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cmd/compile/internal/ssa: erase register copies deterministically

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Fixes #17288.

Change-Id: I2ddd01d14667d5c6a2e19bd70489da8d9869d308
Reviewed-on: https://go-review.googlesource.com/30072
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Matthew Dempsky 2016-09-29 15:08:37 -07:00
parent c1e06dcb61
commit 6dc356a76a
1 changed files with 17 additions and 7 deletions
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24
src/cmd/compile/internal/ssa/regalloc.go
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@ -1707,14 +1707,24 @@ sinking:
}
}
// Erase any copies we never used
for c, used := range s.copies {
if !used && c.Uses == 0 {
if s.f.pass.debug > regDebug {
fmt.Printf("delete copied value %s\n", c.LongString())
// Erase any copies we never used.
// Also, an unused copy might be the only use of another copy,
// so continue erasing until we reach a fixed point.
for {
progress := false
for c, used := range s.copies {
if !used && c.Uses == 0 {
if s.f.pass.debug > regDebug {
fmt.Printf("delete copied value %s\n", c.LongString())
}
c.Args[0].Uses--
f.freeValue(c)
delete(s.copies, c)
progress = true
}
c.Args[0].Uses--
f.freeValue(c)
}
if !progress {
break
}
}