JIT: extend initial profile repair to more cases

[AndyAyersMS]

In particular, fill in profiles for cases where we have an incomplete dynamic profile because a method rapidly transitions to OSR, and that method has important code that is not observed to execute by Tier0 instrumentation (things that happen after the OSR triggering loop exits) so having zero profiles for the remainder causes significant perf degradation.

Filling in the missing profile data entails:

• Allowing repair mode to reset exit likelihoods on zero-weight blocks as well as on inconsistent blocks. Since PGO never saw these blocks run, it has no opinion on their exit likelihoods.
• Adjust loop exit edge likelihoods if we end up capping the cyclic probability in the loop, so that some profile weight will exit the loop and light up any previously zero weight blocks that may follow.

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Issue Details

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In particular, fill in profiles for cases where we have an incomplete dynamic profile because a method rapidly transitions to OSR, and that method has important code that is not observed to execute by Tier0 instrumentation (things that happen after the OSR triggering loop exits) so having zero profiles for the remainder causes significant perf degradation.

Filling in the missing profile data entails:

• Allowing repair mode to reset exit likelihoods on zero-weight blocks as well as on inconsistent blocks. Since PGO never saw these blocks run, it has no opinion on their exit likelihoods.
• Adjust loop exit edge likelihoods if we end up capping the cyclic probability in the loop, so that some profile weight will exit the loop and light up any previously zero weight blocks that may follow.

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

[AndyAyersMS]

See #84264 (comment) for an example.

@EgorBo PTAL
cc @dotnet/jit-contrib

Expect some minor diffs but also a few large ones, in particular in benchmarks.run_pgo where we now properly optimize some methods we had been skimping on.

[EgorBo]

<deleted> ah, nvm, my example didn't use PGO

[AndyAyersMS]

<deleted> ah, nvm, my example didn't use PGO

This repair all happens very early before there are any internal blocks. But I would generally expect internal blocks to be able to inherit weights from their surroundings (or if introducing flow, inherit fractions of weights).

At some point I will introduce a repair that happens later in the phase pipeline, but that's a ways off.

[AndyAyersMS]

Formatting failure looks like some kind of CI glitch.

[AndyAyersMS]

Formatting failure looks like some kind of CI glitch.

Looks like this is hitting other PRs too, opened #84780

[EgorBo]

@AndyAyersMS I'm not sure if that is my PR but I'm seeing asserts in PGO pipelines like this https://helixre107v0xdcypoyl9e7f.blob.core.windows.net/dotnet-runtime-refs-pull-84772-merge-ca986f3aaa67420399/System.Collections.Tests/1/console.b3c01543.log?helixlogtype=result could those be caused by this PR?

[AndyAyersMS]

Yes it could very well be -- can you open an issue?

#84798