[WIP][mono] Add ILLink vector substitutions

[kotlarmilos]

Add ILLink substitutions to allow Vector classes trimming. Size reduction for iOS sample app should be 8%. Similar is done in #79672.

Draft PR should confirm if the runtime works as expected.

cc @ivanpovazan

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Issue Details

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Add ILLink substitutions to allow Vector classes trimming. Size reduction for iOS sample app should be 8%. Similar is done in #79672.

Draft PR should confirm if the runtime works as expected.

cc @ivanpovazan

Author:	kotlarmilos
Assignees:	kotlarmilos
Labels:	linkable-framework
Milestone:	-

[SamMonoRT]

/cc @fanyang-mono

[fanyang-mono]

I am trying to understand the impact of this change. According to

runtime/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems

Line 57 in a21bdff

<ILLinkSubstitutionsXmls Include="$(ILLinkSharedDirectory)ILLink.Substitutions.NoArmIntrinsics.xml" Condition="'$(SupportsArmIntrinsics)' != 'true'" />

ILLink.Substitutions.NoArmIntrinsics.xml will only be included, when SupportsArmIntrinsics is false. Does the value of SupportsArmIntrinsics equal to false on iOS?

[fanyang-mono]

Also, these files are shared between Mono and CoreCLR. I can imagine changing this file would change the behavior of both runtimes. If we want to tailor Mono runtime behavior but not changing CoreCLR, we probably should create a new file.

[ivanpovazan]

ILLink.Substitutions.NoArmIntrinsics.xml will only be included, when SupportsArmIntrinsics is false. Does the value of SupportsArmIntrinsics equal to false on iOS?

@fanyang-mono I believe when targeting iOS devices most of the time the target architecture is arm64, which means that from:

runtime/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems

Line 16 in a21bdff

<SupportsArmIntrinsics Condition="'$(Platform)' == 'arm64'">true</SupportsArmIntrinsics>

the linker would actually include NoX86Intrinsics.xml

[kotlarmilos]

Also, these files are shared between Mono and CoreCLR. I can imagine changing this file would change the behavior of both runtimes. If we want to tailor Mono runtime behavior but not changing CoreCLR, we probably should create a new file.

Makes sense.

the linker would actually include NoX86Intrinsics.xml

In both scenarios there should a size reduction as some code will be trimmed.

[kotlarmilos]

Finding is that in AOT mode for iOS apps we are not allowed to trim fallback code in vectors as JIT and Interpreter don't support vector intrinsics yet. Once vector intrinsics are supported in JIT and Interpreter we will be allowed to trim the fallback code.