Adding upstream version 1.20.14.upstream/1.20.14upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1800 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/ssa/expand_calls.go b/src/cmd/compile/internal/ssa/expand_calls.go
new file mode 100644
index 0000000..a5daa14
--- /dev/null
+++ b/src/cmd/compile/internal/ssa/expand_calls.go
@@ -0,0 +1,1800 @@
+// Copyright 2020 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/abi"
+	"cmd/compile/internal/base"
+	"cmd/compile/internal/ir"
+	"cmd/compile/internal/types"
+	"cmd/internal/src"
+	"fmt"
+	"sort"
+)
+
+type selKey struct {
+	from          *Value // what is selected from
+	offsetOrIndex int64  // whatever is appropriate for the selector
+	size          int64
+	typ           *types.Type
+}
+
+type Abi1RO uint8 // An offset within a parameter's slice of register indices, for abi1.
+
+func isBlockMultiValueExit(b *Block) bool {
+	return (b.Kind == BlockRet || b.Kind == BlockRetJmp) && b.Controls[0] != nil && b.Controls[0].Op == OpMakeResult
+}
+
+func badVal(s string, v *Value) error {
+	return fmt.Errorf("%s %s", s, v.LongString())
+}
+
+// removeTrivialWrapperTypes unwraps layers of
+// struct { singleField SomeType } and [1]SomeType
+// until a non-wrapper type is reached.  This is useful
+// for working with assignments to/from interface data
+// fields (either second operand to OpIMake or OpIData)
+// where the wrapping or type conversion can be elided
+// because of type conversions/assertions in source code
+// that do not appear in SSA.
+func removeTrivialWrapperTypes(t *types.Type) *types.Type {
+	for {
+		if t.IsStruct() && t.NumFields() == 1 {
+			t = t.Field(0).Type
+			continue
+		}
+		if t.IsArray() && t.NumElem() == 1 {
+			t = t.Elem()
+			continue
+		}
+		break
+	}
+	return t
+}
+
+// A registerCursor tracks which register is used for an Arg or regValues, or a piece of such.
+type registerCursor struct {
+	// TODO(register args) convert this to a generalized target cursor.
+	storeDest *Value // if there are no register targets, then this is the base of the store.
+	regsLen   int    // the number of registers available for this Arg/result (which is all in registers or not at all)
+	nextSlice Abi1RO // the next register/register-slice offset
+	config    *abi.ABIConfig
+	regValues *[]*Value // values assigned to registers accumulate here
+}
+
+func (rc *registerCursor) String() string {
+	dest := "<none>"
+	if rc.storeDest != nil {
+		dest = rc.storeDest.String()
+	}
+	regs := "<none>"
+	if rc.regValues != nil {
+		regs = ""
+		for i, x := range *rc.regValues {
+			if i > 0 {
+				regs = regs + "; "
+			}
+			regs = regs + x.LongString()
+		}
+	}
+	// not printing the config because that has not been useful
+	return fmt.Sprintf("RCSR{storeDest=%v, regsLen=%d, nextSlice=%d, regValues=[%s]}", dest, rc.regsLen, rc.nextSlice, regs)
+}
+
+// next effectively post-increments the register cursor; the receiver is advanced,
+// the old value is returned.
+func (c *registerCursor) next(t *types.Type) registerCursor {
+	rc := *c
+	if int(c.nextSlice) < c.regsLen {
+		w := c.config.NumParamRegs(t)
+		c.nextSlice += Abi1RO(w)
+	}
+	return rc
+}
+
+// plus returns a register cursor offset from the original, without modifying the original.
+func (c *registerCursor) plus(regWidth Abi1RO) registerCursor {
+	rc := *c
+	rc.nextSlice += regWidth
+	return rc
+}
+
+const (
+	// Register offsets for fields of built-in aggregate types; the ones not listed are zero.
+	RO_complex_imag = 1
+	RO_string_len   = 1
+	RO_slice_len    = 1
+	RO_slice_cap    = 2
+	RO_iface_data   = 1
+)
+
+func (x *expandState) regWidth(t *types.Type) Abi1RO {
+	return Abi1RO(x.abi1.NumParamRegs(t))
+}
+
+// regOffset returns the register offset of the i'th element of type t
+func (x *expandState) regOffset(t *types.Type, i int) Abi1RO {
+	// TODO maybe cache this in a map if profiling recommends.
+	if i == 0 {
+		return 0
+	}
+	if t.IsArray() {
+		return Abi1RO(i) * x.regWidth(t.Elem())
+	}
+	if t.IsStruct() {
+		k := Abi1RO(0)
+		for j := 0; j < i; j++ {
+			k += x.regWidth(t.FieldType(j))
+		}
+		return k
+	}
+	panic("Haven't implemented this case yet, do I need to?")
+}
+
+// at returns the register cursor for component i of t, where the first
+// component is numbered 0.
