[dev.ssa] cmd/compile: start arguments as spilled

Declare a function's arguments as having already been
spilled so their use just requires a restore.

Allow spill locations to be portions of larger objects the stack.
Required to load portions of compound input arguments.

Rename the memory input to InputMem.  Use Arg for the
pre-spilled argument values.

Change-Id: I8fe2a03ffbba1022d98bfae2052b376b96d32dda
Reviewed-on: https://go-review.googlesource.com/16536
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

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

@@ -484,6 +484,9 @@ func compile(fn *Node) {
 
 	if ssafn != nil && usessa {
 		genssa(ssafn, ptxt, gcargs, gclocals)
+		if Curfn.Func.Endlineno != 0 {
+			lineno = Curfn.Func.Endlineno
+		}
 		return
 	}
 	Genlist(Curfn.Func.Enter)

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

@@ -97,7 +97,7 @@ func buildssa(fn *Node) (ssafn *ssa.Func, usessa bool) {
 	// Allocate starting values
 	s.labels = map[string]*ssaLabel{}
 	s.labeledNodes = map[*Node]*ssaLabel{}
-	s.startmem = s.entryNewValue0(ssa.OpArg, ssa.TypeMem)
+	s.startmem = s.entryNewValue0(ssa.OpInitMem, ssa.TypeMem)
 	s.sp = s.entryNewValue0(ssa.OpSP, Types[TUINTPTR]) // TODO: use generic pointer type (unsafe.Pointer?) instead
 	s.sb = s.entryNewValue0(ssa.OpSB, Types[TUINTPTR])
 
@@ -3168,6 +3168,12 @@ func (s *state) lookupVarIncoming(b *ssa.Block, t ssa.Type, name *Node) *ssa.Val
 		if name == &memVar {
 			return s.startmem
 		}
+		if canSSA(name) {
+			v := s.entryNewValue0A(ssa.OpArg, t, name)
+			// v starts with AuxInt == 0.
+			s.addNamedValue(name, v)
+			return v
+		}
 		// variable is live at the entry block.  Load it.
 		addr := s.decladdrs[name]
 		if addr == nil {
@@ -3239,18 +3245,21 @@ func (s *state) addNamedValue(n *Node, v *ssa.Value) {
 		// Don't track autotmp_ variables.
 		return
 	}
-	if n.Class == PPARAM || n.Class == PPARAMOUT {
-		// TODO: Remove this
+	if n.Class == PAUTO && (v.Type.IsString() || v.Type.IsSlice() || v.Type.IsInterface()) {
+		// TODO: can't handle auto compound objects with pointers yet.
+		// The live variable analysis barfs because we don't put VARDEF
+		// pseudos in the right place when we spill to these nodes.
 		return
 	}
 	if n.Class == PAUTO && n.Xoffset != 0 {
 		s.Fatalf("AUTO var with offset %s %d", n, n.Xoffset)
 	}
-	values, ok := s.f.NamedValues[n]
+	loc := ssa.LocalSlot{N: n, Type: n.Type, Off: 0}
+	values, ok := s.f.NamedValues[loc]
 	if !ok {
-		s.f.Names = append(s.f.Names, n)
+		s.f.Names = append(s.f.Names, loc)
 	}
-	s.f.NamedValues[n] = append(values, v)
+	s.f.NamedValues[loc] = append(values, v)
 }
 
 // an unresolved branch
@@ -3873,11 +3882,17 @@ func (s *genState) genValue(v *ssa.Value) {
 			return
 		}
 		p := Prog(movSizeByType(v.Type))
-		n := autoVar(v.Args[0])
+		n, off := autoVar(v.Args[0])
 		p.From.Type = obj.TYPE_MEM
-		p.From.Name = obj.NAME_AUTO
 		p.From.Node = n
 		p.From.Sym = Linksym(n.Sym)
+		p.From.Offset = off
+		if n.Class == PPARAM {
+			p.From.Name = obj.NAME_PARAM
+			p.From.Offset += n.Xoffset
+		} else {
+			p.From.Name = obj.NAME_AUTO
+		}
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = regnum(v)
 
@@ -3889,11 +3904,17 @@ func (s *genState) genValue(v *ssa.Value) {
 		p := Prog(movSizeByType(v.Type))
 		p.From.Type = obj.TYPE_REG
 		p.From.Reg = regnum(v.Args[0])
-		n := autoVar(v)
+		n, off := autoVar(v)
 		p.To.Type = obj.TYPE_MEM
-		p.To.Name = obj.NAME_AUTO
 		p.To.Node = n
 		p.To.Sym = Linksym(n.Sym)
+		p.To.Offset = off
+		if n.Class == PPARAM {
+			p.To.Name = obj.NAME_PARAM
+			p.To.Offset += n.Xoffset
+		} else {
+			p.To.Name = obj.NAME_AUTO
+		}
 	case ssa.OpPhi:
 		// just check to make sure regalloc and stackalloc did it right
 		if v.Type.IsMemory() {
@@ -3912,9 +3933,10 @@ func (s *genState) genValue(v *ssa.Value) {
 			v.Fatalf("const value %v shouldn't have a location", v)
 		}
 
-	case ssa.OpArg:
+	case ssa.OpInitMem:
 		// memory arg needs no code
-		// TODO: check that only mem arg goes here.
+	case ssa.OpArg:
+		// input args need no code
 	case ssa.OpAMD64LoweredGetClosurePtr:
 		// Output is hardwired to DX only,
 		// and DX contains the closure pointer on
@@ -4476,9 +4498,11 @@ func regnum(v *ssa.Value) int16 {
 	return ssaRegToReg[reg.(*ssa.Register).Num]
 }
 
-// autoVar returns a *Node representing the auto variable assigned to v.
-func autoVar(v *ssa.Value) *Node {
-	return v.Block.Func.RegAlloc[v.ID].(*ssa.LocalSlot).N.(*Node)
+// autoVar returns a *Node and int64 representing the auto variable and offset within it
+// where v should be spilled.
+func autoVar(v *ssa.Value) (*Node, int64) {
+	loc := v.Block.Func.RegAlloc[v.ID].(ssa.LocalSlot)
+	return loc.N.(*Node), loc.Off
 }
 
 // ssaExport exports a bunch of compiler services for the ssa backend.

