cmd/compile: adjust lineno during import to get Pos right

Binary import sometimes constructs nodes using functions
that use the global lineno for the Position.  This causes
spurious numbers to appear in the assembly and the
debugging output.

Fix (targeted, because late in the cycle): save and restore
lineno around bimport calls known to use lineno-sensitive
functions.

Updates #22600.
(Comment: "This is a weird line to step through")

Change-Id: I9c4094670380609fe4b6696443fb02579521c596
Reviewed-on: https://go-review.googlesource.com/80115
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/gc/bimport.go

@@ -202,6 +202,13 @@ func Import(imp *types.Pkg, in *bufio.Reader) {
 			}
 			f.Func.Inl.Set(body)
 			f.Func.InlCost = int32(inlCost)
+			if Debug['E'] > 0 && Debug['m'] > 2 && f.Func.Inl.Len() != 0 {
+				if Debug['m'] > 3 {
+					fmt.Printf("inl body for %v: %+v\n", f, f.Func.Inl)
+				} else {
+					fmt.Printf("inl body for %v: %v\n", f, f.Func.Inl)
+				}
+			}
 			funcbody()
 		} else {
 			// function already imported - read body but discard declarations
@@ -369,7 +376,11 @@ func (p *importer) obj(tag int) {
 
 		n := newfuncnamel(pos, sym)
 		n.Type = sig
+		// TODO(mdempsky): Stop clobbering n.Pos in declare.
+		savedlineno := lineno
+		lineno = pos
 		declare(n, PFUNC)
+		lineno = savedlineno
 		p.funcList = append(p.funcList, n)
 		importlist = append(importlist, n)
 
@@ -377,9 +388,6 @@ func (p *importer) obj(tag int) {
 
 		if Debug['E'] > 0 {
 			fmt.Printf("import [%q] func %v \n", p.imp.Path, n)
-			if Debug['m'] > 2 && n.Func.Inl.Len() != 0 {
-				fmt.Printf("inl body: %v\n", n.Func.Inl)
-			}
 		}
 
 	default:
@@ -493,7 +501,11 @@ func (p *importer) typ() *types.Type {
 
 		// read underlying type
 		t0 := p.typ()
+		// TODO(mdempsky): Stop clobbering n.Pos in declare.
+		savedlineno := lineno
+		lineno = pos
 		p.importtype(t, t0)
+		lineno = savedlineno
 
 		// interfaces don't have associated methods
 		if t0.IsInterface() {
@@ -547,9 +559,6 @@ func (p *importer) typ() *types.Type {
 
 			if Debug['E'] > 0 {
 				fmt.Printf("import [%q] meth %v \n", p.imp.Path, n)
-				if Debug['m'] > 2 && n.Func.Inl.Len() != 0 {
-					fmt.Printf("inl body: %v\n", n.Func.Inl)
-				}
 			}
 		}
 
@@ -963,21 +972,26 @@ func (p *importer) node() *Node {
 	//	unimplemented
 
 	case OPTRLIT:
-		n := npos(p.pos(), p.expr())
+		pos := p.pos()
+		n := npos(pos, p.expr())
 		if !p.bool() /* !implicit, i.e. '&' operator */ {
 			if n.Op == OCOMPLIT {
 				// Special case for &T{...}: turn into (*T){...}.
-				n.Right = nod(OIND, n.Right, nil)
+				n.Right = nodl(pos, OIND, n.Right, nil)
 				n.Right.SetImplicit(true)
 			} else {
-				n = nod(OADDR, n, nil)
+				n = nodl(pos, OADDR, n, nil)
 			}
 		}
 		return n
 
 	case OSTRUCTLIT:
-		n := nodl(p.pos(), OCOMPLIT, nil, typenod(p.typ()))
+		// TODO(mdempsky): Export position information for OSTRUCTKEY nodes.
+		savedlineno := lineno
+		lineno = p.pos()
+		n := nodl(lineno, OCOMPLIT, nil, typenod(p.typ()))
 		n.List.Set(p.elemList()) // special handling of field names
+		lineno = savedlineno
 		return n
 
 	// case OARRAYLIT, OSLICELIT, OMAPLIT:

src/cmd/compile/internal/ssa/testdata/hist.opt-dlv.nexts

@@ -8,9 +8,7 @@
 61:		sink = dx + dy            //gdb-opt=(dx,dy)
 63:		hist := make([]int, 7)                                //gdb-opt=(sink,dx/O,dy/O)
 64:		var reader io.Reader = strings.NewReader(cannedInput) //gdb-dbg=(hist/A,cannedInput/A)
-19:		"strings"
 65:		if len(os.Args) > 1 {
-14:		"bufio"
 74:		for scanner.Scan() { //gdb-opt=(scanner/A)
 76:			i, err := strconv.ParseInt(s, 10, 64)
 77:			if err != nil { //gdb-dbg=(i) //gdb-opt=(err,hist,i)