+func (c *registerCursor) at(t *types.Type, i int) registerCursor {
+	rc := *c
+	if i == 0 || c.regsLen == 0 {
+		return rc
+	}
+	if t.IsArray() {
+		w := c.config.NumParamRegs(t.Elem())
+		rc.nextSlice += Abi1RO(i * w)
+		return rc
+	}
+	if t.IsStruct() {
+		for j := 0; j < i; j++ {
+			rc.next(t.FieldType(j))
+		}
+		return rc
+	}
+	panic("Haven't implemented this case yet, do I need to?")
+}
+
+func (c *registerCursor) init(regs []abi.RegIndex, info *abi.ABIParamResultInfo, result *[]*Value, storeDest *Value) {
+	c.regsLen = len(regs)
+	c.nextSlice = 0
+	if len(regs) == 0 {
+		c.storeDest = storeDest // only save this if there are no registers, will explode if misused.
+		return
+	}
+	c.config = info.Config()
+	c.regValues = result
+}
+
+func (c *registerCursor) addArg(v *Value) {
+	*c.regValues = append(*c.regValues, v)
+}
+
+func (c *registerCursor) hasRegs() bool {
+	return c.regsLen > 0
+}
+
+type expandState struct {
+	f                  *Func
+	abi1               *abi.ABIConfig
+	debug              int // odd values log lost statement markers, so likely settings are 1 (stmts), 2 (expansion), and 3 (both)
+	canSSAType         func(*types.Type) bool
+	regSize            int64
+	sp                 *Value
+	typs               *Types
+	ptrSize            int64
+	hiOffset           int64
+	lowOffset          int64
+	hiRo               Abi1RO
+	loRo               Abi1RO
+	namedSelects       map[*Value][]namedVal
+	sdom               SparseTree
+	commonSelectors    map[selKey]*Value // used to de-dupe selectors
+	commonArgs         map[selKey]*Value // used to de-dupe OpArg/OpArgIntReg/OpArgFloatReg
+	memForCall         map[ID]*Value     // For a call, need to know the unique selector that gets the mem.
+	transformedSelects map[ID]bool       // OpSelectN after rewriting, either created or renumbered.
+	indentLevel        int               // Indentation for debugging recursion
+}
+
+// intPairTypes returns the pair of 32-bit int types needed to encode a 64-bit integer type on a target
+// that has no 64-bit integer registers.
+func (x *expandState) intPairTypes(et types.Kind) (tHi, tLo *types.Type) {
+	tHi = x.typs.UInt32
+	if et == types.TINT64 {
+		tHi = x.typs.Int32
+	}
+	tLo = x.typs.UInt32
+	return
+}
+
+// isAlreadyExpandedAggregateType returns whether a type is an SSA-able "aggregate" (multiple register) type
+// that was expanded in an earlier phase (currently, expand_calls is intended to run after decomposeBuiltin,
+// so this is all aggregate types -- small struct and array, complex, interface, string, slice, and 64-bit
+// integer on 32-bit).
+func (x *expandState) isAlreadyExpandedAggregateType(t *types.Type) bool {
+	if !x.canSSAType(t) {
+		return false
+	}
+	return t.IsStruct() || t.IsArray() || t.IsComplex() || t.IsInterface() || t.IsString() || t.IsSlice() ||
+		(t.Size() > x.regSize && (t.IsInteger() || (x.f.Config.SoftFloat && t.IsFloat())))
+}
+
+// offsetFrom creates an offset from a pointer, simplifying chained offsets and offsets from SP
+// TODO should also optimize offsets from SB?
+func (x *expandState) offsetFrom(b *Block, from *Value, offset int64, pt *types.Type) *Value {
+	ft := from.Type
+	if offset == 0 {
+		if ft == pt {
+			return from
+		}
+		// This captures common, (apparently) safe cases.  The unsafe cases involve ft == uintptr
+		if (ft.IsPtr() || ft.IsUnsafePtr()) && pt.IsPtr() {
+			return from
+		}
+	}
+	// Simplify, canonicalize
+	for from.Op == OpOffPtr {
+		offset += from.AuxInt
+		from = from.Args[0]
+	}
+	if from == x.sp {
+		return x.f.ConstOffPtrSP(pt, offset, x.sp)
+	}
+	return b.NewValue1I(from.Pos.WithNotStmt(), OpOffPtr, pt, offset, from)
+}
+
+// splitSlots splits one "field" (specified by sfx, offset, and ty) out of the LocalSlots in ls and returns the new LocalSlots this generates.
+func (x *expandState) splitSlots(ls []*LocalSlot, sfx string, offset int64, ty *types.Type) []*LocalSlot {
+	var locs []*LocalSlot
+	for i := range ls {
+		locs = append(locs, x.f.SplitSlot(ls[i], sfx, offset, ty))
+	}
+	return locs
+}
+
+// prAssignForArg returns the ABIParamAssignment for v, assumed to be an OpArg.