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

@@ -83,8 +83,8 @@ type pass struct {
 var passes = [...]pass{
 	{"phielim", phielim},
 	{"copyelim", copyelim},
-	{"decompose", decompose},
 	{"early deadcode", deadcode}, // remove generated dead code to avoid doing pointless work during opt
+	{"decompose", decompose},
 	{"opt", opt},
 	{"opt deadcode", deadcode}, // remove any blocks orphaned during opt
 	{"generic cse", cse},

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

@@ -103,7 +103,7 @@ func (c *Config) Frontend() Frontend { return c.fe }
 // NewFunc returns a new, empty function object
 func (c *Config) NewFunc() *Func {
 	// TODO(khr): should this function take name, type, etc. as arguments?
-	return &Func{Config: c, NamedValues: map[GCNode][]*Value{}}
+	return &Func{Config: c, NamedValues: map[LocalSlot][]*Value{}}
 }
 
 func (c *Config) Logf(msg string, args ...interface{})            { c.fe.Logf(msg, args...) }

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

@@ -162,24 +162,38 @@ func deadcode(f *Func) {
 	}
 	f.Blocks = f.Blocks[:i]
 
-	// Remove dead entries from namedValues map.
-	for name, values := range f.NamedValues {
-		i := 0
+	// Remove dead & duplicate entries from namedValues map.
+	s := newSparseSet(f.NumValues())
+	i = 0
+	for _, name := range f.Names {
+		j := 0
+		s.clear()
+		values := f.NamedValues[name]
 		for _, v := range values {
 			for v.Op == OpCopy {
 				v = v.Args[0]
 			}
-			if live[v.ID] {
-				values[i] = v
+			if live[v.ID] && !s.contains(v.ID) {
+				values[j] = v
+				j++
+				s.add(v.ID)
+			}
+		}
+		if j == 0 {
+			delete(f.NamedValues, name)
+		} else {
+			f.Names[i] = name
 			i++
+			for k := len(values) - 1; k >= j; k-- {
+				values[k] = nil
 			}
+			f.NamedValues[name] = values[:j]
 		}
-		f.NamedValues[name] = values[:i]
-		tail := values[i:]
-		for j := range tail {
-			tail[j] = nil
 	}
+	for k := len(f.Names) - 1; k >= i; k-- {
+		f.Names[k] = LocalSlot{}
 	}
+	f.Names = f.Names[:i]
 
 	// TODO: renumber Blocks and Values densely?
 	// TODO: save dead Values and Blocks for reuse?  Or should we just let GC handle it?

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

@@ -10,7 +10,7 @@ func TestDeadLoop(t *testing.T) {
 	c := testConfig(t)
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Goto("exit")),
 		Bloc("exit",
 			Exit("mem")),
@@ -40,7 +40,7 @@ func TestDeadValue(t *testing.T) {
 	c := testConfig(t)
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("deadval", OpConst64, TypeInt64, 37, nil),
 			Goto("exit")),
 		Bloc("exit",
@@ -64,7 +64,7 @@ func TestNeverTaken(t *testing.T) {
 	fun := Fun(c, "entry",
 		Bloc("entry",
 			Valu("cond", OpConstBool, TypeBool, 0, nil),
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			If("cond", "then", "else")),
 		Bloc("then",
 			Goto("exit")),
@@ -98,7 +98,7 @@ func TestNestedDeadBlocks(t *testing.T) {
 	c := testConfig(t)
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("cond", OpConstBool, TypeBool, 0, nil),
 			If("cond", "b2", "b4")),
 		Bloc("b2",

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

@@ -12,7 +12,7 @@ func TestDeadStore(t *testing.T) {
 	ptrType := &TypeImpl{Size_: 8, Ptr: true, Name: "testptr", Elem_: elemType} // dummy for testing
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("start", OpArg, TypeMem, 0, ".mem"),
+			Valu("start", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("sb", OpSB, TypeInvalid, 0, nil),
 			Valu("v", OpConstBool, TypeBool, 1, nil),
 			Valu("addr1", OpAddr, ptrType, 0, nil, "sb"),
@@ -47,7 +47,7 @@ func TestDeadStorePhi(t *testing.T) {
 	ptrType := &TypeImpl{Size_: 8, Ptr: true, Name: "testptr"} // dummy for testing
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("start", OpArg, TypeMem, 0, ".mem"),
+			Valu("start", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("sb", OpSB, TypeInvalid, 0, nil),
 			Valu("v", OpConstBool, TypeBool, 1, nil),
 			Valu("addr", OpAddr, ptrType, 0, nil, "sb"),
@@ -74,7 +74,7 @@ func TestDeadStoreTypes(t *testing.T) {
 	t2 := &TypeImpl{Size_: 4, Ptr: true, Name: "t2"}
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("start", OpArg, TypeMem, 0, ".mem"),
+			Valu("start", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("sb", OpSB, TypeInvalid, 0, nil),
 			Valu("v", OpConstBool, TypeBool, 1, nil),
 			Valu("addr1", OpAddr, t1, 0, nil, "sb"),

