cmd/internal/obj: eliminate Curp

Remove the global obj.Link.Curp.

In asmz.go, replace the only use by passing it as an argument.
In asm0.go and asm9.go, it was written but never read.
In asm5.go and asm7.go, thread it through as an argument.

Passes toolstash-check -all.

Updates #15756

Change-Id: I1a0faa89e768820f35d73a8b37ec8088d78d15f7
Reviewed-on: https://go-review.googlesource.com/38715
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/internal/obj/link.go

@@ -730,7 +730,6 @@ type Link struct {
 	Sym_mod       *LSym
 	Sym_modu      *LSym
 	Plan9privates *LSym
-	Curp          *Prog
 	Printp        *Prog
 	Blitrl        *Prog
 	Elitrl        *Prog

src/cmd/internal/obj/mips/asm0.go

@@ -391,7 +391,6 @@ func span0(ctxt *obj.Link, cursym *obj.LSym) {
 	var m int
 	var o *Optab
 	for p = p.Link; p != nil; p = p.Link {
-		ctxt.Curp = p
 		p.Pc = c
 		o = oplook(ctxt, p)
 		m = int(o.size)
@@ -482,7 +481,6 @@ func span0(ctxt *obj.Link, cursym *obj.LSym) {
 	var out [4]uint32
 	for p := cursym.Text.Link; p != nil; p = p.Link {
 		ctxt.Pc = p.Pc
-		ctxt.Curp = p
 		o = oplook(ctxt, p)
 		if int(o.size) > 4*len(out) {
 			log.Fatalf("out array in span0 is too small, need at least %d for %v", o.size/4, p)

src/cmd/internal/obj/plist.go

@@ -136,7 +136,6 @@ func flushplist(ctxt *Link, plist *Plist, freeProgs bool) {
 
 	// Add to running list in ctxt.
 	ctxt.Text = append(ctxt.Text, text...)
-	ctxt.Curp = nil
 	if freeProgs {
 		ctxt.freeProgs()
 	}

src/cmd/internal/obj/ppc64/asm9.go

@@ -570,7 +570,6 @@ func span9(ctxt *obj.Link, cursym *obj.LSym) {
 	var m int
 	var o *Optab
 	for p = p.Link; p != nil; p = p.Link {
-		ctxt.Curp = p
 		p.Pc = c
 		o = oplook(ctxt, p)
 		m = int(o.size)
@@ -658,7 +657,6 @@ func span9(ctxt *obj.Link, cursym *obj.LSym) {
 	var out [6]uint32
 	for p := cursym.Text.Link; p != nil; p = p.Link {
 		ctxt.Pc = p.Pc
-		ctxt.Curp = p
 		o = oplook(ctxt, p)
 		if int(o.size) > 4*len(out) {
 			log.Fatalf("out array in span9 is too small, need at least %d for %v", o.size/4, p)

src/cmd/internal/obj/s390x/asmz.go

@@ -415,8 +415,7 @@ func spanz(ctxt *obj.Link, cursym *obj.LSym) {
 			}
 			p.Pc = pc
 			ctxt.Pc = p.Pc
-			ctxt.Curp = p
-			asmout(ctxt, &buffer)
+			asmout(ctxt, p, &buffer)
 			if pc == int64(len(buffer)) {
 				switch p.As {
 				case obj.ANOP, obj.AFUNCDATA, obj.APCDATA, obj.ATEXT:
@@ -2549,8 +2548,7 @@ func branchMask(ctxt *obj.Link, p *obj.Prog) uint32 {
 	return 0xF
 }
 
-func asmout(ctxt *obj.Link, asm *[]byte) {
-	p := ctxt.Curp
+func asmout(ctxt *obj.Link, p *obj.Prog, asm *[]byte) {
 	o := oplook(ctxt, p)
 	ctxt.Printp = p