src/cmd/compile/internal/ssa/decompose.go - go - Git at Google

 // Copyright 2015 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.

 package ssa

 import "cmd/compile/internal/types"

 // decompose converts phi ops on compound builtin types into phi
 // ops on simple types.
 // (The remaining compound ops are decomposed with rewrite rules.)
 func decomposeBuiltIn(f *Func) {
 	for _, b := range f.Blocks {
 		for _, v := range b.Values {
 			if v.Op != OpPhi {
 				continue
 			}
 			decomposeBuiltInPhi(v)
 		}
 	}

 	// 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.
 	var newNames []LocalSlot
 	for _, name := range f.Names {
 		t := name.Type
 		switch {
 		case t.IsInteger() && t.Size() > f.Config.RegSize:
 			var elemType *types.Type
 			if t.IsSigned() {
 				elemType = f.Config.Types.Int32
 			} else {
 				elemType = f.Config.Types.UInt32
 			}
 			hiName, loName := f.fe.SplitInt64(name)
 			newNames = append(newNames, hiName, loName)
 			for _, v := range f.NamedValues[name] {
 				hi := v.Block.NewValue1(v.Pos, OpInt64Hi, elemType, v)
 				lo := v.Block.NewValue1(v.Pos, OpInt64Lo, f.Config.Types.UInt32, v)
 				f.NamedValues[hiName] = append(f.NamedValues[hiName], hi)
 				f.NamedValues[loName] = append(f.NamedValues[loName], lo)
 			}
 			delete(f.NamedValues, name)
 		case t.IsComplex():
 			var elemType *types.Type
 			if t.Size() == 16 {
 				elemType = f.Config.Types.Float64
 			} else {
 				elemType = f.Config.Types.Float32
 			}
 			rName, iName := f.fe.SplitComplex(name)
 			newNames = append(newNames, rName, iName)
 			for _, v := range f.NamedValues[name] {
 				r := v.Block.NewValue1(v.Pos, OpComplexReal, elemType, v)
 				i := v.Block.NewValue1(v.Pos, OpComplexImag, elemType, v)
 				f.NamedValues[rName] = append(f.NamedValues[rName], r)
 				f.NamedValues[iName] = append(f.NamedValues[iName], i)
 			}
 			delete(f.NamedValues, name)
 		case t.IsString():
 			ptrType := f.Config.Types.BytePtr
 			lenType := f.Config.Types.Int
 			ptrName, lenName := f.fe.SplitString(name)
 			newNames = append(newNames, ptrName, lenName)
 			for _, v := range f.NamedValues[name] {
 				ptr := v.Block.NewValue1(v.Pos, OpStringPtr, ptrType, v)
 				len := v.Block.NewValue1(v.Pos, OpStringLen, lenType, v)
 				f.NamedValues[ptrName] = append(f.NamedValues[ptrName], ptr)
 				f.NamedValues[lenName] = append(f.NamedValues[lenName], len)
 			}
 			delete(f.NamedValues, name)
 		case t.IsSlice():
 			ptrType := f.Config.Types.BytePtr
 			lenType := f.Config.Types.Int
 			ptrName, lenName, capName := f.fe.SplitSlice(name)
 			newNames = append(newNames, ptrName, lenName, capName)
 			for _, v := range f.NamedValues[name] {
 				ptr := v.Block.NewValue1(v.Pos, OpSlicePtr, ptrType, v)
 				len := v.Block.NewValue1(v.Pos, OpSliceLen, lenType, v)
 				cap := v.Block.NewValue1(v.Pos, 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)
 			}
 			delete(f.NamedValues, name)
 		case t.IsInterface():
 			ptrType := f.Config.Types.BytePtr
 			typeName, dataName := f.fe.SplitInterface(name)
 			newNames = append(newNames, typeName, dataName)
 			for _, v := range f.NamedValues[name] {
 				typ := v.Block.NewValue1(v.Pos, OpITab, ptrType, v)
 				data := v.Block.NewValue1(v.Pos, OpIData, ptrType, v)
 				f.NamedValues[typeName] = append(f.NamedValues[typeName], typ)
 				f.NamedValues[dataName] = append(f.NamedValues[dataName], data)
 			}
 			delete(f.NamedValues, name)
 		case t.IsFloat():
 			// floats are never decomposed, even ones bigger than RegSize
 		case t.Size() > f.Config.RegSize:
 			f.Fatalf("undecomposed named type %v %v", name, t)
 		default:
 			newNames = append(newNames, name)
 		}
 	}
 	f.Names = newNames
 }

