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Don't always do optimistic HW intrinsic expansion #89282

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merged 1 commit into from
Jul 24, 2023

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MichalStrehovsky
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"Optimistic" expansion means we generate a method body for IsSupported that returns true/false depending on the currently running CPU.

Don't do this when --instruction-set:native was specified because native should mean "exactly this, as if I was using a JIT". Also don't do this when optimizing for size (saves 0.6% on hello world). I was going back and forth whether to do this when user specifies instruction sets manually, but it would be a "breaking" change to pull out the optimistic part.

I also though about #87865 (comment) (adding ?), but that one would have odd failure modes --instruction-set:avx? is not supportable by RyuJIT and there are others. The rules are bespoke.

Cc @dotnet/ilc-contrib

"Optimistic" expansion means we generate a method body for `IsSupported` that returns true/false depending on the currently running CPU. Don't do this when `--instruction-set:native` was specified because native should mean "exactly this". Also don't do this when optimizing for size (saves 0.6% on hello world). I was going back and forth whether to do this when user specifies instruction sets manually, but decided it would be a "breaking" change.
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ghost commented Jul 21, 2023

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Issue Details

"Optimistic" expansion means we generate a method body for IsSupported that returns true/false depending on the currently running CPU.

Don't do this when --instruction-set:native was specified because native should mean "exactly this, as if I was using a JIT". Also don't do this when optimizing for size (saves 0.6% on hello world). I was going back and forth whether to do this when user specifies instruction sets manually, but it would be a "breaking" change to pull out the optimistic part.

I also though about #87865 (comment) (adding ?), but that one would have odd failure modes --instruction-set:avx? is not supportable by RyuJIT and there are others. The rules are bespoke.

Cc @dotnet/ilc-contrib

Author: MichalStrehovsky
Assignees: MichalStrehovsky
Labels:

area-crossgen2-coreclr, area-NativeAOT-coreclr

Milestone: -

@MichalStrehovsky MichalStrehovsky merged commit 78b45ad into dotnet:main Jul 24, 2023
@MichalStrehovsky MichalStrehovsky deleted the optimistic branch July 24, 2023 01:54
@ghost ghost locked as resolved and limited conversation to collaborators Aug 23, 2023
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