Revert "cmd/compile, cmd/link, runtime: make defers low-cost through inline code and extra funcdata"

This reverts CL 190098.

Reason for revert: broke several builders.

Change-Id: I69161352f9ded02537d8815f259c4d391edd9220
Reviewed-on: https://go-review.googlesource.com/c/go/+/201519
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Dan Scales <danscales@google.com>

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

@@ -371,7 +371,6 @@ func (e *Escape) stmt(n *Node) {
 		e.stmts(n.Right.Ninit)
 		e.call(e.addrs(n.List), n.Right, nil)
 	case ORETURN:
-		e.curfn.Func.numReturns++
 		results := e.curfn.Type.Results().FieldSlice()
 		for i, v := range n.List.Slice() {
 			e.assign(asNode(results[i].Nname), v, "return", n)
@@ -379,16 +378,6 @@ func (e *Escape) stmt(n *Node) {
 	case OCALLFUNC, OCALLMETH, OCALLINTER, OCLOSE, OCOPY, ODELETE, OPANIC, OPRINT, OPRINTN, ORECOVER:
 		e.call(nil, n, nil)
 	case OGO, ODEFER:
-		if n.Op == ODEFER {
-			e.curfn.Func.SetHasDefer(true)
-			e.curfn.Func.numDefers++
-			if e.curfn.Func.numDefers > maxOpenDefers {
-				// Don't allow open defers if there are more than
-				// 8 defers in the function, since we use a single
-				// byte to record active defers.
-				e.curfn.Func.SetOpenCodedDeferDisallowed(true)
-			}
-		}
 		e.stmts(n.Left.Ninit)
 		e.call(nil, n.Left, n)
 
@@ -883,13 +872,8 @@ func (e *Escape) augmentParamHole(k EscHole, where *Node) EscHole {
 	// non-transient location to avoid arguments from being
 	// transiently allocated.
 	if where.Op == ODEFER && e.loopDepth == 1 {
-		// force stack allocation of defer record, unless open-coded
-		// defers are used (see ssa.go)
-		where.Esc = EscNever
+		where.Esc = EscNever // force stack allocation of defer record (see ssa.go)
 		return e.later(k)
-	} else if where.Op == ODEFER {
-		// If any defer occurs in a loop, open-coded defers cannot be used
-		e.curfn.Func.SetOpenCodedDeferDisallowed(true)
 	}
 
 	return e.heapHole()

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

@@ -52,7 +52,6 @@ var (
 	Debug_typecheckinl int
 	Debug_gendwarfinl  int
 	Debug_softfloat    int
-	Debug_defer        int
 )
 
 // Debug arguments.
@@ -82,7 +81,6 @@ var debugtab = []struct {
 	{"typecheckinl", "eager typechecking of inline function bodies", &Debug_typecheckinl},
 	{"dwarfinl", "print information about DWARF inlined function creation", &Debug_gendwarfinl},
 	{"softfloat", "force compiler to emit soft-float code", &Debug_softfloat},
-	{"defer", "print information about defer compilation", &Debug_defer},
 }
 
 const debugHelpHeader = `usage: -d arg[,arg]* and arg is <key>[=<value>]

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

@@ -294,9 +294,6 @@ func addGCLocals() {
 			}
 			ggloblsym(x, int32(len(x.P)), attr)
 		}
-		if x := s.Func.OpenCodedDeferInfo; x != nil {
-			ggloblsym(x, int32(len(x.P)), obj.RODATA|obj.DUPOK)
-		}
 	}
 }
 

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

@@ -338,7 +338,6 @@ func deferstruct(stksize int64) *types.Type {
 		makefield("siz", types.Types[TUINT32]),
 		makefield("started", types.Types[TBOOL]),
 		makefield("heap", types.Types[TBOOL]),
-		makefield("openDefer", types.Types[TBOOL]),
 		makefield("sp", types.Types[TUINTPTR]),
 		makefield("pc", types.Types[TUINTPTR]),
 		// Note: the types here don't really matter. Defer structures
@@ -347,9 +346,6 @@ func deferstruct(stksize int64) *types.Type {
 		makefield("fn", types.Types[TUINTPTR]),
 		makefield("_panic", types.Types[TUINTPTR]),
 		makefield("link", types.Types[TUINTPTR]),
-		makefield("framepc", types.Types[TUINTPTR]),
-		makefield("varp", types.Types[TUINTPTR]),
-		makefield("fd", types.Types[TUINTPTR]),
 		makefield("args", argtype),
 	}
 

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

@@ -20,7 +20,7 @@ func TestSizeof(t *testing.T) {
 		_32bit uintptr     // size on 32bit platforms
 		_64bit uintptr     // size on 64bit platforms
 	}{
-		{Func{}, 124, 224},
+		{Func{}, 116, 208},
 		{Name{}, 32, 56},
 		{Param{}, 24, 48},
 		{Node{}, 76, 128},

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

@@ -29,10 +29,6 @@ var ssaDumpStdout bool // whether to dump to stdout
 var ssaDumpCFG string  // generate CFGs for these phases
 const ssaDumpFile = "ssa.html"
 
-// The max number of defers in a function using open-coded defers. We enforce this
-// limit because the deferBits bitmask is currently a single byte (to minimize code size)
-const maxOpenDefers = 8
-
 // ssaDumpInlined holds all inlined functions when ssaDump contains a function name.
 var ssaDumpInlined []*Node
 
@@ -169,107 +165,6 @@ func initssaconfig() {
 	SigPanic = sysfunc("sigpanic")
 }
 
-// getParam returns the Field of ith param of node n (which is a
-// function/method/interface call), where the receiver of a method call is
-// considered as the 0th parameter. This does not include the receiver of an
-// interface call.
-func getParam(n *Node, i int) *types.Field {
-	t := n.Left.Type
-	if n.Op == OCALLMETH {
-		if i == 0 {
-			return t.Recv()
-		}
-		return t.Params().Field(i - 1)
-	}
-	return t.Params().Field(i)
-}
-
-// dvarint writes a varint v to the funcdata in symbol x and returns the new offset
-func dvarint(x *obj.LSym, off int, v int64) int {
-	if v < 0 || v > 1e9 {
-		panic(fmt.Sprintf("dvarint: bad offset for funcdata - %v", v))
-	}
-	if v < 1<<7 {
-		return duint8(x, off, uint8(v))
-	}
-	off = duint8(x, off, uint8((v&127)|128))
-	if v < 1<<14 {
-		return duint8(x, off, uint8(v>>7))
-	}
-	off = duint8(x, off, uint8(((v>>7)&127)|128))
-	if v < 1<<21 {
-		return duint8(x, off, uint8(v>>14))
-	}
-	off = duint8(x, off, uint8(((v>>14)&127)|128))
-	if v < 1<<28 {
-		return duint8(x, off, uint8(v>>21))
-	}
-	off = duint8(x, off, uint8(((v>>21)&127)|128))
-	return duint8(x, off, uint8(v>>28))
-}
-
-// emitOpenDeferInfo emits FUNCDATA information about the defers in a function
-// that is using open-coded defers.  This funcdata is used to determine the active
-// defers in a function and execute those defers during panic processing.
-//
-// The funcdata is all encoded in varints (since values will almost always be less
-// than 128, but stack offsets could potentially be up to 2Gbyte). All "locations"
-// for stack variables are specified as the number of bytes below varp for their
-// starting address. The format is:
-//
-//  - Max total argument size among all the defers
-//  - Location of the deferBits variable
-//  - Number of defers in the function
-//  - Information about each defer call, in reverse order of appearance in the function:
-//    - Total argument size of the call
-//    - Location of the closure value to call
-//    - 1 or 0 to indicate if there is a receiver for the call
-//      - If yes, then the location of the receiver value
-//    - Number of arguments
-//    - Information about each argument
-//      - Location of the stored defer argument in this function's frame
-//      - Size of the argument
-//      - Offset of where argument should be placed in the args frame when making call
-func emitOpenDeferInfo(s state) {
-	x := Ctxt.Lookup(s.curfn.Func.lsym.Name + ".opendefer")
-	s.curfn.Func.lsym.Func.OpenCodedDeferInfo = x
-	off := 0
-
-	// Compute maxargsize (max size of arguments for all defers)
-	// first, so we can output it first to the funcdata
-	var maxargsize int64
-	for i := len(s.opendefers) - 1; i >= 0; i-- {
-		r := s.opendefers[i]
-		argsize := r.n.Left.Type.ArgWidth()
-		if argsize > maxargsize {
-			maxargsize = argsize
-		}
-	}
-	off = dvarint(x, off, maxargsize)
-	off = dvarint(x, off, -s.deferBitsTemp.Xoffset)
-	off = dvarint(x, off, int64(len(s.opendefers)))
-
-	// Write in reverse-order, for ease of running in that order at runtime
-	for i := len(s.opendefers) - 1; i >= 0; i-- {
-		r := s.opendefers[i]
-		off = dvarint(x, off, r.n.Left.Type.ArgWidth())
-		off = dvarint(x, off, -r.closureNode.Xoffset)
-		if r.rcvrNode != nil {
-			off = dvarint(x, off, 1)
-			off = dvarint(x, off, -r.rcvrNode.Xoffset)
-		} else {
-			off = dvarint(x, off, 0)
-		}
-		off = dvarint(x, off, int64(len(r.argNodes)))
-		for j, arg := range r.argNodes {
-			f := getParam(r.n, j)
-			off = dvarint(x, off, -arg.Xoffset)
-			off = dvarint(x, off, f.Type.Size())
-			off = dvarint(x, off, f.Offset)
-		}
-	}
-}
-
 // buildssa builds an SSA function for fn.
 // worker indicates which of the backend workers is doing the processing.
 func buildssa(fn *Node, worker int) *ssa.Func {
@@ -332,48 +227,11 @@ func buildssa(fn *Node, worker int) *ssa.Func {
 	s.labeledNodes = map[*Node]*ssaLabel{}
 	s.fwdVars = map[*Node]*ssa.Value{}
 	s.startmem = s.entryNewValue0(ssa.OpInitMem, types.TypeMem)
-
-	s.hasOpenDefers = Debug['N'] == 0 && s.hasdefer && !s.curfn.Func.OpenCodedDeferDisallowed()
-	if s.hasOpenDefers && s.curfn.Func.Exit.Len() > 0 {
-		// Skip doing open defers if there is any extra exit code (likely
-		// copying heap-allocated return values or race detection), since
-		// we will not generate that code in the case of the extra
-		// deferreturn/ret segment.
-		s.hasOpenDefers = false
-	}
-	if s.hasOpenDefers &&
-		s.curfn.Func.numReturns*s.curfn.Func.numDefers > 15 {
-		// Since we are generating defer calls at every exit for
-		// open-coded defers, skip doing open-coded defers if there are
-		// too many returns (especially if there are multiple defers).
-		// Open-coded defers are most important for improving performance
-		// for smaller functions (which don't have many returns).
-		s.hasOpenDefers = false
-	}
-
 	s.sp = s.entryNewValue0(ssa.OpSP, types.Types[TUINTPTR]) // TODO: use generic pointer type (unsafe.Pointer?) instead
 	s.sb = s.entryNewValue0(ssa.OpSB, types.Types[TUINTPTR])
 
