[JIT] On importing a CEE_INITOBJ for a simd, construct a VecCon(0)

[TIHan]

When we handle CEE_INITOBJ in the importer, if we know that the type is a simd type, then construct a VecCon(0) for the zero-initialization instead of an IntCon(0).

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Issue Details

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When handle CEE_INITOBJ in the importer, if we know that the type is a simd type, then constructor a VecCon(0) for the zero-initialization instead of an IntCon(0).

Author:	TIHan
Assignees:	-
Labels:	area-CodeGen-coreclr
Milestone:	-

[TIHan]

@dotnet/jit-contrib this is ready. cc @tannergooding @kunalspathak

A few improvements

[SingleAccretion]

I think it is great to make the zero-init form for vectors canonical with CNS_VEC, but we should make this change everywhere and fully disallow ASG(simd, CNS_INT 0). This will allow for some code simplification (e. g. in VN, or the recent local morph fix).

[TIHan]

we should make this change everywhere and fully disallow ASG(simd, CNS_INT 0)

I agree, we will make another PR to handle it. @tannergooding knows of the several places to do this so I'll let him handle it.

[tannergooding]

LGTM. I think we should have an issue tracking the other cleanup so we can get to the desired outcome of no more ASG(SIMD, 0)

[TIHan]

@dotnet/jit-contrib this is ready PTAL @jakobbotsch