[dev.debug] cmd/compile: rename dwarf.Var.Offset to StackOffset

After we track decomposition, offset could mean stack offset or offset
in recomposed variable. Disambiguate.

Change-Id: I4d810b8c0dcac7a4ec25ac1e52898f55477025df
Reviewed-on: https://go-review.googlesource.com/50875Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

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

@@ -360,7 +360,7 @@ func debuginfo(fnsym *obj.LSym, curfn interface{}) []dwarf.Scope {
 		dwarfVars = append(dwarfVars, &dwarf.Var{
 			Name:        n.Sym.Name,
 			Abbrev:      abbrev,
-			Offset: int32(offs),
+			StackOffset: int32(offs),
 			Type:        Ctxt.Lookup(typename),
 		})
 

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

@@ -168,7 +168,7 @@ func (v varsByScopeAndOffset) Less(i, j int) bool {
 	if v.scopes[i] != v.scopes[j] {
 		return v.scopes[i] < v.scopes[j]
 	}
-	return v.vars[i].Offset < v.vars[j].Offset
+	return v.vars[i].StackOffset < v.vars[j].StackOffset
 }
 
 func (v varsByScopeAndOffset) Swap(i, j int) {

src/cmd/internal/dwarf/dwarf.go

@@ -27,7 +27,7 @@ type Sym interface {
 type Var struct {
 	Name        string
 	Abbrev      int // Either DW_ABRV_AUTO or DW_ABRV_PARAM
-	Offset int32
+	StackOffset int32
 	Scope       int32
 	Type        Sym
 }
@@ -749,9 +749,9 @@ func putvar(ctxt Context, s Sym, v *Var, encbuf []byte) {
 	Uleb128put(ctxt, s, int64(v.Abbrev))
 	putattr(ctxt, s, v.Abbrev, DW_FORM_string, DW_CLS_STRING, int64(len(n)), n)
 	loc := append(encbuf[:0], DW_OP_call_frame_cfa)
-	if v.Offset != 0 {
+	if v.StackOffset != 0 {
 		loc = append(loc, DW_OP_consts)
-		loc = AppendSleb128(loc, int64(v.Offset))
+		loc = AppendSleb128(loc, int64(v.StackOffset))
 		loc = append(loc, DW_OP_plus)
 	}
 	putattr(ctxt, s, v.Abbrev, DW_FORM_block1, DW_CLS_BLOCK, int64(len(loc)), loc)
@@ -759,9 +759,9 @@ func putvar(ctxt Context, s Sym, v *Var, encbuf []byte) {
 }
 
 // VarsByOffset attaches the methods of sort.Interface to []*Var,
-// sorting in increasing Offset.
+// sorting in increasing StackOffset.
 type VarsByOffset []*Var
 
 func (s VarsByOffset) Len() int           { return len(s) }
-func (s VarsByOffset) Less(i, j int) bool { return s[i].Offset < s[j].Offset }
+func (s VarsByOffset) Less(i, j int) bool { return s[i].StackOffset < s[j].StackOffset }
 func (s VarsByOffset) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }