[llvm] [StructurizeCFG] Order IF Else block using Heuristics (PR #139605)

Mon May 12 11:39:35 PDT 2025

https://github.com/VigneshwarJ created https://github.com/llvm/llvm-project/pull/139605

Then and Else block order in SCC is arbitrary. But based on the order, after structurization there are cases where there might be extra VGPR copies due to interference during register coelescing.

This patch introduces heuristics to order the then and else block based on the potential VGPR copies to maximize coelescing.

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