[RISCV][NFC] Avoid iteration and division while selecting SHXADD instructions #158851
+104
−78
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
…ructions Should improve compilation time.
|
@llvm/pr-subscribers-backend-risc-v Author: Piotr Fusik (pfusik) ChangesShould improve compilation time. Full diff: https://github.com/llvm/llvm-project/pull/158851.diff 3 Files Affected:
diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 9d90eb0a65218..fab9a7e962158 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -16371,43 +16371,60 @@ static SDValue expandMul(SDNode *N, SelectionDAG &DAG,
SDValue X = N->getOperand(0);
if (Subtarget.hasShlAdd(3)) {
- for (uint64_t Divisor : {3, 5, 9}) {
- if (MulAmt % Divisor != 0)
- continue;
- uint64_t MulAmt2 = MulAmt / Divisor;
- // 3/5/9 * 2^N -> shl (shXadd X, X), N
- if (isPowerOf2_64(MulAmt2)) {
- SDLoc DL(N);
- SDValue X = N->getOperand(0);
- // Put the shift first if we can fold a zext into the
- // shift forming a slli.uw.
- if (X.getOpcode() == ISD::AND && isa<ConstantSDNode>(X.getOperand(1)) &&
- X.getConstantOperandVal(1) == UINT64_C(0xffffffff)) {
- SDValue Shl = DAG.getNode(ISD::SHL, DL, VT, X,
- DAG.getConstant(Log2_64(MulAmt2), DL, VT));
- return DAG.getNode(RISCVISD::SHL_ADD, DL, VT, Shl,
- DAG.getConstant(Log2_64(Divisor - 1), DL, VT),
- Shl);
- }
- // Otherwise, put rhe shl second so that it can fold with following
- // instructions (e.g. sext or add).
- SDValue Mul359 =
- DAG.getNode(RISCVISD::SHL_ADD, DL, VT, X,
- DAG.getConstant(Log2_64(Divisor - 1), DL, VT), X);
- return DAG.getNode(ISD::SHL, DL, VT, Mul359,
- DAG.getConstant(Log2_64(MulAmt2), DL, VT));
- }
-
- // 3/5/9 * 3/5/9 -> shXadd (shYadd X, X), (shYadd X, X)
- if (MulAmt2 == 3 || MulAmt2 == 5 || MulAmt2 == 9) {
- SDLoc DL(N);
- SDValue Mul359 =
- DAG.getNode(RISCVISD::SHL_ADD, DL, VT, X,
- DAG.getConstant(Log2_64(Divisor - 1), DL, VT), X);
- return DAG.getNode(RISCVISD::SHL_ADD, DL, VT, Mul359,
- DAG.getConstant(Log2_64(MulAmt2 - 1), DL, VT),
- Mul359);
+ int Shift;
+ if (int ShXAmount = isShifted359(MulAmt, Shift)) {
+ // 3/5/9 * 2^N -> shl (shXadd X, X), N
+ SDLoc DL(N);
+ SDValue X = N->getOperand(0);
+ // Put the shift first if we can fold a zext into the shift forming
+ // a slli.uw.
+ if (X.getOpcode() == ISD::AND && isa<ConstantSDNode>(X.getOperand(1)) &&
+ X.getConstantOperandVal(1) == UINT64_C(0xffffffff)) {
+ SDValue Shl =
+ DAG.getNode(ISD::SHL, DL, VT, X, DAG.getConstant(Shift, DL, VT));
+ return DAG.getNode(RISCVISD::SHL_ADD, DL, VT, Shl,
+ DAG.getConstant(ShXAmount, DL, VT), Shl);
}
+ // Otherwise, put the shl second so that it can fold with following
+ // instructions (e.g. sext or add).
+ SDValue Mul359 = DAG.getNode(RISCVISD::SHL_ADD, DL, VT, X,
+ DAG.getConstant(ShXAmount, DL, VT), X);
+ return DAG.getNode(ISD::SHL, DL, VT, Mul359,
+ DAG.getConstant(Shift, DL, VT));
+ }
+
+ // 3/5/9 * 3/5/9 -> shXadd (shYadd X, X), (shYadd X, X)
+ int ShX;
+ int ShY;
+ switch (MulAmt) {
+ case 3 * 5:
+ ShY = 1;
+ ShX = 2;
+ break;
+ case 3 * 9:
+ ShY = 1;
+ ShX = 3;
+ break;
+ case 5 * 5:
+ ShX = ShY = 2;
+ break;
+ case 5 * 9:
+ ShY = 2;
+ ShX = 3;
+ break;
+ case 9 * 9:
+ ShX = ShY = 3;
+ break;
+ default:
+ ShX = ShY = 0;
+ break;
+ }
+ if (ShX) {
+ SDLoc DL(N);
+ SDValue Mul359 = DAG.getNode(RISCVISD::SHL_ADD, DL, VT, X,
+ DAG.getConstant(ShY, DL, VT), X);
+ return DAG.getNode(RISCVISD::SHL_ADD, DL, VT, Mul359,
+ DAG.getConstant(ShX, DL, VT), Mul359);
}
// If this is a power 2 + 2/4/8, we can use a shift followed by a single
@@ -16430,18 +16447,14 @@ static SDValue expandMul(SDNode *N, SelectionDAG &DAG,
// variants we could implement. e.g.
