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[dev.ssa] cmd/compile: tweak init function prologue

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We used to compare the init state with == to 0 and 2, which
requires 2 comparisons.  Instead, compare with 1 and use
<, ==.  That requires only one comparison.

This isn't a big deal performance-wise, as it is just init
code.  But there is a fair amount of init code, so this
should help a bit with code size.

Change-Id: I4a2765f1005776f0edce28ac143f4b7596d95a68
Reviewed-on: https://go-review.googlesource.com/18948
Reviewed-by: David Chase <drchase@google.com>
This commit is contained in:
Keith Randall 2016-01-26 15:55:05 -08:00
parent f94e0745b3
commit f3575a9561
1 changed files with 15 additions and 16 deletions
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31
src/cmd/compile/internal/gc/init.go
View file

@ -33,10 +33,10 @@ func renameinit() *Sym {
// hand-craft the following initialization code
// var initdone· uint8 (1)
// func init() (2)
// if initdone· != 0 { (3)
// if initdone· == 2 (4)
// return
// throw(); (5)
// if initdone· > 1 { (3)
// return (3a)
// if initdone· == 1 { (4)
// throw(); (4a)
// }
// initdone· = 1; (6)
// // over all matching imported symbols
@ -118,22 +118,21 @@ func fninit(n *NodeList) {
// (3)
a := Nod(OIF, nil, nil)
a.Left = Nod(ONE, gatevar, Nodintconst(0))
a.Left = Nod(OGT, gatevar, Nodintconst(1))
a.Likely = 1
r = list(r, a)
// (3a)
a.Nbody = list1(Nod(ORETURN, nil, nil))
// (4)
b := Nod(OIF, nil, nil)
b.Left = Nod(OEQ, gatevar, Nodintconst(2))
b.Nbody = list1(Nod(ORETURN, nil, nil))
a.Nbody = list1(b)
// (5)
b = syslook("throwinit", 0)
b = Nod(OCALL, b, nil)
a.Nbody = list(a.Nbody, b)
b.Left = Nod(OEQ, gatevar, Nodintconst(1))
// this actually isn't likely, but code layout is better
// like this: no JMP needed after the call.
b.Likely = 1
r = list(r, b)
// (4a)
b.Nbody = list1(Nod(OCALL, syslook("throwinit", 0), nil))
// (6)
a = Nod(OAS, gatevar, Nodintconst(1))