTEND, DL, XLenVT, N->getOperand(0));
SDValue NewRes = DAG.getNode(N->getOpcode(), DL, XLenVT, NewOp);
// ReplaceNodeResults requires we maintain the same type for the return
@@ -13345,6 +13348,35 @@ static SDValue combineSubOfBoolean(SDNode *N, SelectionDAG &DAG) {
return DAG.getNode(ISD::ADD, DL, VT, NewLHS, NewRHS);
}
+// Looks for (sub (shl X, 8), X) where only bits 8, 16, 24, 32, etc. of X are
+// non-zero. Replace with orc.b.
+static SDValue combineSubShiftToOrcB(SDNode *N, SelectionDAG &DAG,
+ const RISCVSubtarget &Subtarget) {
+ if (!Subtarget.hasStdExtZbb())
+ return SDValue();
+
+ EVT VT = N->getValueType(0);
+
+ if (VT != Subtarget.getXLenVT() && VT != MVT::i32 && VT != MVT::i16)
+ return SDValue();
+
+ SDValue N0 = N->getOperand(0);
+ SDValue N1 = N->getOperand(1);
+
+ if (N0.getOpcode() != ISD::SHL || N0.getOperand(0) != N1 || !N0.hasOneUse())
+ return SDValue();
+
+ auto *ShAmtC = dyn_cast<ConstantSDNode>(N0.getOperand(1));
+ if (!ShAmtC || ShAmtC->getZExtValue() != 8)
+ return SDValue();
+
+ APInt Mask = APInt::getSplat(VT.getSizeInBits(), APInt(8, 0xfe));
+ if (!DAG.MaskedValueIsZero(N1, Mask))
+ return SDValue();
+
+ return DAG.getNode(RISCVISD::ORC_B, SDLoc(N), VT, N1);
+}
+
static SDValue performSUBCombine(SDNode *N, SelectionDAG &DAG,
const RISCVSubtarget &Subtarget) {
if (SDValue V = combineSubOfBoolean(N, DAG))
@@ -13367,6 +13399,8 @@ static SDValue performSUBCombine(SDNode *N, SelectionDAG &DAG,
if (SDValue V = combineBinOpOfZExt(N, DAG))
return V;
+ if (SDValue V = combineSubShiftToOrcB(N, DAG, Subtarget))
+ return V;
// fold (sub x, (select lhs, rhs, cc, 0, y)) ->
// (select lhs, rhs, cc, x, (sub x, y))
diff --git a/llvm/test/CodeGen/RISCV/rv32zbb.ll b/llvm/test/CodeGen/RISCV/rv32zbb.ll
index f25aa0de89da88..cb9fc6c16333e0 100644
--- a/llvm/test/CodeGen/RISCV/rv32zbb.ll
+++ b/llvm/test/CodeGen/RISCV/rv32zbb.ll
@@ -1356,3 +1356,64 @@ define i64 @bswap_i64(i64 %a) {
%1 = call i64 @llvm.bswap.i64(i64 %a)
ret i64 %1
}
+
+define i16 @orc_b_i16(i16 %a) {
+; RV32I-LABEL: orc_b_i16:
+; RV32I: # %bb.0:
+; RV32I-NEXT: andi a0, a0, 257
+; RV32I-NEXT: slli a1, a0, 8
+; RV32I-NEXT: sub a0, a1, a0
+; RV32I-NEXT: ret
+;
+; RV32ZBB-LABEL: orc_b_i16:
+; RV32ZBB: # %bb.0:
+; RV32ZBB-NEXT: andi a0, a0, 257
+; RV32ZBB-NEXT: orc.b a0, a0
+; RV32ZBB-NEXT: ret
+ %1 = and i16 %a, 257
+ %2 = mul nuw i16 %1, 255
+ ret i16 %2
+}
+
+define i32 @orc_b_i32(i32 %a) {
+; RV32I-LABEL: orc_b_i32:
+; RV32I: # %bb.0:
+; RV32I-NEXT: lui a1, 4112
+; RV32I-NEXT: addi a1, a1, 257
+; RV32I-NEXT: and a0, a0, a1
+; RV32I-NEXT: slli a1, a0, 8
+; RV32I-NEXT: sub a0, a1, a0
+; RV32I-NEXT: ret
+;
+; RV32ZBB-LABEL: orc_b_i32:
+; RV32ZBB: # %bb.0:
+; RV32ZBB-NEXT: lui a1, 4112