 	s.startBlock(s.f.Entry)
 	s.vars[&memVar] = s.startmem
-	if s.hasOpenDefers {
-		// Create the deferBits variable and stack slot.  deferBits is a
-		// bitmask showing which of the open-coded defers in this function
-		// have been activated.
-		deferBitsTemp := tempAt(src.NoXPos, s.curfn, types.Types[TUINT8])
-		s.deferBitsTemp = deferBitsTemp
-		// For this value, AuxInt is initialized to zero by default
-		startDeferBits := s.entryNewValue0(ssa.OpConst8, types.Types[TUINT8])
-		s.vars[&deferBitsVar] = startDeferBits
-		s.deferBitsAddr = s.addr(deferBitsTemp, false)
-		s.store(types.Types[TUINT8], s.deferBitsAddr, startDeferBits)
-		// Make sure that the deferBits stack slot is kept alive (for use
-		// by panics) and stores to deferBits are not eliminated, even if
-		// all checking code on deferBits in the function exit can be
-		// eliminated, because the defer statements were all
-		// unconditional.
-		s.vars[&memVar] = s.newValue1Apos(ssa.OpVarLive, types.TypeMem, deferBitsTemp, s.mem(), false)
-	}
 
 	// Generate addresses of local declarations
 	s.decladdrs = map[*Node]*ssa.Value{}
@@ -429,11 +287,6 @@ func buildssa(fn *Node, worker int) *ssa.Func {
 
 	// Main call to ssa package to compile function
 	ssa.Compile(s.f)
-
-	if s.hasOpenDefers {
-		emitOpenDeferInfo(s)
-	}
-
 	return s.f
 }
 
@@ -522,29 +375,6 @@ func (s *state) updateUnsetPredPos(b *ssa.Block) {
 	}
 }
 
-// Information about each open-coded defer.
-type openDeferInfo struct {
-	// The ODEFER node representing the function call of the defer
-	n *Node
-	// If defer call is closure call, the address of the argtmp where the
-	// closure is stored.
-	closure *ssa.Value
-	// The node representing the argtmp where the closure is stored - used for
-	// function, method, or interface call, to store a closure that panic
-	// processing can use for this defer.
-	closureNode *Node
-	// If defer call is interface call, the address of the argtmp where the
-	// receiver is stored
-	rcvr *ssa.Value
-	// The node representing the argtmp where the receiver is stored
-	rcvrNode *Node
-	// The addresses of the argtmps where the evaluated arguments of the defer
-	// function call are stored.
-	argVals []*ssa.Value
-	// The nodes representing the argtmps where the args of the defer are stored
-	argNodes []*Node
-}
-
 type state struct {
 	// configuration (arch) information
 	config *ssa.Config
@@ -586,9 +416,6 @@ type state struct {
 	startmem *ssa.Value
 	sp       *ssa.Value
 	sb       *ssa.Value
-	// value representing address of where deferBits autotmp is stored
-	deferBitsAddr *ssa.Value
-	deferBitsTemp *Node
 
 	// line number stack. The current line number is top of stack
 	line []src.XPos
@@ -605,19 +432,6 @@ type state struct {
 	cgoUnsafeArgs bool
 	hasdefer      bool // whether the function contains a defer statement
 	softFloat     bool
-	hasOpenDefers bool // whether we are doing open-coded defers
-
-	// If doing open-coded defers, list of info about the defer calls in
-	// scanning order. Hence, at exit we should run these defers in reverse
-	// order of this list
-	opendefers []*openDeferInfo
-	// For open-coded defers, this is the beginning and end blocks of the last
-	// defer exit code that we have generated so far. We use these to share
-	// code between exits if the shareDeferExits option (disabled by default)
-	// is on.
-	lastDeferExit       *ssa.Block // Entry block of last defer exit code we generated
-	lastDeferFinalBlock *ssa.Block // Final block of last defer exit code we generated
-	lastDeferCount      int        // Number of defers encountered at that point
 }
 
 type funcLine struct {
@@ -655,13 +469,12 @@ var (
 	memVar = Node{Op: ONAME, Sym: &types.Sym{Name: "mem"}}
 
 	// dummy nodes for temporary variables
-	ptrVar       = Node{Op: ONAME, Sym: &types.Sym{Name: "ptr"}}
-	lenVar       = Node{Op: ONAME, Sym: &types.Sym{Name: "len"}}
-	newlenVar    = Node{Op: ONAME, Sym: &types.Sym{Name: "newlen"}}
-	capVar       = Node{Op: ONAME, Sym: &types.Sym{Name: "cap"}}
-	typVar       = Node{Op: ONAME, Sym: &types.Sym{Name: "typ"}}
-	okVar        = Node{Op: ONAME, Sym: &types.Sym{Name: "ok"}}
-	deferBitsVar = Node{Op: ONAME, Sym: &types.Sym{Name: "deferBits"}}
+	ptrVar    = Node{Op: ONAME, Sym: &types.Sym{Name: "ptr"}}
+	lenVar    = Node{Op: ONAME, Sym: &types.Sym{Name: "len"}}
+	newlenVar = Node{Op: ONAME, Sym: &types.Sym{Name: "newlen"}}
+	capVar    = Node{Op: ONAME, Sym: &types.Sym{Name: "cap"}}
+	typVar    = Node{Op: ONAME, Sym: &types.Sym{Name: "typ"}}
+	okVar     = Node{Op: ONAME, Sym: &types.Sym{Name: "ok"}}
 )
 
 // startBlock sets the current block we're generating code in to b.
@@ -1052,27 +865,11 @@ func (s *state) stmt(n *Node) {
 			}
 		}
 	case ODEFER:
-		if Debug_defer > 0 {
-			var defertype string
-			if s.hasOpenDefers {
-				defertype = "open-coded"
-			} else if n.Esc == EscNever {
-				defertype = "stack-allocated"
-			} else {
-				defertype = "heap-allocated"
-			}
-			Warnl(n.Pos, "defer: %s defer in function %s",
-				defertype, s.curfn.funcname())
-		}
-		if s.hasOpenDefers {
-			s.openDeferRecord(n.Left)
-		} else {
-			d := callDefer
-			if n.Esc == EscNever {
-				d = callDeferStack
-			}
-			s.call(n.Left, d)
+		d := callDefer
+		if n.Esc == EscNever {
+			d = callDeferStack
 		}
+		s.call(n.Left, d)
 	case OGO:
 		s.call(n.Left, callGo)
 
@@ -1489,28 +1286,12 @@ func (s *state) stmt(n *Node) {
 	}
 }
 
-// If true, share as many open-coded defer exits as possible (with the downside of
-// worse line-number information)
-const shareDeferExits = false
-
 // exit processes any code that needs to be generated just before returning.
 // It returns a BlockRet block that ends the control flow. Its control value
 // will be set to the final memory state.
 func (s *state) exit() *ssa.Block {
 	if s.hasdefer {
-		if s.hasOpenDefers {
-			if shareDeferExits && s.lastDeferExit != nil && len(s.opendefers) == s.lastDeferCount {
-				if s.curBlock.Kind != ssa.BlockPlain {
-					panic("Block for an exit should be BlockPlain")
-				}
-				s.curBlock.AddEdgeTo(s.lastDeferExit)
-				s.endBlock()
-				return s.lastDeferFinalBlock
-			}
-			s.openDeferExit()
-		} else {
-			s.rtcall(Deferreturn, true, nil)
-		}
+		s.rtcall(Deferreturn, true, nil)
 	}
 
 	// Run exit code. Typically, this code copies heap-allocated PPARAMOUT
@@ -1533,9 +1314,6 @@ func (s *state) exit() *ssa.Block {
 	b := s.endBlock()
 	b.Kind = ssa.BlockRet
 	b.SetControl(m)
-	if s.hasdefer && s.hasOpenDefers {
-		s.lastDeferFinalBlock = b
-	}
 	return b
 }
 
@@ -3986,230 +3764,6 @@ func (s *state) intrinsicArgs(n *Node) []*ssa.Value {
 	return args
 }
 
-// openDeferRecord adds code to evaluate and store the args for an open-code defer
-// call, and records info about the defer, so we can generate proper code on the
-// exit paths. n is the sub-node of the defer node that is the actual function
-// call. We will also record funcdata information on where the args are stored
-// (as well as the deferBits variable), and this will enable us to run the proper
-// defer calls during panics.
-func (s *state) openDeferRecord(n *Node) {
-	index := len(s.opendefers)
-
-	// Do any needed expression evaluation for the args (including the
-	// receiver, if any). This may be evaluating something like 'autotmp_3 =
-	// once.mutex'. Such a statement will create a mapping in s.vars[] from
-	// the autotmp name to the evaluated SSA arg value, but won't do any
-	// stores to the stack.
-	s.stmtList(n.List)
-
-	args := []*ssa.Value{}
-	argNodes := []*Node{}
-
-	opendefer := &openDeferInfo{
-		n: n,
-	}
-	fn := n.Left
-	if n.Op == OCALLFUNC {
-		// We must always store the function value in a stack slot for the
-		// runtime panic code to use. But in the defer exit code, we will
-		// call the function directly if it is a static function.
-		closureVal := s.expr(fn)
-		closure := s.openDeferSave(fn, fn.Type, closureVal)
-		opendefer.closureNode = closure.Aux.(*Node)
-		if !(fn.Op == ONAME && fn.Class() == PFUNC) {
-			opendefer.closure = closure
-		}
-	} else if n.Op == OCALLMETH {
-		if fn.Op != ODOTMETH {
-			Fatalf("OCALLMETH: n.Left not an ODOTMETH: %v", fn)
-		}
-		closureVal := s.getMethodClosure(fn)
-		// We must always store the function value in a stack slot for the
-		// runtime panic code to use. But in the defer exit code, we will
-		// call the method directly.
-		closure := s.openDeferSave(fn, fn.Type, closureVal)
-		opendefer.closureNode = closure.Aux.(*Node)
-	} else {
-		if fn.Op != ODOTINTER {
-			Fatalf("OCALLINTER: n.Left not an ODOTINTER: %v", fn.Op)
-		}
-		closure, rcvr := s.getClosureAndRcvr(fn)
-		opendefer.closure = s.openDeferSave(fn, closure.Type, closure)
-		// Important to get the receiver type correct, so it is recognized
-		// as a pointer for GC purposes.
-		opendefer.rcvr = s.openDeferSave(nil, fn.Type.Recv().Type, rcvr)
-		opendefer.closureNode = opendefer.closure.Aux.(*Node)
-		opendefer.rcvrNode = opendefer.rcvr.Aux.(*Node)
-	}
-	for _, argn := range n.Rlist.Slice() {
-		v := s.openDeferSave(argn, argn.Type, s.expr(argn))
-		args = append(args, v)
-		argNodes = append(argNodes, v.Aux.(*Node))
-	}
-	opendefer.argVals = args
-	opendefer.argNodes = argNodes
-	s.opendefers = append(s.opendefers, opendefer)
-
-	// Update deferBits only after evaluation and storage to stack of
-	// args/receiver/interface is successful.
-	bitvalue := s.constInt8(types.Types[TUINT8], 1<<uint(index))
-	newDeferBits := s.newValue2(ssa.OpOr8, types.Types[TUINT8], s.variable(&deferBitsVar, types.Types[TUINT8]), bitvalue)
-	s.vars[&deferBitsVar] = newDeferBits
-	s.store(types.Types[TUINT8], s.deferBitsAddr, newDeferBits)
-}
-
-// openDeferSave generates SSA nodes to store a value val (with type t) for an
-// open-coded defer on the stack at an explicit autotmp location, so it can be
-// reloaded and used for the appropriate call on exit. n is the associated node,
-// which is only needed if the associated type is non-SSAable. It returns an SSA
-// value representing a pointer to the stack location.
-func (s *state) openDeferSave(n *Node, t *types.Type, val *ssa.Value) *ssa.Value {
-	argTemp := tempAt(val.Pos.WithNotStmt(), s.curfn, t)
-	var addrArgTemp *ssa.Value
-	// Use OpVarLive to make sure stack slots for the args, etc. are not
-	// removed by dead-store elimination
-	if s.curBlock.ID != s.f.Entry.ID {
-		// Force the argtmp storing this defer function/receiver/arg to be
-		// declared in the entry block, so that it will be live for the
-		// defer exit code (which will actually access it only if the
-		// associated defer call has been activated).
-		s.defvars[s.f.Entry.ID][&memVar] = s.entryNewValue1A(ssa.OpVarDef, types.TypeMem, argTemp, s.defvars[s.f.Entry.ID][&memVar])
-		s.defvars[s.f.Entry.ID][&memVar] = s.entryNewValue1A(ssa.OpVarLive, types.TypeMem, argTemp, s.defvars[s.f.Entry.ID][&memVar])
-		addrArgTemp = s.entryNewValue2A(ssa.OpLocalAddr, types.NewPtr(argTemp.Type), argTemp, s.sp, s.defvars[s.f.Entry.ID][&memVar])
-	} else {
-		// Special case if we're still in the entry block. We can't use
-		// the above code, since s.defvars[s.f.Entry.ID] isn't defined
-		// until we end the entry block with s.endBlock().
-		s.vars[&memVar] = s.newValue1Apos(ssa.OpVarDef, types.TypeMem, argTemp, s.mem(), false)
-		s.vars[&memVar] = s.newValue1Apos(ssa.OpVarLive, types.TypeMem, argTemp, s.mem(), false)
-		addrArgTemp = s.newValue2Apos(ssa.OpLocalAddr, types.NewPtr(argTemp.Type), argTemp, s.sp, s.mem(), false)
-	}
-	if types.Haspointers(t) {
-		// Since we may use this argTemp during exit depending on the
-		// deferBits, we must define it unconditionally on entry.
-		// Therefore, we must make sure it is zeroed out in the entry
-		// block if it contains pointers, else GC may wrongly follow an
-		// uninitialized pointer value.
-		argTemp.Name.SetNeedzero(true)
-	}
-	if !canSSAType(t) {
-		if n.Op != ONAME {
-			panic(fmt.Sprintf("Non-SSAable value should be a named location: %v", n))
-		}
-		a := s.addr(n, false)
-		s.move(t, addrArgTemp, a)
-		return addrArgTemp
-	}
-	// We are storing to the stack, hence we can avoid the full checks in
-	// storeType() (no write barrier) and do a simple store().
-	s.store(t, addrArgTemp, val)
-	return addrArgTemp
-}
-
-// openDeferExit generates SSA for processing all the open coded defers at exit.
-// The code involves loading deferBits, and checking each of the bits to see if
-// the corresponding defer statement was executed. For each bit that is turned
-// on, the associated defer call is made.
-func (s *state) openDeferExit() {
-	deferExit := s.f.NewBlock(ssa.BlockPlain)
-	s.endBlock().AddEdgeTo(deferExit)
-	s.startBlock(deferExit)
-	s.lastDeferExit = deferExit
-	s.lastDeferCount = len(s.opendefers)
-	zeroval := s.constInt8(types.Types[TUINT8], 0)
-	// Test for and run defers in reverse order
-	for i := len(s.opendefers) - 1; i >= 0; i-- {
-		r := s.opendefers[i]
-		bCond := s.f.NewBlock(ssa.BlockPlain)
-		bEnd := s.f.NewBlock(ssa.BlockPlain)
-
-		deferBits := s.variable(&deferBitsVar, types.Types[TUINT8])
-		// Generate code to check if the bit associated with the current
-		// defer is set.
-		bitval := s.constInt8(types.Types[TUINT8], 1<<uint(i))
-		andval := s.newValue2(ssa.OpAnd8, types.Types[TUINT8], deferBits, bitval)
-		eqVal := s.newValue2(ssa.OpEq8, types.Types[TBOOL], andval, zeroval)
-		b := s.endBlock()
-		b.Kind = ssa.BlockIf
-		b.SetControl(eqVal)
-		b.AddEdgeTo(bEnd)
-		b.AddEdgeTo(bCond)
-		bCond.AddEdgeTo(bEnd)
-		s.startBlock(bCond)
-
-		// Clear this bit in deferBits and force store back to stack, so
-		// we will not try to re-run this defer call if this defer call panics.
-		nbitval := s.newValue1(ssa.OpCom8, types.Types[TUINT8], bitval)
-		maskedval := s.newValue2(ssa.OpAnd8, types.Types[TUINT8], deferBits, nbitval)
-		s.store(types.Types[TUINT8], s.deferBitsAddr, maskedval)
-		// Use this value for following tests, so we keep previous
-		// bits cleared.
-		s.vars[&deferBitsVar] = maskedval
-
-		// Generate code to call the function call of the defer, using the
-		// closure/receiver/args that were stored in argtmps at the point
-		// of the defer statement.
-		argStart := Ctxt.FixedFrameSize()
-		fn := r.n.Left
-		stksize := fn.Type.ArgWidth()
-		if r.rcvr != nil {
-			// rcvr in case of OCALLINTER
-			v := s.load(r.rcvr.Type.Elem(), r.rcvr)
-			addr := s.constOffPtrSP(s.f.Config.Types.UintptrPtr, argStart)
-			s.store(types.Types[TUINTPTR], addr, v)
-		}
-		for j, argAddrVal := range r.argVals {
-			f := getParam(r.n, j)
-			pt := types.NewPtr(f.Type)
-			addr := s.constOffPtrSP(pt, argStart+f.Offset)
-			if !canSSAType(f.Type) {
-				s.move(f.Type, addr, argAddrVal)
-			} else {
-				argVal := s.load(f.Type, argAddrVal)
-				s.storeType(f.Type, addr, argVal, 0, false)
-			}
-		}
-		var call *ssa.Value
-		if r.closure != nil {
-			v := s.load(r.closure.Type.Elem(), r.closure)
-			s.maybeNilCheckClosure(v, callDefer)
-			codeptr := s.rawLoad(types.Types[TUINTPTR], v)
-			call = s.newValue3(ssa.OpClosureCall, types.TypeMem, codeptr, v, s.mem())
-		} else {
-			// Do a static call if the original call was a static function or method
-			call = s.newValue1A(ssa.OpStaticCall, types.TypeMem, fn.Sym.Linksym(), s.mem())
-		}
-		call.AuxInt = stksize
-		s.vars[&memVar] = call
-		// Make sure that the stack slots with pointers are kept live
-		// through the call (which is a pre-emption point). Also, we will
-		// use the first call of the last defer exit to compute liveness
-		// for the deferreturn, so we want all stack slots to be live.
-		if r.closureNode != nil {
-			s.vars[&memVar] = s.newValue1Apos(ssa.OpVarLive, types.TypeMem, r.closureNode, s.mem(), false)
-		}
-		if r.rcvrNode != nil {
-			if types.Haspointers(r.rcvrNode.Type) {
-				s.vars[&memVar] = s.newValue1Apos(ssa.OpVarLive, types.TypeMem, r.rcvrNode, s.mem(), false)
-			}
-		}
-		for _, argNode := range r.argNodes {
-			if types.Haspointers(argNode.Type) {
-				s.vars[&memVar] = s.newValue1Apos(ssa.OpVarLive, types.TypeMem, argNode, s.mem(), false)
-			}
-		}
-
-		if i == len(s.opendefers)-1 {
-			// Record the call of the first defer. This will be used
-			// to set liveness info for the deferreturn (which is also
-			// used for any location that causes a runtime panic)
-			s.f.LastDeferExit = call
-		}
-		s.endBlock()
-		s.startBlock(bEnd)
-	}
-}
-
 // Calls the function n using the specified call type.
 // Returns the address of the return value (or nil if none).
 func (s *state) call(n *Node, k callKind) *ssa.Value {
@@ -4225,10 +3779,11 @@ func (s *state) call(n *Node, k callKind) *ssa.Value {
 			break
 		}
 		closure = s.expr(fn)
-		if k != callDefer && k != callDeferStack {
-			// Deferred nil function needs to panic when the function is invoked,
-			// not the point of defer statement.
-			s.maybeNilCheckClosure(closure, k)
+		if k != callDefer && k != callDeferStack && (thearch.LinkArch.Family == sys.Wasm || objabi.GOOS == "aix" && k != callGo) {
+			// Deferred nil function needs to panic when the function is invoked, not the point of defer statement.
+			// On AIX, the closure needs to be verified as fn can be nil, except if it's a call go. This needs to be handled by the runtime to have the "go of nil func value" error.
+			// TODO(neelance): On other architectures this should be eliminated by the optimization steps
+			s.nilCheck(closure)
 		}
 	case OCALLMETH:
 		if fn.Op != ODOTMETH {
@@ -4238,20 +3793,35 @@ func (s *state) call(n *Node, k callKind) *ssa.Value {
 			sym = fn.Sym
 			break
 		}
-		closure = s.getMethodClosure(fn)
+		// Make a name n2 for the function.
+		// fn.Sym might be sync.(*Mutex).Unlock.
+		// Make a PFUNC node out of that, then evaluate it.
+		// We get back an SSA value representing &sync.(*Mutex).Unlock·f.
+		// We can then pass that to defer or go.
+		n2 := newnamel(fn.Pos, fn.Sym)
+		n2.Name.Curfn = s.curfn
+		n2.SetClass(PFUNC)
+		// n2.Sym already existed, so it's already marked as a function.
+		n2.Pos = fn.Pos
+		n2.Type = types.Types[TUINT8] // dummy type for a static closure. Could use runtime.funcval if we had it.
+		closure = s.expr(n2)
 		// Note: receiver is already present in n.Rlist, so we don't
 		// want to set it here.
 	case OCALLINTER:
 		if fn.Op != ODOTINTER {
 			s.Fatalf("OCALLINTER: n.Left not an ODOTINTER: %v", fn.Op)
 		}
-		var iclosure *ssa.Value
-		iclosure, rcvr = s.getClosureAndRcvr(fn)
+		i := s.expr(fn.Left)
+		itab := s.newValue1(ssa.OpITab, types.Types[TUINTPTR], i)
+		s.nilCheck(itab)
+		itabidx := fn.Xoffset + 2*int64(Widthptr) + 8 // offset of fun field in runtime.itab
+		itab = s.newValue1I(ssa.OpOffPtr, s.f.Config.Types.UintptrPtr, itabidx, itab)
 		if k == callNormal {
-			codeptr = s.load(types.Types[TUINTPTR], iclosure)
+			codeptr = s.load(types.Types[TUINTPTR], itab)
 		} else {
-			closure = iclosure
+			closure = itab
 		}
+		rcvr = s.newValue1(ssa.OpIData, types.Types[TUINTPTR], i)
 	}
 	dowidth(fn.Type)
 	stksize := fn.Type.ArgWidth() // includes receiver, args, and results
@@ -4277,22 +3847,18 @@ func (s *state) call(n *Node, k callKind) *ssa.Value {
 			s.constInt32(types.Types[TUINT32], int32(stksize)))
 		// 1: started, set in deferprocStack
 		// 2: heap, set in deferprocStack
-		// 3: openDefer
-		// 4: sp, set in deferprocStack
-		// 5: pc, set in deferprocStack
-		// 6: fn
+		// 3: sp, set in deferprocStack
+		// 4: pc, set in deferprocStack
+		// 5: fn
 		s.store(closure.Type,
-			s.newValue1I(ssa.OpOffPtr, closure.Type.PtrTo(), t.FieldOff(6), addr),
+			s.newValue1I(ssa.OpOffPtr, closure.Type.PtrTo(), t.FieldOff(5), addr),
 			closure)
-		// 7: panic, set in deferprocStack
-		// 8: link, set in deferprocStack
-		// 9: framepc
-		// 10: varp
-		// 11: fd
+		// 6: panic, set in deferprocStack
+		// 7: link, set in deferprocStack
 
