[all-commits] [llvm/llvm-project] 385f59: [llvm-mca] Teach MCA constant registers do not cre...

[Rin Dobrescu via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 385f59f9f570b77bf8bd636ba2f65a08a7227499
      https://github.com/llvm/llvm-project/commit/385f59f9f570b77bf8bd636ba2f65a08a7227499
  Author: Rin Dobrescu <irina.dobrescu at arm.com>
  Date:   2024-05-03 (Fri, 03 May 2024)

  Changed paths:
    M llvm/include/llvm/MC/MCRegisterInfo.h
    M llvm/lib/MCA/InstrBuilder.cpp
    M llvm/test/tools/llvm-mca/AArch64/HiSilicon/tsv110-forwarding.s
    A llvm/test/tools/llvm-mca/AArch64/Neoverse/V1-zero-dependency.s
    M llvm/utils/TableGen/RegisterInfoEmitter.cpp

  Log Message:
  -----------
  [llvm-mca] Teach MCA constant registers do not create dependencies (#89387)

Constant registers like the zero registers XZR and WZR are treated as
any other register by LLVM-MCA. This can create non existent dependency
chains.
Currently there is no method in MCA to query if a register is constant.
This patch fixes the issue by adding a bool Constant
variable to MCRegisterDesc that is true for constant registers. Since
constant registers do not create dependencies, it makes sense to add
this check to MCA.



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