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

@@ -29,8 +29,75 @@ func decompose(f *Func) {
 			}
 		}
 	}
-	// TODO: decompose complex?
 	// TODO: decompose 64-bit ops on 32-bit archs?
+
+	// Split up named values into their components.
+	// NOTE: the component values we are making are dead at this point.
+	// We must do the opt pass before any deadcode elimination or we will
+	// lose the name->value correspondence.
+	for _, name := range f.Names {
+		t := name.Type
+		switch {
+		case t.IsComplex():
+			var elemType Type
+			if t.Size() == 16 {
+				elemType = f.Config.fe.TypeFloat64()
+			} else {
+				elemType = f.Config.fe.TypeFloat32()
+			}
+			rName := LocalSlot{name.N, elemType, name.Off}
+			iName := LocalSlot{name.N, elemType, name.Off + elemType.Size()}
+			f.Names = append(f.Names, rName, iName)
+			for _, v := range f.NamedValues[name] {
+				r := v.Block.NewValue1(v.Line, OpComplexReal, elemType, v)
+				i := v.Block.NewValue1(v.Line, OpComplexImag, elemType, v)
+				f.NamedValues[rName] = append(f.NamedValues[rName], r)
+				f.NamedValues[iName] = append(f.NamedValues[iName], i)
+			}
+		case t.IsString():
+			ptrType := f.Config.fe.TypeBytePtr()
+			lenType := f.Config.fe.TypeInt()
+			ptrName := LocalSlot{name.N, ptrType, name.Off}
+			lenName := LocalSlot{name.N, lenType, name.Off + f.Config.PtrSize}
+			f.Names = append(f.Names, ptrName, lenName)
+			for _, v := range f.NamedValues[name] {
+				ptr := v.Block.NewValue1(v.Line, OpStringPtr, ptrType, v)
+				len := v.Block.NewValue1(v.Line, OpStringLen, lenType, v)
+				f.NamedValues[ptrName] = append(f.NamedValues[ptrName], ptr)
+				f.NamedValues[lenName] = append(f.NamedValues[lenName], len)
+			}
+		case t.IsSlice():
+			ptrType := f.Config.fe.TypeBytePtr()
+			lenType := f.Config.fe.TypeInt()
+			ptrName := LocalSlot{name.N, ptrType, name.Off}
+			lenName := LocalSlot{name.N, lenType, name.Off + f.Config.PtrSize}
+			capName := LocalSlot{name.N, lenType, name.Off + 2*f.Config.PtrSize}
+			f.Names = append(f.Names, ptrName, lenName, capName)
+			for _, v := range f.NamedValues[name] {
+				ptr := v.Block.NewValue1(v.Line, OpSlicePtr, ptrType, v)
+				len := v.Block.NewValue1(v.Line, OpSliceLen, lenType, v)
+				cap := v.Block.NewValue1(v.Line, OpSliceCap, lenType, v)
+				f.NamedValues[ptrName] = append(f.NamedValues[ptrName], ptr)
+				f.NamedValues[lenName] = append(f.NamedValues[lenName], len)
+				f.NamedValues[capName] = append(f.NamedValues[capName], cap)
+			}
+		case t.IsInterface():
+			ptrType := f.Config.fe.TypeBytePtr()
+			typeName := LocalSlot{name.N, ptrType, name.Off}
+			dataName := LocalSlot{name.N, ptrType, name.Off + f.Config.PtrSize}
+			f.Names = append(f.Names, typeName, dataName)
+			for _, v := range f.NamedValues[name] {
+				typ := v.Block.NewValue1(v.Line, OpITab, ptrType, v)
+				data := v.Block.NewValue1(v.Line, OpIData, ptrType, v)
+				f.NamedValues[typeName] = append(f.NamedValues[typeName], typ)
+				f.NamedValues[dataName] = append(f.NamedValues[dataName], data)
+			}
+			//case t.IsStruct():
+			// TODO
+		case t.Size() > f.Config.IntSize:
+			f.Unimplementedf("undecomposed type %s", t)
+		}
+	}
 }
 
 func decomposeStringPhi(v *Value) {

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

@@ -20,7 +20,7 @@ func genLinear(size int) []bloc {
 	var blocs []bloc
 	blocs = append(blocs,
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Goto(blockn(0)),
 		),
 	)
@@ -43,7 +43,7 @@ func genFwdBack(size int) []bloc {
 	var blocs []bloc
 	blocs = append(blocs,
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("p", OpConstBool, TypeBool, 1, nil),
 			Goto(blockn(0)),
 		),
@@ -73,7 +73,7 @@ func genManyPred(size int) []bloc {
 	var blocs []bloc
 	blocs = append(blocs,
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("p", OpConstBool, TypeBool, 1, nil),
 			Goto(blockn(0)),
 		),
@@ -111,7 +111,7 @@ func genMaxPred(size int) []bloc {
 	var blocs []bloc
 	blocs = append(blocs,
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("p", OpConstBool, TypeBool, 1, nil),
 			Goto(blockn(0)),
 		),
@@ -136,7 +136,7 @@ func genMaxPredValue(size int) []bloc {
 	var blocs []bloc
 	blocs = append(blocs,
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("p", OpConstBool, TypeBool, 1, nil),
 			Goto(blockn(0)),
 		),
@@ -223,7 +223,7 @@ func TestDominatorsSingleBlock(t *testing.T) {
 	c := testConfig(t)
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Exit("mem")))
 