+func (x *expandState) prAssignForArg(v *Value) *abi.ABIParamAssignment {
+	if v.Op != OpArg {
+		panic(badVal("Wanted OpArg, instead saw", v))
+	}
+	return ParamAssignmentForArgName(x.f, v.Aux.(*ir.Name))
+}
+
+// ParamAssignmentForArgName returns the ABIParamAssignment for f's arg with matching name.
+func ParamAssignmentForArgName(f *Func, name *ir.Name) *abi.ABIParamAssignment {
+	abiInfo := f.OwnAux.abiInfo
+	ip := abiInfo.InParams()
+	for i, a := range ip {
+		if a.Name == name {
+			return &ip[i]
+		}
+	}
+	panic(fmt.Errorf("Did not match param %v in prInfo %+v", name, abiInfo.InParams()))
+}
+
+// indent increments (or decrements) the indentation.
+func (x *expandState) indent(n int) {
+	x.indentLevel += n
+}
+
+// Printf does an indented fmt.Printf on te format and args.
+func (x *expandState) Printf(format string, a ...interface{}) (n int, err error) {
+	if x.indentLevel > 0 {
+		fmt.Printf("%[1]*s", x.indentLevel, "")
+	}
+	return fmt.Printf(format, a...)
+}
+
+// Calls that need lowering have some number of inputs, including a memory input,
+// and produce a tuple of (value1, value2, ..., mem) where valueK may or may not be SSA-able.
+
+// With the current ABI those inputs need to be converted into stores to memory,
+// rethreading the call's memory input to the first, and the new call now receiving the last.
+
+// With the current ABI, the outputs need to be converted to loads, which will all use the call's
+// memory output as their input.
+
+// rewriteSelect recursively walks from leaf selector to a root (OpSelectN, OpLoad, OpArg)
+// through a chain of Struct/Array/builtin Select operations.  If the chain of selectors does not
+// end in an expected root, it does nothing (this can happen depending on compiler phase ordering).
+// The "leaf" provides the type, the root supplies the container, and the leaf-to-root path
+// accumulates the offset.
+// It emits the code necessary to implement the leaf select operation that leads to the root.
+//
+// TODO when registers really arrive, must also decompose anything split across two registers or registers and memory.
+func (x *expandState) rewriteSelect(leaf *Value, selector *Value, offset int64, regOffset Abi1RO) []*LocalSlot {
+	if x.debug > 1 {
+		x.indent(3)
+		defer x.indent(-3)
+		x.Printf("rewriteSelect(%s; %s; memOff=%d; regOff=%d)\n", leaf.LongString(), selector.LongString(), offset, regOffset)
+	}
+	var locs []*LocalSlot
+	leafType := leaf.Type
+	if len(selector.Args) > 0 {
+		w := selector.Args[0]
+		if w.Op == OpCopy {
+			for w.Op == OpCopy {
+				w = w.Args[0]
+			}
+			selector.SetArg(0, w)
+		}
+	}
+	switch selector.Op {
+	case OpArgIntReg, OpArgFloatReg:
+		if leafType == selector.Type { // OpIData leads us here, sometimes.
+			leaf.copyOf(selector)
+		} else {
+			x.f.Fatalf("Unexpected %s type, selector=%s, leaf=%s\n", selector.Op.String(), selector.LongString(), leaf.LongString())
+		}
+		if x.debug > 1 {
+			x.Printf("---%s, break\n", selector.Op.String())
+		}
+	case OpArg:
+		if !x.isAlreadyExpandedAggregateType(selector.Type) {
+			if leafType == selector.Type { // OpIData leads us here, sometimes.
+				x.newArgToMemOrRegs(selector, leaf, offset, regOffset, leafType, leaf.Pos)
+			} else {
+				x.f.Fatalf("Unexpected OpArg type, selector=%s, leaf=%s\n", selector.LongString(), leaf.LongString())
+			}
+			if x.debug > 1 {
+				x.Printf("---OpArg, break\n")
+			}
+			break
+		}
+		switch leaf.Op {
+		case OpIData, OpStructSelect, OpArraySelect:
+			leafType = removeTrivialWrapperTypes(leaf.Type)
+		}
+		x.newArgToMemOrRegs(selector, leaf, offset, regOffset, leafType, leaf.Pos)
+
+		for _, s := range x.namedSelects[selector] {
+			locs = append(locs, x.f.Names[s.locIndex])
+		}
+
+	case OpLoad: // We end up here because of IData of immediate structures.
+		// Failure case:
+		// (note the failure case is very rare; w/o this case, make.bash and run.bash both pass, as well as
+		// the hard cases of building {syscall,math,math/cmplx,math/bits,go/constant} on ppc64le and mips-softfloat).
