[PATCH] D88177: [AArch64][GlobalISel] Infer whether G_PHI is going to be a FPR in regbankselect

[Jessica Paquette via Phabricator via llvm-commits]

paquette created this revision.
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Some instructions (G_LOAD, G_SELECT, G_UNMERGE_VALUES) check if their uses will define/use FPRs (using `onlyUsesFP` and `onlyDefinesFP`).

The register bank of a use isn't necessarily known when an instruction asks for this.

Teach `hasFPConstraints` to look at the instructions feeding into a G_PHI when its destination bank is unknown. If any of them are FPR, assume the entire G_PHI will also be assigned a FPR.

Since a phi can have many inputs, and those inputs can in turn be phis, restrict the search depth to a very low number.

Also improve the docs for `hasFPConstraints` and friends a little.

This is a 0.3% code size improvement on CTMark/Bullet at -O3, and a 0.2% code size improvement at CTMark/pairlocalalign at -O3.


https://reviews.llvm.org/D88177

Files:
  llvm/lib/Target/AArch64/GISel/AArch64RegisterBankInfo.cpp
  llvm/lib/Target/AArch64/GISel/AArch64RegisterBankInfo.h
  llvm/test/CodeGen/AArch64/GlobalISel/regbank-fp-use-def.mir

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