Perform ldr to ldp peephole optimization

[kunalspathak]

In #77540 we started replacing consecutive loads and stores with ldp and stp except if they are for local variables. See #77540 (review) for details. For loads, turns out that we do not need offset tracking for loads and gc-liveness tracking for ldp is already present. So this PR just relaxes the rule and enable the optimization for 2 consecutive loads.

For non-gc stores too, it enabled the peephole optimization because those variables do not need gc liveness tracking.

Contributes to #81278 and #55365
Fixes: #35132 and #35130

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Issue Details

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In local asmdiff verification, I see that the gcrefs are correctly tracked. Just double check if there are any GC holes.

Contributes to #81278

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

[kunalspathak]

/azp run runtime-coreclr gcstress0x3-gcstress0xc

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[kunalspathak]

@dotnet/jit-contrib

gcstress run is clean.

[kunalspathak]

Diffs from earlier run.

[BruceForstall]

Diffs

Diffs look great.

[BruceForstall]

You didn't update the comment above: "Don't do this if either instruction had a local variable." It would be useful to update this and provide more detail about why ldr is allowed.

It also occurs to me that you could also allow str of locals if both str are non-GC types, e.g., floating-point/SIMD, or even TYP_INT. I still think in both ldr and str cases it would be helpful in DEBUG to be able to annotate JitDisasm with the local var (+offset) being read/written, for each local.

[kunalspathak]

You didn't update the comment above: "Don't do this if either instruction had a local variable." It would be useful to update this and provide more detail about why ldr is allowed.

Done

It also occurs to me that you could also allow str of locals if both str are non-GC types, e.g., floating-point/SIMD, or even TYP_INT.

That's true. Added it.

I still think in both ldr and str cases it would be helpful in DEBUG to be able to annotate JitDisasm with the local var (+offset) being read/written, for each local.

Can we do it as a follow-up PR? I will open a .NET 8 tracking issue for it.

[BruceForstall]

Can we do it as a follow-up PR?

yes. And please open an issue.

[kunalspathak]

yes. And please open an issue.

#84504

[kunalspathak]

/azp run runtime-coreclr gcstress0x3-gcstress0xc

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[kunalspathak]

gc-stress failures are unrelated.