 	doms := map[string]string{}
@@ -238,7 +238,7 @@ func TestDominatorsSimple(t *testing.T) {
 	c := testConfig(t)
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Goto("a")),
 		Bloc("a",
 			Goto("b")),
@@ -266,7 +266,7 @@ func TestDominatorsMultPredFwd(t *testing.T) {
 	c := testConfig(t)
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("p", OpConstBool, TypeBool, 1, nil),
 			If("p", "a", "c")),
 		Bloc("a",
@@ -294,7 +294,7 @@ func TestDominatorsDeadCode(t *testing.T) {
 	c := testConfig(t)
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("p", OpConstBool, TypeBool, 0, nil),
 			If("p", "b3", "b5")),
 		Bloc("b2", Exit("mem")),
@@ -319,7 +319,7 @@ func TestDominatorsMultPredRev(t *testing.T) {
 		Bloc("entry",
 			Goto("first")),
 		Bloc("first",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("p", OpConstBool, TypeBool, 1, nil),
 			Goto("a")),
 		Bloc("a",
@@ -348,7 +348,7 @@ func TestDominatorsMultPred(t *testing.T) {
 	c := testConfig(t)
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("p", OpConstBool, TypeBool, 1, nil),
 			If("p", "a", "c")),
 		Bloc("a",
@@ -376,7 +376,7 @@ func TestPostDominators(t *testing.T) {
 	c := testConfig(t)
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("p", OpConstBool, TypeBool, 1, nil),
 			If("p", "a", "c")),
 		Bloc("a",
@@ -403,7 +403,7 @@ func TestInfiniteLoop(t *testing.T) {
 	// note lack of an exit block
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("p", OpConstBool, TypeBool, 1, nil),
 			Goto("a")),
 		Bloc("a",

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

@@ -26,12 +26,11 @@ type Func struct {
 	// when register allocation is done, maps value ids to locations
 	RegAlloc []Location
 
-	// map from *gc.Node to set of Values that represent that Node.
-	// The Node must be an ONAME with PPARAM, PPARAMOUT, or PAUTO class.
-	NamedValues map[GCNode][]*Value
+	// map from LocalSlot to set of Values that we want to store in that slot.
+	NamedValues map[LocalSlot][]*Value
 	// Names is a copy of NamedValues.Keys.  We keep a separate list
 	// of keys to make iteration order deterministic.
-	Names []GCNode
+	Names []LocalSlot
 }
 
 // NumBlocks returns an integer larger than the id of any Block in the Func.

