[all-commits] [llvm/llvm-project] 131708: [AArch64][SME] Support saving/restoring ZT0 in the...

[Benjamin Maxwell via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 1317083530b95fcf052f3017394a7719a67546fa
      https://github.com/llvm/llvm-project/commit/1317083530b95fcf052f3017394a7719a67546fa
  Author: Benjamin Maxwell <benjamin.maxwell at arm.com>
  Date:   2025-12-01 (Mon, 01 Dec 2025)

  Changed paths:
    M llvm/lib/Target/AArch64/AArch64ExpandPseudoInsts.cpp
    M llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
    M llvm/lib/Target/AArch64/AArch64SMEInstrInfo.td
    M llvm/lib/Target/AArch64/MachineSMEABIPass.cpp
    M llvm/test/CodeGen/AArch64/sme-peephole-opts.ll
    M llvm/test/CodeGen/AArch64/sme-za-exceptions.ll
    M llvm/test/CodeGen/AArch64/sme-zt0-state.ll

  Log Message:
  -----------
  [AArch64][SME] Support saving/restoring ZT0 in the MachineSMEABIPass (#166362)

This patch extends the MachineSMEABIPass to support ZT0. This is done
with the addition of two new states:

- `ACTIVE_ZT0_SAVED`
  * This is used when calling a function that shares ZA, but does not 
    share ZT0 (i.e., no ZT0 attributes)
  * This state indicates ZT0 must be saved to the save slot, but ZA must 
    remain on, with no lazy save setup
- `LOCAL_COMMITTED`
  * This is used for saving ZT0 in functions without ZA state
  * This state indicates ZA is off and ZT0 has been saved
  * This state is general enough to support ZA, but the required 
    transitions have not been implemented†

To aid with readability, the state transitions have been reworked to a
switch of `transitionFrom(<FromState>).to(<ToState>)`, rather than 
nested ifs, which helps manage more transitions.

† This could be implemented to handle some cases of undefined behavior
better.



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