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cmd/compile: improve domorder documentation

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domorder has some non-obvious useful properties
that we’re relying on in cse.
Document them and provide an argument that they hold.
While we’re here, do some minor renaming.

The argument is a re-working of a private email
exchange with Todd Neal and David Chase.

Change-Id: Ie154e0521bde642f5f11e67fc542c5eb938258be
Reviewed-on: https://go-review.googlesource.com/23449
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 2016-05-26 12:16:53 -07:00
parent 2deb9209de
commit 13a5b1faee
2 changed files with 41 additions and 14 deletions
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19
src/cmd/compile/internal/ssa/cse.go
View file

@ -137,10 +137,9 @@ func cse(f *Func) {
// if v and w are in the same equivalence class and v dominates w.
rewrite := make([]*Value, f.NumValues())
for _, e := range partition {
sort.Sort(sortbyentry{e, f.sdom})
sort.Sort(partitionByDom{e, f.sdom})
for i := 0; i < len(e)-1; i++ {
// e is sorted by entry value so maximal dominant element should be
// found first in the slice
// e is sorted by domorder, so a maximal dominant element is first in the slice
v := e[i]
if v == nil {
continue
@ -157,9 +156,7 @@ func cse(f *Func) {
rewrite[w.ID] = v
e[j] = nil
} else {
// since the blocks are assorted in ascending order by entry number
// once we know that we don't dominate a block we can't dominate any
// 'later' block
// e is sorted by domorder, so v.Block doesn't dominate any subsequent blocks in e
break
}
}
@ -311,15 +308,15 @@ func (sv sortvalues) Less(i, j int) bool {
return v.ID < w.ID
}
type sortbyentry struct {
type partitionByDom struct {
a []*Value // array of values
sdom SparseTree
}
func (sv sortbyentry) Len() int { return len(sv.a) }
func (sv sortbyentry) Swap(i, j int) { sv.a[i], sv.a[j] = sv.a[j], sv.a[i] }
func (sv sortbyentry) Less(i, j int) bool {
func (sv partitionByDom) Len() int { return len(sv.a) }
func (sv partitionByDom) Swap(i, j int) { sv.a[i], sv.a[j] = sv.a[j], sv.a[i] }
func (sv partitionByDom) Less(i, j int) bool {
v := sv.a[i]
w := sv.a[j]
return sv.sdom.maxdomorder(v.Block) < sv.sdom.maxdomorder(w.Block)
return sv.sdom.domorder(v.Block) < sv.sdom.domorder(w.Block)
}