2 files changed, 31 insertions, 18 deletions

diff --git a/src/cmd/compile/internal/ssagen/abi.go b/src/cmd/compile/internal/ssagen/abi.go
index 6d8c53e722..c54a734c75 100644
--- a/src/cmd/compile/internal/ssagen/abi.go
+++ b/src/cmd/compile/internal/ssagen/abi.go
@@ -382,18 +382,16 @@ func makeABIWrapper(f *ir.Func, wrapperABI obj.ABI) {
 	}
 
 	var tail ir.Node
+	call := ir.NewCallExpr(base.Pos, ir.OCALL, f.Nname, nil)
+	call.Args = ir.ParamNames(tfn.Type())
+	call.IsDDD = tfn.Type().IsVariadic()
+	tail = call
 	if tailcall {
-		tail = ir.NewTailCallStmt(base.Pos, f.Nname)
-	} else {
-		call := ir.NewCallExpr(base.Pos, ir.OCALL, f.Nname, nil)
-		call.Args = ir.ParamNames(tfn.Type())
-		call.IsDDD = tfn.Type().IsVariadic()
-		tail = call
-		if tfn.Type().NumResults() > 0 {
-			n := ir.NewReturnStmt(base.Pos, nil)
-			n.Results = []ir.Node{call}
-			tail = n
-		}
+		tail = ir.NewTailCallStmt(base.Pos, call)
+	} else if tfn.Type().NumResults() > 0 {
+		n := ir.NewReturnStmt(base.Pos, nil)
+		n.Results = []ir.Node{call}
+		tail = n
 	}
 	fn.Body.Append(tail)
 
diff --git a/src/cmd/compile/internal/ssagen/ssa.go b/src/cmd/compile/internal/ssagen/ssa.go
index 1e7eda94fc..346a801508 100644
--- a/src/cmd/compile/internal/ssagen/ssa.go
+++ b/src/cmd/compile/internal/ssagen/ssa.go
@@ -1696,9 +1696,11 @@ func (s *state) stmt(n ir.Node) {
 
 	case ir.OTAILCALL:
 		n := n.(*ir.TailCallStmt)
-		b := s.exit()
-		b.Kind = ssa.BlockRetJmp // override BlockRet
-		b.Aux = callTargetLSym(n.Target)
+		s.callResult(n.Call, callTail)
+		call := s.mem()
+		b := s.endBlock()
+		b.Kind = ssa.BlockRetJmp // could use BlockExit. BlockRetJmp is mostly for clarity.
+		b.SetControl(call)
 
 	case ir.OCONTINUE, ir.OBREAK:
 		n := n.(*ir.BranchStmt)
@@ -3645,6 +3647,7 @@ const (
 	callDefer
 	callDeferStack
 	callGo
+	callTail
 )
 
 type sfRtCallDef struct {
@@ -4911,13 +4914,13 @@ func (s *state) call(n *ir.CallExpr, k callKind, returnResultAddr bool) *ssa.Val
 		}
 	}
 
-	if k != callNormal && (len(n.Args) != 0 || n.Op() == ir.OCALLINTER || n.X.Type().NumResults() != 0) {
+	if k != callNormal && k != callTail && (len(n.Args) != 0 || n.Op() == ir.OCALLINTER || n.X.Type().NumResults() != 0) {
 		s.Fatalf("go/defer call with arguments: %v", n)
 	}
 
 	switch n.Op() {
 	case ir.OCALLFUNC:
-		if k == callNormal && fn.Op() == ir.ONAME && fn.(*ir.Name).Class == ir.PFUNC {
+		if (k == callNormal || k == callTail) && fn.Op() == ir.ONAME && fn.(*ir.Name).Class == ir.PFUNC {
 			fn := fn.(*ir.Name)
 			callee = fn
 			if buildcfg.Experiment.RegabiArgs {
@@ -4971,7 +4974,7 @@ func (s *state) call(n *ir.CallExpr, k callKind, returnResultAddr bool) *ssa.Val
 	stksize := params.ArgWidth() // includes receiver, args, and results
 
 	res := n.X.Type().Results()
-	if k == callNormal {
+	if k == callNormal || k == callTail {
 		for _, p := range params.OutParams() {
 			ACResults = append(ACResults, p.Type)
 		}
@@ -5018,7 +5021,7 @@ func (s *state) call(n *ir.CallExpr, k callKind, returnResultAddr bool) *ssa.Val
 		// These are written in SP-offset order.
 		argStart := base.Ctxt.FixedFrameSize()
 		// Defer/go args.
-		if k != callNormal {
+		if k != callNormal && k != callTail {
 			// Write closure (arg to newproc/deferproc).
 			ACArgs = append(ACArgs, types.Types[types.TUINTPTR]) // not argExtra
 			callArgs = append(callArgs, closure)
@@ -5068,6 +5071,10 @@ func (s *state) call(n *ir.CallExpr, k callKind, returnResultAddr bool) *ssa.Val
 		case callee != nil:
 			aux := ssa.StaticAuxCall(callTargetLSym(callee), params)
 			call = s.newValue0A(ssa.OpStaticLECall, aux.LateExpansionResultType(), aux)
+			if k == callTail {
+				call.Op = ssa.OpTailLECall
+				stksize = 0 // Tail call does not use stack. We reuse caller's frame.
+			}
 		default:
 			s.Fatalf("bad call type %v %v", n.Op(), n)
 		}
@@ -7399,6 +7406,14 @@ func (s *State) Call(v *ssa.Value) *obj.Prog {
 	return p
 }
 
+// TailCall returns a new tail call instruction for the SSA value v.
+// It is like Call, but for a tail call.
+func (s *State) TailCall(v *ssa.Value) *obj.Prog {
+	p := s.Call(v)
+	p.As = obj.ARET
+	return p
+}
+
 // PrepareCall prepares to emit a CALL instruction for v and does call-related bookkeeping.
 // It must be called immediately before emitting the actual CALL instruction,
 // since it emits PCDATA for the stack map at the call (calls are safe points).