[dev.regabi] cmd/compile: add ir.TailCallStmt

This CL splits out ORETJMP as a new TailCallStmt node, separate from
the other BranchStmt nodes. In doing so, this allows us to change it
from identifying a function by *types.Sym to identifying one by
directly pointing to the *ir.Func.

While here, also rename the operation to OTAILCALL.

Passes toolstash -cmp.

Change-Id: I273e6ea5d92bf3005ae02fb59b3240a190a6cf1b
Reviewed-on: https://go-review.googlesource.com/c/go/+/284227
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

src/cmd/compile/internal/deadcode/deadcode.go

@@ -75,7 +75,7 @@ func stmts(nn *ir.Nodes) {
 				// might be the target of a goto. See issue 28616.
 				if body := body; len(body) != 0 {
 					switch body[(len(body) - 1)].Op() {
-					case ir.ORETURN, ir.ORETJMP, ir.OPANIC:
+					case ir.ORETURN, ir.OTAILCALL, ir.OPANIC:
 						if i > lastLabel {
 							cut = true
 						}

src/cmd/compile/internal/escape/escape.go

@@ -534,8 +534,8 @@ func (e *escape) stmt(n ir.Node) {
 		e.stmts(n.Call.Init())
 		e.call(nil, n.Call, n)
 
-	case ir.ORETJMP:
-		// TODO(mdempsky): What do? esc.go just ignores it.
+	case ir.OTAILCALL:
+		// TODO(mdempsky): Treat like a normal call? esc.go used to just ignore it.
 	}
 }
 

src/cmd/compile/internal/inline/inl.go

@@ -359,7 +359,7 @@ func (v *hairyVisitor) doNode(n ir.Node) error {
 		ir.OGO,
 		ir.ODEFER,
 		ir.ODCLTYPE, // can't print yet
-		ir.ORETJMP:
+		ir.OTAILCALL:
 		return errors.New("unhandled op " + n.Op().String())
 
 	case ir.OAPPEND:

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

@@ -378,9 +378,9 @@ func stmtFmt(n Node, s fmt.State) {
 		n := n.(*ReturnStmt)
 		fmt.Fprintf(s, "return %.v", n.Results)
 
-	case ORETJMP:
-		n := n.(*BranchStmt)
-		fmt.Fprintf(s, "retjmp %v", n.Label)
+	case OTAILCALL:
+		n := n.(*TailCallStmt)
+		fmt.Fprintf(s, "tailcall %v", n.Target)
 
 	case OINLMARK:
 		n := n.(*InlineMarkStmt)

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

@@ -306,8 +306,8 @@ const (
 	OLINKSYMOFFSET // offset within a name
 
 	// arch-specific opcodes
-	ORETJMP // return to other function
-	OGETG   // runtime.getg() (read g pointer)
+	OTAILCALL // tail call to another function
+	OGETG     // runtime.getg() (read g pointer)
 
 	OEND
 )

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

@@ -144,17 +144,14 @@ func NewBlockStmt(pos src.XPos, list []Node) *BlockStmt {
 }
 
 // A BranchStmt is a break, continue, fallthrough, or goto statement.
-//
-// For back-end code generation, Op may also be RETJMP (return+jump),
-// in which case the label names another function entirely.
 type BranchStmt struct {
 	miniStmt
 	Label *types.Sym // label if present
 }
 
 func NewBranchStmt(pos src.XPos, op Op, label *types.Sym) *BranchStmt {
 	switch op {
-	case OBREAK, OCONTINUE, OFALL, OGOTO, ORETJMP:
+	case OBREAK, OCONTINUE, OFALL, OGOTO:
 		// ok
 	default:
 		panic("NewBranch " + op.String())
@@ -384,6 +381,23 @@ func NewSwitchStmt(pos src.XPos, tag Node, cases []*CaseClause) *SwitchStmt {
 	return n
 }
 
