[dev.link] cmd/link: move findfunctab to a generated symbol

Basically removes all allocation from findfunctab:

Findfunctab_GC                172kB ± 0%       0kB ± 0%   ~     (p=1.000 n=1+1)

Change-Id: I246f7d2751317886b658f7ef672fb30b3c519668
Reviewed-on: https://go-review.googlesource.com/c/go/+/239281
Run-TryBot: Jeremy Faller <jeremy@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>

diff --git a/src/cmd/link/internal/ld/pcln.go b/src/cmd/link/internal/ld/pcln.go
index 81f1a2d40b3b3fde111c2bb583a52eff7980c612..5bbfbb02c12064618eaa0cd5fcc9048e181b4e7e 100644 (file)
--- a/src/cmd/link/internal/ld/pcln.go
+++ b/src/cmd/link/internal/ld/pcln.go
@@ -585,9 +585,6 @@ const (
 // a given text symbols is a container (outer sym).
 func (ctxt *Link) findfunctab(container loader.Bitmap) {
        ldr := ctxt.loader
-       t := ldr.CreateSymForUpdate("runtime.findfunctab", 0)
-       t.SetType(sym.SRODATA)
-       ldr.SetAttrLocal(t.Sym(), true)
 
        // find min and max address
        min := ldr.SymValue(ctxt.Textp[0])
@@ -598,67 +595,74 @@ func (ctxt *Link) findfunctab(container loader.Bitmap) {
        // that map to that subbucket.
        n := int32((max - min + SUBBUCKETSIZE - 1) / SUBBUCKETSIZE)
 
-       indexes := make([]int32, n)
-       for i := int32(0); i < n; i++ {
-               indexes[i] = NOIDX
-       }
-       idx := int32(0)
-       for i, s := range ctxt.Textp {
-               if !emitPcln(ctxt, s, container) {
-                       continue
-               }
-               p := ldr.SymValue(s)
-               var e loader.Sym
-               i++
-               if i < len(ctxt.Textp) {
-                       e = ctxt.Textp[i]
+       nbuckets := int32((max - min + BUCKETSIZE - 1) / BUCKETSIZE)
+
+       size := 4*int64(nbuckets) + int64(n)
+
+       writeFindFuncTab := func(_ *Link, s loader.Sym) {
+               t := ldr.MakeSymbolUpdater(s)
+
+               indexes := make([]int32, n)
+               for i := int32(0); i < n; i++ {
+                       indexes[i] = NOIDX
                }
-               for e != 0 && !emitPcln(ctxt, e, container) && i < len(ctxt.Textp) {
-                       e = ctxt.Textp[i]
+               idx := int32(0)
+               for i, s := range ctxt.Textp {
+                       if !emitPcln(ctxt, s, container) {
+                               continue
+                       }
+                       p := ldr.SymValue(s)
+                       var e loader.Sym
                        i++
-               }
-               q := max
-               if e != 0 {
-                       q = ldr.SymValue(e)
-               }
+                       if i < len(ctxt.Textp) {
+                               e = ctxt.Textp[i]
+                       }
+                       for e != 0 && !emitPcln(ctxt, e, container) && i < len(ctxt.Textp) {
+                               e = ctxt.Textp[i]
+                               i++
+                       }
+                       q := max
+                       if e != 0 {
+                               q = ldr.SymValue(e)
+                       }
+
+                       //print("%d: [%lld %lld] %s\n", idx, p, q, s->name);
+                       for ; p < q; p += SUBBUCKETSIZE {
+                               i = int((p - min) / SUBBUCKETSIZE)
+                               if indexes[i] > idx {
+                                       indexes[i] = idx
+                               }
+                       }
 
-               //print("%d: [%lld %lld] %s\n", idx, p, q, s->name);
-               for ; p < q; p += SUBBUCKETSIZE {
-                       i = int((p - min) / SUBBUCKETSIZE)
+                       i = int((q - 1 - min) / SUBBUCKETSIZE)
                        if indexes[i] > idx {
                                indexes[i] = idx
                        }
+                       idx++
                }
 
-               i = int((q - 1 - min) / SUBBUCKETSIZE)
-               if indexes[i] > idx {
-                       indexes[i] = idx
-               }
-               idx++
-       }
-
-       // allocate table
-       nbuckets := int32((max - min + BUCKETSIZE - 1) / BUCKETSIZE)
-
-       t.Grow(4*int64(nbuckets) + int64(n))
-
-       // fill in table
-       for i := int32(0); i < nbuckets; i++ {
-               base := indexes[i*SUBBUCKETS]
-               if base == NOIDX {
-                       Errorf(nil, "hole in findfunctab")
-               }
-               t.SetUint32(ctxt.Arch, int64(i)*(4+SUBBUCKETS), uint32(base))
-               for j := int32(0); j < SUBBUCKETS && i*SUBBUCKETS+j < n; j++ {
-                       idx = indexes[i*SUBBUCKETS+j]
-                       if idx == NOIDX {
+               // fill in table
+               for i := int32(0); i < nbuckets; i++ {
+                       base := indexes[i*SUBBUCKETS]
+                       if base == NOIDX {
                                Errorf(nil, "hole in findfunctab")
                        }
-                       if idx-base >= 256 {
-                               Errorf(nil, "too many functions in a findfunc bucket! %d/%d %d %d", i, nbuckets, j, idx-base)
-                       }
+                       t.SetUint32(ctxt.Arch, int64(i)*(4+SUBBUCKETS), uint32(base))
+                       for j := int32(0); j < SUBBUCKETS && i*SUBBUCKETS+j < n; j++ {
+                               idx = indexes[i*SUBBUCKETS+j]
+                               if idx == NOIDX {
+                                       Errorf(nil, "hole in findfunctab")
+                               }
+                               if idx-base >= 256 {
+                                       Errorf(nil, "too many functions in a findfunc bucket! %d/%d %d %d", i, nbuckets, j, idx-base)
+                               }
 
-                       t.SetUint8(ctxt.Arch, int64(i)*(4+SUBBUCKETS)+4+int64(j), uint8(idx-base))
+                               t.SetUint8(ctxt.Arch, int64(i)*(4+SUBBUCKETS)+4+int64(j), uint8(idx-base))
+                       }
                }
        }
+
+       s := ctxt.createGeneratorSymbol("runtime.findfunctab", 0, sym.SRODATA, size, writeFindFuncTab)
+       ldr.SetAttrReachable(s, true)
+       ldr.SetAttrLocal(s, true)
 }