cmd/internal/obj: separate code layout from object writing

This will allow the compiler to crunch Prog lists down to code as each
function is compiled, instead of waiting until the end, which should
reduce the working set of the compiler. But not until Go 1.7.

This also makes it easier to write some machine code output tests
for the assembler, which is why it's being done now.

For #13822.

Change-Id: I0811123bc6e5717cebb8948f9cea18e1b9baf6f7
Reviewed-on: https://go-review.googlesource.com/18311Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/internal/obj/link.go

@@ -610,6 +610,12 @@ type Link struct {
 	Version            int
 	Textp              *LSym
 	Etextp             *LSym
+
+	// state for writing objects
+	Text  *LSym
+	Data  *LSym
+	Etext *LSym
+	Edata *LSym
 }
 
 // The smallest possible offset from the hardware stack pointer to a local

src/cmd/internal/obj/objfile.go

@@ -111,6 +111,11 @@ import (
 // out a Go object file.  The linker does not call this; the linker
 // does not write out object files.
 func Writeobjdirect(ctxt *Link, b *Biobuf) {
+	Flushplist(ctxt)
+	Writeobjfile(ctxt, b)
+}
+
+func Flushplist(ctxt *Link) {
 	var flag int
 	var s *LSym
 	var p *Prog
@@ -119,13 +124,11 @@ func Writeobjdirect(ctxt *Link, b *Biobuf) {
 
 	// Build list of symbols, and assign instructions to lists.
 	// Ignore ctxt->plist boundaries. There are no guarantees there,
-	// and the C compilers and assemblers just use one big list.
-	var text *LSym
-
+	// and the assemblers just use one big list.
 	var curtext *LSym
-	var data *LSym
+	var text *LSym
 	var etext *LSym
-	var edata *LSym
+
 	for pl := ctxt.Plist; pl != nil; pl = pl.Link {
 		for p = pl.Firstpc; p != nil; p = plink {
 			if ctxt.Debugasm != 0 && ctxt.Debugvlog != 0 {
@@ -174,10 +177,10 @@ func Writeobjdirect(ctxt *Link, b *Biobuf) {
 					log.Fatalf("symbol %s listed multiple times", s.Name)
 				}
 				s.Onlist = 1
-				if data == nil {
-					data = s
+				if ctxt.Data == nil {
+					ctxt.Data = s
 				} else {
-					edata.Next = s
+					ctxt.Edata.Next = s
 				}
 				s.Next = nil
 				s.Size = p.To.Offset
@@ -195,7 +198,7 @@ func Writeobjdirect(ctxt *Link, b *Biobuf) {
 				} else if flag&TLSBSS != 0 {
 					s.Type = STLSBSS
 				}
-				edata = s
+				ctxt.Edata = s
 				continue
 			}
 
@@ -298,6 +301,17 @@ func Writeobjdirect(ctxt *Link, b *Biobuf) {
 		linkpcln(ctxt, s)
 	}
 
+	// Add to running list in ctxt.
+	if ctxt.Etext == nil {
+		ctxt.Text = text
+	} else {
+		ctxt.Etext.Next = text
+	}
+	ctxt.Etext = etext
+	ctxt.Plist = nil
+}
+
+func Writeobjfile(ctxt *Link, b *Biobuf) {
 	// Emit header.
 	Bputc(b, 0)
 
@@ -312,10 +326,10 @@ func Writeobjdirect(ctxt *Link, b *Biobuf) {
 	wrstring(b, "")
 
 	// Emit symbols.
-	for s := text; s != nil; s = s.Next {
+	for s := ctxt.Text; s != nil; s = s.Next {
 		writesym(ctxt, b, s)
 	}
-	for s := data; s != nil; s = s.Next {
+	for s := ctxt.Data; s != nil; s = s.Next {
 		writesym(ctxt, b, s)
 	}