cmd/link: make Pciter more idiomatic

Rename it to PCIter and convert it to use methods.

Set pcscale once, during construction, to make call sites clearer.

Change some ints to bools.

Use a simple iteration termination condition,
instead of the cap comparison from the c2go translation.

Instead of requiring a Pcdata, which requires one caller
to synthesize a fake Pcdata, just ask for a byte slice.

Passes toolstash-check.

Change-Id: I811da0e929cf4a806bd6d70357ccf2911cd0c737
Reviewed-on: https://go-review.googlesource.com/c/go/+/171770
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/link/internal/ld/dwarf.go

@@ -1205,28 +1205,28 @@ func writelines(ctxt *Link, unit *compilationUnit, ls *sym.Symbol) {
 	file := 1
 	ls.AddAddr(ctxt.Arch, s)
 
-	var pcfile Pciter
-	var pcline Pciter
-	var pcstmt Pciter
+	pcfile := newPCIter(ctxt)
+	pcline := newPCIter(ctxt)
+	pcstmt := newPCIter(ctxt)
 	for i, s := range unit.lib.Textp {
 		finddebugruntimepath(s)
 
-		pciterinit(ctxt, &pcfile, &s.FuncInfo.Pcfile)
-		pciterinit(ctxt, &pcline, &s.FuncInfo.Pcline)
+		pcfile.init(s.FuncInfo.Pcfile.P)
+		pcline.init(s.FuncInfo.Pcline.P)
 
 		isStmtSym := dwarfFuncSym(ctxt, s, dwarf.IsStmtPrefix, false)
 		if isStmtSym != nil && len(isStmtSym.P) > 0 {
-			pciterinit(ctxt, &pcstmt, &sym.Pcdata{P: isStmtSym.P})
+			pcstmt.init(isStmtSym.P)
 		} else {
 			// Assembly files lack a pcstmt section, we assume that every instruction
 			// is a valid statement.
-			pcstmt.done = 1
+			pcstmt.done = true
 			pcstmt.value = 1
 		}
 
 		var thispc uint32
 		// TODO this loop looks like it could exit with work remaining.
-		for pcfile.done == 0 && pcline.done == 0 {
+		for !pcfile.done && !pcline.done {
 			// Only changed if it advanced
 			if int32(file) != pcfile.value {
 				ls.AddUint8(dwarf.DW_LNS_set_file)
@@ -1266,18 +1266,18 @@ func writelines(ctxt *Link, unit *compilationUnit, ls *sym.Symbol) {
 			if pcline.nextpc < thispc {
 				thispc = pcline.nextpc
 			}
-			if pcstmt.done == 0 && pcstmt.nextpc < thispc {
+			if !pcstmt.done && pcstmt.nextpc < thispc {
 				thispc = pcstmt.nextpc
 			}
 
 			if pcfile.nextpc == thispc {
-				pciternext(&pcfile)
+				pcfile.next()
 			}
-			if pcstmt.done == 0 && pcstmt.nextpc == thispc {
-				pciternext(&pcstmt)
+			if !pcstmt.done && pcstmt.nextpc == thispc {
+				pcstmt.next()
 			}
 			if pcline.nextpc == thispc {
-				pciternext(&pcline)
+				pcline.next()
 			}
 		}
 		if is_stmt == 0 && i < len(unit.lib.Textp)-1 {
@@ -1442,7 +1442,7 @@ func writeframes(ctxt *Link, syms []*sym.Symbol) []*sym.Symbol {
 	fs.AddBytes(zeros[:pad])
 
 	var deltaBuf []byte
-	var pcsp Pciter
+	pcsp := newPCIter(ctxt)
 	for _, s := range ctxt.Textp {
 		if s.FuncInfo == nil {
 			continue
@@ -1451,7 +1451,7 @@ func writeframes(ctxt *Link, syms []*sym.Symbol) []*sym.Symbol {
 		// Emit a FDE, Section 6.4.1.
 		// First build the section contents into a byte buffer.
 		deltaBuf = deltaBuf[:0]
-		for pciterinit(ctxt, &pcsp, &s.FuncInfo.Pcsp); pcsp.done == 0; pciternext(&pcsp) {
+		for pcsp.init(s.FuncInfo.Pcsp.P); !pcsp.done; pcsp.next() {
 			nextpc := pcsp.nextpc
 
 			// pciterinit goes up to the end of the function,

src/cmd/link/internal/ld/lib.go

@@ -2112,9 +2112,9 @@ func stkcheck(ctxt *Link, up *chain, depth int) int {
 
 	endr := len(s.R)
 	var ch1 chain
-	var pcsp Pciter
+	pcsp := newPCIter(ctxt)
 	var r *sym.Reloc
-	for pciterinit(ctxt, &pcsp, &s.FuncInfo.Pcsp); pcsp.done == 0; pciternext(&pcsp) {
+	for pcsp.init(s.FuncInfo.Pcsp.P); !pcsp.done; pcsp.next() {
 		// pcsp.value is in effect for [pcsp.pc, pcsp.nextpc).
 