+// A TailCallStmt is a tail call statement, which is used for back-end
+// code generation to jump directly to another function entirely.
+type TailCallStmt struct {
+	miniStmt
+	Target *Name
+}
+
+func NewTailCallStmt(pos src.XPos, target *Name) *TailCallStmt {
+	if target.Op() != ONAME || target.Class != PFUNC {
+		base.FatalfAt(pos, "tail call to non-func %v", target)
+	}
+	n := &TailCallStmt{Target: target}
+	n.pos = pos
+	n.op = OTAILCALL
+	return n
+}
+
 // A TypeSwitchGuard is the [Name :=] X.(type) in a type switch.
 type TypeSwitchGuard struct {
 	miniNode

src/cmd/compile/internal/reflectdata/reflect.go

@@ -1794,7 +1794,7 @@ func methodWrapper(rcvr *types.Type, method *types.Field) *obj.LSym {
 		}
 		as := ir.NewAssignStmt(base.Pos, nthis, typecheck.ConvNop(left, rcvr))
 		fn.Body.Append(as)
-		fn.Body.Append(ir.NewBranchStmt(base.Pos, ir.ORETJMP, ir.MethodSym(methodrcvr, method.Sym)))
+		fn.Body.Append(ir.NewTailCallStmt(base.Pos, method.Nname.(*ir.Name)))
 	} else {
 		fn.SetWrapper(true) // ignore frame for panic+recover matching
 		call := ir.NewCallExpr(base.Pos, ir.OCALL, dot, nil)

src/cmd/compile/internal/ssagen/abi.go

@@ -303,7 +303,7 @@ func makeABIWrapper(f *ir.Func, wrapperABI obj.ABI) {
 	var tail ir.Node
 	if tfn.Type().NumResults() == 0 && tfn.Type().NumParams() == 0 && tfn.Type().NumRecvs() == 0 && !(base.Ctxt.Arch.Name == "ppc64le" && base.Ctxt.Flag_dynlink) {
 
-		tail = ir.NewBranchStmt(base.Pos, ir.ORETJMP, f.Nname.Sym())
+		tail = ir.NewTailCallStmt(base.Pos, f.Nname)
 	} else {
 		call := ir.NewCallExpr(base.Pos, ir.OCALL, f.Nname, nil)
 		call.Args = ir.ParamNames(tfn.Type())

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

@@ -1580,11 +1580,11 @@ func (s *state) stmt(n ir.Node) {
 		b := s.exit()
 		b.Pos = s.lastPos.WithIsStmt()
 
-	case ir.ORETJMP:
-		n := n.(*ir.BranchStmt)
+	case ir.OTAILCALL:
+		n := n.(*ir.TailCallStmt)
 		b := s.exit()
 		b.Kind = ssa.BlockRetJmp // override BlockRet
-		b.Aux = callTargetLSym(n.Label, s.curfn.LSym)
+		b.Aux = callTargetLSym(n.Target.Sym(), s.curfn.LSym)
 
 	case ir.OCONTINUE, ir.OBREAK:
 		n := n.(*ir.BranchStmt)

src/cmd/compile/internal/typecheck/typecheck.go

@@ -857,8 +857,8 @@ func typecheck1(n ir.Node, top int) ir.Node {
 		n := n.(*ir.ReturnStmt)
 		return tcReturn(n)
 
-	case ir.ORETJMP:
-		n := n.(*ir.BranchStmt)
+	case ir.OTAILCALL:
+		n := n.(*ir.TailCallStmt)
 		return n
 
 	case ir.OSELECT:
@@ -2023,7 +2023,7 @@ func isTermNode(n ir.Node) bool {
 		n := n.(*ir.BlockStmt)
 		return isTermNodes(n.List)
 
-	case ir.OGOTO, ir.ORETURN, ir.ORETJMP, ir.OPANIC, ir.OFALL:
+	case ir.OGOTO, ir.ORETURN, ir.OTAILCALL, ir.OPANIC, ir.OFALL:
 		return true
 
 	case ir.OFOR, ir.OFORUNTIL:

src/cmd/compile/internal/walk/order.go

@@ -692,7 +692,7 @@ func (o *orderState) stmt(n ir.Node) {
 		ir.OFALL,
 		ir.OGOTO,
 		ir.OLABEL,
-		ir.ORETJMP:
+		ir.OTAILCALL:
 		o.out = append(o.out, n)
 
 	// Special: handle call arguments.

src/cmd/compile/internal/walk/stmt.go

@@ -136,8 +136,8 @@ func walkStmt(n ir.Node) ir.Node {
 		n := n.(*ir.ReturnStmt)
 		return walkReturn(n)
 
-	case ir.ORETJMP:
-		n := n.(*ir.BranchStmt)
+	case ir.OTAILCALL:
+		n := n.(*ir.TailCallStmt)
 		return n
 
 	case ir.OINLMARK: