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[JIT] X64 - Three instruction replacement sequence for multiply in certain cases #76981

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merged 25 commits into from
Oct 20, 2022
Merged

[JIT] X64 - Three instruction replacement sequence for multiply in certain cases #76981

merged 25 commits into from
Oct 20, 2022

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TIHan
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@TIHan TIHan commented Oct 13, 2022 •
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Description

Will resolve a subset of: #75119

The changes handle integer multiplication cases when a constant is one away from being the power of 2.
Some performance results are here.

Examples:

        [MethodImpl(MethodImplOptions.NoInlining)]
        static ulong UInt64_MultiplyWith15(ulong value)
        {
            // X64:      mov [[REG0:[a-z]+]], [[REG1:[a-z]+]]
            // X64-NEXT: shl [[REG0]], 4
            // X64-NEXT: sub [[REG0]], [[REG1]]
            return value * 15;
        }

        [MethodImpl(MethodImplOptions.NoInlining)]
        static ulong UInt64_MultiplyWith17(ulong value)
        {
            // X64:      mov [[REG0:[a-z]+]], [[REG1:[a-z]+]]
            // X64-NEXT: shl [[REG0]], 4
            // X64-NEXT: add [[REG0]], [[REG1]]
            return value * 17;
        }

These can technically be further optimized with lea I believe, but I'm going to do those in a separate PR.

I made very trivial updates to SuperFileCheck since I encountered a bug when writing the disasm tests for this.

Acceptance Criteria

  • Disasm tests

@dotnet-issue-labeler dotnet-issue-labeler bot added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label Oct 13, 2022
@ghost ghost assigned TIHan Oct 13, 2022
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ghost commented Oct 13, 2022

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch
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Issue Details

Experimenting based on this issue #75119

Author: TIHan
Assignees: TIHan
Labels:

area-CodeGen-coreclr
Milestone: -

@runfoapp runfoapp bot mentioned this pull request Oct 13, 2022
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@build-analysis build-analysis bot mentioned this pull request Oct 13, 2022
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@TIHan TIHan changed the title Using 3 instruction sequence for x64 multiply [JIT] X64 - Three instruction replacement sequence for multiply in certain cases Oct 14, 2022
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TIHan commented Oct 14, 2022

This is ready. @dotnet/jit-contrib - @kunalspathak PTAL

@TIHan TIHan marked this pull request as ready for review October 14, 2022 23:38
@TIHan TIHan mentioned this pull request Oct 17, 2022
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TIHan commented Oct 18, 2022 •
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@dotnet/jit-contrib ping again, this is ready and is passing CI, diffs

There is a slight size increase, but based on the perfscore, and benchmarks mentioned in the description, execution time is faster.

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kunalspathak commented Oct 19, 2022 via email

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kunalspathak approved these changes Oct 19, 2022
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LGTM

TIHan added 2 commits October 19, 2022 12:38
@TIHan
Feedback. Removed use of FULL-LINE as it is more readable not strictl…
214625f 
…y necessary. Forgot to add an additional instruction to a disasm test.
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TIHan commented Oct 20, 2022

CI did pass except for formatting and a timeout issue. Merging now.

@TIHan TIHan merged commit ccd9d16 into dotnet:main Oct 20, 2022
@TIHan TIHan deleted the mul-opt-x64 branch October 20, 2022 01:16
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@kunalspathak kunalspathak kunalspathak approved these changes

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