 func decomposeBuiltInPhi(v *Value) {
 	switch {
 	case v.Type.IsInteger() && v.Type.Size() > v.Block.Func.Config.RegSize:
 		decomposeInt64Phi(v)
 	case v.Type.IsComplex():
 		decomposeComplexPhi(v)
 	case v.Type.IsString():
 		decomposeStringPhi(v)
 	case v.Type.IsSlice():
 		decomposeSlicePhi(v)
 	case v.Type.IsInterface():
 		decomposeInterfacePhi(v)
 	case v.Type.IsFloat():
 		// floats are never decomposed, even ones bigger than RegSize
 	case v.Type.Size() > v.Block.Func.Config.RegSize:
 		v.Fatalf("undecomposed type %s", v.Type)
 	}
 }

 func decomposeStringPhi(v *Value) {
 	types := &v.Block.Func.Config.Types
 	ptrType := types.BytePtr
 	lenType := types.Int

 	ptr := v.Block.NewValue0(v.Pos, OpPhi, ptrType)
 	len := v.Block.NewValue0(v.Pos, OpPhi, lenType)
 	for _, a := range v.Args {
 		ptr.AddArg(a.Block.NewValue1(v.Pos, OpStringPtr, ptrType, a))
 		len.AddArg(a.Block.NewValue1(v.Pos, OpStringLen, lenType, a))
 	}
 	v.reset(OpStringMake)
 	v.AddArg(ptr)
 	v.AddArg(len)
 }

 func decomposeSlicePhi(v *Value) {
 	types := &v.Block.Func.Config.Types
 	ptrType := types.BytePtr
 	lenType := types.Int

 	ptr := v.Block.NewValue0(v.Pos, OpPhi, ptrType)
 	len := v.Block.NewValue0(v.Pos, OpPhi, lenType)
 	cap := v.Block.NewValue0(v.Pos, OpPhi, lenType)
 	for _, a := range v.Args {
 		ptr.AddArg(a.Block.NewValue1(v.Pos, OpSlicePtr, ptrType, a))
 		len.AddArg(a.Block.NewValue1(v.Pos, OpSliceLen, lenType, a))
 		cap.AddArg(a.Block.NewValue1(v.Pos, OpSliceCap, lenType, a))
 	}
 	v.reset(OpSliceMake)
 	v.AddArg(ptr)
 	v.AddArg(len)
 	v.AddArg(cap)
 }

 func decomposeInt64Phi(v *Value) {
 	cfgtypes := &v.Block.Func.Config.Types
 	var partType *types.Type
 	if v.Type.IsSigned() {
 		partType = cfgtypes.Int32
 	} else {
 		partType = cfgtypes.UInt32
 	}

 	hi := v.Block.NewValue0(v.Pos, OpPhi, partType)
 	lo := v.Block.NewValue0(v.Pos, OpPhi, cfgtypes.UInt32)
 	for _, a := range v.Args {
 		hi.AddArg(a.Block.NewValue1(v.Pos, OpInt64Hi, partType, a))
 		lo.AddArg(a.Block.NewValue1(v.Pos, OpInt64Lo, cfgtypes.UInt32, a))
 	}
 	v.reset(OpInt64Make)
 	v.AddArg(hi)
 	v.AddArg(lo)
 }

 func decomposeComplexPhi(v *Value) {
 	cfgtypes := &v.Block.Func.Config.Types
 	var partType *types.Type
 	switch z := v.Type.Size(); z {
 	case 8:
 		partType = cfgtypes.Float32
 	case 16:
 		partType = cfgtypes.Float64
 	default:
 		v.Fatalf("decomposeComplexPhi: bad complex size %d", z)
 	}

 	real := v.Block.NewValue0(v.Pos, OpPhi, partType)
 	imag := v.Block.NewValue0(v.Pos, OpPhi, partType)
 	for _, a := range v.Args {
 		real.AddArg(a.Block.NewValue1(v.Pos, OpComplexReal, partType, a))
 		imag.AddArg(a.Block.NewValue1(v.Pos, OpComplexImag, partType, a))
 	}
 	v.reset(OpComplexMake)
 	v.AddArg(real)
 	v.AddArg(imag)
 }

 func decomposeInterfacePhi(v *Value) {
 	ptrType := v.Block.Func.Config.Types.BytePtr

 	itab := v.Block.NewValue0(v.Pos, OpPhi, ptrType)
 	data := v.Block.NewValue0(v.Pos, OpPhi, ptrType)
 	for _, a := range v.Args {
 		itab.AddArg(a.Block.NewValue1(v.Pos, OpITab, ptrType, a))
 		data.AddArg(a.Block.NewValue1(v.Pos, OpIData, ptrType, a))
 	}
 	v.reset(OpIMake)
 	v.AddArg(itab)
 	v.AddArg(data)
 }

 func decomposeUser(f *Func) {
 	for _, b := range f.Blocks {
 		for _, v := range b.Values {
 			if v.Op != OpPhi {
 				continue
 			}
 			decomposeUserPhi(v)
 		}
 	}
 	// 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.
 	i := 0
 	var fnames []LocalSlot
 	var newNames []LocalSlot
 	for _, name := range f.Names {
 		t := name.Type
 		switch {
 		case t.IsStruct():
 			n := t.NumFields()
 			fnames = fnames[:0]
 			for i := 0; i < n; i++ {
 				fnames = append(fnames, f.fe.SplitStruct(name, i))
 			}
 			for _, v := range f.NamedValues[name] {
 				for i := 0; i < n; i++ {
 					x := v.Block.NewValue1I(v.Pos, OpStructSelect, t.FieldType(i), int64(i), v)
 					f.NamedValues[fnames[i]] = append(f.NamedValues[fnames[i]], x)
 				}
 			}
 			delete(f.NamedValues, name)
 			newNames = append(newNames, fnames...)
 		case t.IsArray():
 			if t.NumElem() == 0 {
 				// TODO(khr): Not sure what to do here.  Probably nothing.
 				// Names for empty arrays aren't important.
 				break
 			}
 			if t.NumElem() != 1 {
 				f.Fatalf("array not of size 1")
 			}
 			elemName := f.fe.SplitArray(name)
 			for _, v := range f.NamedValues[name] {
 				e := v.Block.NewValue1I(v.Pos, OpArraySelect, t.ElemType(), 0, v)
 				f.NamedValues[elemName] = append(f.NamedValues[elemName], e)
 			}

 		default:
 			f.Names[i] = name
 			i++
 		}
 	}
 	f.Names = f.Names[:i]
 	f.Names = append(f.Names, newNames...)
 }

 func decomposeUserPhi(v *Value) {
 	switch {
 	case v.Type.IsStruct():
 		decomposeStructPhi(v)
 	case v.Type.IsArray():
 		decomposeArrayPhi(v)
 	}
 }

 // decomposeStructPhi replaces phi-of-struct with structmake(phi-for-each-field),
 // and then recursively decomposes the phis for each field.
 func decomposeStructPhi(v *Value) {
 	t := v.Type
 	n := t.NumFields()
 	var fields [MaxStruct]*Value
 	for i := 0; i < n; i++ {
 		fields[i] = v.Block.NewValue0(v.Pos, OpPhi, t.FieldType(i))
 	}
 	for _, a := range v.Args {
 		for i := 0; i < n; i++ {
 			fields[i].AddArg(a.Block.NewValue1I(v.Pos, OpStructSelect, t.FieldType(i), int64(i), a))
 		}
 	}
 	v.reset(StructMakeOp(n))
 	v.AddArgs(fields[:n]...)

 	// Recursively decompose phis for each field.
 	for _, f := range fields[:n] {
 		decomposeUserPhi(f)
 	}
 }

 // decomposeArrayPhi replaces phi-of-array with arraymake(phi-of-array-element),
 // and then recursively decomposes the element phi.
 func decomposeArrayPhi(v *Value) {
 	t := v.Type
 	if t.NumElem() == 0 {
 		v.reset(OpArrayMake0)
 		return
 	}
 	if t.NumElem() != 1 {
 		v.Fatalf("SSAable array must have no more than 1 element")
 	}
 	elem := v.Block.NewValue0(v.Pos, OpPhi, t.ElemType())
 	for _, a := range v.Args {
 		elem.AddArg(a.Block.NewValue1I(v.Pos, OpArraySelect, t.ElemType(), 0, a))
 	}
 	v.reset(OpArrayMake1)
 	v.AddArg(elem)

 	// Recursively decompose elem phi.
 	decomposeUserPhi(elem)
 }

 // MaxStruct is the maximum number of fields a struct
 // can have and still be SSAable.
 const MaxStruct = 4

