cmd/compile: remove references to *gc.Node in docs

ssa.Sym is only implemented by *ir.Name or *obj.LSym.

Change-Id: Ia171db618abd8b438fcc2cf402f40f3fe3ec6833
Reviewed-on: https://go-review.googlesource.com/c/go/+/660995
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

src/cmd/compile/internal/ssa/_gen/genericOps.go

@@ -359,7 +359,7 @@ var genericOps = []opData{
 	// If the variable is a global, the base pointer will be SB and
 	// the Aux field will be a *obj.LSym.
 	// If the variable is a local, the base pointer will be SP and
-	// the Aux field will be a *gc.Node.
+	// the Aux field will be a *ir.Name
 	{name: "Addr", argLength: 1, aux: "Sym", symEffect: "Addr"},      // Address of a variable.  Arg0=SB.  Aux identifies the variable.
 	{name: "LocalAddr", argLength: 2, aux: "Sym", symEffect: "Addr"}, // Address of a variable.  Arg0=SP. Arg1=mem. Aux identifies the variable.
 
@@ -543,9 +543,9 @@ var genericOps = []opData{
 	// Unknown value. Used for Values whose values don't matter because they are dead code.
 	{name: "Unknown"},
 
-	{name: "VarDef", argLength: 1, aux: "Sym", typ: "Mem", symEffect: "None", zeroWidth: true}, // aux is a *gc.Node of a variable that is about to be initialized.  arg0=mem, returns mem
+	{name: "VarDef", argLength: 1, aux: "Sym", typ: "Mem", symEffect: "None", zeroWidth: true}, // aux is a *ir.Name of a variable that is about to be initialized.  arg0=mem, returns mem
 	// TODO: what's the difference between VarLive and KeepAlive?
-	{name: "VarLive", argLength: 1, aux: "Sym", symEffect: "Read", zeroWidth: true}, // aux is a *gc.Node of a variable that must be kept live.  arg0=mem, returns mem
+	{name: "VarLive", argLength: 1, aux: "Sym", symEffect: "Read", zeroWidth: true}, // aux is a *ir.Name of a variable that must be kept live.  arg0=mem, returns mem
 	{name: "KeepAlive", argLength: 2, typ: "Mem", zeroWidth: true},                  // arg[0] is a value that must be kept alive until this mark.  arg[1]=mem, returns mem
 
 	// InlMark marks the start of an inlined function body. Its AuxInt field

src/cmd/compile/internal/ssa/_gen/rulegen.go

@@ -1771,7 +1771,7 @@ func (op opData) auxType() string {
 	case "String":
 		return "string"
 	case "Sym":
-		// Note: a Sym can be an *obj.LSym, a *gc.Node, or nil.
+		// Note: a Sym can be an *obj.LSym, a *ir.Name, or nil.
 		return "Sym"
 	case "SymOff":
 		return "Sym"

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

@@ -356,7 +356,7 @@ const (
 	auxCCop                   // auxInt is a ssa.Op that represents a flags-to-bool conversion (e.g. LessThan)
 	auxNameOffsetInt8         // aux is a &struct{Name ir.Name, Offset int64}; auxInt is index in parameter registers array
 	auxString                 // aux is a string
-	auxSym                    // aux is a symbol (a *gc.Node for locals, an *obj.LSym for globals, or nil for none)
+	auxSym                    // aux is a symbol (a *ir.Name for locals, an *obj.LSym for globals, or nil for none)
 	auxSymOff                 // aux is a symbol, auxInt is an offset
 	auxSymValAndOff           // aux is a symbol, auxInt is a ValAndOff
 	auxTyp                    // aux is a type
@@ -388,12 +388,12 @@ const (
 
 // A Sym represents a symbolic offset from a base register.
 // Currently a Sym can be one of 3 things:
-//   - a *gc.Node, for an offset from SP (the stack pointer)
+//   - a *ir.Name, for an offset from SP (the stack pointer)
 //   - a *obj.LSym, for an offset from SB (the global pointer)
 //   - nil, for no offset
 type Sym interface {
+	Aux
 	CanBeAnSSASym()
-	CanBeAnSSAAux()
 }
 
 // A ValAndOff is used by the several opcodes. It holds

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

@@ -1426,7 +1426,7 @@ func (s *regAllocState) regalloc(f *Func) {
 					// value live at this point.
 					v.SetArg(0, s.makeSpill(a, b))
 				} else if _, ok := a.Aux.(*ir.Name); ok && vi.rematerializeable {
-					// Rematerializeable value with a gc.Node. This is the address of
+					// Rematerializeable value with a *ir.Name. This is the address of
 					// a stack object (e.g. an LEAQ). Keep the object live.
 					// Change it to VarLive, which is what plive expects for locals.
 					v.Op = OpVarLive