 		// Then, store all the arguments of the defer call.
 		ft := fn.Type
-		off := t.FieldOff(12)
+		off := t.FieldOff(8)
 		args := n.Rlist.Slice()
 
 		// Set receiver (for interface calls). Always a pointer.
@@ -4407,44 +3973,6 @@ func (s *state) call(n *Node, k callKind) *ssa.Value {
 	return s.constOffPtrSP(types.NewPtr(fp.Type), fp.Offset+Ctxt.FixedFrameSize())
 }
 
-// maybeNilCheckClosure checks if a nil check of a closure is needed in some
-// architecture-dependent situations and, if so, emits the nil check.
-func (s *state) maybeNilCheckClosure(closure *ssa.Value, k callKind) {
-	if thearch.LinkArch.Family == sys.Wasm || objabi.GOOS == "aix" && k != callGo {
-		// On AIX, the closure needs to be verified as fn can be nil, except if it's a call go. This needs to be handled by the runtime to have the "go of nil func value" error.
-		// TODO(neelance): On other architectures this should be eliminated by the optimization steps
-		s.nilCheck(closure)
-	}
-}
-
-// getMethodClosure returns a value representing the closure for a method call
-func (s *state) getMethodClosure(fn *Node) *ssa.Value {
-	// Make a name n2 for the function.
-	// fn.Sym might be sync.(*Mutex).Unlock.
-	// Make a PFUNC node out of that, then evaluate it.
-	// We get back an SSA value representing &sync.(*Mutex).Unlock·f.
-	// We can then pass that to defer or go.
-	n2 := newnamel(fn.Pos, fn.Sym)
-	n2.Name.Curfn = s.curfn
-	n2.SetClass(PFUNC)
-	// n2.Sym already existed, so it's already marked as a function.
-	n2.Pos = fn.Pos
-	n2.Type = types.Types[TUINT8] // dummy type for a static closure. Could use runtime.funcval if we had it.
-	return s.expr(n2)
-}
-
-// getClosureAndRcvr returns values for the appropriate closure and receiver of an
-// interface call
-func (s *state) getClosureAndRcvr(fn *Node) (*ssa.Value, *ssa.Value) {
-	i := s.expr(fn.Left)
-	itab := s.newValue1(ssa.OpITab, types.Types[TUINTPTR], i)
-	s.nilCheck(itab)
-	itabidx := fn.Xoffset + 2*int64(Widthptr) + 8 // offset of fun field in runtime.itab
-	closure := s.newValue1I(ssa.OpOffPtr, s.f.Config.Types.UintptrPtr, itabidx, itab)
-	rcvr := s.newValue1(ssa.OpIData, types.Types[TUINTPTR], i)
-	return closure, rcvr
-}
-
 // etypesign returns the signed-ness of e, for integer/pointer etypes.
 // -1 means signed, +1 means unsigned, 0 means non-integer/non-pointer.
 func etypesign(e types.EType) int8 {
@@ -5618,16 +5146,6 @@ func (s *state) addNamedValue(n *Node, v *ssa.Value) {
 	s.f.NamedValues[loc] = append(values, v)
 }
 
-// Generate a disconnected call to a runtime routine and a return.
-func gencallret(pp *Progs, sym *obj.LSym) *obj.Prog {
-	p := pp.Prog(obj.ACALL)
-	p.To.Type = obj.TYPE_MEM
-	p.To.Name = obj.NAME_EXTERN
-	p.To.Sym = sym
-	p = pp.Prog(obj.ARET)
-	return p
-}
-
 // Branch is an unresolved branch.
 type Branch struct {
 	P *obj.Prog  // branch instruction
@@ -5663,11 +5181,6 @@ type SSAGenState struct {
 
 	// wasm: The number of values on the WebAssembly stack. This is only used as a safeguard.
 	OnWasmStackSkipped int
-
-	// Liveness index for the first function call in the final defer exit code
-	// path that we generated. All defer functions and args should be live at
-	// this point. This will be used to set the liveness for the deferreturn.
-	lastDeferLiveness LivenessIndex
 }
 
 // Prog appends a new Prog.
@@ -5795,17 +5308,6 @@ func genssa(f *ssa.Func, pp *Progs) {
 	s.livenessMap = liveness(e, f, pp)
 	emitStackObjects(e, pp)
 
-	openDeferInfo := e.curfn.Func.lsym.Func.OpenCodedDeferInfo
-	if openDeferInfo != nil {
-		// This function uses open-coded defers -- write out the funcdata
-		// info that we computed at the end of genssa.
-		p := pp.Prog(obj.AFUNCDATA)
-		Addrconst(&p.From, objabi.FUNCDATA_OpenCodedDeferInfo)
-		p.To.Type = obj.TYPE_MEM
-		p.To.Name = obj.NAME_EXTERN
-		p.To.Sym = openDeferInfo
-	}
-
 	// Remember where each block starts.
 	s.bstart = make([]*obj.Prog, f.NumBlocks())
 	s.pp = pp
@@ -5870,12 +5372,6 @@ func genssa(f *ssa.Func, pp *Progs) {
 			// Attach this safe point to the next
 			// instruction.
 			s.pp.nextLive = s.livenessMap.Get(v)
-
-			// Remember the liveness index of the first defer call of
-			// the last defer exit
-			if v.Block.Func.LastDeferExit != nil && v == v.Block.Func.LastDeferExit {
-				s.lastDeferLiveness = s.pp.nextLive
-			}
 			switch v.Op {
 			case ssa.OpInitMem:
 				// memory arg needs no code
@@ -5959,13 +5455,6 @@ func genssa(f *ssa.Func, pp *Progs) {
 		// nop (which will never execute) after the call.
 		thearch.Ginsnop(pp)
 	}
-	if openDeferInfo != nil {
-		// When doing open-coded defers, generate a disconnected call to
-		// deferreturn and a return. This will be used to during panic
-		// recovery to unwind the stack and return back to the runtime.
-		s.pp.nextLive = s.lastDeferLiveness
-		gencallret(pp, Deferreturn)
-	}
 
 	if inlMarks != nil {
 		// We have some inline marks. Try to find other instructions we're

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

@@ -491,9 +491,7 @@ type Func struct {
 
 	Pragma syntax.Pragma // go:xxx function annotations
 
-	flags      bitset16
-	numDefers  int // number of defer calls in the function
-	numReturns int // number of explicit returns in the function
+	flags bitset16
 
 	// nwbrCalls records the LSyms of functions called by this
 	// function for go:nowritebarrierrec analysis. Only filled in
@@ -529,37 +527,34 @@ const (
 	funcNeedctxt                  // function uses context register (has closure variables)
 	funcReflectMethod             // function calls reflect.Type.Method or MethodByName
 	funcIsHiddenClosure
-	funcHasDefer                 // contains a defer statement
-	funcNilCheckDisabled         // disable nil checks when compiling this function
-	funcInlinabilityChecked      // inliner has already determined whether the function is inlinable
-	funcExportInline             // include inline body in export data
-	funcInstrumentBody           // add race/msan instrumentation during SSA construction
-	funcOpenCodedDeferDisallowed // can't do open-coded defers
+	funcHasDefer            // contains a defer statement
+	funcNilCheckDisabled    // disable nil checks when compiling this function
+	funcInlinabilityChecked // inliner has already determined whether the function is inlinable
+	funcExportInline        // include inline body in export data
+	funcInstrumentBody      // add race/msan instrumentation during SSA construction
 )
 
