[dev.regabi] cmd/compile: eliminate more SetOrig

This CL consolidates and cleans up fmt.go's logic for skipping past
Nodes introduced during typechecking. This allows eliminating SetOrig
on ConvExpr and Name. Also changes ConstExpr.SetOrig to a panic for
good measure.

The only remaining SetOrig uses now are for rewriting multi-value
"f(g())" calls and "return g()" statements, and type-checking
composite literals. It should be possible to eliminate both of those
as well.

Passes buildall w/ toolstash -cmp.

Change-Id: I478aea1a17dfb7a784293b930bf9081637eb2d7a
Reviewed-on: https://go-review.googlesource.com/c/go/+/275179
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

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

@@ -523,7 +523,6 @@ func assignconvfn(n ir.Node, t *types.Type, context func() string) ir.Node {
 	r.SetType(t)
 	r.SetTypecheck(1)
 	r.SetImplicit(true)
-	r.(ir.OrigNode).SetOrig(ir.Orig(n))
 	return r
 }
 

src/cmd/compile/internal/ir/expr.go

@@ -321,7 +321,7 @@ func (n *ConstExpr) Format(s fmt.State, verb rune) { FmtNode(n, s, verb) }
 func (n *ConstExpr) rawCopy() Node                 { c := *n; return &c }
 func (n *ConstExpr) Sym() *types.Sym               { return n.orig.Sym() }
 func (n *ConstExpr) Orig() Node                    { return n.orig }
-func (n *ConstExpr) SetOrig(orig Node)             { n.orig = orig }
+func (n *ConstExpr) SetOrig(orig Node)             { panic(n.no("SetOrig")) }
 func (n *ConstExpr) Val() constant.Value           { return n.val }
 
 // A ConvExpr is a conversion Type(X).
@@ -344,8 +344,6 @@ func NewConvExpr(pos src.XPos, op Op, typ *types.Type, x Node) *ConvExpr {
 func (n *ConvExpr) String() string                { return fmt.Sprint(n) }
 func (n *ConvExpr) Format(s fmt.State, verb rune) { FmtNode(n, s, verb) }
 func (n *ConvExpr) rawCopy() Node                 { c := *n; return &c }
-func (n *ConvExpr) Orig() Node                    { return n.orig }
-func (n *ConvExpr) SetOrig(x Node)                { n.orig = x }
 func (n *ConvExpr) Left() Node                    { return n.X }
 func (n *ConvExpr) SetLeft(x Node)                { n.X = x }
 

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

@@ -1071,6 +1071,7 @@ var OpPrec = []int{
 	OCALL:          8,
 	OCAP:           8,
 	OCLOSE:         8,
+	OCOMPLIT:       8,
 	OCONVIFACE:     8,
 	OCONVNOP:       8,
 	OCONV:          8,
@@ -1179,15 +1180,30 @@ var OpPrec = []int{
 }
 
 func exprFmt(n Node, s fmt.State, prec int, mode FmtMode) {
-	for n != nil && n.Implicit() && (n.Op() == ODEREF || n.Op() == OADDR) {
+	for {
-		n = n.Left()
-	}
-
 		if n == nil {
 			fmt.Fprint(s, "<N>")
 			return
 		}
 
+		// We always want the original, if any.
+		if o := Orig(n); o != n {
+			n = o
+			continue
+		}
+
+		// Skip implicit operations introduced during typechecking.
+		switch n.Op() {
+		case OADDR, ODEREF, OCONV, OCONVNOP, OCONVIFACE:
+			if n.Implicit() {
+				n = n.Left()
+				continue
+			}
+		}
+
+		break
+	}
+
 	nprec := OpPrec[n.Op()]
 	if n.Op() == OTYPE && n.Sym() != nil {
 		nprec = 8
@@ -1206,16 +1222,10 @@ func exprFmt(n Node, s fmt.State, prec int, mode FmtMode) {
 		fmt.Fprint(s, "nil")
 
 	case OLITERAL: // this is a bit of a mess
-		if mode == FErr {
+		if mode == FErr && n.Sym() != nil {
-			if orig := Orig(n); orig != nil && orig != n {
-				exprFmt(orig, s, prec, mode)
-				return
-			}
-			if n.Sym() != nil {
 			fmt.Fprint(s, smodeString(n.Sym(), mode))
 			return
 		}
-		}
 
 		needUnparen := false
 		if n.Type() != nil && !n.Type().IsUntyped() {
@@ -1558,13 +1568,6 @@ func exprFmt(n Node, s fmt.State, prec int, mode FmtMode) {
 
 func nodeFmt(n Node, s fmt.State, flag FmtFlag, mode FmtMode) {
 	t := n.Type()
-
-	// We almost always want the original.
-	// TODO(gri) Why the special case for OLITERAL?
-	if n.Op() != OLITERAL && Orig(n) != nil {
-		n = Orig(n)
-	}
-
 	if flag&FmtLong != 0 && t != nil {
 		if t.Kind() == types.TNIL {
 			fmt.Fprint(s, "nil")

src/cmd/compile/internal/ir/name.go

@@ -155,8 +155,6 @@ func (n *Name) rawCopy() Node                 { c := *n; return &c }
 func (n *Name) Name() *Name                   { return n }
 func (n *Name) Sym() *types.Sym               { return n.sym }
 func (n *Name) SetSym(x *types.Sym)           { n.sym = x }
-func (n *Name) Orig() Node                    { return n.orig }
-func (n *Name) SetOrig(x Node)                { n.orig = x }
 func (n *Name) SubOp() Op                     { return n.subOp }
 func (n *Name) SetSubOp(x Op)                 { n.subOp = x }
 func (n *Name) Class() Class                  { return n.class }