cmd/link: replace custom hashmap in DWARF writer

Also stop creating a map for each symbol, as it does not seem to help.

Linking juju:
	tip:  real 0m5.470s user 0m6.131s
	this: real 0m4.811s user 0m5.582s

Change-Id: Ib3d931c996396a00942581770ff32df1eb8d6615
Reviewed-on: https://go-review.googlesource.com/20140
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

diff --git a/src/cmd/link/internal/ld/dwarf.go b/src/cmd/link/internal/ld/dwarf.go
index 4b6e51ff4b91651b76be08716a51799e0bfaacc1..31fc5792f087ee96ec384b8397322566c43fdbdd 100644 (file)
--- a/src/cmd/link/internal/ld/dwarf.go
+++ b/src/cmd/link/internal/ld/dwarf.go
@@ -485,18 +485,6 @@ func writeabbrev() {
 /*
  * Debugging Information Entries and their attributes.
  */
-const (
-       HASHSIZE = 107
-)
-
-func dwarfhashstr(s string) uint32 {
-       h := uint32(0)
-       for s != "" {
-               h = h + h + h + uint32(s[0])
-               s = s[1:]
-       }
-       return h % HASHSIZE
-}
 
 // For DW_CLS_string and _block, value should contain the length, and
 // data the data, for _reference, value is 0 and data is a DWDie* to
@@ -518,9 +506,8 @@ type DWDie struct {
        attr   *DWAttr
        // offset into .debug_info section, i.e relative to
        // infoo. only valid after call to putdie()
-       offs  int64
-       hash  []*DWDie // optional index of children by name, enabled by mkindex()
-       hlink *DWDie   // bucket chain in parent's index
+       offs int64
+       hash map[string]*DWDie // optional index of DWAttr by name, enabled by mkindex()
 }
 
 /*
@@ -580,16 +567,14 @@ func newdie(parent *DWDie, abbrev int, name string) *DWDie {
        newattr(die, DW_AT_name, DW_CLS_STRING, int64(len(name)), name)
 
        if parent.hash != nil {
-               h := int(dwarfhashstr(name))
-               die.hlink = parent.hash[h]
-               parent.hash[h] = die
+               parent.hash[name] = die
        }
 
        return die
 }
 
 func mkindex(die *DWDie) {
-       die.hash = make([]*DWDie, HASHSIZE)
+       die.hash = make(map[string]*DWDie)
 }
 
 func walktypedef(die *DWDie) *DWDie {
@@ -610,7 +595,6 @@ func walktypedef(die *DWDie) *DWDie {
 func find(die *DWDie, name string) *DWDie {
        var prev *DWDie
        for ; die != prev; prev, die = die, walktypedef(die) {
-
                if die.hash == nil {
                        for a := die.child; a != nil; a = a.link {
                                if name == getattr(a, DW_AT_name).data {
@@ -619,28 +603,9 @@ func find(die *DWDie, name string) *DWDie {
                        }
                        continue
                }
-
-               h := int(dwarfhashstr(name))
-               a := die.hash[h]
-
-               if a == nil {
-                       continue
-               }
-
-               if name == getattr(a, DW_AT_name).data {
+               if a := die.hash[name]; a != nil {
                        return a
                }
-
-               // Move found ones to head of the list.
-               for b := a.hlink; b != nil; b = b.hlink {
-                       if name == getattr(b, DW_AT_name).data {
-                               a.hlink = b.hlink
-                               b.hlink = die.hash[h]
-                               die.hash[h] = b
-                               return b
-                       }
-                       a = b
-               }
        }
        return nil
 }
@@ -1621,12 +1586,9 @@ func writelines() {
                }
 
                var (
-                       dt      int
-                       offs    int64
-                       varhash [HASHSIZE]*DWDie
+                       dt, da int
+                       offs   int64
                )
-               da := 0
-               dwfunc.hash = varhash[:] // enable indexing of children by name
                for a := s.Autom; a != nil; a = a.Link {
                        switch a.Name {
                        case obj.A_AUTO:
@@ -1678,8 +1640,6 @@ func writelines() {
 
                        da++
                }
-
-               dwfunc.hash = nil
        }
 
        flushunit(dwinfo, epc, epcs, unitstart, int32(headerend-unitstart-10))