 // StructMakeOp returns the opcode to construct a struct with the
 // given number of fields.
 func StructMakeOp(nf int) Op {
 	switch nf {
 	case 0:
 		return OpStructMake0
 	case 1:
 		return OpStructMake1
 	case 2:
 		return OpStructMake2
 	case 3:
 		return OpStructMake3
 	case 4:
 		return OpStructMake4
 	}
 	panic("too many fields in an SSAable struct")
 }
	// Copyright 2015 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.

	package ssa

	import "cmd/compile/internal/types"

	// decompose converts phi ops on compound builtin types into phi
	// ops on simple types.
	// (The remaining compound ops are decomposed with rewrite rules.)
	func decomposeBuiltIn(f *Func) {
	for _, b := range f.Blocks {
	for _, v := range b.Values {
	if v.Op != OpPhi {
	continue
	}
	decomposeBuiltInPhi(v)
	}
	}

	// 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.
	var newNames []LocalSlot
	for _, name := range f.Names {
	t := name.Type
	switch {
	case t.IsInteger() && t.Size() > f.Config.RegSize:
	var elemType *types.Type
	if t.IsSigned() {
	elemType = f.Config.Types.Int32
	} else {
	elemType = f.Config.Types.UInt32
	}
	hiName, loName := f.fe.SplitInt64(name)
	newNames = append(newNames, hiName, loName)
	for _, v := range f.NamedValues[name] {
	hi := v.Block.NewValue1(v.Pos, OpInt64Hi, elemType, v)
	lo := v.Block.NewValue1(v.Pos, OpInt64Lo, f.Config.Types.UInt32, v)
	f.NamedValues[hiName] = append(f.NamedValues[hiName], hi)
	f.NamedValues[loName] = append(f.NamedValues[loName], lo)
	}
	delete(f.NamedValues, name)
	case t.IsComplex():
	var elemType *types.Type
	if t.Size() == 16 {
	elemType = f.Config.Types.Float64
	} else {
	elemType = f.Config.Types.Float32
	}
	rName, iName := f.fe.SplitComplex(name)
	newNames = append(newNames, rName, iName)
	for _, v := range f.NamedValues[name] {
	r := v.Block.NewValue1(v.Pos, OpComplexReal, elemType, v)
	i := v.Block.NewValue1(v.Pos, OpComplexImag, elemType, v)
	f.NamedValues[rName] = append(f.NamedValues[rName], r)
	f.NamedValues[iName] = append(f.NamedValues[iName], i)
	}
	delete(f.NamedValues, name)
	case t.IsString():
	ptrType := f.Config.Types.BytePtr
	lenType := f.Config.Types.Int
	ptrName, lenName := f.fe.SplitString(name)
	newNames = append(newNames, ptrName, lenName)
	for _, v := range f.NamedValues[name] {
	ptr := v.Block.NewValue1(v.Pos, OpStringPtr, ptrType, v)
	len := v.Block.NewValue1(v.Pos, OpStringLen, lenType, v)
	f.NamedValues[ptrName] = append(f.NamedValues[ptrName], ptr)
	f.NamedValues[lenName] = append(f.NamedValues[lenName], len)
	}
	delete(f.NamedValues, name)
	case t.IsSlice():
	ptrType := f.Config.Types.BytePtr
	lenType := f.Config.Types.Int
	ptrName, lenName, capName := f.fe.SplitSlice(name)
	newNames = append(newNames, ptrName, lenName, capName)
	for _, v := range f.NamedValues[name] {
	ptr := v.Block.NewValue1(v.Pos, OpSlicePtr, ptrType, v)
	len := v.Block.NewValue1(v.Pos, OpSliceLen, lenType, v)
	cap := v.Block.NewValue1(v.Pos, 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)
	}
	delete(f.NamedValues, name)
	case t.IsInterface():
	ptrType := f.Config.Types.BytePtr
	typeName, dataName := f.fe.SplitInterface(name)
	newNames = append(newNames, typeName, dataName)
	for _, v := range f.NamedValues[name] {
	typ := v.Block.NewValue1(v.Pos, OpITab, ptrType, v)
	data := v.Block.NewValue1(v.Pos, OpIData, ptrType, v)
	f.NamedValues[typeName] = append(f.NamedValues[typeName], typ)
	f.NamedValues[dataName] = append(f.NamedValues[dataName], data)
	}
	delete(f.NamedValues, name)
	case t.IsFloat():
	// floats are never decomposed, even ones bigger than RegSize
	case t.Size() > f.Config.RegSize:
	f.Fatalf("undecomposed named type %v %v", name, t)
	default:
	newNames = append(newNames, name)
	}
	}
	f.Names = newNames
	}

