cmd/compile: canonicalize comparison argument order
Ensure that any comparison between two values has the same argument
order. This helps ensure that they can be eliminated during the
lowered CSE pass which will be particularly important if we eliminate
the Greater and Geq ops (see #37316).
Example:
CMP R0, R1
BLT L1
CMP R1, R0 // different order, cannot eliminate
BEQ L2
CMP R0, R1
BLT L1
CMP R0, R1 // same order, can eliminate
BEQ L2
This does have some drawbacks. Notably comparisons might 'flip'
direction in the assembly output after even small changes to the
code or compiler. It should help make optimizations more reliable
however.
compilecmp master -> HEAD
master (
218f4572f5): text/template: make reflect.Value indirections more robust
HEAD (
f1661fef3e): cmd/compile: canonicalize comparison argument order
platform: linux/amd64
file before after Δ %
api
6063927 6068023 +4096 +0.068%
asm
5191757 5183565 -8192 -0.158%
cgo
4893518 4901710 +8192 +0.167%
cover
5330345 5326249 -4096 -0.077%
fix
3417778 3421874 +4096 +0.120%
pprof
14889456 14885360 -4096 -0.028%
test2json
2848138 2844042 -4096 -0.144%
trace
11746239 11733951 -12288 -0.105%
total
132739173 132722789 -16384 -0.012%
Change-Id: I11736b3fe2a4553f6fc65018f475e88217fa22f9
Reviewed-on: https://go-review.googlesource.com/c/go/+/220425
Run-TryBot: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>