Revert "cmd/compile: Enable inlining of tail calls"

This reverts CL 650455 and CL 655816.

Reason for revert: it causes #73747. Properly fixing it gets into
trickiness with defer/recover, wrapper, and inlining. We're late
in the Go 1.25 release cycle.

Fixes #73747.

Change-Id: Ifb343d522b18fec3fec73a7c886678032ac8e4df
Reviewed-on: https://go-review.googlesource.com/c/go/+/678575
Reviewed-by: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

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

@@ -785,7 +785,7 @@ func inlineCallCheck(callerfn *ir.Func, call *ir.CallExpr) (bool, bool) {
 	if call.Op() != ir.OCALLFUNC {
 		return false, false
 	}
-	if call.GoDefer {
+	if call.GoDefer || call.NoInline {
 		return false, false
 	}
 

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

@@ -279,7 +279,12 @@ func (s *inlClosureState) mark(n ir.Node) ir.Node {
 
 	ok := match(n)
 
+	// can't wrap TailCall's child into ParenExpr
+	if t, ok := n.(*ir.TailCallStmt); ok {
+		ir.EditChildren(t.Call, s.mark)
+	} else {
 		ir.EditChildren(n, s.mark)
+	}
 
 	if ok {
 		if p == nil {
@@ -317,23 +322,6 @@ func (s *inlClosureState) unparenthesize() {
 			n = paren.X
 		}
 		ir.EditChildren(n, unparen)
-		// special case for tail calls: if the tail call was inlined, transform
-		// the tail call to a return stmt if the inlined function was not void,
-		// otherwise replace it with the inlined expression followed by a return.
-		if tail, ok := n.(*ir.TailCallStmt); ok {
-			if inl, done := tail.Call.(*ir.InlinedCallExpr); done {
-				if len(inl.ReturnVars) != 0 {
-					ret := ir.NewReturnStmt(tail.Pos(), []ir.Node{inl})
-					if len(inl.ReturnVars) > 1 {
-						typecheck.RewriteMultiValueCall(ret, inl)
-					}
-					n = ret
-				} else {
-					ret := ir.NewReturnStmt(tail.Pos(), nil)
-					n = ir.NewBlockStmt(tail.Pos(), []ir.Node{inl, ret})
-				}
-			}
-		}
 		return n
 	}
 	ir.EditChildren(s.fn, unparen)
@@ -370,9 +358,11 @@ func (s *inlClosureState) fixpoint() bool {
 }
 
 func match(n ir.Node) bool {
-	switch n.(type) {
+	switch n := n.(type) {
 	case *ir.CallExpr:
 		return true
+	case *ir.TailCallStmt:
+		n.Call.NoInline = true // can't inline yet
 	}
 	return false
 }

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

@@ -191,6 +191,7 @@ type CallExpr struct {
 	KeepAlive []*Name // vars to be kept alive until call returns
 	IsDDD     bool
 	GoDefer   bool // whether this call is part of a go or defer statement
+	NoInline  bool // whether this call must not be inlined
 }
 
 func NewCallExpr(pos src.XPos, op Op, fun Node, args []Node) *CallExpr {

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

@@ -2202,13 +2202,13 @@ func (n *TailCallStmt) doChildrenWithHidden(do func(Node) bool) bool {
 func (n *TailCallStmt) editChildren(edit func(Node) Node) {
 	editNodes(n.init, edit)
 	if n.Call != nil {
-		n.Call = edit(n.Call)
+		n.Call = edit(n.Call).(*CallExpr)
 	}
 }
 func (n *TailCallStmt) editChildrenWithHidden(edit func(Node) Node) {
 	editNodes(n.init, edit)
 	if n.Call != nil {
-		n.Call = edit(n.Call)
+		n.Call = edit(n.Call).(*CallExpr)
 	}
 }
 

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

@@ -479,7 +479,7 @@ func NewSwitchStmt(pos src.XPos, tag Node, cases []*CaseClause) *SwitchStmt {
 // code generation to jump directly to another function entirely.
 type TailCallStmt struct {
 	miniStmt
-	Call Node // the underlying call
+	Call *CallExpr // the underlying call
 }
 
 func NewTailCallStmt(pos src.XPos, call *CallExpr) *TailCallStmt {

src/cmd/compile/internal/noder/reader.go

@@ -3996,11 +3996,12 @@ func addTailCall(pos src.XPos, fn *ir.Func, recv ir.Node, method *types.Field) {
 
 	if recv.Type() != nil && recv.Type().IsPtr() && method.Type.Recv().Type.IsPtr() &&
 		method.Embedded != 0 && !types.IsInterfaceMethod(method.Type) &&
+		!unifiedHaveInlineBody(ir.MethodExprName(dot).Func) &&
 		!(base.Ctxt.Arch.Name == "ppc64le" && base.Ctxt.Flag_dynlink) {
 		if base.Debug.TailCall != 0 {
 			base.WarnfAt(fn.Nname.Type().Recv().Type.Elem().Pos(), "tail call emitted for the method %v wrapper", method.Nname)
 		}
-		// Prefer OTAILCALL to reduce code size (the called method can be inlined).
+		// Prefer OTAILCALL to reduce code size (except the case when the called method can be inlined).
 		fn.Body.Append(ir.NewTailCallStmt(pos, call))
 		return
 	}

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

@@ -1921,7 +1921,7 @@ func (s *state) stmt(n ir.Node) {
 
 	case ir.OTAILCALL:
 		n := n.(*ir.TailCallStmt)
-		s.callResult(n.Call.(*ir.CallExpr), callTail)
+		s.callResult(n.Call, callTail)
 		call := s.mem()
 		b := s.endBlock()
 		b.Kind = ssa.BlockRetJmp // could use BlockExit. BlockRetJmp is mostly for clarity.

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

@@ -137,7 +137,7 @@ assignOK:
 	if cr > len(rhs) {
 		stmt := stmt.(*ir.AssignListStmt)
 		stmt.SetOp(ir.OAS2FUNC)
-		r := rhs[0]
+		r := rhs[0].(*ir.CallExpr)
 		rtyp := r.Type()
 
 		mismatched := false

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

@@ -139,8 +139,7 @@ func walkStmt(n ir.Node) ir.Node {
 		n := n.(*ir.TailCallStmt)
 
 		var init ir.Nodes
-		call := n.Call.(*ir.CallExpr)
-		call.Fun = walkExpr(call.Fun, &init)
+		n.Call.Fun = walkExpr(n.Call.Fun, &init)
 
 		if len(init) > 0 {
 			init.Append(n)

test/tailcall.go

@@ -7,14 +7,16 @@
 package p
 
 // Test that when generating wrappers for methods, we generate a tail call to the pointer version of
-// the method.
+// the method, if that method is not inlineable. We use go:noinline here to force the non-inlineability
+// condition.
 
+//go:noinline
 func (f *Foo) Get2Vals() [2]int { return [2]int{f.Val, f.Val + 1} }
-func (f *Foo) Get3Vals() (int, int, int) { return f.Val, f.Val + 1, f.Val + 2 }
+func (f *Foo) Get3Vals() [3]int { return [3]int{f.Val, f.Val + 1, f.Val + 2} }
 
 type Foo struct{ Val int }
 
-type Bar struct { // ERROR "tail call emitted for the method \(\*Foo\).Get2Vals wrapper" "tail call emitted for the method \(\*Foo\).Get3Vals wrapper"
+type Bar struct { // ERROR "tail call emitted for the method \(\*Foo\).Get2Vals wrapper"
 	int64
 	*Foo // needs a method wrapper
 	string