	func decomposeBuiltInPhi(v *Value) {
	switch {
	case v.Type.IsInteger() && v.Type.Size() > v.Block.Func.Config.RegSize:
	decomposeInt64Phi(v)
	case v.Type.IsComplex():
	decomposeComplexPhi(v)
	case v.Type.IsString():
	decomposeStringPhi(v)
	case v.Type.IsSlice():
	decomposeSlicePhi(v)
	case v.Type.IsInterface():
	decomposeInterfacePhi(v)
	case v.Type.IsFloat():
	// floats are never decomposed, even ones bigger than RegSize
	case v.Type.Size() > v.Block.Func.Config.RegSize:
	v.Fatalf("undecomposed type %s", v.Type)
	}
	}

	func decomposeStringPhi(v *Value) {
	types := &v.Block.Func.Config.Types
	ptrType := types.BytePtr
	lenType := types.Int

	ptr := v.Block.NewValue0(v.Pos, OpPhi, ptrType)
	len := v.Block.NewValue0(v.Pos, OpPhi, lenType)
	for _, a := range v.Args {
	ptr.AddArg(a.Block.NewValue1(v.Pos, OpStringPtr, ptrType, a))
	len.AddArg(a.Block.NewValue1(v.Pos, OpStringLen, lenType, a))
	}
	v.reset(OpStringMake)
	v.AddArg(ptr)
	v.AddArg(len)
	}

	func decomposeSlicePhi(v *Value) {
	types := &v.Block.Func.Config.Types
	ptrType := types.BytePtr
	lenType := types.Int

	ptr := v.Block.NewValue0(v.Pos, OpPhi, ptrType)
	len := v.Block.NewValue0(v.Pos, OpPhi, lenType)
	cap := v.Block.NewValue0(v.Pos, OpPhi, lenType)
	for _, a := range v.Args {
	ptr.AddArg(a.Block.NewValue1(v.Pos, OpSlicePtr, ptrType, a))
	len.AddArg(a.Block.NewValue1(v.Pos, OpSliceLen, lenType, a))
	cap.AddArg(a.Block.NewValue1(v.Pos, OpSliceCap, lenType, a))
	}
	v.reset(OpSliceMake)
	v.AddArg(ptr)
	v.AddArg(len)
	v.AddArg(cap)
	}

	func decomposeInt64Phi(v *Value) {
	cfgtypes := &v.Block.Func.Config.Types
	var partType *types.Type
	if v.Type.IsSigned() {
	partType = cfgtypes.Int32
	} else {
	partType = cfgtypes.UInt32
	}

	hi := v.Block.NewValue0(v.Pos, OpPhi, partType)
	lo := v.Block.NewValue0(v.Pos, OpPhi, cfgtypes.UInt32)
	for _, a := range v.Args {
	hi.AddArg(a.Block.NewValue1(v.Pos, OpInt64Hi, partType, a))
	lo.AddArg(a.Block.NewValue1(v.Pos, OpInt64Lo, cfgtypes.UInt32, a))
	}
	v.reset(OpInt64Make)
	v.AddArg(hi)
	v.AddArg(lo)
	}

	func decomposeComplexPhi(v *Value) {
	cfgtypes := &v.Block.Func.Config.Types
	var partType *types.Type
	switch z := v.Type.Size(); z {
	case 8:
	partType = cfgtypes.Float32
	case 16:
	partType = cfgtypes.Float64
	default:
	v.Fatalf("decomposeComplexPhi: bad complex size %d", z)
	}

	real := v.Block.NewValue0(v.Pos, OpPhi, partType)
	imag := v.Block.NewValue0(v.Pos, OpPhi, partType)
	for _, a := range v.Args {
	real.AddArg(a.Block.NewValue1(v.Pos, OpComplexReal, partType, a))
	imag.AddArg(a.Block.NewValue1(v.Pos, OpComplexImag, partType, a))
	}
	v.reset(OpComplexMake)
	v.AddArg(real)
	v.AddArg(imag)
	}

	func decomposeInterfacePhi(v *Value) {
	ptrType := v.Block.Func.Config.Types.BytePtr

