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[RISCV] Eliminate dead li after emitting VSETVLIs #65934

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merged 1 commit into from
Dec 13, 2023
Merged

[RISCV] Eliminate dead li after emitting VSETVLIs #65934

merged 1 commit into from
Dec 13, 2023

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dtcxzyw
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@dtcxzyw dtcxzyw commented Sep 11, 2023

As discussed in D158759, RISCVInsertVSETVLI introduces dead li instructions. These instructions were exceptionally rewritten by the following peephole pass RISCVDeadRegisterDefinitions.

This patch tracks li instructions that set AVL operands and does DCE after emitting VSETVLIs.

@dtcxzyw dtcxzyw requested a review from a team as a code owner September 11, 2023 08:18
preames
preames requested changes Sep 11, 2023
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llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp Outdated Show resolved Hide resolved
llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp Outdated Show resolved Hide resolved
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dtcxzyw commented Sep 24, 2023

Ping.

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dtcxzyw commented Oct 3, 2023

Ping.

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dtcxzyw commented Oct 11, 2023

Gentle ping.

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dtcxzyw commented Oct 16, 2023

Ping.

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dtcxzyw commented Oct 30, 2023

Ping.

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topperc commented Oct 30, 2023

@preames do you have concerns with this patch?

@dtcxzyw dtcxzyw requested a review from lukel97 November 8, 2023 16:43
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lukel97 commented Nov 8, 2023 •
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Oh nice, I'm running into something similar in #71657. Are all these dead ADDIs coming from the backwards local postpass?

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dtcxzyw commented Nov 11, 2023

Oh nice, I'm running into something similar in #71657. Are all these dead ADDIs coming from the backwards local postpass?

Yes. I believe this PR can address the issue.

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lukel97 commented Nov 13, 2023

Oh nice, I'm running into something similar in #71657. Are all these dead ADDIs coming from the backwards local postpass?

Yes. I believe this PR can address the issue.

My suspicion is that these LIs only become dead because the backwards local postpass deletes a vsetvli that had an ADDI AVL. Would it be easier then to just check if they are dead in doLocalPostpass rather than keeping around a vector of instructions? I.e. something similar to 8ae868b

@dtcxzyw dtcxzyw force-pushed the rv-vsetvli-post-dce branch 2 times, most recently from eddadd5 to f38258e Compare November 13, 2023 12:38
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lukel97 reviewed Nov 14, 2023
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llvm/lib/Target/RISCV/RISCVInstrInfo.h Outdated Show resolved Hide resolved
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dtcxzyw commented Nov 20, 2023

Ping.

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dtcxzyw commented Dec 13, 2023

Ping.

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LGTM

llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp Outdated Show resolved Hide resolved
@dtcxzyw dtcxzyw merged commit 3564c85 into llvm:main Dec 13, 2023
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@dtcxzyw dtcxzyw deleted the rv-vsetvli-post-dce branch December 13, 2023 15:18
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@lukel97 lukel97 lukel97 approved these changes

@preames preames Awaiting requested review from preames

@asb asb Awaiting requested review from asb

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@sunshaoce sunshaoce Awaiting requested review from sunshaoce

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@topperc topperc Awaiting requested review from topperc

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