Tianqing Wang 3d494bfc7f [SimplifyCFG] Increase budget for FoldTwoEntryPHINode() if the branch is unpredictable. (#98495) ...

The `!unpredictable` metadata has been present for a long time, but
it's usage in optimizations is still limited. This patch teaches
`FoldTwoEntryPHINode()` to be more aggressive with an unpredictable
branch to reduce mispredictions.

A TTI interface `getBranchMispredictPenalty()` is added to distinguish
between different hardwares to ensure we don't go too far for simpler
cores. For simplicity, only a naive x86 implementation is included for
the time being.

2024-07-23 07:47:21 +08:00

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