+		//
+		// GOSSAFUNC='(*dumper).dump' go build -gcflags=-l -tags=math_big_pure_go cmd/compile/internal/gc
+		// cmd/compile/internal/gc/dump.go:136:14: internal compiler error: '(*dumper).dump': not lowered: v827, StructSelect PTR PTR
+		// b2: ← b1
+		// v20 (+142) = StaticLECall <interface {},mem> {AuxCall{reflect.Value.Interface([reflect.Value,0])[interface {},24]}} [40] v8 v1
+		// v21 (142) = SelectN <mem> [1] v20
+		// v22 (142) = SelectN <interface {}> [0] v20
+		// b15: ← b8
+		// v71 (+143) = IData <Nodes> v22 (v[Nodes])
+		// v73 (+146) = StaticLECall <[]*Node,mem> {AuxCall{"".Nodes.Slice([Nodes,0])[[]*Node,8]}} [32] v71 v21
+		//
+		// translates (w/o the "case OpLoad:" above) to:
+		//
+		// b2: ← b1
+		// v20 (+142) = StaticCall <mem> {AuxCall{reflect.Value.Interface([reflect.Value,0])[interface {},24]}} [40] v715
+		// v23 (142) = Load <*uintptr> v19 v20
+		// v823 (142) = IsNonNil <bool> v23
+		// v67 (+143) = Load <*[]*Node> v880 v20
+		// b15: ← b8
+		// v827 (146) = StructSelect <*[]*Node> [0] v67
+		// v846 (146) = Store <mem> {*[]*Node} v769 v827 v20
+		// v73 (+146) = StaticCall <mem> {AuxCall{"".Nodes.Slice([Nodes,0])[[]*Node,8]}} [32] v846
+		// i.e., the struct select is generated and remains in because it is not applied to an actual structure.
+		// The OpLoad was created to load the single field of the IData
+		// This case removes that StructSelect.
+		if leafType != selector.Type {
+			if x.f.Config.SoftFloat && selector.Type.IsFloat() {
+				if x.debug > 1 {
+					x.Printf("---OpLoad, break\n")
+				}
+				break // softfloat pass will take care of that
+			}
+			x.f.Fatalf("Unexpected Load as selector, leaf=%s, selector=%s\n", leaf.LongString(), selector.LongString())
+		}
+		leaf.copyOf(selector)
+		for _, s := range x.namedSelects[selector] {
+			locs = append(locs, x.f.Names[s.locIndex])
+		}
+
+	case OpSelectN:
+		// TODO(register args) result case
+		// if applied to Op-mumble-call, the Aux tells us which result, regOffset specifies offset within result.  If a register, should rewrite to OpSelectN for new call.
+		// TODO these may be duplicated. Should memoize. Intermediate selectors will go dead, no worries there.
+		call := selector.Args[0]
+		call0 := call
+		aux := call.Aux.(*AuxCall)
+		which := selector.AuxInt
+		if x.transformedSelects[selector.ID] {
+			// This is a minor hack.  Either this select has had its operand adjusted (mem) or
+			// it is some other intermediate node that was rewritten to reference a register (not a generic arg).
+			// This can occur with chains of selection/indexing from single field/element aggregates.
+			leaf.copyOf(selector)
+			break
+		}
+		if which == aux.NResults() { // mem is after the results.
+			// rewrite v as a Copy of call -- the replacement call will produce a mem.
+			if leaf != selector {
+				panic(fmt.Errorf("Unexpected selector of memory, selector=%s, call=%s, leaf=%s", selector.LongString(), call.LongString(), leaf.LongString()))
+			}
+			if aux.abiInfo == nil {
+				panic(badVal("aux.abiInfo nil for call", call))
+			}
+			if existing := x.memForCall[call.ID]; existing == nil {
+				selector.AuxInt = int64(aux.abiInfo.OutRegistersUsed())
+				x.memForCall[call.ID] = selector
+				x.transformedSelects[selector.ID] = true // operand adjusted
+			} else {
+				selector.copyOf(existing)
+			}
+
+		} else {
+			leafType := removeTrivialWrapperTypes(leaf.Type)
+			if x.canSSAType(leafType) {
+				pt := types.NewPtr(leafType)
+				// Any selection right out of the arg area/registers has to be same Block as call, use call as mem input.
+				// Create a "mem" for any loads that need to occur.
+				if mem := x.memForCall[call.ID]; mem != nil {
+					if mem.Block != call.Block {
+						panic(fmt.Errorf("selector and call need to be in same block, selector=%s; call=%s", selector.LongString(), call.LongString()))
+					}
+					call = mem
+				} else {
+					mem = call.Block.NewValue1I(call.Pos.WithNotStmt(), OpSelectN, types.TypeMem, int64(aux.abiInfo.OutRegistersUsed()), call)
+					x.transformedSelects[mem.ID] = true // select uses post-expansion indexing
+					x.memForCall[call.ID] = mem
+					call = mem
+				}
+				outParam := aux.abiInfo.OutParam(int(which))
+				if len(outParam.Registers) > 0 {
+					firstReg := uint32(0)
+					for i := 0; i < int(which); i++ {
+						firstReg += uint32(len(aux.abiInfo.OutParam(i).Registers))
+					}
+					reg := int64(regOffset + Abi1RO(firstReg))
+					if leaf.Block == call.Block {
+						leaf.reset(OpSelectN)
+						leaf.SetArgs1(call0)
+						leaf.Type = leafType
+						leaf.AuxInt = reg
+						x.transformedSelects[leaf.ID] = true // leaf, rewritten to use post-expansion indexing.
