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[RISCV] Add Tune to DontSinkSplatOperands #79199

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Merged
merged 5 commits into from
Jan 25, 2024
Merged

[RISCV] Add Tune to DontSinkSplatOperands #79199

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99aad5a
[RISCV] Add Tune to DontSinkSplatOperands
michaelmaitland Jan 23, 2024
d0cab7b
!fixme update description to include wx and wf
michaelmaitland Jan 24, 2024
8115ab4
!fixup add RUN with sinking
michaelmaitland Jan 24, 2024
4ce060a
!fixup change feature name
michaelmaitland Jan 25, 2024
6fac8a3
!fixup DONT->NO
michaelmaitland Jan 25, 2024
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7 changes: 7 additions & 0 deletions llvm/lib/Target/RISCV/RISCVFeatures.td
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Original file line number Diff line number Diff line change
Expand Up @@ -1082,6 +1082,13 @@ def TuneShortForwardBranchOpt
def HasShortForwardBranchOpt : Predicate<"Subtarget->hasShortForwardBranchOpt()">;
def NoShortForwardBranchOpt : Predicate<"!Subtarget->hasShortForwardBranchOpt()">;

// Some subtargets require a S2V transfer buffer to move scalars into vectors.
// FIXME: Forming .vx/.vf/.wx/.wf can reduce register pressure.
def TuneNoSinkSplatOperands
: SubtargetFeature<"no-sink-splat-operands", "SinkSplatOperands",
"false", "Disable sink splat operands to enable .vx, .vf,"
".wx, and .wf instructions">;

def TuneConditionalCompressedMoveFusion
: SubtargetFeature<"conditional-cmv-fusion", "HasConditionalCompressedMoveFusion",
"true", "Enable branch+c.mv fusion">;
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8 changes: 8 additions & 0 deletions llvm/lib/Target/RISCV/RISCVISelLowering.cpp
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Expand Up @@ -2000,6 +2000,14 @@ bool RISCVTargetLowering::shouldSinkOperands(
if (!I->getType()->isVectorTy() || !Subtarget.hasVInstructions())
return false;

// Don't sink splat operands if the target prefers it. Some targets requires
// S2V transfer buffers and we can run out of them copying the same value
// repeatedly.
// FIXME: It could still be worth doing if it would improve vector register
// pressure and prevent a vector spill.
if (!Subtarget.sinkSplatOperands())
return false;

for (auto OpIdx : enumerate(I->operands())) {
if (!canSplatOperand(I, OpIdx.index()))
continue;
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