[llvm] [APInt][NFC] Add branch hints to APInt single-word (PR #219437)

[Fangrui Song via llvm-commits]

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MaskRay wrote:

Unfortunately, no.

`__builtin_likely -> llvm.expect --LowerExpectIntrinsics--> !prof "branch_weights"`

LowerExpectIntrinsics is very early in ModuleSimplification pipeline, before inliner.

https://github.com/llvm/llvm-project/pull/219437