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internal/pkgbits: fix performance of rawReloc

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There was a TODO about quadratic performance, and indeed,
it can get bad.  Added a map, made some integers that are
unlikely to exceed a few million into 32-bit integers.

Change-Id: I6facf2eabc00483e943b326ca8dcae2f778093da
Reviewed-on: https://go-review.googlesource.com/c/go/+/422297
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
This commit is contained in:
David Chase 2022-08-09 14:07:02 -04:00
parent 8003efe1b5
commit 6b80b62fd1
2 changed files with 13 additions and 9 deletions
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18
src/internal/pkgbits/encoder.go
View File

@ -151,8 +151,9 @@ func (pw *PkgEncoder) NewEncoderRaw(k RelocKind) Encoder {
type Encoder struct {
p *PkgEncoder
Relocs []RelocEnt
Data bytes.Buffer // accumulated element bitstream data
Relocs []RelocEnt
RelocMap map[RelocEnt]uint32
Data bytes.Buffer // accumulated element bitstream data
encodingRelocHeader bool
@ -214,15 +215,18 @@ func (w *Encoder) rawVarint(x int64) {
}
func (w *Encoder) rawReloc(r RelocKind, idx Index) int {
// TODO(mdempsky): Use map for lookup; this takes quadratic time.
for i, rEnt := range w.Relocs {
if rEnt.Kind == r && rEnt.Idx == idx {
return i
e := RelocEnt{r, idx}
if w.RelocMap != nil {
if i, ok := w.RelocMap[e]; ok {
return int(i)
}
} else {
w.RelocMap = make(map[RelocEnt]uint32)
}
i := len(w.Relocs)
w.Relocs = append(w.Relocs, RelocEnt{r, idx})
w.RelocMap[e] = uint32(i)
w.Relocs = append(w.Relocs, e)
return i
}

4
src/internal/pkgbits/reloc.go
View File

@ -5,11 +5,11 @@
package pkgbits
// A RelocKind indicates a particular section within a unified IR export.
type RelocKind int
type RelocKind int32
// An Index represents a bitstream element index within a particular
// section.
type Index int
type Index int32
// A relocEnt (relocation entry) is an entry in an element's local
// reference table.