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cmd/compile: add more non-ID comparisons to schedule

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These comparisons are fairly arbitrary,
but they should be more stable in the face
of other compiler changes than value ID.

This reduces the number of value ID
comparisons in schedule while running
make.bash from 542,442 to 99,703.

There are lots of changes to generated code
from this change, but they appear to
be overall neutral.

It is possible to further reduce the
number of comparisons in schedule;
I have changes locally that reduce the
number to about 25,000 during make.bash.
However, the changes are increasingly
complex and arcane, and reduce in much less
code churn. Given that the goal is stability,
that suggests that this is a reasonable
place to stop, at least for now.

Change-Id: Ie3a75f84fd3f3fdb102fcd0b29299950ea66b827
Reviewed-on: https://go-review.googlesource.com/c/go/+/229799
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Josh Bleecher Snyder 2020-04-23 16:22:37 -07:00
parent 943a0d02d1
commit 80ced39396
1 changed files with 10 additions and 0 deletions
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10
src/cmd/compile/internal/ssa/schedule.go
View File

@ -5,6 +5,7 @@
package ssa
import (
"cmd/compile/internal/types"
"container/heap"
"sort"
)
@ -62,6 +63,15 @@ func (h ValHeap) Less(i, j int) bool {
if c := x.Uses - y.Uses; c != 0 {
return c < 0 // smaller uses come later
}
// These comparisons are fairly arbitrary.
// The goal here is stability in the face
// of unrelated changes elsewhere in the compiler.
if c := x.AuxInt - y.AuxInt; c != 0 {
return c > 0
}
if cmp := x.Type.Compare(y.Type); cmp != types.CMPeq {
return cmp == types.CMPgt
}
return x.ID > y.ID
}