+					} else {
+						w := call.Block.NewValue1I(leaf.Pos, OpSelectN, leafType, reg, call0)
+						x.transformedSelects[w.ID] = true // select, using post-expansion indexing.
+						leaf.copyOf(w)
+					}
+				} else {
+					off := x.offsetFrom(x.f.Entry, x.sp, offset+aux.OffsetOfResult(which), pt)
+					if leaf.Block == call.Block {
+						leaf.reset(OpLoad)
+						leaf.SetArgs2(off, call)
+						leaf.Type = leafType
+					} else {
+						w := call.Block.NewValue2(leaf.Pos, OpLoad, leafType, off, call)
+						leaf.copyOf(w)
+						if x.debug > 1 {
+							x.Printf("---new %s\n", w.LongString())
+						}
+					}
+				}
+				for _, s := range x.namedSelects[selector] {
+					locs = append(locs, x.f.Names[s.locIndex])
+				}
+			} else {
+				x.f.Fatalf("Should not have non-SSA-able OpSelectN, selector=%s", selector.LongString())
+			}
+		}
+
+	case OpStructSelect:
+		w := selector.Args[0]
+		var ls []*LocalSlot
+		if w.Type.Kind() != types.TSTRUCT { // IData artifact
+			ls = x.rewriteSelect(leaf, w, offset, regOffset)
+		} else {
+			fldi := int(selector.AuxInt)
+			ls = x.rewriteSelect(leaf, w, offset+w.Type.FieldOff(fldi), regOffset+x.regOffset(w.Type, fldi))
+			if w.Op != OpIData {
+				for _, l := range ls {
+					locs = append(locs, x.f.SplitStruct(l, int(selector.AuxInt)))
+				}
+			}
+		}
+
+	case OpArraySelect:
+		w := selector.Args[0]
+		index := selector.AuxInt
+		x.rewriteSelect(leaf, w, offset+selector.Type.Size()*index, regOffset+x.regOffset(w.Type, int(index)))
+
+	case OpInt64Hi:
+		w := selector.Args[0]
+		ls := x.rewriteSelect(leaf, w, offset+x.hiOffset, regOffset+x.hiRo)
+		locs = x.splitSlots(ls, ".hi", x.hiOffset, leafType)
+
+	case OpInt64Lo:
+		w := selector.Args[0]
+		ls := x.rewriteSelect(leaf, w, offset+x.lowOffset, regOffset+x.loRo)
+		locs = x.splitSlots(ls, ".lo", x.lowOffset, leafType)
+
+	case OpStringPtr:
+		ls := x.rewriteSelect(leaf, selector.Args[0], offset, regOffset)
+		locs = x.splitSlots(ls, ".ptr", 0, x.typs.BytePtr)
+
+	case OpSlicePtr, OpSlicePtrUnchecked:
+		w := selector.Args[0]
+		ls := x.rewriteSelect(leaf, w, offset, regOffset)
+		locs = x.splitSlots(ls, ".ptr", 0, types.NewPtr(w.Type.Elem()))
+
+	case OpITab:
+		w := selector.Args[0]
+		ls := x.rewriteSelect(leaf, w, offset, regOffset)
+		sfx := ".itab"
+		if w.Type.IsEmptyInterface() {
+			sfx = ".type"
+		}
+		locs = x.splitSlots(ls, sfx, 0, x.typs.Uintptr)
+
+	case OpComplexReal:
+		ls := x.rewriteSelect(leaf, selector.Args[0], offset, regOffset)
+		locs = x.splitSlots(ls, ".real", 0, selector.Type)
+
+	case OpComplexImag:
+		ls := x.rewriteSelect(leaf, selector.Args[0], offset+selector.Type.Size(), regOffset+RO_complex_imag) // result is FloatNN, width of result is offset of imaginary part.
+		locs = x.splitSlots(ls, ".imag", selector.Type.Size(), selector.Type)
+
+	case OpStringLen, OpSliceLen:
+		ls := x.rewriteSelect(leaf, selector.Args[0], offset+x.ptrSize, regOffset+RO_slice_len)
+		locs = x.splitSlots(ls, ".len", x.ptrSize, leafType)
+
+	case OpIData:
+		ls := x.rewriteSelect(leaf, selector.Args[0], offset+x.ptrSize, regOffset+RO_iface_data)
+		locs = x.splitSlots(ls, ".data", x.ptrSize, leafType)
+
+	case OpSliceCap:
+		ls := x.rewriteSelect(leaf, selector.Args[0], offset+2*x.ptrSize, regOffset+RO_slice_cap)
+		locs = x.splitSlots(ls, ".cap", 2*x.ptrSize, leafType)
+
+	case OpCopy: // If it's an intermediate result, recurse
+		locs = x.rewriteSelect(leaf, selector.Args[0], offset, regOffset)
+		for _, s := range x.namedSelects[selector] {
+			// this copy may have had its own name, preserve that, too.
