[all-commits] [llvm/llvm-project] 963287: Add a baseline test for D131958

[Alexander Richardson via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 963287acbf42867a8f7a14b1db0043daf22174f2
      https://github.com/llvm/llvm-project/commit/963287acbf42867a8f7a14b1db0043daf22174f2
  Author: Alex Richardson <alexrichardson at google.com>
  Date:   2022-09-21 (Wed, 21 Sep 2022)

  Changed paths:
    A llvm/test/CodeGen/AArch64/avoid-zero-copy.mir
    A llvm/test/CodeGen/Mips/avoid-zero-copy.mir

  Log Message:
  -----------
  Add a baseline test for D131958

This test shows that the save of MIPS $zero to a callee-saved register
is not elided by the machine-cp pass.

Differential Revision: https://reviews.llvm.org/D131957


  Commit: b84be9f2f1acb7229e4a4fa12e0832854c22bd57
      https://github.com/llvm/llvm-project/commit/b84be9f2f1acb7229e4a4fa12e0832854c22bd57
  Author: Alex Richardson <Alexander.Richardson at cl.cam.ac.uk>
  Date:   2022-09-21 (Wed, 21 Sep 2022)

  Changed paths:
    M llvm/test/CodeGen/AArch64/avoid-zero-copy.mir
    M llvm/test/CodeGen/Mips/avoid-zero-copy.mir
    M llvm/test/CodeGen/RISCV/double-convert.ll
    M llvm/utils/TableGen/RegisterInfoEmitter.cpp

  Log Message:
  -----------
  Add all constant physical registers to callee preserved masks

This allows MachineCopyPropagation to eliminate copies of constant registers
such as zero registers. They were previously not being eliminated as the
check for MO.clobbersPhysReg(AvailSrc) would return true for constant
registers such as MIPS $zero.

To avoid having to manually add the zero registers to all CalleeSavedRegs
instantiations in tablegen, I instead added a new isConstant bit to the
Register and set this for MIPS, RISC-V, and AArch64 zero registers.
RegisterInfoEmitter.cpp looks at this flag and adds all constant registers
to the preserved register mask.

This may also benefit other passes but so far I have only seen differences
in MachineCopyPropagation. In the future it might make sense to generate
`isConstantPhysReg()` from this information.

Original source: https://github.com/CTSRD-CHERI/llvm-project/commit/8588d8b81458ed6d87b674893e7752e6a6915574

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D131958


Compare: https://github.com/llvm/llvm-project/compare/9926ad17525a...b84be9f2f1ac