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[dev.link] cmd/link: experiment new reloc accessors in deadcode pass

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There is a small speedup:

(linking cmd/compile)

name       old time/op    new time/op    delta
Deadcode     57.1ms ± 1%    53.5ms ± 1%   -6.44%  (p=0.008 n=5+5)

With this, we don't need a slice to read the relocations, reduce
some allocations.

name       old alloc/op   new alloc/op   delta
Deadcode     4.16MB ± 0%    3.84MB ± 0%   -7.85%  (p=0.008 n=5+5)

Change-Id: Icd41c05682ba3f293a8cb9d2fe818e39d7276e5a
Reviewed-on: https://go-review.googlesource.com/c/go/+/222244
Reviewed-by: Than McIntosh <thanm@google.com>
This commit is contained in:
Cherry Zhang 2020-03-05 16:43:37 -05:00
parent c951514da9
commit cf5c718cba
4 changed files with 93 additions and 59 deletions
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18
src/cmd/link/internal/loader/loader.go
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@ -520,6 +520,12 @@ func (l *Loader) resolve(r *oReader, s goobj2.SymRef) Sym {
var rr *oReader
switch p := s.PkgIdx; p {
case goobj2.PkgIdxInvalid:
// {0, X} with non-zero X is never a valid sym reference from a Go object.
// We steal this space for symbol references from external objects.
// In this case, X is just the global index.
if l.isExtReader(r) {
return Sym(s.SymIdx)
}
if s.SymIdx != 0 {
panic("bad sym ref")
}
@ -1448,10 +1454,14 @@ func (relocs *Relocs) At(j int) Reloc {
func (relocs *Relocs) At2(j int) Reloc2 {
if relocs.l.isExtReader(relocs.r) {
// TODO: implement this. How? Maybe we can construct the reloc
// data for external symbols in the same byte form as the one
// in the object file?
panic("not implemented")
pp := relocs.l.payloads[relocs.li]
r := pp.relocs[j]
// XXX populate a goobj2.Reloc from external reloc record.
// Ugly. Maybe we just want to use this format to store the
// reloc record in the first place?
var b goobj2.Reloc2
b.Set(r.Off, r.Size, uint8(r.Type), r.Add, goobj2.SymRef{PkgIdx: 0, SymIdx: uint32(r.Sym)})
return Reloc2{&b, relocs.r, relocs.l}
}
return Reloc2{relocs.r.Reloc2(relocs.li, j), relocs.r, relocs.l}
}