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

@@ -18,7 +18,7 @@
 //
 //   fun := Fun("entry",
 //       Bloc("entry",
-//           Valu("mem", OpArg, TypeMem, 0, ".mem"),
+//           Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 //           Goto("exit")),
 //       Bloc("exit",
 //           Exit("mem")),
@@ -263,7 +263,7 @@ func TestArgs(t *testing.T) {
 			Valu("a", OpConst64, TypeInt64, 14, nil),
 			Valu("b", OpConst64, TypeInt64, 26, nil),
 			Valu("sum", OpAdd64, TypeInt64, 0, nil, "a", "b"),
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Goto("exit")),
 		Bloc("exit",
 			Exit("mem")))
@@ -286,7 +286,7 @@ func TestEquiv(t *testing.T) {
 					Valu("a", OpConst64, TypeInt64, 14, nil),
 					Valu("b", OpConst64, TypeInt64, 26, nil),
 					Valu("sum", OpAdd64, TypeInt64, 0, nil, "a", "b"),
-					Valu("mem", OpArg, TypeMem, 0, ".mem"),
+					Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 					Goto("exit")),
 				Bloc("exit",
 					Exit("mem"))),
@@ -295,7 +295,7 @@ func TestEquiv(t *testing.T) {
 					Valu("a", OpConst64, TypeInt64, 14, nil),
 					Valu("b", OpConst64, TypeInt64, 26, nil),
 					Valu("sum", OpAdd64, TypeInt64, 0, nil, "a", "b"),
-					Valu("mem", OpArg, TypeMem, 0, ".mem"),
+					Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 					Goto("exit")),
 				Bloc("exit",
 					Exit("mem"))),
@@ -307,7 +307,7 @@ func TestEquiv(t *testing.T) {
 					Valu("a", OpConst64, TypeInt64, 14, nil),
 					Valu("b", OpConst64, TypeInt64, 26, nil),
 					Valu("sum", OpAdd64, TypeInt64, 0, nil, "a", "b"),
-					Valu("mem", OpArg, TypeMem, 0, ".mem"),
+					Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 					Goto("exit")),
 				Bloc("exit",
 					Exit("mem"))),
@@ -318,7 +318,7 @@ func TestEquiv(t *testing.T) {
 					Valu("a", OpConst64, TypeInt64, 14, nil),
 					Valu("b", OpConst64, TypeInt64, 26, nil),
 					Valu("sum", OpAdd64, TypeInt64, 0, nil, "a", "b"),
-					Valu("mem", OpArg, TypeMem, 0, ".mem"),
+					Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 					Goto("exit"))),
 		},
 	}
@@ -335,26 +335,26 @@ func TestEquiv(t *testing.T) {
 		{
 			Fun(c, "entry",
 				Bloc("entry",
-					Valu("mem", OpArg, TypeMem, 0, ".mem"),
+					Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 					Goto("exit")),
 				Bloc("exit",
 					Exit("mem"))),
 			Fun(c, "entry",
 				Bloc("entry",
-					Valu("mem", OpArg, TypeMem, 0, ".mem"),
+					Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 					Exit("mem"))),
 		},
 		// value order changed
 		{
 			Fun(c, "entry",
 				Bloc("entry",
-					Valu("mem", OpArg, TypeMem, 0, ".mem"),
+					Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 					Valu("b", OpConst64, TypeInt64, 26, nil),
 					Valu("a", OpConst64, TypeInt64, 14, nil),
 					Exit("mem"))),
 			Fun(c, "entry",
 				Bloc("entry",
-					Valu("mem", OpArg, TypeMem, 0, ".mem"),
+					Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 					Valu("a", OpConst64, TypeInt64, 14, nil),
 					Valu("b", OpConst64, TypeInt64, 26, nil),
 					Exit("mem"))),
@@ -363,12 +363,12 @@ func TestEquiv(t *testing.T) {
 		{
 			Fun(c, "entry",
 				Bloc("entry",
-					Valu("mem", OpArg, TypeMem, 0, ".mem"),
+					Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 					Valu("a", OpConst64, TypeInt64, 14, nil),
 					Exit("mem"))),
 			Fun(c, "entry",
 				Bloc("entry",
-					Valu("mem", OpArg, TypeMem, 0, ".mem"),
+					Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 					Valu("a", OpConst64, TypeInt64, 26, nil),
 					Exit("mem"))),
 		},
@@ -376,12 +376,12 @@ func TestEquiv(t *testing.T) {
 		{
 			Fun(c, "entry",
 				Bloc("entry",
-					Valu("mem", OpArg, TypeMem, 0, ".mem"),
+					Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 					Valu("a", OpConst64, TypeInt64, 0, 14),
 					Exit("mem"))),
 			Fun(c, "entry",
 				Bloc("entry",
-					Valu("mem", OpArg, TypeMem, 0, ".mem"),
+					Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 					Valu("a", OpConst64, TypeInt64, 0, 26),
 					Exit("mem"))),
 		},
@@ -389,14 +389,14 @@ func TestEquiv(t *testing.T) {
 		{
 			Fun(c, "entry",
 				Bloc("entry",
-					Valu("mem", OpArg, TypeMem, 0, ".mem"),
+					Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 					Valu("a", OpConst64, TypeInt64, 14, nil),
 					Valu("b", OpConst64, TypeInt64, 26, nil),
 					Valu("sum", OpAdd64, TypeInt64, 0, nil, "a", "b"),
 					Exit("mem"))),
 			Fun(c, "entry",
 				Bloc("entry",
-					Valu("mem", OpArg, TypeMem, 0, ".mem"),
+					Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 					Valu("a", OpConst64, TypeInt64, 0, nil),
 					Valu("b", OpConst64, TypeInt64, 14, nil),
 					Valu("sum", OpAdd64, TypeInt64, 0, nil, "b", "a"),

src/cmd/compile/internal/ssa/gen/generic.rules

@@ -188,12 +188,12 @@
 (Load <t> ptr mem) && t.IsString() ->
   (StringMake
     (Load <config.fe.TypeBytePtr()> ptr mem)
-    (Load <config.fe.TypeUintptr()>
-      (OffPtr <config.fe.TypeUintptr().PtrTo()> [config.PtrSize] ptr)
+    (Load <config.fe.TypeInt()>
+      (OffPtr <config.fe.TypeInt().PtrTo()> [config.PtrSize] ptr)
       mem))
 (Store [2*config.PtrSize] dst (StringMake ptr len) mem) ->
   (Store [config.PtrSize]
-    (OffPtr <config.fe.TypeUintptr().PtrTo()> [config.PtrSize] dst)
+    (OffPtr <config.fe.TypeInt().PtrTo()> [config.PtrSize] dst)
     len
     (Store [config.PtrSize] dst ptr mem))
 
@@ -215,18 +215,18 @@
 (Load <t> ptr mem) && t.IsSlice() ->
   (SliceMake
     (Load <config.fe.TypeBytePtr()> ptr mem)
-    (Load <config.fe.TypeUintptr()>
-      (OffPtr <config.fe.TypeUintptr().PtrTo()> [config.PtrSize] ptr)
+    (Load <config.fe.TypeInt()>
+      (OffPtr <config.fe.TypeInt().PtrTo()> [config.PtrSize] ptr)
       mem)
-    (Load <config.fe.TypeUintptr()>
-      (OffPtr <config.fe.TypeUintptr().PtrTo()> [2*config.PtrSize] ptr)
+    (Load <config.fe.TypeInt()>
+      (OffPtr <config.fe.TypeInt().PtrTo()> [2*config.PtrSize] ptr)
       mem))
 (Store [3*config.PtrSize] dst (SliceMake ptr len cap) mem) ->
   (Store [config.PtrSize]
-    (OffPtr <config.fe.TypeUintptr().PtrTo()> [2*config.PtrSize] dst)
+    (OffPtr <config.fe.TypeInt().PtrTo()> [2*config.PtrSize] dst)
     cap
     (Store [config.PtrSize]
-      (OffPtr <config.fe.TypeUintptr().PtrTo()> [config.PtrSize] dst)
+      (OffPtr <config.fe.TypeInt().PtrTo()> [config.PtrSize] dst)
       len
       (Store [config.PtrSize] dst ptr mem)))
 
