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cmd/compile: optimize absorbing InvertFlags into Noov comparisons for arm64

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Previously (LessThanNoov (InvertFlags x)) is lowered as:
CSET
CSET
BIC
With this CL it's lowered as:
CSET
CSEL
This saves one instruction.

Similarly (GreaterEqualNoov (InvertFlags x)) is now lowered as:
CSET
CSINC

$ benchstat old.bench new.bench
goos: linux
goarch: arm64
                       │  old.bench  │             new.bench              │
                       │   sec/op    │   sec/op     vs base               │
InvertLessThanNoov-160   2.249n ± 2%   2.190n ± 1%  -2.62% (p=0.003 n=10)

Change-Id: Idd8979b7f4fe466e74b1a201c4aba7f1b0cffb0b
Reviewed-on: https://go-review.googlesource.com/c/go/+/526237
Reviewed-by: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Eric Fang <eric.fang@arm.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
This commit is contained in:
eric fang 2023-09-12 03:01:33 +00:00 • committed by Eric Fang
parent dd881027c3
commit ace1494d92
4 changed files with 43 additions and 12 deletions
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13
test/codegen/comparisons.go
View file

@ -788,3 +788,16 @@ func cmp7() {
cmp5[string]("") // force instantiation
cmp6[string]("") // force instantiation
}
type Point struct {
X, Y int
}
// invertLessThanNoov checks (LessThanNoov (InvertFlags x)) is lowered as
// CMP, CSET, CSEL instruction sequence. InvertFlags are only generated under
// certain conditions, see canonLessThan, so if the code below does not
// generate an InvertFlags OP, this check may fail.
func invertLessThanNoov(p1, p2, p3 Point) bool {
// arm64:`CMP`,`CSET`,`CSEL`
return (p1.X-p3.X)*(p2.Y-p3.Y)-(p2.X-p3.X)*(p1.Y-p3.Y) < 0
}