+			locs = append(locs, x.f.Names[s.locIndex])
+		}
+
+	default:
+		// Ignore dead ends. These can occur if this phase is run before decompose builtin (which is not intended, but allowed).
+	}
+
+	return locs
+}
+
+func (x *expandState) rewriteDereference(b *Block, base, a, mem *Value, offset, size int64, typ *types.Type, pos src.XPos) *Value {
+	source := a.Args[0]
+	dst := x.offsetFrom(b, base, offset, source.Type)
+	if a.Uses == 1 && a.Block == b {
+		a.reset(OpMove)
+		a.Pos = pos
+		a.Type = types.TypeMem
+		a.Aux = typ
+		a.AuxInt = size
+		a.SetArgs3(dst, source, mem)
+		mem = a
+	} else {
+		mem = b.NewValue3A(pos, OpMove, types.TypeMem, typ, dst, source, mem)
+		mem.AuxInt = size
+	}
+	return mem
+}
+
+var indexNames [1]string = [1]string{"[0]"}
+
+// pathTo returns the selection path to the leaf type at offset within container.
+// e.g. len(thing.field[0]) => ".field[0].len"
+// this is for purposes of generating names ultimately fed to a debugger.
+func (x *expandState) pathTo(container, leaf *types.Type, offset int64) string {
+	if container == leaf || offset == 0 && container.Size() == leaf.Size() {
+		return ""
+	}
+	path := ""
+outer:
+	for {
+		switch container.Kind() {
+		case types.TARRAY:
+			container = container.Elem()
+			if container.Size() == 0 {
+				return path
+			}
+			i := offset / container.Size()
+			offset = offset % container.Size()
+			// If a future compiler/ABI supports larger SSA/Arg-able arrays, expand indexNames.
+			path = path + indexNames[i]
+			continue
+		case types.TSTRUCT:
+			for i := 0; i < container.NumFields(); i++ {
+				fld := container.Field(i)
+				if fld.Offset+fld.Type.Size() > offset {
+					offset -= fld.Offset
+					path += "." + fld.Sym.Name
+					container = fld.Type
+					continue outer
+				}
+			}
+			return path
+		case types.TINT64, types.TUINT64:
+			if container.Size() == x.regSize {
+				return path
+			}
+			if offset == x.hiOffset {
+				return path + ".hi"
+			}
+			return path + ".lo"
+		case types.TINTER:
+			if offset != 0 {
+				return path + ".data"
+			}
+			if container.IsEmptyInterface() {
+				return path + ".type"
+			}
+			return path + ".itab"
+
+		case types.TSLICE:
+			if offset == 2*x.regSize {
+				return path + ".cap"
+			}
+			fallthrough
+		case types.TSTRING:
+			if offset == 0 {
+				return path + ".ptr"
+			}
+			return path + ".len"
+		case types.TCOMPLEX64, types.TCOMPLEX128:
+			if offset == 0 {
+				return path + ".real"
+			}
+			return path + ".imag"
+		}
+		return path
+	}
+}
+
+// decomposeArg is a helper for storeArgOrLoad.
+// It decomposes a Load or an Arg into smaller parts and returns the new mem.
+// If the type does not match one of the expected aggregate types, it returns nil instead.
+// Parameters:
+//
+//	pos           -- the location of any generated code.
+//	b             -- the block into which any generated code should normally be placed
+//	source        -- the value, possibly an aggregate, to be stored.
+//	mem           -- the mem flowing into this decomposition (loads depend on it, stores updated it)
+//	t             -- the type of the value to be stored
+//	storeOffset   -- if the value is stored in memory, it is stored at base (see storeRc) + storeOffset
+//	loadRegOffset -- regarding source as a value in registers, the register offset in ABI1.  Meaningful only if source is OpArg.
+//	storeRc       -- storeRC; if the value is stored in registers, this specifies the registers.
+//	                 StoreRc also identifies whether the target is registers or memory, and has the base for the store operation.
+func (x *expandState) decomposeArg(pos src.XPos, b *Block, source, mem *Value, t *types.Type, storeOffset int64, loadRegOffset Abi1RO, storeRc registerCursor) *Value {
+
+	pa := x.prAssignForArg(source)
+	var locs []*LocalSlot
+	for _, s := range x.namedSelects[source] {
+		locs = append(locs, x.f.Names[s.locIndex])
+	}
+
+	if len(pa.Registers) > 0 {
+		// Handle the in-registers case directly
+		rts, offs := pa.RegisterTypesAndOffsets()
+		last := loadRegOffset + x.regWidth(t)
+		if offs[loadRegOffset] != 0 {
+			// Document the problem before panicking.