-func (f *Func) Dupok() bool                    { return f.flags&funcDupok != 0 }
-func (f *Func) Wrapper() bool                  { return f.flags&funcWrapper != 0 }
-func (f *Func) Needctxt() bool                 { return f.flags&funcNeedctxt != 0 }
-func (f *Func) ReflectMethod() bool            { return f.flags&funcReflectMethod != 0 }
-func (f *Func) IsHiddenClosure() bool          { return f.flags&funcIsHiddenClosure != 0 }
-func (f *Func) HasDefer() bool                 { return f.flags&funcHasDefer != 0 }
-func (f *Func) NilCheckDisabled() bool         { return f.flags&funcNilCheckDisabled != 0 }
-func (f *Func) InlinabilityChecked() bool      { return f.flags&funcInlinabilityChecked != 0 }
-func (f *Func) ExportInline() bool             { return f.flags&funcExportInline != 0 }
-func (f *Func) InstrumentBody() bool           { return f.flags&funcInstrumentBody != 0 }
-func (f *Func) OpenCodedDeferDisallowed() bool { return f.flags&funcOpenCodedDeferDisallowed != 0 }
+func (f *Func) Dupok() bool               { return f.flags&funcDupok != 0 }
+func (f *Func) Wrapper() bool             { return f.flags&funcWrapper != 0 }
+func (f *Func) Needctxt() bool            { return f.flags&funcNeedctxt != 0 }
+func (f *Func) ReflectMethod() bool       { return f.flags&funcReflectMethod != 0 }
+func (f *Func) IsHiddenClosure() bool     { return f.flags&funcIsHiddenClosure != 0 }
+func (f *Func) HasDefer() bool            { return f.flags&funcHasDefer != 0 }
+func (f *Func) NilCheckDisabled() bool    { return f.flags&funcNilCheckDisabled != 0 }
+func (f *Func) InlinabilityChecked() bool { return f.flags&funcInlinabilityChecked != 0 }
+func (f *Func) ExportInline() bool        { return f.flags&funcExportInline != 0 }
+func (f *Func) InstrumentBody() bool      { return f.flags&funcInstrumentBody != 0 }
 
-func (f *Func) SetDupok(b bool)                    { f.flags.set(funcDupok, b) }
-func (f *Func) SetWrapper(b bool)                  { f.flags.set(funcWrapper, b) }
-func (f *Func) SetNeedctxt(b bool)                 { f.flags.set(funcNeedctxt, b) }
-func (f *Func) SetReflectMethod(b bool)            { f.flags.set(funcReflectMethod, b) }
-func (f *Func) SetIsHiddenClosure(b bool)          { f.flags.set(funcIsHiddenClosure, b) }
-func (f *Func) SetHasDefer(b bool)                 { f.flags.set(funcHasDefer, b) }
-func (f *Func) SetNilCheckDisabled(b bool)         { f.flags.set(funcNilCheckDisabled, b) }
-func (f *Func) SetInlinabilityChecked(b bool)      { f.flags.set(funcInlinabilityChecked, b) }
-func (f *Func) SetExportInline(b bool)             { f.flags.set(funcExportInline, b) }
-func (f *Func) SetInstrumentBody(b bool)           { f.flags.set(funcInstrumentBody, b) }
-func (f *Func) SetOpenCodedDeferDisallowed(b bool) { f.flags.set(funcOpenCodedDeferDisallowed, b) }
+func (f *Func) SetDupok(b bool)               { f.flags.set(funcDupok, b) }
+func (f *Func) SetWrapper(b bool)             { f.flags.set(funcWrapper, b) }
+func (f *Func) SetNeedctxt(b bool)            { f.flags.set(funcNeedctxt, b) }
+func (f *Func) SetReflectMethod(b bool)       { f.flags.set(funcReflectMethod, b) }
+func (f *Func) SetIsHiddenClosure(b bool)     { f.flags.set(funcIsHiddenClosure, b) }
+func (f *Func) SetHasDefer(b bool)            { f.flags.set(funcHasDefer, b) }
+func (f *Func) SetNilCheckDisabled(b bool)    { f.flags.set(funcNilCheckDisabled, b) }
+func (f *Func) SetInlinabilityChecked(b bool) { f.flags.set(funcInlinabilityChecked, b) }
+func (f *Func) SetExportInline(b bool)        { f.flags.set(funcExportInline, b) }
+func (f *Func) SetInstrumentBody(b bool)      { f.flags.set(funcInstrumentBody, b) }
 
 func (f *Func) setWBPos(pos src.XPos) {
 	if Debug_wb != 0 {

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

@@ -213,6 +213,7 @@ func walkstmt(n *Node) *Node {
 		yyerror("case statement out of place")
 
 	case ODEFER:
+		Curfn.Func.SetHasDefer(true)
 		fallthrough
 	case OGO:
 		switch n.Left.Op {

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

@@ -170,11 +170,6 @@ func elimDeadAutosGeneric(f *Func) {
 			return
 		case OpVarLive:
 			// Don't delete the auto if it needs to be kept alive.
-
-			// We depend on this check to keep the autotmp stack slots
-			// for open-coded defers from being removed (since they
-			// may not be used by the inline code, but will be used by
-			// panic processing).
 			n, ok := v.Aux.(GCNode)
 			if !ok || n.StorageClass() != ClassAuto {
 				return

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

@@ -32,16 +32,8 @@ type Func struct {
 	Type   *types.Type // type signature of the function.
 	Blocks []*Block    // unordered set of all basic blocks (note: not indexable by ID)
 	Entry  *Block      // the entry basic block
-
-	// If we are using open-coded defers, this is the first call to a deferred
-	// function in the final defer exit sequence that we generated. This call
-	// should be after all defer statements, and will have all args, etc. of
-	// all defer calls as live. The liveness info of this call will be used
-	// for the deferreturn/ret segment generated for functions with open-coded
-	// defers.
-	LastDeferExit *Value
-	bid           idAlloc // block ID allocator
-	vid           idAlloc // value ID allocator
+	bid    idAlloc     // block ID allocator
+	vid    idAlloc     // value ID allocator
 
 	// Given an environment variable used for debug hash match,
 	// what file (if any) receives the yes/no logging?

src/cmd/internal/obj/link.go

@@ -405,11 +405,10 @@ type FuncInfo struct {
 	dwarfAbsFnSym      *LSym
 	dwarfDebugLinesSym *LSym
 
-	GCArgs             *LSym
-	GCLocals           *LSym
-	GCRegs             *LSym
-	StackObjects       *LSym
-	OpenCodedDeferInfo *LSym
+	GCArgs       *LSym
+	GCLocals     *LSym
+	GCRegs       *LSym
+	StackObjects *LSym
 }
 
 type InlMark struct {

src/cmd/internal/objabi/funcdata.go

@@ -15,12 +15,11 @@ const (
 	PCDATA_StackMapIndex = 1
 	PCDATA_InlTreeIndex  = 2
 
-	FUNCDATA_ArgsPointerMaps    = 0
-	FUNCDATA_LocalsPointerMaps  = 1
-	FUNCDATA_RegPointerMaps     = 2
-	FUNCDATA_StackObjects       = 3
-	FUNCDATA_InlTree            = 4
-	FUNCDATA_OpenCodedDeferInfo = 5
+	FUNCDATA_ArgsPointerMaps   = 0
+	FUNCDATA_LocalsPointerMaps = 1
+	FUNCDATA_RegPointerMaps    = 2
+	FUNCDATA_StackObjects      = 3
+	FUNCDATA_InlTree           = 4
 
 	// ArgsSizeUnknown is set in Func.argsize to mark all functions
 	// whose argument size is unknown (C vararg functions, and

src/cmd/internal/objabi/funcid.go

@@ -85,12 +85,6 @@ func GetFuncID(name, file string) FuncID {
 		return FuncID_panicwrap
 	case "runtime.handleAsyncEvent":
 		return FuncID_handleAsyncEvent
-	case "runtime.deferreturn":
-		// Don't show in the call stack (used when invoking defer functions)
-		return FuncID_wrapper
-	case "runtime.runOpenDeferFrame":
-		// Don't show in the call stack (used when invoking defer functions)
-		return FuncID_wrapper
 	}
 	if file == "<autogenerated>" {
 		return FuncID_wrapper

src/cmd/internal/objabi/stack.go

@@ -18,7 +18,7 @@ const (
 )
 
 // Initialize StackGuard and StackLimit according to target system.
-var StackGuard = 896*stackGuardMultiplier() + StackSystem
+var StackGuard = 880*stackGuardMultiplier() + StackSystem
 var StackLimit = StackGuard - StackSystem - StackSmall
 
 // stackGuardMultiplier returns a multiplier to apply to the default

src/cmd/link/internal/ld/pcln.go

@@ -11,7 +11,6 @@ import (
 	"cmd/internal/sys"
 	"cmd/link/internal/sym"
 	"encoding/binary"
-	"fmt"
 	"log"
 	"os"
 	"path/filepath"
@@ -256,23 +255,13 @@ func (ctxt *Link) pclntab() {
 			}
 			if r.Type.IsDirectJump() && r.Sym != nil && r.Sym.Name == "runtime.deferreturn" {
 				if ctxt.Arch.Family == sys.Wasm {
-					deferreturn = lastWasmAddr - 1
+					deferreturn = lastWasmAddr
 				} else {
 					// Note: the relocation target is in the call instruction, but
 					// is not necessarily the whole instruction (for instance, on
 					// x86 the relocation applies to bytes [1:5] of the 5 byte call
 					// instruction).
 					deferreturn = uint32(r.Off)
-					switch ctxt.Arch.Family {
-					case sys.AMD64, sys.I386, sys.MIPS, sys.MIPS64, sys.RISCV64:
-						deferreturn--
-					case sys.PPC64, sys.ARM, sys.ARM64:
-						// no change
-					case sys.S390X:
-						deferreturn -= 2
-					default:
-						panic(fmt.Sprint("Unhandled architecture:", ctxt.Arch.Family))
-					}
 				}
 				break // only need one
 			}

src/cmd/link/internal/ld/symtab.go

@@ -498,8 +498,7 @@ func (ctxt *Link) symtab() {
 		case strings.HasPrefix(s.Name, "gcargs."),
 			strings.HasPrefix(s.Name, "gclocals."),
 			strings.HasPrefix(s.Name, "gclocals·"),
-			strings.HasPrefix(s.Name, "inltree."),
-			strings.HasSuffix(s.Name, ".opendefer"):
+			strings.HasPrefix(s.Name, "inltree."):
 			s.Type = sym.SGOFUNC
 			s.Attr |= sym.AttrNotInSymbolTable
 			s.Outer = symgofunc

