[PATCH] D80585: [AArch64][GlobalISel] Do not modify predicate when optimizing G_ICMP

[Jessica Paquette via Phabricator via llvm-commits]

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

This fixes a bug in `tryOptArithImmedIntegerCompare`.

It is unsafe to update the predicate on a MachineOperand when optimizing a G_ICMP, because it may be used in more than one place.

For example, when we are optimizing G_SELECT, we allow compares which are used in more than one G_SELECT. If we modify the G_ICMP, then we'll break one of the G_SELECTs.

Since the compare is being produced to either

1. Select a G_ICMP
2. Fold a G_ICMP into an instruction when profitable

there's no reason to actually modify it. The change is local to the specific compare.

Instead, pass a `CmpInst::Predicate` to `tryOptArithImmedIntegerCompare` which can be modified by reference.


https://reviews.llvm.org/D80585

Files:
  llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
  llvm/test/CodeGen/AArch64/GlobalISel/select-arith-immed-compare.mir

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