[all-commits] [llvm/llvm-project] bbb958: [TII] NFCI: Simplify the interface for isTrivially...

[sdesmalen-arm via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: bbb95893ded91fc2a639ea304684b22fc6f2d5a3
      https://github.com/llvm/llvm-project/commit/bbb95893ded91fc2a639ea304684b22fc6f2d5a3
  Author: Sander de Smalen <sander.desmalen at arm.com>
  Date:   2023-08-07 (Mon, 07 Aug 2023)

  Changed paths:
    M llvm/include/llvm/CodeGen/MachineInstr.h
    M llvm/include/llvm/CodeGen/TargetInstrInfo.h
    M llvm/include/llvm/MC/MCInstrDesc.h
    M llvm/lib/CodeGen/TargetInstrInfo.cpp
    M llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
    M llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
    M llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
    M llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.cpp
    M llvm/lib/Target/X86/X86InstrInfo.cpp

  Log Message:
  -----------
  [TII] NFCI: Simplify the interface for isTriviallyReMaterializable

Currently `isTriviallyReMaterializable` calls
`isReallyTriviallyReMaterializable` and
`isReallyTriviallyReMaterializableGeneric`. The two interfaces
are confusing, but there are also some real issues with this.

The documentation of this function (see below) suggests that
`isReallyTriviallyRematerializable` allows the target to override the
default behaviour.

  /// For instructions with opcodes for which the M_REMATERIALIZABLE flag is
  /// set, this hook lets the target specify whether the instruction is actually
  /// trivially rematerializable, taking into consideration its operands.

It however implements something different. The default behaviour
is the analysis done in `isReallyTriviallyReMaterializableGeneric`,
which is testing if it is safe to rematerialize the MachineInstr.

The result of `isReallyTriviallyReMaterializable` is only considered if
`isReallyTriviallyReMaterializableGeneric` returns `false`.  That means
there is no way to override the default behaviour if
`isReallyTriviallyReMaterializableGeneric` returns true (i.e. it is safe to
rematerialize, but we'd rather not).

By making this a single interface, we can override the interface to do either.

Reviewed By: craig.topper, nemanjai

Differential Revision: https://reviews.llvm.org/D156520