[PATCH] D103582: [AArch64][GlobalISel] Handle multiple phis in fixupPHIOpBanks

[Jessica Paquette via Phabricator via llvm-commits]

paquette created this revision.
paquette added reviewers: aemerson, jroelofs.
Herald added subscribers: danielkiss, hiraditya, kristof.beyls, rovka.
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If we ended up with two phi instructions in a block, and we needed to fix up the banks for the first one, we'd end up inserting our COPY before the second phi.

E.g.

  %x = G_PHI ...
  %fixup = COPY ...
  %y = G_PHI ...

This is invalid MIR, and breaks assumptions made by the register allocator later down the line. With the verifier enabled, it also emits a verification error.

This teaches `fixupPHIOpBanks` to walk past any phi instructions in the block when emitting the fixup copies.

Here's an example of the crashing code (same as added testcase):
https://godbolt.org/z/h5j1x3o6e


https://reviews.llvm.org/D103582

Files:
  llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
  llvm/test/CodeGen/AArch64/GlobalISel/preselect-process-phis.mir

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