Increase number of assertions (GlobalAP) + VN cache

[EgorBo]

Diffs

This PR does two things:

1. Implements a quick O(1) check to answer: “Do we have any assertions for this VN?”
   I initially tried to use this cache everywhere, but ended up keeping it only in a few places where it had a noticeable TP benefit. This change alone has zero size diffs and reduces the TP regression from change (2) by 2×.
2. Increases the maximum number of assertions (GlobalAP) using a heuristic.
   With help from SPMI, I analyzed 1M methods and built a large table: | BB count | TrackedLocals count | assertions created |. I then fed it to an AI agent, which iterated for a while, generated some Python scripts, and proposed a heuristic (after several rounds of SPMI TP/size feedback). This is the best trade-off between improvements and TP regression that I was able to find. We could potentially incorporate more parameters (e.g., number of conditional blocks against null/constant, number of indirects), but I think the current version is good enough for now.

* I had 3 variants and ended up picking the 3rd one due to better TP results (obviously, less of =256 entities)

NOTE: If I unconditionally set optMaxAssertionCount to 256 the size diffs become ~8% better and TP regresses by 3x

The worst-case +0.3% TP regression should be more than covered by my earlier refactoring PRs that improved TP (the combined net effect should be around -0.5%).

Overall, TP-wise, the most expensive thing is the forward flow analysis

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[Copilot]

Pull request overview

This PR increases Global Assertion Propagation capacity and adds a small VN-based cache to avoid unnecessary full-table assertion scans, benefiting range check/range analysis and assertion propagation throughput.

Changes:

• Adjusts optMaxAssertionCount heuristics to allow tracking more assertions (especially for GlobalAP).
• Introduces optAssertionVNsMap + optAssertionHasAssertionsForVN() to quickly determine if any assertions exist for a given VN (with lazy initialization).
• Uses the VN cache to early-out in range-check assertion merges and GlobalAP local-var assertion propagation.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/coreclr/jit/rangecheck.cpp	Uses the new VN cache to skip assertion scanning when no assertions exist for the VN.
src/coreclr/jit/compiler.h	Adds optAssertionVNsMap and declares optAssertionHasAssertionsForVN().
src/coreclr/jit/assertionprop.cpp	Updates assertion table sizing, populates/queries the VN cache, and applies new early-out paths in GlobalAP.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

[EgorBo]

@AndyAyersMS @dotnet/jit-contrib PTAL. This is still a hacky way (I mean the heuristic) to deal with the TP regression, but it's better than nothing. Very few regressions, lots of improvements, small TP regression overall.

[EgorBo]

ping @AndyAyersMS