+			for i := 0; i < len(rts); i++ {
+				rt := rts[i]
+				off := offs[i]
+				fmt.Printf("rt=%s, off=%d, rt.Width=%d, rt.Align=%d\n", rt.String(), off, rt.Size(), uint8(rt.Alignment()))
+			}
+			panic(fmt.Errorf("offset %d of requested register %d should be zero, source=%s", offs[loadRegOffset], loadRegOffset, source.LongString()))
+		}
+
+		if x.debug > 1 {
+			x.Printf("decompose arg %s has %d locs\n", source.LongString(), len(locs))
+		}
+
+		for i := loadRegOffset; i < last; i++ {
+			rt := rts[i]
+			off := offs[i]
+			w := x.commonArgs[selKey{source, off, rt.Size(), rt}]
+			if w == nil {
+				w = x.newArgToMemOrRegs(source, w, off, i, rt, pos)
+				suffix := x.pathTo(source.Type, rt, off)
+				if suffix != "" {
+					x.splitSlotsIntoNames(locs, suffix, off, rt, w)
+				}
+			}
+			if t.IsPtrShaped() {
+				// Preserve the original store type. This ensures pointer type
+				// properties aren't discarded (e.g, notinheap).
+				if rt.Size() != t.Size() || len(pa.Registers) != 1 || i != loadRegOffset {
+					b.Func.Fatalf("incompatible store type %v and %v, i=%d", t, rt, i)
+				}
+				rt = t
+			}
+			mem = x.storeArgOrLoad(pos, b, w, mem, rt, storeOffset+off, i, storeRc.next(rt))
+		}
+		return mem
+	}
+
+	u := source.Type
+	switch u.Kind() {
+	case types.TARRAY:
+		elem := u.Elem()
+		elemRO := x.regWidth(elem)
+		for i := int64(0); i < u.NumElem(); i++ {
+			elemOff := i * elem.Size()
+			mem = storeOneArg(x, pos, b, locs, indexNames[i], source, mem, elem, elemOff, storeOffset+elemOff, loadRegOffset, storeRc.next(elem))
+			loadRegOffset += elemRO
+			pos = pos.WithNotStmt()
+		}
+		return mem
+	case types.TSTRUCT:
+		for i := 0; i < u.NumFields(); i++ {
+			fld := u.Field(i)
+			mem = storeOneArg(x, pos, b, locs, "."+fld.Sym.Name, source, mem, fld.Type, fld.Offset, storeOffset+fld.Offset, loadRegOffset, storeRc.next(fld.Type))
+			loadRegOffset += x.regWidth(fld.Type)
+			pos = pos.WithNotStmt()
+		}
+		return mem
+	case types.TINT64, types.TUINT64:
+		if t.Size() == x.regSize {
+			break
+		}
+		tHi, tLo := x.intPairTypes(t.Kind())
+		mem = storeOneArg(x, pos, b, locs, ".hi", source, mem, tHi, x.hiOffset, storeOffset+x.hiOffset, loadRegOffset+x.hiRo, storeRc.plus(x.hiRo))
+		pos = pos.WithNotStmt()
+		return storeOneArg(x, pos, b, locs, ".lo", source, mem, tLo, x.lowOffset, storeOffset+x.lowOffset, loadRegOffset+x.loRo, storeRc.plus(x.loRo))
+	case types.TINTER:
+		sfx := ".itab"
+		if u.IsEmptyInterface() {
+			sfx = ".type"
+		}
+		return storeTwoArg(x, pos, b, locs, sfx, ".idata", source, mem, x.typs.Uintptr, x.typs.BytePtr, 0, storeOffset, loadRegOffset, storeRc)
+	case types.TSTRING:
+		return storeTwoArg(x, pos, b, locs, ".ptr", ".len", source, mem, x.typs.BytePtr, x.typs.Int, 0, storeOffset, loadRegOffset, storeRc)
+	case types.TCOMPLEX64:
+		return storeTwoArg(x, pos, b, locs, ".real", ".imag", source, mem, x.typs.Float32, x.typs.Float32, 0, storeOffset, loadRegOffset, storeRc)
+	case types.TCOMPLEX128:
+		return storeTwoArg(x, pos, b, locs, ".real", ".imag", source, mem, x.typs.Float64, x.typs.Float64, 0, storeOffset, loadRegOffset, storeRc)
+	case types.TSLICE:
+		mem = storeOneArg(x, pos, b, locs, ".ptr", source, mem, x.typs.BytePtr, 0, storeOffset, loadRegOffset, storeRc.next(x.typs.BytePtr))
+		return storeTwoArg(x, pos, b, locs, ".len", ".cap", source, mem, x.typs.Int, x.typs.Int, x.ptrSize, storeOffset+x.ptrSize, loadRegOffset+RO_slice_len, storeRc)
+	}
+	return nil
+}
+
+func (x *expandState) splitSlotsIntoNames(locs []*LocalSlot, suffix string, off int64, rt *types.Type, w *Value) {
+	wlocs := x.splitSlots(locs, suffix, off, rt)
+	for _, l := range wlocs {
+		old, ok := x.f.NamedValues[*l]
+		x.f.NamedValues[*l] = append(old, w)
+		if !ok {
+			x.f.Names = append(x.f.Names, l)
+		}
+	}
+}
+
+// decomposeLoad is a helper for storeArgOrLoad.
