[all-commits] [llvm/llvm-project] 6c3fa9: [AArch64][GlobalISel] Select Bcc when it's better ...

[Jessica Paquette via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 6c3fa97d8a628541c82d8981aabefcb2dcb29f17
      https://github.com/llvm/llvm-project/commit/6c3fa97d8a628541c82d8981aabefcb2dcb29f17
  Author: Jessica Paquette <jpaquette at apple.com>
  Date:   2020-12-01 (Tue, 01 Dec 2020)

  Changed paths:
    M llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
    M llvm/test/CodeGen/AArch64/GlobalISel/opt-and-tbnz-tbz.mir
    M llvm/test/CodeGen/AArch64/GlobalISel/tbnz-slt.mir

  Log Message:
  -----------
  [AArch64][GlobalISel] Select Bcc when it's better than TB(N)Z

Instead of falling back to selecting TB(N)Z when we fail to select an
optimized compare against 0, select Bcc instead.

Also simplify selectCompareBranch a little while we're here, because the logic
was kind of hard to follow.

At -O0, this is a 0.1% geomean code size improvement for CTMark.

A simple example of where this can kick in is here:
https://godbolt.org/z/4rra6P

In the example above, GlobalISel currently produces a subs, cset, and tbnz.
SelectionDAG, on the other hand, just emits a compare and b.le.

Differential Revision: https://reviews.llvm.org/D92358