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Poor codegen for "big" (> 4 fields) structs init #71565

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hypeartist opened this issue Jul 1, 2022 · 6 comments · Fixed by #88090
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Poor codegen for "big" (> 4 fields) structs init #71565

hypeartist opened this issue Jul 1, 2022 · 6 comments · Fixed by #88090
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@jakobbotsch
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area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI Priority:2 Work that is important, but not critical for the release question Answer questions and provide assistance, not an issue with source code or documentation.
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8.0.0

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@hypeartist
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hypeartist commented Jul 1, 2022 •
edited by BruceForstall

FWm4DESWIAACiUX

category:cq
theme:structs
skill-level:expert
cost:large
impact:large
@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 Jul 1, 2022
@ghost ghost added the untriaged New issue has not been triaged by the area owner label Jul 1, 2022
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ghost commented Jul 1, 2022

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch
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FWm4DESWIAACiUX

Author: hypeartist
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Labels:

area-CodeGen-coreclr, untriaged
Milestone: -

@jakobbotsch
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This is essentially a duplicate of #6534 -- the JIT does not currently do promotion for structs with more than 4 fields. It is an area that I hope we will be improving in .NET 8.

@hypeartist
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@jakobbotsch Is there any info about what are all those restrictions (#6494 (comment) especially the one about 4 fields limit) based on?

@SingleAccretion
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The 4 fields limit is just a CQ heuristic. Some of the other restrictions represent unimplemented functionality.

@hypeartist
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hypeartist commented Jul 1, 2022 •
edited

@jakobbotsch @SingleAccretion On the second thought my guess is that the issue some way related to ABI stuff - particularly the fact that the number of args that could be passed in regs is 4

@hypeartist
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hypeartist commented Jul 5, 2022 •
edited

Another strangeness.
Method M1C vs M1A. Both operate with the same 'big' struct A:

image

PS: or even like this:

image

@JulieLeeMSFT JulieLeeMSFT added the question Answer questions and provide assistance, not an issue with source code or documentation. label Jul 5, 2022
@JulieLeeMSFT JulieLeeMSFT added this to the 7.0.0 milestone Jul 11, 2022
@ghost ghost removed the untriaged New issue has not been triaged by the area owner label Jul 11, 2022
@jakobbotsch jakobbotsch modified the milestones: 7.0.0, 8.0.0 Jul 12, 2022
@jakobbotsch jakobbotsch mentioned this issue Oct 12, 2022
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@jakobbotsch jakobbotsch added the Priority:2 Work that is important, but not critical for the release label Jun 20, 2023
@jakobbotsch jakobbotsch mentioned this issue Jun 27, 2023
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@ghost ghost added the in-pr There is an active PR which will close this issue when it is merged label Jun 27, 2023
@ghost ghost removed the in-pr There is an active PR which will close this issue when it is merged label Jun 29, 2023
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area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI Priority:2 Work that is important, but not critical for the release question Answer questions and provide assistance, not an issue with source code or documentation.
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JIT: Enable physical promotion by default jakobbotsch/runtime
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@hypeartist @jakobbotsch @SingleAccretion @JulieLeeMSFT