// (2^(1,2,3) * 3,5,9 + 1) << C2
// 2^(C1>3) * 3,5,9 +/- 1
- for (uint64_t Divisor : {3, 5, 9}) {
- uint64_t C = MulAmt - 1;
- if (C <= Divisor)
- continue;
- unsigned TZ = llvm::countr_zero(C);
- if ((C >> TZ) == Divisor && (TZ == 1 || TZ == 2 || TZ == 3)) {
+ if (int ShXAmount = isShifted359(MulAmt - 1, Shift)) {
+ assert(Shift != 0 && "MulAmt=4,6,10 handled before");
+ if (Shift <= 3) {
SDLoc DL(N);
- SDValue Mul359 =
- DAG.getNode(RISCVISD::SHL_ADD, DL, VT, X,
- DAG.getConstant(Log2_64(Divisor - 1), DL, VT), X);
+ SDValue Mul359 = DAG.getNode(RISCVISD::SHL_ADD, DL, VT, X,
+ DAG.getConstant(ShXAmount, DL, VT), X);
return DAG.getNode(RISCVISD::SHL_ADD, DL, VT, Mul359,
- DAG.getConstant(TZ, DL, VT), X);
+ DAG.getConstant(Shift, DL, VT), X);
}
}
@@ -16449,7 +16462,7 @@ static SDValue expandMul(SDNode *N, SelectionDAG &DAG,
if (MulAmt > 2 && isPowerOf2_64((MulAmt - 1) & (MulAmt - 2))) {
unsigned ScaleShift = llvm::countr_zero(MulAmt - 1);
if (ScaleShift >= 1 && ScaleShift < 4) {
- unsigned ShiftAmt = Log2_64(((MulAmt - 1) & (MulAmt - 2)));
+ unsigned ShiftAmt = llvm::countr_zero((MulAmt - 1) & (MulAmt - 2));
SDLoc DL(N);
SDValue Shift1 =
DAG.getNode(ISD::SHL, DL, VT, X, DAG.getConstant(ShiftAmt, DL, VT));
@@ -16462,7 +16475,7 @@ static SDValue expandMul(SDNode *N, SelectionDAG &DAG,
// 2^N - 3/5/9 --> (sub (shl X, C1), (shXadd X, x))
for (uint64_t Offset : {3, 5, 9}) {
if (isPowerOf2_64(MulAmt + Offset)) {
- unsigned ShAmt = Log2_64(MulAmt + Offset);
+ unsigned ShAmt = llvm::countr_zero(MulAmt + Offset);
if (ShAmt >= VT.getSizeInBits())
continue;
SDLoc DL(N);
@@ -16481,21 +16494,16 @@ static SDValue expandMul(SDNode *N, SelectionDAG &DAG,
uint64_t MulAmt2 = MulAmt / Divisor;
// 3/5/9 * 3/5/9 * 2^N - In particular, this covers multiples
// of 25 which happen to be quite common.