 		// Check stack size in effect for this span.

src/cmd/link/internal/ld/link.go

@@ -169,14 +169,3 @@ func addImports(ctxt *Link, l *sym.Library, pn string) {
 	}
 	l.ImportStrings = nil
 }
-
-type Pciter struct {
-	d       sym.Pcdata
-	p       []byte
-	pc      uint32
-	nextpc  uint32
-	pcscale uint32
-	value   int32
-	start   int
-	done    int
-}

src/cmd/link/internal/ld/pcln.go

@@ -16,15 +16,32 @@ import (
 	"strings"
 )
 
-// iteration over encoded pcdata tables.
+// PCIter iterates over encoded pcdata tables.
+type PCIter struct {
+	p       []byte
+	pc      uint32
+	nextpc  uint32
+	pcscale uint32
+	value   int32
+	start   bool
+	done    bool
+}
 
-func pciternext(it *Pciter) {
+// newPCIter creates a PCIter and configures it for ctxt's architecture.
+func newPCIter(ctxt *Link) *PCIter {
+	it := new(PCIter)
+	it.pcscale = uint32(ctxt.Arch.MinLC)
+	return it
+}
+
+// next advances it to the next pc.
+func (it *PCIter) next() {
 	it.pc = it.nextpc
-	if it.done != 0 {
+	if it.done {
 		return
 	}
-	if -cap(it.p) >= -cap(it.d.P[len(it.d.P):]) {
-		it.done = 1
+	if len(it.p) == 0 {
+		it.done = true
 		return
 	}
 
@@ -35,12 +52,12 @@ func pciternext(it *Pciter) {
 	}
 	it.p = it.p[n:]
 
-	if val == 0 && it.start == 0 {
-		it.done = 1
+	if val == 0 && !it.start {
+		it.done = true
 		return
 	}
 
-	it.start = 0
+	it.start = false
 	it.value += int32(val)
 
 	// pc delta
@@ -53,16 +70,16 @@ func pciternext(it *Pciter) {
 	it.nextpc = it.pc + uint32(pc)*it.pcscale
 }
 
-func pciterinit(ctxt *Link, it *Pciter, d *sym.Pcdata) {
-	it.d = *d
-	it.p = it.d.P
+// init prepares it to iterate over p,
+// and advances it to the first pc.
+func (it *PCIter) init(p []byte) {
+	it.p = p
 	it.pc = 0
 	it.nextpc = 0
 	it.value = -1
-	it.start = 1
-	it.done = 0
-	it.pcscale = uint32(ctxt.Arch.MinLC)
-	pciternext(it)
+	it.start = true
+	it.done = false
+	it.next()
 }
 
 func addpctab(ctxt *Link, ftab *sym.Symbol, off int32, d *sym.Pcdata) int32 {
@@ -101,8 +118,8 @@ func renumberfiles(ctxt *Link, files []*sym.Symbol, d *sym.Pcdata) {
 	buf := make([]byte, binary.MaxVarintLen32)
 	newval := int32(-1)
 	var out sym.Pcdata
-	var it Pciter
-	for pciterinit(ctxt, &it, d); it.done == 0; pciternext(&it) {
+	it := newPCIter(ctxt)
+	for it.init(d.P); !it.done; it.next() {
 		// value delta
 		oldval := it.value
 
@@ -316,8 +333,8 @@ func (ctxt *Link) pclntab() {
 			renumberfiles(ctxt, pcln.File, &pcln.Pcfile)
 			if false {
 				// Sanity check the new numbering
-				var it Pciter
-				for pciterinit(ctxt, &it, &pcln.Pcfile); it.done == 0; pciternext(&it) {
+				it := newPCIter(ctxt)
+				for it.init(pcln.Pcfile.P); !it.done; it.next() {
 					if it.value < 1 || it.value > int32(len(ctxt.Filesyms)) {
 						Errorf(s, "bad file number in pcfile: %d not in range [1, %d]\n", it.value, len(ctxt.Filesyms))
 						errorexit()