Merge throw blocks in fgHeadTailMerge

[EgorBo]

Should fix the regression in #122065

Diffs

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Pull request overview

This PR extends the tail merge optimization in fgHeadTailMerge to handle BBJ_THROW blocks in addition to BBJ_RETURN blocks. The change allows the JIT compiler to merge common tail statements from throw blocks, which should fix a regression introduced in a previous PR.

Key Changes

• Modified the block kind check to include both BBJ_RETURN and BBJ_THROW blocks for tail merge consideration
• This enables tail merging optimization to work on throw blocks, similar to how it already works on return blocks

[EgorBo]

PTAL @dotnet/jit-contrib Diffs
I've analyzed a couple of PerfScore regressions and didn't find anything terrible. I guess this PR has no perfscore improvements because it removes blocks with 0 weight, hence no positive impact on PerfScore