	itab := v.Block.NewValue0(v.Pos, OpPhi, ptrType)
	data := v.Block.NewValue0(v.Pos, OpPhi, ptrType)
	for _, a := range v.Args {
	itab.AddArg(a.Block.NewValue1(v.Pos, OpITab, ptrType, a))
	data.AddArg(a.Block.NewValue1(v.Pos, OpIData, ptrType, a))
	}
	v.reset(OpIMake)
	v.AddArg(itab)
	v.AddArg(data)
	}

	func decomposeUser(f *Func) {
	for _, b := range f.Blocks {
	for _, v := range b.Values {
	if v.Op != OpPhi {
	continue
	}
	decomposeUserPhi(v)
	}
	}
	// 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.
	i := 0
	var fnames []LocalSlot
	var newNames []LocalSlot
	for _, name := range f.Names {
	t := name.Type
	switch {
	case t.IsStruct():
	n := t.NumFields()
	fnames = fnames[:0]
	for i := 0; i < n; i++ {
	fnames = append(fnames, f.fe.SplitStruct(name, i))
	}
	for _, v := range f.NamedValues[name] {
	for i := 0; i < n; i++ {
	x := v.Block.NewValue1I(v.Pos, OpStructSelect, t.FieldType(i), int64(i), v)
	f.NamedValues[fnames[i]] = append(f.NamedValues[fnames[i]], x)
	}
	}
	delete(f.NamedValues, name)
	newNames = append(newNames, fnames...)
	case t.IsArray():
	if t.NumElem() == 0 {
	// TODO(khr): Not sure what to do here. Probably nothing.
	// Names for empty arrays aren't important.
	break
	}
	if t.NumElem() != 1 {
	f.Fatalf("array not of size 1")
	}
	elemName := f.fe.SplitArray(name)
	for _, v := range f.NamedValues[name] {
	e := v.Block.NewValue1I(v.Pos, OpArraySelect, t.ElemType(), 0, v)
	f.NamedValues[elemName] = append(f.NamedValues[elemName], e)
	}

	default:
	f.Names[i] = name
	i++
	}
	}
	f.Names = f.Names[:i]
	f.Names = append(f.Names, newNames...)
	}

	func decomposeUserPhi(v *Value) {
	switch {
	case v.Type.IsStruct():
	decomposeStructPhi(v)
	case v.Type.IsArray():
	decomposeArrayPhi(v)
	}
	}

	// decomposeStructPhi replaces phi-of-struct with structmake(phi-for-each-field),
	// and then recursively decomposes the phis for each field.
	func decomposeStructPhi(v *Value) {
	t := v.Type
	n := t.NumFields()
	var fields [MaxStruct]*Value
	for i := 0; i < n; i++ {
	fields[i] = v.Block.NewValue0(v.Pos, OpPhi, t.FieldType(i))
	}
	for _, a := range v.Args {
	for i := 0; i < n; i++ {
	fields[i].AddArg(a.Block.NewValue1I(v.Pos, OpStructSelect, t.FieldType(i), int64(i), a))
	}
	}
	v.reset(StructMakeOp(n))
	v.AddArgs(fields[:n]...)

	// Recursively decompose phis for each field.
	for _, f := range fields[:n] {
	decomposeUserPhi(f)
	}
	}

	// decomposeArrayPhi replaces phi-of-array with arraymake(phi-of-array-element),
	// and then recursively decomposes the element phi.
	func decomposeArrayPhi(v *Value) {
	t := v.Type
	if t.NumElem() == 0 {
	v.reset(OpArrayMake0)
	return
	}
	if t.NumElem() != 1 {
	v.Fatalf("SSAable array must have no more than 1 element")
	}
	elem := v.Block.NewValue0(v.Pos, OpPhi, t.ElemType())
	for _, a := range v.Args {
	elem.AddArg(a.Block.NewValue1I(v.Pos, OpArraySelect, t.ElemType(), 0, a))
	}
	v.reset(OpArrayMake1)
	v.AddArg(elem)

	// Recursively decompose elem phi.
	decomposeUserPhi(elem)
	}

	// MaxStruct is the maximum number of fields a struct
	// can have and still be SSAable.
	const MaxStruct = 4

	// StructMakeOp returns the opcode to construct a struct with the
	// given number of fields.
	func StructMakeOp(nf int) Op {
	switch nf {
	case 0:
	return OpStructMake0
	case 1:
	return OpStructMake1
	case 2:
	return OpStructMake2
	case 3:
	return OpStructMake3
	case 4:
	return OpStructMake4
	}
	panic("too many fields in an SSAable struct")
	}