[all-commits] [llvm/llvm-project] 928305: [AArch64][GlobalISel] Fold G_ADD into the cset for...
Jessica Paquette via All-commits
all-commits at lists.llvm.org
Wed Feb 10 13:28:36 PST 2021
Branch: refs/heads/main
Home: https://github.com/llvm/llvm-project
Commit: 9283058abbec3d2236e69556206b4e66bf52045b
https://github.com/llvm/llvm-project/commit/9283058abbec3d2236e69556206b4e66bf52045b
Author: Jessica Paquette <jpaquette at apple.com>
Date: 2021-02-10 (Wed, 10 Feb 2021)
Changed paths:
M llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
M llvm/test/CodeGen/AArch64/GlobalISel/select-cmp.mir
Log Message:
-----------
[AArch64][GlobalISel] Fold G_ADD into the cset for G_ICMP
When we have a G_ADD which is fed by a G_ICMP on one side, we can fold it into
the cset for the G_ICMP.
e.g. Given
```
%cmp = G_ICMP ... %x, %y
%add = G_ADD %cmp, %z
```
We would normally emit a cmp, cset, and add.
However, `%add` is either `%z` or `%z + 1`. So, we can just use `%z` as the
source of the cset rather than wzr, saving an instruction.
This would probably be cleaner in AArch64PostLegalizerLowering, but we'd need
to change the way we represent G_ICMP to do that, I think. For now, it's
easiest to implement in selection.
This is a 0.1% code size improvement on CTMark/pairlocalalign at -Os.
Example: https://godbolt.org/z/7KdrP8
Differential Revision: https://reviews.llvm.org/D96388
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