[all-commits] [llvm/llvm-project] a2202f: AMDGPU/GlobalISel: Manually RegBankSelect copies

[Matt Arsenault via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: a2202f6a3f1c596d805755c2221a5b5527a1416b
      https://github.com/llvm/llvm-project/commit/a2202f6a3f1c596d805755c2221a5b5527a1416b
  Author: Matt Arsenault <Matthew.Arsenault at amd.com>
  Date:   2020-03-11 (Wed, 11 Mar 2020)

  Changed paths:
    M llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp
    A llvm/test/CodeGen/AMDGPU/GlobalISel/regbankselect-copy.mir

  Log Message:
  -----------
  AMDGPU/GlobalISel: Manually RegBankSelect copies

This was failng on any pre-assigned copy to the VCC bank.

This is something of a workaround for the default implementation in
getInstrMappingImpl, and how it treats copy-like operations in
general.

Copy-like operations are considered to only have one result register
bank, rather than separate banks for each source like a normal
instruction. To avoid potentially mishandling reg_sequence with
impossible operand combinations, the generic implementation errors on
impossible costs. If the bank was already assigned, is treated it
as-if it were an unsatisfiable REG_SEQUENCE mapping. We really don't
get any value from any of what getInstrMappingImpl tries to do for
copies, so just directly emit the simple mapping we really want.