[PATCH] D72814: [AArch64][GlobalISel] Change G_FCONSTANTs feeding into stores into G_CONSTANTS

[Jessica Paquette via Phabricator via llvm-commits]

paquette created this revision.
paquette added a reviewer: aemerson.
Herald added subscribers: Petar.Avramovic, hiraditya, kristof.beyls, rovka.
Herald added a project: LLVM.

Given the following situation:

  x = G_FCONSTANT (something that can't be materialized)
  G_STORE x, some_addr

We know that x must be materialized as at least a single mov. However, at the time of selection, the G_STORE will have been regbankselected to a FPR store.

So, as a result, you'll get an unnecessary fmov into the G_STORE.

Storing a constant value in a GPR and a constant value in a FPR are the same. So, whenever you see a G_FCONSTANT that feeds into only G_STORES, so might as well make it a G_CONSTANT.

This adds a target-specific combine which changes G_FCONSTANTs feeding into G_STOREs into G_CONSTANTs.


https://reviews.llvm.org/D72814

Files:
  llvm/lib/Target/AArch64/AArch64Combine.td
  llvm/lib/Target/AArch64/AArch64PreLegalizerCombiner.cpp
  llvm/test/CodeGen/AArch64/GlobalISel/combine-fconstant.mir

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