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cmd/compile: lazily create true and false Values in shortcircuit

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It is mildly wasteful to always create values
that must sometimes then be dead code eliminated.
Given that it is very easy to avoid, do so.

Noticed when examining a package with thousands
of generated wrappers, each of which uses
only a handful of Values to compile.

Change-Id: If02eb4aa786dfa20f7aa43e8d729dad8b3db2786
Reviewed-on: https://go-review.googlesource.com/41502
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Josh Bleecher Snyder 2017-04-23 05:03:11 -07:00
parent 976a5ce1a8
commit 79e5ef2935
1 changed files with 7 additions and 2 deletions
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9
src/cmd/compile/internal/ssa/shortcircuit.go
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@ -17,8 +17,7 @@ func shortcircuit(f *Func) {
// x = phi(a, ...)
//
// We can replace the "a" in the phi with the constant true.
ct := f.ConstBool(f.Entry.Pos, f.Config.Types.Bool, true)
cf := f.ConstBool(f.Entry.Pos, f.Config.Types.Bool, false)
var ct, cf *Value
for _, b := range f.Blocks {
for _, v := range b.Values {
if v.Op != OpPhi {
@ -37,8 +36,14 @@ func shortcircuit(f *Func) {
continue
}
if e.i == 0 {
if ct == nil {
ct = f.ConstBool(f.Entry.Pos, f.Config.Types.Bool, true)
}
v.SetArg(i, ct)
} else {
if cf == nil {
cf = f.ConstBool(f.Entry.Pos, f.Config.Types.Bool, false)
}
v.SetArg(i, cf)
}
}