cmd/compile: eliminate stkdelta

At this point in the compiler we haven't assigned Xoffset values for
PAUTO variables anyway, so just immediately store the stack offsets
into Xoffset rather than into a global map.

Change-Id: I61eb471c857c8b145fd0895cbd98fd4e8d3c3365
Reviewed-on: https://go-review.googlesource.com/30081
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

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

@@ -286,7 +286,7 @@ func (n *Node) jconv(s fmt.State, flag FmtFlag) {
 	}
 
 	if c == 0 && n.Xoffset != BADWIDTH {
-		fmt.Fprintf(s, " x(%d%+d)", n.Xoffset, stkdelta[n])
+		fmt.Fprintf(s, " x(%d)", n.Xoffset)
 	}
 
 	if n.Class != 0 {

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

@@ -98,11 +98,11 @@ func fixautoused(p *obj.Prog) {
 		}
 
 		if p.From.Name == obj.NAME_AUTO && p.From.Node != nil {
-			p.From.Offset += stkdelta[p.From.Node.(*Node)]
+			p.From.Offset += p.From.Node.(*Node).Xoffset
 		}
 
 		if p.To.Name == obj.NAME_AUTO && p.To.Node != nil {
-			p.To.Offset += stkdelta[p.To.Node.(*Node)]
+			p.To.Offset += p.To.Node.(*Node).Xoffset
 		}
 
 		lp = &p.Link

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

@@ -214,11 +214,6 @@ func (s byStackVar) Len() int           { return len(s) }
 func (s byStackVar) Less(i, j int) bool { return cmpstackvarlt(s[i], s[j]) }
 func (s byStackVar) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
 
-// stkdelta records the stack offset delta for a node
-// during the compaction of the stack frame to remove
-// unused stack slots.
-var stkdelta = map[*Node]int64{}
-
 // TODO(lvd) find out where the PAUTO/OLITERAL nodes come from.
 func allocauto(ptxt *obj.Prog) {
 	Stksize = 0
@@ -282,22 +277,13 @@ func allocauto(ptxt *obj.Prog) {
 			yyerror("stack frame too large (>2GB)")
 		}
 
-		stkdelta[n] = -Stksize - n.Xoffset
+		n.Xoffset = -Stksize
 	}
 
 	Stksize = Rnd(Stksize, int64(Widthreg))
 	stkptrsize = Rnd(stkptrsize, int64(Widthreg))
 
 	fixautoused(ptxt)
-
-	// The debug information needs accurate offsets on the symbols.
-	for _, ln := range Curfn.Func.Dcl {
-		if ln.Class != PAUTO || ln.Op != ONAME {
-			continue
-		}
-		ln.Xoffset += stkdelta[ln]
-		delete(stkdelta, ln)
-	}
 }
 
 func compile(fn *Node) {

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

@@ -4374,12 +4374,13 @@ func AddAux2(a *obj.Addr, v *ssa.Value, offset int64) {
 		a.Name = obj.NAME_PARAM
 		a.Node = n
 		a.Sym = Linksym(n.Orig.Sym)
-		a.Offset += n.Xoffset // TODO: why do I have to add this here?  I don't for auto variables.
+		a.Offset += n.Xoffset
 	case *ssa.AutoSymbol:
 		n := sym.Node.(*Node)
 		a.Name = obj.NAME_AUTO
 		a.Node = n
 		a.Sym = Linksym(n.Sym)
+		// TODO: a.Offset += n.Xoffset once frame offsets for autos are computed during SSA
 	default:
 		v.Fatalf("aux in %s not implemented %#v", v, v.Aux)
 	}