src/runtime/callers_test.go

@@ -5,7 +5,6 @@
 package runtime_test
 
 import (
-	"internal/race"
 	"reflect"
 	"runtime"
 	"strings"
@@ -13,19 +12,19 @@ import (
 )
 
 func f1(pan bool) []uintptr {
-	return f2(pan) // line 16
+	return f2(pan) // line 15
 }
 
 func f2(pan bool) []uintptr {
-	return f3(pan) // line 20
+	return f3(pan) // line 19
 }
 
 func f3(pan bool) []uintptr {
 	if pan {
-		panic("f3") // line 25
+		panic("f3") // line 24
 	}
 	ret := make([]uintptr, 20)
-	return ret[:runtime.Callers(0, ret)] // line 28
+	return ret[:runtime.Callers(0, ret)] // line 27
 }
 
 func testCallers(t *testing.T, pcs []uintptr, pan bool) {
@@ -49,16 +48,16 @@ func testCallers(t *testing.T, pcs []uintptr, pan bool) {
 
 	var f3Line int
 	if pan {
-		f3Line = 25
+		f3Line = 24
 	} else {
-		f3Line = 28
+		f3Line = 27
 	}
 	want := []struct {
 		name string
 		line int
 	}{
-		{"f1", 16},
-		{"f2", 20},
+		{"f1", 15},
+		{"f2", 19},
 		{"f3", f3Line},
 	}
 	for _, w := range want {
@@ -189,36 +188,3 @@ func TestCallersDivZeroPanic(t *testing.T) {
 		t.Fatal("did not see divide-by-sizer panic")
 	}
 }
-
-// This test will have a slightly different callstack if non-open-coded defers are
-// called (e.g. if race checks enabled), because of a difference in the way the
-// defer function is invoked.
-func TestCallersDeferNilFuncPanic(t *testing.T) {
-	if race.Enabled {
-		t.Skip("skipping TestCallersDeferNilFuncPanic under race detector")
-	}
-	// Make sure we don't have any extra frames on the stack (due to
-	// open-coded defer processing)
-	state := 1
-	want := []string{"runtime.Callers", "runtime_test.TestCallersDeferNilFuncPanic.func1",
-		"runtime.gopanic", "runtime.panicmem", "runtime.sigpanic",
-		"runtime_test.TestCallersDeferNilFuncPanic"}
-
-	defer func() {
-		if r := recover(); r == nil {
-			t.Fatal("did not panic")
-		}
-		pcs := make([]uintptr, 20)
-		pcs = pcs[:runtime.Callers(0, pcs)]
-		testCallersEqual(t, pcs, want)
-		if state == 1 {
-			t.Fatal("nil defer func panicked at defer time rather than function exit time")
-		}
-
-	}()
-	var f func()
-	defer f()
-	// Use the value of 'state' to make sure nil defer func f causes panic at
-	// function exit, rather than at the defer statement.
-	state = 2
-}

src/runtime/defer_test.go

@@ -15,11 +15,11 @@ import (
 // unconditional panic (hence no return from the function)
 func TestUnconditionalPanic(t *testing.T) {
 	defer func() {
-		if recover() != "testUnconditional" {
+		if recover() == nil {
 			t.Fatal("expected unconditional panic")
 		}
 	}()
-	panic("testUnconditional")
+	panic("panic should be recovered")
 }
 
 var glob int = 3
@@ -30,7 +30,7 @@ func TestOpenAndNonOpenDefers(t *testing.T) {
 	for {
 		// Non-open defer because in a loop
 		defer func(n int) {
-			if recover() != "testNonOpenDefer" {
+			if recover() == nil {
 				t.Fatal("expected testNonOpen panic")
 			}
 		}(3)
@@ -45,7 +45,7 @@ func TestOpenAndNonOpenDefers(t *testing.T) {
 //go:noinline
 func testOpen(t *testing.T, arg int) {
 	defer func(n int) {
-		if recover() != "testOpenDefer" {
+		if recover() == nil {
 			t.Fatal("expected testOpen panic")
 		}
 	}(4)
@@ -61,7 +61,7 @@ func TestNonOpenAndOpenDefers(t *testing.T) {
 	for {
 		// Non-open defer because in a loop
 		defer func(n int) {
-			if recover() != "testNonOpenDefer" {
+			if recover() == nil {
 				t.Fatal("expected testNonOpen panic")
 			}
 		}(3)
@@ -80,7 +80,7 @@ func TestConditionalDefers(t *testing.T) {
 	list = make([]int, 0, 10)
 
 	defer func() {
-		if recover() != "testConditional" {
+		if recover() == nil {
 			t.Fatal("expected panic")
 		}
 		want := []int{4, 2, 1}
@@ -106,7 +106,7 @@ func testConditionalDefers(n int) {
 			defer doappend(4)
 		}
 	}
-	panic("testConditional")
+	panic("test")
 }
 
 // Test that there is no compile-time or run-time error if an open-coded defer
@@ -174,52 +174,3 @@ func TestRecoverMatching(t *testing.T) {
 	}()
 	panic("panic1")
 }
-
-type nonSSAable [128]byte
-
-type bigStruct struct {
-	x, y, z, w, p, q int64
-}
-
-func mknonSSAable() nonSSAable {
-	globint1++
-	return nonSSAable{0, 0, 0, 0, 5}
-}
-
-var globint1, globint2 int
-
-//go:noinline
-func sideeffect(n int64) int64 {
-	globint2++
-	return n
-}
-
-// Test that nonSSAable arguments to defer are handled correctly and only evaluated once.
-func TestNonSSAableArgs(t *testing.T) {
-	globint1 = 0
-	globint2 = 0
-	var save1 byte
-	var save2 int64
-
-	defer func() {
-		if globint1 != 1 {
-			t.Fatal(fmt.Sprintf("globint1:  wanted: 1, got %v", globint1))
-		}
-		if save1 != 5 {
-			t.Fatal(fmt.Sprintf("save1:  wanted: 5, got %v", save1))
-		}
-		if globint2 != 1 {
-			t.Fatal(fmt.Sprintf("globint2:  wanted: 1, got %v", globint2))
-		}
-		if save2 != 2 {
-			t.Fatal(fmt.Sprintf("save2:  wanted: 2, got %v", save2))
-		}
-	}()
-
-	defer func(n nonSSAable) {
-		save1 = n[4]
-	}(mknonSSAable())
-	defer func(b bigStruct) {
-		save2 = b.y
-	}(bigStruct{1, 2, 3, 4, 5, sideeffect(6)})
-}

src/runtime/funcdata.h

@@ -17,7 +17,6 @@
 #define FUNCDATA_RegPointerMaps 2
 #define FUNCDATA_StackObjects 3
 #define FUNCDATA_InlTree 4
-#define FUNCDATA_OpenCodedDeferInfo 5 /* info for func with open-coded defers */
 
 // Pseudo-assembly statements.
 

src/runtime/panic.go

@@ -10,19 +10,6 @@ import (
 	"unsafe"
 )
 
-// We have two different ways of doing defers. The older way involves creating a
-// defer record at the time that a defer statement is executing and adding it to a
-// defer chain. This chain is inspected by the deferreturn call at all function
-// exits in order to run the appropriate defer calls. A cheaper way (which we call
-// open-coded defers) is used for functions in which no defer statements occur in
-// loops. In that case, we simply store the defer function/arg information into
-// specific stack slots at the point of each defer statement, as well as setting a
-// bit in a bitmask. At each function exit, we add inline code to directly make
-// the appropriate defer calls based on the bitmask and fn/arg information stored
-// on the stack. During panic/Goexit processing, the appropriate defer calls are
-// made using extra funcdata info that indicates the exact stack slots that
-// contain the bitmask and defer fn/args.
-
 // Check to make sure we can really generate a panic. If the panic
 // was generated from the runtime, or from inside malloc, then convert
 // to a throw of msg.
@@ -276,24 +263,19 @@ func deferprocStack(d *_defer) {
 	// are initialized here.
 	d.started = false
 	d.heap = false
-	d.openDefer = false
 	d.sp = getcallersp()
 	d.pc = getcallerpc()
-	d.framepc = 0
-	d.varp = 0
 	// The lines below implement:
 	//   d.panic = nil
-	//   d.fp = nil
 	//   d.link = gp._defer
 	//   gp._defer = d
-	// But without write barriers. The first three are writes to
+	// But without write barriers. The first two are writes to
 	// the stack so they don't need a write barrier, and furthermore
 	// are to uninitialized memory, so they must not use a write barrier.
-	// The fourth write does not require a write barrier because we
+	// The third write does not require a write barrier because we
 	// explicitly mark all the defer structures, so we don't need to
 	// keep track of pointers to them with a write barrier.
 	*(*uintptr)(unsafe.Pointer(&d._panic)) = 0
-	*(*uintptr)(unsafe.Pointer(&d.fd)) = 0
 	*(*uintptr)(unsafe.Pointer(&d.link)) = uintptr(unsafe.Pointer(gp._defer))
 	*(*uintptr)(unsafe.Pointer(&gp._defer)) = uintptr(unsafe.Pointer(d))
 
@@ -481,12 +463,8 @@ func freedefer(d *_defer) {
 	// started causing a nosplit stack overflow via typedmemmove.
 	d.siz = 0
 	d.started = false
-	d.openDefer = false
 	d.sp = 0
 	d.pc = 0
-	d.framepc = 0
-	d.varp = 0
-	d.fd = nil
 	// d._panic and d.fn must be nil already.
 	// If not, we would have called freedeferpanic or freedeferfn above,
 	// both of which throw.
@@ -515,11 +493,9 @@ func freedeferfn() {
 // to have been called by the caller of deferreturn at the point
 // just before deferreturn was called. The effect is that deferreturn
 // is called again and again until there are no more deferred functions.
-//
-// Declared as nosplit, because the function should not be preempted once we start
-// modifying the caller's frame in order to reuse the frame to call the deferred
-// function.
-//
+// Cannot split the stack because we reuse the caller's frame to
+// call the deferred function.
+
 // The single argument isn't actually used - it just has its address
 // taken so it can be matched against pending defers.
 //go:nosplit
@@ -533,15 +509,6 @@ func deferreturn(arg0 uintptr) {
 	if d.sp != sp {
 		return
 	}
-	if d.openDefer {
-		done := runOpenDeferFrame(gp, d)
-		if !done {
-			throw("unfinished open-coded defers in deferreturn")
-		}
-		gp._defer = d.link
-		freedefer(d)
-		return
-	}
 
