[PATCH] D107305: [GlobalISel] Combine G_ASSERT_*EXT + G_LOAD -> G_S/ZEXTLOAD

[Jessica Paquette via Phabricator via llvm-commits]

paquette created this revision.
paquette added reviewers: aemerson, arsenm.
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CallLowering can emit hint instructions (G_ASSERT_ZEXT, G_ASSERT_SEXT) to communicate whether or not a parameter/return value is expected to be sign or zero extended.

When we run into one of these along with a G_LOAD, we need to be careful to select the correct type of extended load.

e.g.

https://godbolt.org/z/x3oG4s3MT

In the above example, without this patch, GISel will not emit a sign-extended load. SDAG has the correct behaviour here.

The work here is identical to how we already combine G_SEXT_INREG with G_LOAD. However, because this can be important for ABI-conformance, it needs to run at all optimization levels. So, this is split out into its own combine which runs under `combines_for_extload`.


https://reviews.llvm.org/D107305

Files:
  llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h
  llvm/include/llvm/Target/GlobalISel/Combine.td
  llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
  llvm/test/CodeGen/AArch64/GlobalISel/combine-hint-extload.mir

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