cmd/link: pre-resolve package reference

Pre-resolve package index references, so it doesn't need to do a
map lookup in every cross-package symbol reference resolution. It
increases the memory usage very slightly (O(# imported packages)).

Change-Id: Ia76c97ac51f1c2c2d5ea7ae34853850ec69ef0a8
Reviewed-on: https://go-review.googlesource.com/c/go/+/253604
Run-TryBot: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

diff --git a/src/cmd/link/internal/loader/loader.go b/src/cmd/link/internal/loader/loader.go
index 8fd10b0848da697906505247b838c09841f4c984..43a0352e0bb4502bc2f245e31705aa77b59c4528 100644 (file)
--- a/src/cmd/link/internal/loader/loader.go
+++ b/src/cmd/link/internal/loader/loader.go
@@ -93,11 +93,12 @@ type oReader struct {
        version      int    // version of static symbol
        flags        uint32 // read from object file
        pkgprefix    string
-       syms         []Sym  // Sym's global index, indexed by local index
-       ndef         int    // cache goobj.Reader.NSym()
-       nhashed64def int    // cache goobj.Reader.NHashed64Def()
-       nhasheddef   int    // cache goobj.Reader.NHashedDef()
-       objidx       uint32 // index of this reader in the objs slice
+       syms         []Sym    // Sym's global index, indexed by local index
+       pkg          []uint32 // indices of referenced package by PkgIdx (index into loader.objs array)
+       ndef         int      // cache goobj.Reader.NSym()
+       nhashed64def int      // cache goobj.Reader.NHashed64Def()
+       nhasheddef   int      // cache goobj.Reader.NHashedDef()
+       objidx       uint32   // index of this reader in the objs slice
 }
 
 // Total number of defined symbols (package symbols, hashed symbols, and
@@ -219,7 +220,7 @@ type Loader struct {
 
        deferReturnTramp map[Sym]bool // whether the symbol is a trampoline of a deferreturn call
 
-       objByPkg map[string]*oReader // map package path to its Go object reader
+       objByPkg map[string]uint32 // map package path to the index of its Go object reader
 
        anonVersion int // most recently assigned ext static sym pseudo-version
 
@@ -331,7 +332,7 @@ func NewLoader(flags uint32, elfsetstring elfsetstringFunc, reporter *ErrorRepor
                objSyms:              make([]objSym, 1, 100000),    // reserve index 0 for nil symbol
                extReader:            extReader,
                symsByName:           [2]map[string]Sym{make(map[string]Sym, 80000), make(map[string]Sym, 50000)}, // preallocate ~2MB for ABI0 and ~1MB for ABI1 symbols
-               objByPkg:             make(map[string]*oReader),
+               objByPkg:             make(map[string]uint32),
                outer:                make(map[Sym]Sym),
                sub:                  make(map[Sym]Sym),
                dynimplib:            make(map[Sym]string),
@@ -370,7 +371,7 @@ func (l *Loader) addObj(pkg string, r *oReader) Sym {
        }
        pkg = objabi.PathToPrefix(pkg) // the object file contains escaped package path
        if _, ok := l.objByPkg[pkg]; !ok {
-               l.objByPkg[pkg] = r
+               l.objByPkg[pkg] = r.objidx
        }
        i := Sym(len(l.objSyms))
        l.start[r] = i
@@ -635,12 +636,7 @@ func (l *Loader) resolve(r *oReader, s goobj.SymRef) Sym {
        case goobj.PkgIdxSelf:
                rr = r
        default:
-               pkg := r.Pkg(int(p))
-               var ok bool
-               rr, ok = l.objByPkg[pkg]
-               if !ok {
-                       log.Fatalf("reference of nonexisted package %s, from %v", pkg, r.unit.Lib)
-               }
+               rr = l.objs[r.pkg[p]].r
        }
        return l.toGlobal(rr, s.SymIdx)
 }
@@ -2195,6 +2191,18 @@ func loadObjRefs(l *Loader, r *oReader, arch *sys.Arch) {
                }
        }
 
+       // referenced packages
+       npkg := r.NPkg()
+       r.pkg = make([]uint32, npkg)
+       for i := 1; i < npkg; i++ { // PkgIdx 0 is a dummy invalid package
+               pkg := r.Pkg(i)
+               objidx, ok := l.objByPkg[pkg]
+               if !ok {
+                       log.Fatalf("reference of nonexisted package %s, from %v", pkg, r.unit.Lib)
+               }
+               r.pkg[i] = objidx
+       }
+
        // load flags of package refs
        for i, n := 0, r.NRefFlags(); i < n; i++ {
                rf := r.RefFlags(i)