 	// Moving arguments around.
 	//
@@ -577,8 +544,6 @@ func Goexit() {
 	// This code is similar to gopanic, see that implementation
 	// for detailed comments.
 	gp := getg()
-	addOneOpenDeferFrame(gp, getcallerpc(), unsafe.Pointer(getcallersp()))
-
 	for {
 		d := gp._defer
 		if d == nil {
@@ -589,26 +554,13 @@ func Goexit() {
 				d._panic.aborted = true
 				d._panic = nil
 			}
-			if !d.openDefer {
-				d.fn = nil
-				gp._defer = d.link
-				freedefer(d)
-				continue
-			}
+			d.fn = nil
+			gp._defer = d.link
+			freedefer(d)
+			continue
 		}
 		d.started = true
-		if d.openDefer {
-			done := runOpenDeferFrame(gp, d)
-			if !done {
-				// We should always run all defers in the frame,
-				// since there is no panic associated with this
-				// defer that can be recovered.
-				throw("unfinished open-coded defers in Goexit")
-			}
-			addOneOpenDeferFrame(gp, 0, nil)
-		} else {
-			reflectcall(nil, unsafe.Pointer(d.fn), deferArgs(d), uint32(d.siz), uint32(d.siz))
-		}
+		reflectcall(nil, unsafe.Pointer(d.fn), deferArgs(d), uint32(d.siz), uint32(d.siz))
 		if gp._defer != d {
 			throw("bad defer entry in Goexit")
 		}
@@ -655,182 +607,6 @@ func printpanics(p *_panic) {
 	print("\n")
 }
 
-// addOneOpenDeferFrame scans the stack for the first frame (if any) with
-// open-coded defers and if it finds one, adds a single record to the defer chain
-// for that frame. If sp is non-nil, it starts the stack scan from the frame
-// specified by sp. If sp is nil, it uses the sp from the current defer record
-// (which has just been finished). Hence, it continues the stack scan from the
-// frame of the defer that just finished. It skips any frame that already has an
-// open-coded _defer record, which would have been been created from a previous
-// (unrecovered) panic.
-//
-// Note: All entries of the defer chain (including this new open-coded entry) have
-// their pointers (including sp) adjusted properly if the stack moves while
-// running deferred functions. Also, it is safe to pass in the sp arg (which is
-// the direct result of calling getcallersp()), because all pointer variables
-// (including arguments) are adjusted as needed during stack copies.
-func addOneOpenDeferFrame(gp *g, pc uintptr, sp unsafe.Pointer) {
-	var prevDefer *_defer
-	if sp == nil {
-		prevDefer = gp._defer
-		pc = prevDefer.framepc
-		sp = unsafe.Pointer(prevDefer.sp)
-	}
-	systemstack(func() {
-		gentraceback(pc, uintptr(sp), 0, gp, 0, nil, 0x7fffffff,
-			func(frame *stkframe, unused unsafe.Pointer) bool {
-				if prevDefer != nil && prevDefer.sp == frame.sp {
-					// Skip the frame for the previous defer that
-					// we just finished (and was used to set
-					// where we restarted the stack scan)
-					return true
-				}
-				f := frame.fn
-				fd := funcdata(f, _FUNCDATA_OpenCodedDeferInfo)
-				if fd == nil {
-					return true
-				}
-				// Insert the open defer record in the
-				// chain, in order sorted by sp.
-				d := gp._defer
-				var prev *_defer
-				for d != nil {
-					dsp := d.sp
-					if frame.sp < dsp {
-						break
-					}
-					if frame.sp == dsp {
-						if !d.openDefer {
-							throw("duplicated defer entry")
-						}
-						return true
-					}
-					prev = d
-					d = d.link
-				}
-				if frame.fn.deferreturn == 0 {
-					throw("missing deferreturn")
-				}
-
-				maxargsize, _ := readvarintUnsafe(fd)
-				d1 := newdefer(int32(maxargsize))
-				d1.openDefer = true
-				d1._panic = nil
-				// These are the pc/sp to set after we've
-				// run a defer in this frame that did a
-				// recover. We return to a special
-				// deferreturn that runs any remaining
-				// defers and then returns from the
-				// function.
-				d1.pc = frame.fn.entry + uintptr(frame.fn.deferreturn)
-				d1.varp = frame.varp
-				d1.fd = fd
-				// Save the SP/PC associated with current frame,
-				// so we can continue stack trace later if needed.
-				d1.framepc = frame.pc
-				d1.sp = frame.sp
-				d1.link = d
-				if prev == nil {
-					gp._defer = d1
-				} else {
-					prev.link = d1
-				}
-				// Stop stack scanning after adding one open defer record
-				return false
-			},
-			nil, 0)
-	})
-}
-
-// readvarintUnsafe reads the uint32 in varint format starting at fd, and returns the
-// uint32 and a pointer to the byte following the varint.
-//
-// There is a similar function runtime.readvarint, which takes a slice of bytes,
-// rather than an unsafe pointer. These functions are duplicated, because one of
-// the two use cases for the functions would get slower if the functions were
-// combined.
-func readvarintUnsafe(fd unsafe.Pointer) (uint32, unsafe.Pointer) {
-	var r uint32
-	var shift int
-	for {
-		b := *(*uint8)((unsafe.Pointer(fd)))
-		fd = add(fd, unsafe.Sizeof(b))
-		if b < 128 {
-			return r + uint32(b)<<shift, fd
-		}
-		r += ((uint32(b) &^ 128) << shift)
-		shift += 7
-		if shift > 28 {
-			panic("Bad varint")
-		}
-	}
-}
-
-// runOpenDeferFrame runs the active open-coded defers in the frame specified by
-// d. It normally processes all active defers in the frame, but stops immediately
-// if a defer does a successful recover. It returns true if there are no
-// remaining defers to run in the frame.
-func runOpenDeferFrame(gp *g, d *_defer) bool {
-	done := true
-	fd := d.fd
-
-	// Skip the maxargsize
-	_, fd = readvarintUnsafe(fd)
-	deferBitsOffset, fd := readvarintUnsafe(fd)
-	nDefers, fd := readvarintUnsafe(fd)
-	deferBits := *(*uint8)(unsafe.Pointer(d.varp - uintptr(deferBitsOffset)))
-
-	for i := int(nDefers) - 1; i >= 0; i-- {
-		// read the funcdata info for this defer
-		var argWidth, closureOffset, hasRcvrOffset, rcvrOffset, nArgs uint32
-		argWidth, fd = readvarintUnsafe(fd)
-		closureOffset, fd = readvarintUnsafe(fd)
-		hasRcvrOffset, fd = readvarintUnsafe(fd)
-		if hasRcvrOffset > 0 {
-			rcvrOffset, fd = readvarintUnsafe(fd)
-		}
-		nArgs, fd = readvarintUnsafe(fd)
-		if deferBits&(1<<i) == 0 {
-			for j := uint32(0); j < nArgs; j++ {
-				_, fd = readvarintUnsafe(fd)
-				_, fd = readvarintUnsafe(fd)
-				_, fd = readvarintUnsafe(fd)
-			}
-			continue
-		}
-		closure := *(**funcval)(unsafe.Pointer(d.varp - uintptr(closureOffset)))
-		d.fn = closure
-		deferArgs := deferArgs(d)
-		if hasRcvrOffset > 0 {
-			*(*unsafe.Pointer)(deferArgs) = *(*unsafe.Pointer)((unsafe.Pointer)((d.varp - uintptr(rcvrOffset))))
-		}
-		for j := uint32(0); j < nArgs; j++ {
-			var argOffset, argLen, argCallOffset uint32
-			argOffset, fd = readvarintUnsafe(fd)
-			argLen, fd = readvarintUnsafe(fd)
-			argCallOffset, fd = readvarintUnsafe(fd)
-			memmove(unsafe.Pointer(uintptr(deferArgs)+uintptr(argCallOffset)),
-				unsafe.Pointer(d.varp-uintptr(argOffset)),
-				uintptr(argLen))
-		}
-		deferBits = deferBits &^ (1 << i)
-		*(*uint8)(unsafe.Pointer(d.varp - uintptr(deferBitsOffset))) = deferBits
-		if d._panic != nil {
-			d._panic.argp = unsafe.Pointer(getargp(0))
-		}
-		reflectcall(nil, unsafe.Pointer(closure), deferArgs, argWidth, argWidth)
-		d.fn = nil
-		// These args are just a copy, so can be cleared immediately
-		memclrNoHeapPointers(deferArgs, uintptr(argWidth))
-		if d._panic != nil && d._panic.recovered {
-			done = deferBits == 0
-			break
-		}
-	}
-
-	return done
-}
-
 // The implementation of the predeclared function panic.
 func gopanic(e interface{}) {
 	gp := getg()
@@ -870,10 +646,6 @@ func gopanic(e interface{}) {
 
 	atomic.Xadd(&runningPanicDefers, 1)
 
-	// By calculating getcallerpc/getcallersp here, we avoid scanning the
-	// gopanic frame (stack scanning is slow...)
-	addOneOpenDeferFrame(gp, getcallerpc(), unsafe.Pointer(getcallersp()))
-
 	for {
 		d := gp._defer
 		if d == nil {
@@ -887,16 +659,10 @@ func gopanic(e interface{}) {
 				d._panic.aborted = true
 			}
 			d._panic = nil
-			if !d.openDefer {
-				// For open-coded defers, we need to process the
-				// defer again, in case there are any other defers
-				// to call in the frame (not including the defer
-				// call that caused the panic).
-				d.fn = nil
-				gp._defer = d.link
-				freedefer(d)
-				continue
-			}
+			d.fn = nil
+			gp._defer = d.link
+			freedefer(d)
+			continue
 		}
 
 		// Mark defer as started, but keep on list, so that traceback
@@ -909,16 +675,8 @@ func gopanic(e interface{}) {
 		// will find d in the list and will mark d._panic (this panic) aborted.
 		d._panic = (*_panic)(noescape(unsafe.Pointer(&p)))
 
-		done := true
-		if d.openDefer {
-			done = runOpenDeferFrame(gp, d)
-			if done && !d._panic.recovered {
-				addOneOpenDeferFrame(gp, 0, nil)
-			}
-		} else {
-			p.argp = unsafe.Pointer(getargp(0))
-			reflectcall(nil, unsafe.Pointer(d.fn), deferArgs(d), uint32(d.siz), uint32(d.siz))
-		}
+		p.argp = unsafe.Pointer(getargp(0))
+		reflectcall(nil, unsafe.Pointer(d.fn), deferArgs(d), uint32(d.siz), uint32(d.siz))
 		p.argp = nil
 
 		// reflectcall did not panic. Remove d.
@@ -926,52 +684,18 @@ func gopanic(e interface{}) {
 			throw("bad defer entry in panic")
 		}
 		d._panic = nil
+		d.fn = nil
+		gp._defer = d.link
 