@@ -261,3 +261,30 @@
 
 // Get rid of Convert ops for pointer arithmetic on unsafe.Pointer.
 (Convert (Add64 (Convert ptr) off)) -> (Add64 ptr off)
+
+// Decompose compound argument values
+(Arg {n} [off]) && v.Type.IsString() ->
+  (StringMake
+    (Arg <config.fe.TypeBytePtr()> {n} [off])
+    (Arg <config.fe.TypeInt()> {n} [off+config.PtrSize]))
+
+(Arg {n} [off]) && v.Type.IsSlice() ->
+  (SliceMake
+    (Arg <config.fe.TypeBytePtr()> {n} [off])
+    (Arg <config.fe.TypeInt()> {n} [off+config.PtrSize])
+    (Arg <config.fe.TypeInt()> {n} [off+2*config.PtrSize]))
+
+(Arg {n} [off]) && v.Type.IsInterface() ->
+  (IMake
+    (Arg <config.fe.TypeBytePtr()> {n} [off])
+    (Arg <config.fe.TypeBytePtr()> {n} [off+config.PtrSize]))
+
+(Arg {n} [off]) && v.Type.IsComplex() && v.Type.Size() == 16 ->
+  (ComplexMake
+    (Arg <config.fe.TypeFloat64()> {n} [off])
+    (Arg <config.fe.TypeFloat64()> {n} [off+8]))
+
+(Arg {n} [off]) && v.Type.IsComplex() && v.Type.Size() == 8 ->
+  (ComplexMake
+    (Arg <config.fe.TypeFloat32()> {n} [off])
+    (Arg <config.fe.TypeFloat32()> {n} [off+4]))

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

@@ -260,7 +260,8 @@ var genericOps = []opData{
 	// TODO: Const32F, ...
 
 	// Constant-like things
-	{name: "Arg"}, // memory input to the function.
+	{name: "InitMem"}, // memory input to the function.
+	{name: "Arg"},     // argument to the function.  aux=GCNode of arg, off = offset in that arg.
 
 	// The address of a variable.  arg0 is the base pointer (SB or SP, depending
 	// on whether it is a global or stack variable).  The Aux field identifies the

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

@@ -472,3 +472,7 @@ func (p htmlFuncPrinter) startDepCycle() {
 func (p htmlFuncPrinter) endDepCycle() {
 	fmt.Fprintln(p.w, "</span>")
 }
+
+func (p htmlFuncPrinter) named(n LocalSlot, vals []*Value) {
+	// TODO
+}

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

@@ -4,6 +4,8 @@
 
 package ssa
 
+import "fmt"
+
 // A place that an ssa variable can reside.
 type Location interface {
 	Name() string // name to use in assembly templates: %rax, 16(%rsp), ...
@@ -21,10 +23,16 @@ func (r *Register) Name() string {
 }
 
 // A LocalSlot is a location in the stack frame.
+// It is (possibly a subpiece of) a PPARAM, PPARAMOUT, or PAUTO ONAME node.
 type LocalSlot struct {
-	N GCNode // a *gc.Node for an auto variable
+	N    GCNode // an ONAME *gc.Node representing a variable on the stack
+	Type Type   // type of slot
+	Off  int64  // offset of slot in N
 }
 
-func (s *LocalSlot) Name() string {
-	return s.N.String()
+func (s LocalSlot) Name() string {
+	if s.Off == 0 {
+		return fmt.Sprintf("%s[%s]", s.N, s.Type)
+	}
+	return fmt.Sprintf("%s+%d[%s]", s.N, s.Off, s.Type)
 }

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

@@ -21,7 +21,7 @@ func checkLower(f *Func) {
 				continue // lowered
 			}
 			switch v.Op {
-			case OpSP, OpSB, OpArg, OpCopy, OpPhi, OpVarDef, OpVarKill:
+			case OpSP, OpSB, OpInitMem, OpArg, OpCopy, OpPhi, OpVarDef, OpVarKill:
 				continue // ok not to lower
 			}
 			s := "not lowered: " + v.Op.String() + " " + v.Type.SimpleString()

