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Do not eliminate casts from FP types when optimizing narrow stores #53667

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SingleAccretion
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@SingleAccretion SingleAccretion commented Jun 3, 2021

An optimization in morph was deleting casts on the RHS of a narrow store if the cast-to-type
was wider than the type being stored. This is only valid for casts from integral types, as the backend
does not handle STOREIND(byte*, double), nor is there an instruction to go from an XMM register to a narrow memory location on x86/x64.

The issue is not reproducible right now because fgMorphCast wraps the casts in question, but it is an invalid IR transformation nonetheless, and similar code in fgMorphSmpOpOptional guards against non-integral sources.

Also, while I was there, modernized the code a little bit.

@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 Jun 3, 2021
@SingleAccretion SingleAccretion force-pushed the Fix-Potential-Issue-With-Cast-Elimination-For-Stores branch from ff54d81 to 4dd49bb Compare June 3, 2021 09:36
@SingleAccretion SingleAccretion marked this pull request as ready for review June 3, 2021 14:47
An optimization in morph was deleting casts
on the RHS of a narrow store if the cast-to-type
was wider than the type being stored. This is only
valid for casts from integral types, as the backend
does not handle "STOREIND(byte*, double)", nor is there
an instruction to go from an XMM register to a narrow
memory location on x86/x64.

The issue is not reproducible right now because
fgMorphCast wraps the casts in question, but it is
an invalid IR transformation nonetheless, and similar
code in fgMorphSmpOpOptional guards against non-integral sources.
@SingleAccretion SingleAccretion force-pushed the Fix-Potential-Issue-With-Cast-Elimination-For-Stores branch from 4dd49bb to 94de26a Compare June 7, 2021 20:50
@tannergooding
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CC. @dotnet/jit-contrib, community PR

@JulieLeeMSFT
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@kunalspathak @dotnet/jit-contrib PTAL community PR.

@kunalspathak
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@SingleAccretion - No asmdiffs?

@SingleAccretion
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No asmdiffs?

Yes, no diffs as expected.

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@kunalspathak kunalspathak left a comment

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LGTM

@kunalspathak kunalspathak merged commit 53db2ec into dotnet:main Jul 13, 2021
@SingleAccretion SingleAccretion deleted the Fix-Potential-Issue-With-Cast-Elimination-For-Stores branch July 13, 2021 16:49
@ghost ghost locked as resolved and limited conversation to collaborators Aug 12, 2021
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4 participants