From: Than McIntosh <thanm@google.com>
Date: Thu, 28 Jun 2018 19:42:20 +0000 (-0400)
Subject: cmd/link: use side table instead of sym.Symbol 'Reachparent' field
X-Git-Tag: go1.11beta2~221
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=32bc0976f9c4333e4a9247d6acc908972c6c5d79;p=gostls13.git

cmd/link: use side table instead of sym.Symbol 'Reachparent' field

The sym.Symbol 'Reachparent' field is used only when field tracking
is enabled. So as to use less memory for the common case where
field tracking is not enabled, remove this field and use a side
table stored in the context to achieve the same functionality.

Updates #26186

Change-Id: Idc5f8b0aa323689d4d51dddb5d1b0341a37bb7d2
Reviewed-on: https://go-review.googlesource.com/121915
Reviewed-by: Ian Lance Taylor <iant@golang.org>
---

diff --git a/src/cmd/link/internal/ld/deadcode.go b/src/cmd/link/internal/ld/deadcode.go
index ce0fe1f7a1..540f4068cb 100644
--- a/src/cmd/link/internal/ld/deadcode.go
+++ b/src/cmd/link/internal/ld/deadcode.go
@@ -190,7 +190,9 @@ func (d *deadcodepass) mark(s, parent *sym.Symbol) {
 		fmt.Printf("%s -> %s\n", p, s.Name)
 	}
 	s.Attr |= sym.AttrReachable
-	s.Reachparent = parent
+	if d.ctxt.Reachparent != nil {
+		d.ctxt.Reachparent[s] = parent
+	}
 	d.markQueue = append(d.markQueue, s)
 }
 
diff --git a/src/cmd/link/internal/ld/go.go b/src/cmd/link/internal/ld/go.go
index 8d50332c7c..eb6c2ccc83 100644
--- a/src/cmd/link/internal/ld/go.go
+++ b/src/cmd/link/internal/ld/go.go
@@ -294,7 +294,7 @@ func fieldtrack(ctxt *Link) {
 			s.Attr |= sym.AttrNotInSymbolTable
 			if s.Attr.Reachable() {
 				buf.WriteString(s.Name[9:])
-				for p := s.Reachparent; p != nil; p = p.Reachparent {
+				for p := ctxt.Reachparent[s]; p != nil; p = ctxt.Reachparent[p] {
 					buf.WriteString("\t")
 					buf.WriteString(p.Name)
 				}
diff --git a/src/cmd/link/internal/ld/link.go b/src/cmd/link/internal/ld/link.go
index 2e66cf857c..bf57544357 100644
--- a/src/cmd/link/internal/ld/link.go
+++ b/src/cmd/link/internal/ld/link.go
@@ -86,6 +86,9 @@ type Link struct {
 	// unresolvedSymSet is a set of erroneous unresolved references.
 	// Used to avoid duplicated error messages.
 	unresolvedSymSet map[unresolvedSymKey]bool
+
+	// Used to implement field tracking.
+	Reachparent map[*sym.Symbol]*sym.Symbol
 }
 
 type unresolvedSymKey struct {
diff --git a/src/cmd/link/internal/ld/main.go b/src/cmd/link/internal/ld/main.go
index d7929d59fd..23462f1154 100644
--- a/src/cmd/link/internal/ld/main.go
+++ b/src/cmd/link/internal/ld/main.go
@@ -34,6 +34,7 @@ import (
 	"bufio"
 	"cmd/internal/objabi"
 	"cmd/internal/sys"
+	"cmd/link/internal/sym"
 	"flag"
 	"log"
 	"os"
@@ -144,6 +145,10 @@ func Main(arch *sys.Arch, theArch Arch) {
 		}
 	}
 
+	if objabi.Fieldtrack_enabled != 0 {
+		ctxt.Reachparent = make(map[*sym.Symbol]*sym.Symbol)
+	}
+
 	startProfile()
 	if ctxt.BuildMode == BuildModeUnset {
 		ctxt.BuildMode = BuildModeExe
diff --git a/src/cmd/link/internal/sym/symbol.go b/src/cmd/link/internal/sym/symbol.go
index b3ff6c4e19..8893dcf0d6 100644
--- a/src/cmd/link/internal/sym/symbol.go
+++ b/src/cmd/link/internal/sym/symbol.go
@@ -31,17 +31,16 @@ type Symbol struct {
 	// ElfType is set for symbols read from shared libraries by ldshlibsyms. It
 	// is not set for symbols defined by the packages being linked or by symbols
 	// read by ldelf (and so is left as elf.STT_NOTYPE).
-	ElfType     elf.SymType
-	Sub         *Symbol
-	Outer       *Symbol
-	Gotype      *Symbol
-	Reachparent *Symbol
-	File        string
-	Dynimplib   string
-	Dynimpvers  string
-	Sect        *Section
-	FuncInfo    *FuncInfo
-	Lib         *Library // Package defining this symbol
+	ElfType    elf.SymType
+	Sub        *Symbol
+	Outer      *Symbol
+	Gotype     *Symbol
+	File       string
+	Dynimplib  string
+	Dynimpvers string
+	Sect       *Section
+	FuncInfo   *FuncInfo
+	Lib        *Library // Package defining this symbol
 	// P contains the raw symbol data.
 	P []byte
 	R []Reloc