[PATCH] D65024: [GlobalISel][AArch64] Contract trivial same-size cross-bank copies into G_STOREs

[Jessica Paquette via Phabricator via llvm-commits]

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

Sometimes, you can end up with cross-bank copies between same-sized GPRs and FPRs, which feed into G_STOREs. When these copies feed only into stores, they aren't necessary; we can just store using the original register bank.

This provides some minor code size savings for some floating point SPEC benchmarks. (Around 0.2% for 453.povray and 450.soplex)

This issue doesn't seem to show up due to regbankselect or anything similar. So, this patch introduces an early select function, `contractCrossBankCopyIntoStore` which performs the contraction when possible. The selector then continues normally and selects the correct store opcode, eliminating needless copies along the way.


https://reviews.llvm.org/D65024

Files:
  llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
  llvm/test/CodeGen/AArch64/GlobalISel/contract-store.mir

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