- for (uint64_t Divisor2 : {3, 5, 9}) {
- if (MulAmt2 % Divisor2 != 0)
- continue;
- uint64_t MulAmt3 = MulAmt2 / Divisor2;
- if (isPowerOf2_64(MulAmt3)) {
- SDLoc DL(N);
- SDValue Mul359A =
- DAG.getNode(RISCVISD::SHL_ADD, DL, VT, X,
- DAG.getConstant(Log2_64(Divisor - 1), DL, VT), X);
- SDValue Mul359B = DAG.getNode(
- RISCVISD::SHL_ADD, DL, VT, Mul359A,
- DAG.getConstant(Log2_64(Divisor2 - 1), DL, VT), Mul359A);
- return DAG.getNode(ISD::SHL, DL, VT, Mul359B,
- DAG.getConstant(Log2_64(MulAmt3), DL, VT));
- }
+ if (int ShBAmount = isShifted359(MulAmt2, Shift)) {
+ SDLoc DL(N);
+ SDValue Mul359A =
+ DAG.getNode(RISCVISD::SHL_ADD, DL, VT, X,
+ DAG.getConstant(Log2_64(Divisor - 1), DL, VT), X);
+ SDValue Mul359B =
+ DAG.getNode(RISCVISD::SHL_ADD, DL, VT, Mul359A,
+ DAG.getConstant(ShBAmount, DL, VT), Mul359A);
+ return DAG.getNode(ISD::SHL, DL, VT, Mul359B,
+ DAG.getConstant(Shift, DL, VT));
}
}
}
diff --git a/llvm/lib/Target/RISCV/RISCVInstrInfo.cpp b/llvm/lib/Target/RISCV/RISCVInstrInfo.cpp
index f816112f70140..794ec5f6cc3dd 100644
--- a/llvm/lib/Target/RISCV/RISCVInstrInfo.cpp
+++ b/llvm/lib/Target/RISCV/RISCVInstrInfo.cpp
@@ -4492,24 +4492,23 @@ void RISCVInstrInfo::mulImm(MachineFunction &MF, MachineBasicBlock &MBB,
.addReg(DestReg, RegState::Kill)
.addImm(ShiftAmount)
.setMIFlag(Flag);
- } else if (STI.hasShlAdd(3) &&
- ((Amount % 3 == 0 && isPowerOf2_64(Amount / 3)) ||
- (Amount % 5 == 0 && isPowerOf2_64(Amount / 5)) ||
- (Amount % 9 == 0 && isPowerOf2_64(Amount / 9)))) {
+ } else if (int ShXAmount, ShiftAmount;
+ STI.hasShlAdd(3) &&
+ (ShXAmount = isShifted359(Amount, ShiftAmount)) != 0) {
// We can use Zba SHXADD+SLLI instructions for multiply in some cases.
unsigned Opc;
- uint32_t ShiftAmount;
- if (Amount % 9 == 0) {
- Opc = RISCV::SH3ADD;
- ShiftAmount = Log2_64(Amount / 9);
- } else if (Amount % 5 == 0) {
- Opc = RISCV::SH2ADD;
- ShiftAmount = Log2_64(Amount / 5);
- } else if (Amount % 3 == 0) {
+ switch (ShXAmount) {
+ case 1:
Opc = RISCV::SH1ADD;
- ShiftAmount = Log2_64(Amount / 3);
- } else {
- llvm_unreachable("implied by if-clause");
+ break;
+ case 2:
+ Opc = RISCV::SH2ADD;
+ break;
+ case 3:
+ Opc = RISCV::SH3ADD;
+ break;
+ default:
+ llvm_unreachable("unexpected result of isShifted359");
}
if (ShiftAmount)
BuildMI(MBB, II, DL, get(RISCV::SLLI), DestReg)
diff --git a/llvm/lib/Target/RISCV/RISCVInstrInfo.h b/llvm/lib/Target/RISCV/RISCVInstrInfo.h
index 57ec431749ebe..fe3f1bfd5e2a1 100644
--- a/llvm/lib/Target/RISCV/RISCVInstrInfo.h
+++ b/llvm/lib/Target/RISCV/RISCVInstrInfo.h
@@ -25,6 +25,22 @@
namespace llvm {
+template <typename T> int isShifted359(T Value, int &Shift) {
+ if (Value == 0)
+ return 0;
+ Shift = llvm::countr_zero(Value);
+ switch (Value >> Shift) {
+ case 3:
+ return 1;
+ case 5:
+ return 2;
+ case 9:
+ return 3;
+ default:
+ return 0;
+ }
+}
+
class RISCVSubtarget;
static const MachineMemOperand::Flags MONontemporalBit0 =
|
mshockwave
reviewed
Sep 16, 2025
preames
reviewed
Sep 17, 2025
I haven't looked at the assembly, but if both levels of 3/5/9 loops are unrolled, that's quite some binary bloat. The point is that we can match the |
topperc
reviewed
Oct 6, 2025
|
|
||
| namespace llvm { | ||
|
|
||
| template <typename T> int isShifted359(T Value, int &Shift) { |
There was a problem hiding this comment.
Add a description comment?
|
LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/59/builds/25300 Here is the relevant piece of the build log for the reference |
|
LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/95/builds/18635 Here is the relevant piece of the build log for the reference |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Should improve compilation time.