JIT: normalize edge likelihood when collapsing BBJ_COND to BBJ_ALWAYS

[AndyAyersMS]

Set the merged edge likelihood to 1.0 when a BBJ_COND degenerates so the profile stays consistent, and report the failing block when the check asserts.

Fixes #130785

[AndyAyersMS]

@EgorBo PTAL
fyi @dotnet/jit-contrib

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[Copilot]

Pull request overview

This PR adjusts CoreCLR JIT profile-consistency handling in two places: (1) it adds a “dump-only” mode to the debug profile-weight checker so it can log details before asserting, and (2) it ensures edge-likelihood invariants are maintained when conditional branches are collapsed to unconditional branches.

Changes:

• Extend fgDebugCheckProfileWeights with a dump mode and re-run the check with verbose=true to emit diagnostics prior to asserting on inconsistent profile data.
• Normalize the successor edge likelihood when converting a degenerate BBJ_COND to BBJ_ALWAYS.
• Update the Compiler declaration to match the new fgDebugCheckProfileWeights signature.

Reviewed changes

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

File	Description
src/coreclr/jit/fgprofile.cpp	Adds dump mode and a verbose re-run to print profile inconsistency details before asserting.
src/coreclr/jit/fgopt.cpp	Adjusts edge likelihood handling when removing a conditional jump that always targets the same block.
src/coreclr/jit/compiler.h	Updates the fgDebugCheckProfileWeights declaration to include the new optional dump parameter.

Comments suppressed due to low confidence (1)

src/coreclr/jit/fgprofile.cpp:4867

• In dump mode, the unflaggedBlocks path is completely suppressed (no JITDUMP, no assert). This defeats the purpose of re-running with dump=true to log details before asserting, since missing BBF_PROF_WEIGHT flags will still assert without any diagnostic output when verbose was originally false. Consider always emitting the JITDUMP, and only gating the assert on !dump.

    if ((unflaggedBlocks > 0) && !dump)
    {
        JITDUMP("%d blocks are missing BBF_PROF_WEIGHT flag.\n", unflaggedBlocks);
        assert(!"Missing BBF_PROF_WEIGHT flag");
    }