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

@@ -21,7 +21,7 @@ func benchmarkNilCheckDeep(b *testing.B, depth int) {
 	var blocs []bloc
 	blocs = append(blocs,
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("sb", OpSB, TypeInvalid, 0, nil),
 			Goto(blockn(0)),
 		),
@@ -67,7 +67,7 @@ func TestNilcheckSimple(t *testing.T) {
 	c := NewConfig("amd64", DummyFrontend{t}, nil)
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("sb", OpSB, TypeInvalid, 0, nil),
 			Goto("checkPtr")),
 		Bloc("checkPtr",
@@ -104,7 +104,7 @@ func TestNilcheckDomOrder(t *testing.T) {
 	c := NewConfig("amd64", DummyFrontend{t}, nil)
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("sb", OpSB, TypeInvalid, 0, nil),
 			Goto("checkPtr")),
 		Bloc("checkPtr",
@@ -140,7 +140,7 @@ func TestNilcheckAddr(t *testing.T) {
 	c := NewConfig("amd64", DummyFrontend{t}, nil)
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("sb", OpSB, TypeInvalid, 0, nil),
 			Goto("checkPtr")),
 		Bloc("checkPtr",
@@ -173,7 +173,7 @@ func TestNilcheckAddPtr(t *testing.T) {
 	c := NewConfig("amd64", DummyFrontend{t}, nil)
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("sb", OpSB, TypeInvalid, 0, nil),
 			Goto("checkPtr")),
 		Bloc("checkPtr",
@@ -207,7 +207,7 @@ func TestNilcheckPhi(t *testing.T) {
 	c := NewConfig("amd64", DummyFrontend{t}, nil)
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("sb", OpSB, TypeInvalid, 0, nil),
 			Valu("sp", OpSP, TypeInvalid, 0, nil),
 			Valu("baddr", OpAddr, TypeBool, 0, "b", "sp"),
@@ -251,7 +251,7 @@ func TestNilcheckKeepRemove(t *testing.T) {
 	c := NewConfig("amd64", DummyFrontend{t}, nil)
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("sb", OpSB, TypeInvalid, 0, nil),
 			Goto("checkPtr")),
 		Bloc("checkPtr",
@@ -299,7 +299,7 @@ func TestNilcheckInFalseBranch(t *testing.T) {
 	c := NewConfig("amd64", DummyFrontend{t}, nil)
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("sb", OpSB, TypeInvalid, 0, nil),
 			Goto("checkPtr")),
 		Bloc("checkPtr",
@@ -350,7 +350,7 @@ func TestNilcheckUser(t *testing.T) {
 	c := NewConfig("amd64", DummyFrontend{t}, nil)
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("sb", OpSB, TypeInvalid, 0, nil),
 			Goto("checkPtr")),
 		Bloc("checkPtr",
@@ -389,7 +389,7 @@ func TestNilcheckBug(t *testing.T) {
 	c := NewConfig("amd64", DummyFrontend{t}, nil)
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("sb", OpSB, TypeInvalid, 0, nil),
 			Goto("checkPtr")),
 		Bloc("checkPtr",

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

@@ -475,6 +475,7 @@ const (
 	OpConst64F
 	OpConstInterface
 	OpConstSlice
+	OpInitMem
 	OpArg
 	OpAddr
 	OpSP
@@ -3987,6 +3988,10 @@ var opcodeTable = [...]opInfo{
 		name:    "ConstSlice",
 		generic: true,
 	},
+	{
+		name:    "InitMem",
+		generic: true,
+	},
 	{
 		name:    "Arg",
 		generic: true,

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

@@ -28,6 +28,7 @@ type funcPrinter interface {
 	value(v *Value, live bool)
 	startDepCycle()
 	endDepCycle()
+	named(n LocalSlot, vals []*Value)
 }
 
 type stringFuncPrinter struct {
@@ -73,6 +74,10 @@ func (p stringFuncPrinter) startDepCycle() {
 
 func (p stringFuncPrinter) endDepCycle() {}
 
+func (p stringFuncPrinter) named(n LocalSlot, vals []*Value) {
+	fmt.Fprintf(p.w, "name %s: %v\n", n.Name(), vals)
+}
+
 func fprintFunc(p funcPrinter, f *Func) {
 	reachable, live := findlive(f)
 	p.header(f)
@@ -136,4 +141,7 @@ func fprintFunc(p funcPrinter, f *Func) {
 
 		p.endBlock(b)
 	}
+	for name, vals := range f.NamedValues {
+		p.named(name, vals)
+	}
 }

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

@@ -759,6 +759,16 @@ func (s *regAllocState) regalloc(f *Func) {
 				pc++
 				continue
 			}
+			if v.Op == OpArg {
+				// Args are "pre-spilled" values.  We don't allocate
+				// any register here.  We just set up the spill pointer to
+				// point at itself and any later user will restore it to use it.
+				s.values[v.ID].spill = v
+				s.values[v.ID].spillUsed = true // use is guaranteed
+				b.Values = append(b.Values, v)
+				pc++
+				continue
+			}
 			s.clearUses(pc*2 - 1)
 			regspec := opcodeTable[v.Op].reg
 			if regDebug {

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

@@ -10,7 +10,7 @@ func TestLiveControlOps(t *testing.T) {
 	c := testConfig(t)
 	f := Fun(c, "entry",
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("x", OpAMD64MOVBconst, TypeInt8, 0, 1),
 			Valu("y", OpAMD64MOVBconst, TypeInt8, 0, 2),
 			Valu("a", OpAMD64TESTB, TypeBool, 0, nil, "x", "y"),

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

@@ -11,7 +11,7 @@ func TestSchedule(t *testing.T) {
 	cases := []fun{
 		Fun(c, "entry",
 			Bloc("entry",
-				Valu("mem0", OpArg, TypeMem, 0, ".mem"),
+				Valu("mem0", OpInitMem, TypeMem, 0, ".mem"),
 				Valu("ptr", OpConst64, TypeInt64, 0xABCD, nil),
 				Valu("v", OpConst64, TypeInt64, 12, nil),
 				Valu("mem1", OpStore, TypeMem, 8, nil, "ptr", "v", "mem0"),

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

@@ -28,7 +28,7 @@ func makeConstShiftFunc(c *Config, amount int64, op Op, typ Type) fun {
 	ptyp := &TypeImpl{Size_: 8, Ptr: true, Name: "ptr"}
 	fun := Fun(c, "entry",
 		Bloc("entry",
-			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("mem", OpInitMem, TypeMem, 0, ".mem"),
 			Valu("SP", OpSP, TypeUInt64, 0, nil),
 			Valu("argptr", OpOffPtr, ptyp, 8, nil, "SP"),
 			Valu("resptr", OpOffPtr, ptyp, 16, nil, "SP"),