 		// trigger shrinkage to test stack copy. See stack_test.go:TestStackPanic
 		//GC()
 
 		pc := d.pc
 		sp := unsafe.Pointer(d.sp) // must be pointer so it gets adjusted during stack copy
-		if done {
-			d.fn = nil
-			gp._defer = d.link
-			freedefer(d)
-		}
+		freedefer(d)
 		if p.recovered {
 			atomic.Xadd(&runningPanicDefers, -1)
 
-			if done {
-				// Remove any remaining non-started, open-coded defer
-				// entry after a recover (there's at most one, if we just
-				// ran a non-open-coded defer), since the entry will
-				// become out-dated and the defer will be executed
-				// normally.
-				d := gp._defer
-				var prev *_defer
-				for d != nil {
-					if d.openDefer {
-						if d.started {
-							// This defer is started but we
-							// are in the middle of a
-							// defer-panic-recover inside of
-							// it, so don't remove it or any
-							// further defer entries
-							break
-						}
-						if prev == nil {
-							gp._defer = d.link
-						} else {
-							prev.link = d.link
-						}
-						freedefer(d)
-						break
-					} else {
-						prev = d
-						d = d.link
-					}
-				}
-			}
-
 			gp._panic = p.link
 			// Aborted panics are marked but remain on the g.panic list.
 			// Remove them from the list.
@@ -1079,7 +803,7 @@ func recovery(gp *g) {
 	}
 
 	// Make the deferproc for this d return again,
-	// this time returning 1. The calling function will
+	// this time returning 1.  The calling function will
 	// jump to the standard return epilogue.
 	gp.sched.sp = sp
 	gp.sched.pc = pc

src/runtime/runtime2.go

@@ -701,7 +701,7 @@ type _func struct {
 	nameoff int32   // function name
 
 	args        int32  // in/out args size
-	deferreturn uint32 // offset of start of a deferreturn call instruction from entry, if any.
+	deferreturn uint32 // offset of a deferreturn block from entry, if any.
 
 	pcsp      int32
 	pcfile    int32
@@ -774,7 +774,7 @@ func extendRandom(r []byte, n int) {
 }
 
 // A _defer holds an entry on the list of deferred calls.
-// If you add a field here, add code to clear it in freedefer and deferProcStack
+// If you add a field here, add code to clear it in freedefer.
 // This struct must match the code in cmd/compile/internal/gc/reflect.go:deferstruct
 // and cmd/compile/internal/gc/ssa.go:(*state).call.
 // Some defers will be allocated on the stack and some on the heap.
@@ -785,27 +785,11 @@ type _defer struct {
 	siz     int32 // includes both arguments and results
 	started bool
 	heap    bool
-	// openDefer indicates that this _defer is for a frame with open-coded
-	// defers. We have only one defer record for the entire frame (which may
-	// currently have 0, 1, or more defers active).
-	openDefer bool
-	sp        uintptr // sp at time of defer
-	pc        uintptr // pc at time of defer
-	fn        *funcval
-	_panic    *_panic // panic that is running defer
-	link      *_defer
-
-	// If openDefer is true, the fields below record values about the stack
-	// frame and associated function that has the open-coded defer(s). sp
-	// above will be the sp for the frame, and pc will be address of the
-	// deferreturn call in the function.
-	fd   unsafe.Pointer // funcdata for the function associated with the frame
-	varp uintptr        // value of varp for the stack frame
-	// framepc is the current pc associated with the stack frame. Together,
-	// with sp above (which is the sp associated with the stack frame),
-	// framepc/sp can be used as pc/sp pair to continue a stack trace via
-	// gentraceback().
-	framepc uintptr
+	sp      uintptr // sp at time of defer
+	pc      uintptr
+	fn      *funcval
+	_panic  *_panic // panic that is running defer
+	link    *_defer
 }
 
 // A _panic holds information about an active panic.

src/runtime/runtime_test.go

@@ -89,7 +89,7 @@ func BenchmarkDefer(b *testing.B) {
 }
 
 func defer1() {
-	func(x, y, z int) {
+	defer func(x, y, z int) {
 		if recover() != nil || x != 1 || y != 2 || z != 3 {
 			panic("bad recover")
 		}

src/runtime/stack.go

@@ -91,7 +91,7 @@ const (
 
 	// The stack guard is a pointer this many bytes above the
 	// bottom of the stack.
-	_StackGuard = 896*sys.StackGuardMultiplier + _StackSystem
+	_StackGuard = 880*sys.StackGuardMultiplier + _StackSystem
 
 	// After a stack split check the SP is allowed to be this
 	// many bytes below the stack guard. This saves an instruction
@@ -736,8 +736,6 @@ func adjustdefers(gp *g, adjinfo *adjustinfo) {
 		adjustpointer(adjinfo, unsafe.Pointer(&d.sp))
 		adjustpointer(adjinfo, unsafe.Pointer(&d._panic))
 		adjustpointer(adjinfo, unsafe.Pointer(&d.link))
-		adjustpointer(adjinfo, unsafe.Pointer(&d.varp))
-		adjustpointer(adjinfo, unsafe.Pointer(&d.fd))
 	}
 
 	// Adjust defer argument blocks the same way we adjust active stack frames.

src/runtime/symtab.go

@@ -216,12 +216,11 @@ const (
 	_PCDATA_StackMapIndex = 1
 	_PCDATA_InlTreeIndex  = 2
 
-	_FUNCDATA_ArgsPointerMaps    = 0
-	_FUNCDATA_LocalsPointerMaps  = 1
-	_FUNCDATA_RegPointerMaps     = 2
-	_FUNCDATA_StackObjects       = 3
-	_FUNCDATA_InlTree            = 4
-	_FUNCDATA_OpenCodedDeferInfo = 5
+	_FUNCDATA_ArgsPointerMaps   = 0
+	_FUNCDATA_LocalsPointerMaps = 1
+	_FUNCDATA_RegPointerMaps    = 2
+	_FUNCDATA_StackObjects      = 3
+	_FUNCDATA_InlTree           = 4
 
 	_ArgsSizeUnknown = -0x80000000
 )

test/defererrcheck.go

@@ -1,86 +0,0 @@
-// errorcheck -0 -l -d=defer
-
-// Copyright 2019 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// check that open-coded defers are used in expected situations
-
-package main
-
-import "fmt"
-
-var glob = 3
-
-func f1() {
-
-	for i := 0; i < 10; i++ {
-		fmt.Println("loop")
-	}
-	defer func() { // ERROR "open-coded defer in function f1"
-		fmt.Println("defer")
-	}()
-}
-
-func f2() {
-	for {
-		defer func() { // ERROR "heap-allocated defer in function f2"
-			fmt.Println("defer1")
-		}()
-		if glob > 2 {
-			break
-		}
-	}
-	defer func() { // ERROR "stack-allocated defer in function f2"
-		fmt.Println("defer2")
-	}()
-}
-
-func f3() {
-	defer func() { // ERROR "stack-allocated defer in function f3"
-		fmt.Println("defer2")
-	}()
-	for {
-		defer func() { // ERROR "heap-allocated defer in function f3"
-			fmt.Println("defer1")
-		}()
-		if glob > 2 {
-			break
-		}
-	}
-}
-
-func f4() {
-	defer func() { // ERROR "open-coded defer in function f4"
-		fmt.Println("defer")
-	}()
-label:
-	fmt.Println("goto loop")
-	if glob > 2 {
-		goto label
-	}
-}
-
-func f5() {
-label:
-	fmt.Println("goto loop")
-	defer func() { // ERROR "heap-allocated defer in function f5"
-		fmt.Println("defer")
-	}()
-	if glob > 2 {
-		goto label
-	}
-}
-
-func f6() {
-label:
-	fmt.Println("goto loop")
-	if glob > 2 {
-		goto label
-	}
-	// The current analysis doesn't end a backward goto loop, so this defer is
-	// considered to be inside a loop
-	defer func() { // ERROR "heap-allocated defer in function f6"
-		fmt.Println("defer")
-	}()
-}

test/live.go

@@ -367,19 +367,16 @@ func f24() {
 	m2[[2]string{"x", "y"}] = nil
 }
 
-// Non-open-coded defers should not cause autotmps.  (Open-coded defers do create extra autotmps).
+// defer should not cause spurious ambiguously live variables
+
 func f25(b bool) {
-	for i := 0; i < 2; i++ {
-		// Put in loop to make sure defer is not open-coded
-		defer g25()
-	}
+	defer g25()
 	if b {
 		return
 	}
 	var x string
 	x = g14()
 	printstring(x)
-	return
 }
 
 func g25()
@@ -420,8 +417,7 @@ func f27defer(b bool) {
 		defer call27(func() { x++ }) // ERROR "stack object .autotmp_[0-9]+ struct \{"
 	}
 	defer call27(func() { x++ }) // ERROR "stack object .autotmp_[0-9]+ struct \{"
-	printnl()                    // ERROR "live at call to printnl: .autotmp_[0-9]+ .autotmp_[0-9]+"
-	return                       // ERROR "live at call to call27: .autotmp_[0-9]+"
+	printnl()
 }
 
 // and newproc (go) escapes to the heap
@@ -691,12 +687,12 @@ type R struct{ *T } // ERRORAUTO "live at entry to \(\*R\)\.Foo: \.this ptr" "li
 // In particular, at printint r must be live.
 func f41(p, q *int) (r *int) { // ERROR "live at entry to f41: p q$"
 	r = p
-	defer func() {
+	defer func() { // ERROR "live at call to deferprocStack: q r$" "live at call to deferreturn: r$"
 		recover()
 	}()
-	printint(0) // ERROR "live at call to printint: q r .autotmp_[0-9]+$"
+	printint(0) // ERROR "live at call to printint: q r$"
 	r = q
-	return // ERROR "live at call to f41.func1: r .autotmp_[0-9]+$"
+	return // ERROR "live at call to deferreturn: r$"
 }
 
 func f42() {

test/nosplit.go

@@ -309,17 +309,17 @@ TestCases:
 				name := m[1]
 				size, _ := strconv.Atoi(m[2])
 
-				// The limit was originally 128 but is now 768 (896-128).
+				// The limit was originally 128 but is now 752 (880-128).
 				// Instead of rewriting the test cases above, adjust
 				// the first stack frame to use up the extra bytes.
 				if i == 0 {
-					size += (896 - 128) - 128
+					size += (880 - 128) - 128
 					// Noopt builds have a larger stackguard.
 					// See ../src/cmd/dist/buildruntime.go:stackGuardMultiplier
 					// This increase is included in objabi.StackGuard
 					for _, s := range strings.Split(os.Getenv("GO_GCFLAGS"), " ") {
 						if s == "-N" {
-							size += 896
+							size += 880
 						}
 					}
 				}