JIT: Move loop inversion to after loop recognition

[amanasifkhalid]

Prerequisite to #113709. I expect diffs to go both ways: In some cases, loop canonicalization unlocks pattern-based loop inversion, whereas in other cases, we now recognize fewer loops due to loop inversion no longer introducing new cycles pre-canonicalization.

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[Copilot]

Pull Request Overview

This PR moves the loop inversion phase to after loop recognition, adds immediate block compaction/removal for newly altered test blocks, and triggers a DFS rebuild with fresh loop analysis when any loops were inverted.

• Add single-predecessor block compaction/removal in optInvertWhileLoop
• Recompute the DFS tree and re-run loop finding after any loop inversions
• Relocate the PHASE_INVERT_LOOPS call in the compilation pipeline

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
optimizer.cpp	Inserted block compaction/removal and DFS invalidation
compiler.cpp	Moved the loop inversion phase to a later point in compCompile

Comments suppressed due to low confidence (1)

src/coreclr/jit/compiler.cpp:4668

• Add targeted tests that verify the new phase ordering and ensure that both block compaction and removal occur as expected after loop inversion.

DoPhase(this, PHASE_INVERT_LOOPS, &Compiler::optInvertLoops);