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

@@ -44,6 +44,13 @@ func stackalloc(f *Func) {
 				}
 			case v.Op == OpLoadReg:
 				s.add(v.Args[0].ID)
+			case v.Op == OpArg:
+				// This is an input argument which is pre-spilled.  It is kind of
+				// like a StoreReg, but we don't remove v.ID here because we want
+				// this value to appear live even before this point.  Being live
+				// all the way to the start of the entry block prevents other
+				// values from being allocated to the same slot and clobbering
+				// the input value before we have a chance to load it.
 			}
 		}
 	}
@@ -51,7 +58,7 @@ func stackalloc(f *Func) {
 	// Build map from values to their names, if any.
 	// A value may be associated with more than one name (e.g. after
 	// the assignment i=j). This step picks one name per value arbitrarily.
-	names := make([]GCNode, f.NumValues())
+	names := make([]LocalSlot, f.NumValues())
 	for _, name := range f.Names {
 		// Note: not "range f.NamedValues" above, because
 		// that would be nondeterministic.
@@ -74,9 +81,17 @@ func stackalloc(f *Func) {
 		}
 	}
 
+	// Allocate args to their assigned locations.
+	for _, v := range f.Entry.Values {
+		if v.Op != OpArg {
+			continue
+		}
+		f.setHome(v, LocalSlot{v.Aux.(GCNode), v.Type, v.AuxInt})
+	}
+
 	// For each type, we keep track of all the stack slots we
 	// have allocated for that type.
-	locations := map[Type][]*LocalSlot{}
+	locations := map[Type][]LocalSlot{}
 
 	// Each time we assign a stack slot to a value v, we remember
 	// the slot we used via an index into locations[v.Type].
@@ -99,16 +114,16 @@ func stackalloc(f *Func) {
 
 			// If this is a named value, try to use the name as
 			// the spill location.
-			var name GCNode
+			var name LocalSlot
 			if v.Op == OpStoreReg {
 				name = names[v.Args[0].ID]
 			} else {
 				name = names[v.ID]
 			}
-			if name != nil && v.Type.Equal(name.Typ()) {
+			if name.N != nil && v.Type.Equal(name.Type) {
 				for _, id := range interfere[v.ID] {
 					h := f.getHome(id)
-					if h != nil && h.(*LocalSlot).N == name {
+					if h != nil && h.(LocalSlot) == name {
 						// A variable can interfere with itself.
 						// It is rare, but but it can happen.
 						goto noname
@@ -118,17 +133,16 @@ func stackalloc(f *Func) {
 					for _, a := range v.Args {
 						for _, id := range interfere[a.ID] {
 							h := f.getHome(id)
-							if h != nil && h.(*LocalSlot).N == name {
+							if h != nil && h.(LocalSlot) == name {
 								goto noname
 							}
 						}
 					}
 				}
-				loc := &LocalSlot{name}
-				f.setHome(v, loc)
+				f.setHome(v, name)
 				if v.Op == OpPhi {
 					for _, a := range v.Args {
-						f.setHome(a, loc)
+						f.setHome(a, name)
 					}
 				}
 				continue
@@ -169,7 +183,7 @@ func stackalloc(f *Func) {
 			}
 			// If there is no unused stack slot, allocate a new one.
 			if i == len(locs) {
-				locs = append(locs, &LocalSlot{f.Config.fe.Auto(v.Type)})
+				locs = append(locs, LocalSlot{N: f.Config.fe.Auto(v.Type), Type: v.Type, Off: 0})
 				locations[v.Type] = locs
 			}
 			// Use the stack variable at that index for v.

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

@@ -54,8 +54,8 @@ func tighten(f *Func) {
 		for _, b := range f.Blocks {
 			for i := 0; i < len(b.Values); i++ {
 				v := b.Values[i]
-				if v.Op == OpPhi || v.Op == OpGetClosurePtr || v.Op == OpConvert {
-					// GetClosurePtr must stay in entry block.
+				if v.Op == OpPhi || v.Op == OpGetClosurePtr || v.Op == OpConvert || v.Op == OpArg {
+					// GetClosurePtr & Arg must stay in entry block.
 					// OpConvert must not float over call sites.
 					// TODO do we instead need a dependence edge of some sort for OpConvert?
 					// Would memory do the trick, or do we need something else that relates

src/runtime/runtime-gdb_test.go

@@ -94,9 +94,6 @@ func TestGdbPython(t *testing.T) {
 		"-ex", "echo END\n",
 		"-ex", "echo BEGIN print strvar\n",
 		"-ex", "print strvar",
-		"-ex", "echo END\n",
-		"-ex", "echo BEGIN print ptrvar\n",
-		"-ex", "print ptrvar",
 		"-ex", "echo END\n"}
 
 	// without framepointer, gdb cannot backtrace our non-standard
@@ -151,10 +148,6 @@ func TestGdbPython(t *testing.T) {
 		t.Fatalf("print strvar failed: %s", bl)
 	}
 
-	if bl := blocks["print ptrvar"]; !strVarRe.MatchString(bl) {
-		t.Fatalf("print ptrvar failed: %s", bl)
-	}
-
 	btGoroutineRe := regexp.MustCompile(`^#0\s+runtime.+at`)
 	if bl := blocks["goroutine 2 bt"]; canBackTrace && !btGoroutineRe.MatchString(bl) {
 		t.Fatalf("goroutine 2 bt failed: %s", bl)