+; RV32ZBB-NEXT: addi a1, a1, 257
+; RV32ZBB-NEXT: and a0, a0, a1
+; RV32ZBB-NEXT: orc.b a0, a0
+; RV32ZBB-NEXT: ret
+ %1 = and i32 %a, 16843009
+ %2 = mul nuw i32 %1, 255
+ ret i32 %2
+}
+
+define i64 @orc_b_i64(i64 %a) {
+; CHECK-LABEL: orc_b_i64:
+; CHECK: # %bb.0:
+; CHECK-NEXT: lui a2, 4112
+; CHECK-NEXT: addi a2, a2, 257
+; CHECK-NEXT: and a1, a1, a2
+; CHECK-NEXT: and a0, a0, a2
+; CHECK-NEXT: slli a2, a0, 8
+; CHECK-NEXT: sltu a3, a2, a0
+; CHECK-NEXT: srli a4, a0, 24
+; CHECK-NEXT: slli a5, a1, 8
+; CHECK-NEXT: or a4, a5, a4
+; CHECK-NEXT: sub a1, a4, a1
+; CHECK-NEXT: sub a1, a1, a3
+; CHECK-NEXT: sub a0, a2, a0
+; CHECK-NEXT: ret
+ %1 = and i64 %a, 72340172838076673
+ %2 = mul nuw i64 %1, 255
+ ret i64 %2
+}
diff --git a/llvm/test/CodeGen/RISCV/rv64zbb.ll b/llvm/test/CodeGen/RISCV/rv64zbb.ll
index 4d5ef5db86057b..6c354cc1b446b2 100644
--- a/llvm/test/CodeGen/RISCV/rv64zbb.ll
+++ b/llvm/test/CodeGen/RISCV/rv64zbb.ll
@@ -1494,3 +1494,69 @@ define i64 @bswap_i64(i64 %a) {
%1 = call i64 @llvm.bswap.i64(i64 %a)
ret i64 %1
}
+
+define i16 @orc_b_i16(i16 %a) {
+; RV64I-LABEL: orc_b_i16:
+; RV64I: # %bb.0:
+; RV64I-NEXT: andi a0, a0, 257
+; RV64I-NEXT: slli a1, a0, 8
+; RV64I-NEXT: sub a0, a1, a0
+; RV64I-NEXT: ret
+;
+; RV64ZBB-LABEL: orc_b_i16:
+; RV64ZBB: # %bb.0:
+; RV64ZBB-NEXT: andi a0, a0, 257
+; RV64ZBB-NEXT: orc.b a0, a0
+; RV64ZBB-NEXT: ret
+ %1 = and i16 %a, 257
+ %2 = mul nuw i16 %1, 255
+ ret i16 %2
+}
+
+define i32 @orc_b_i32(i32 %a) {
+; RV64I-LABEL: orc_b_i32:
+; RV64I: # %bb.0:
+; RV64I-NEXT: lui a1, 4112
+; RV64I-NEXT: addi a1, a1, 257
+; RV64I-NEXT: and a0, a0, a1
+; RV64I-NEXT: slli a1, a0, 8
+; RV64I-NEXT: subw a0, a1, a0
+; RV64I-NEXT: ret
+;
+; RV64ZBB-LABEL: orc_b_i32:
+; RV64ZBB: # %bb.0:
+; RV64ZBB-NEXT: lui a1, 4112
+; RV64ZBB-NEXT: addiw a1, a1, 257
+; RV64ZBB-NEXT: and a0, a0, a1
+; RV64ZBB-NEXT: orc.b a0, a0
+; RV64ZBB-NEXT: ret
+ %1 = and i32 %a, 16843009
+ %2 = mul nuw i32 %1, 255
+ ret i32 %2
+}
+
+define i64 @orc_b_i64(i64 %a) {
+; RV64I-LABEL: orc_b_i64:
+; RV64I: # %bb.0:
+; RV64I-NEXT: lui a1, 4112
+; RV64I-NEXT: addiw a1, a1, 257
+; RV64I-NEXT: slli a2, a1, 32
+; RV64I-NEXT: add a1, a1, a2
+; RV64I-NEXT: and a0, a0, a1
+; RV64I-NEXT: slli a1, a0, 8
+; RV64I-NEXT: sub a0, a1, a0
+; RV64I-NEXT: ret
+;
+; RV64ZBB-LABEL: orc_b_i64:
+; RV64ZBB: # %bb.0:
+; RV64ZBB-NEXT: lui a1, 4112
+; RV64ZBB-NEXT: addiw a1, a1, 257
+; RV64ZBB-NEXT: slli a2, a1, 32
+; RV64ZBB-NEXT: add a1, a1, a2
+; RV64ZBB-NEXT: and a0, a0, a1
+; RV64ZBB-NEXT: orc.b a0, a0
+; RV64ZBB-NEXT: ret
+ %1 = and i64 %a, 72340172838076673
+ %2 = mul nuw i64 %1, 255
+ ret i64 %2
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/96680
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