+// It decomposes a Load  into smaller parts and returns the new mem.
+// If the type does not match one of the expected aggregate types, it returns nil instead.
+// Parameters:
+//
+//	pos           -- the location of any generated code.
+//	b             -- the block into which any generated code should normally be placed
+//	source        -- the value, possibly an aggregate, to be stored.
+//	mem           -- the mem flowing into this decomposition (loads depend on it, stores updated it)
+//	t             -- the type of the value to be stored
+//	storeOffset   -- if the value is stored in memory, it is stored at base (see storeRc) + offset
+//	loadRegOffset -- regarding source as a value in registers, the register offset in ABI1.  Meaningful only if source is OpArg.
+//	storeRc       -- storeRC; if the value is stored in registers, this specifies the registers.
+//	                 StoreRc also identifies whether the target is registers or memory, and has the base for the store operation.
+//
+// TODO -- this needs cleanup; it just works for SSA-able aggregates, and won't fully generalize to register-args aggregates.
+func (x *expandState) decomposeLoad(pos src.XPos, b *Block, source, mem *Value, t *types.Type, storeOffset int64, loadRegOffset Abi1RO, storeRc registerCursor) *Value {
+	u := source.Type
+	switch u.Kind() {
+	case types.TARRAY:
+		elem := u.Elem()
+		elemRO := x.regWidth(elem)
+		for i := int64(0); i < u.NumElem(); i++ {
+			elemOff := i * elem.Size()
+			mem = storeOneLoad(x, pos, b, source, mem, elem, elemOff, storeOffset+elemOff, loadRegOffset, storeRc.next(elem))
+			loadRegOffset += elemRO
+			pos = pos.WithNotStmt()
+		}
+		return mem
+	case types.TSTRUCT:
+		for i := 0; i < u.NumFields(); i++ {
+			fld := u.Field(i)
+			mem = storeOneLoad(x, pos, b, source, mem, fld.Type, fld.Offset, storeOffset+fld.Offset, loadRegOffset, storeRc.next(fld.Type))
+			loadRegOffset += x.regWidth(fld.Type)
+			pos = pos.WithNotStmt()
+		}
+		return mem
+	case types.TINT64, types.TUINT64:
+		if t.Size() == x.regSize {
+			break
+		}
+		tHi, tLo := x.intPairTypes(t.Kind())
+		mem = storeOneLoad(x, pos, b, source, mem, tHi, x.hiOffset, storeOffset+x.hiOffset, loadRegOffset+x.hiRo, storeRc.plus(x.hiRo))
+		pos = pos.WithNotStmt()
+		return storeOneLoad(x, pos, b, source, mem, tLo, x.lowOffset, storeOffset+x.lowOffset, loadRegOffset+x.loRo, storeRc.plus(x.loRo))
+	case types.TINTER:
+		return storeTwoLoad(x, pos, b, source, mem, x.typs.Uintptr, x.typs.BytePtr, 0, storeOffset, loadRegOffset, storeRc)
+	case types.TSTRING:
+		return storeTwoLoad(x, pos, b, source, mem, x.typs.BytePtr, x.typs.Int, 0, storeOffset, loadRegOffset, storeRc)
+	case types.TCOMPLEX64:
+		return storeTwoLoad(x, pos, b, source, mem, x.typs.Float32, x.typs.Float32, 0, storeOffset, loadRegOffset, storeRc)
+	case types.TCOMPLEX128:
+		return storeTwoLoad(x, pos, b, source, mem, x.typs.Float64, x.typs.Float64, 0, storeOffset, loadRegOffset, storeRc)
+	case types.TSLICE:
+		mem = storeOneLoad(x, pos, b, source, mem, x.typs.BytePtr, 0, storeOffset, loadRegOffset, storeRc.next(x.typs.BytePtr))
+		return storeTwoLoad(x, pos, b, source, mem, x.typs.Int, x.typs.Int, x.ptrSize, storeOffset+x.ptrSize, loadRegOffset+RO_slice_len, storeRc)
+	}
+	return nil
+}
+
+// storeOneArg creates a decomposed (one step) arg that is then stored.
+// pos and b locate the store instruction, source is the "base" of the value input,
+// mem is the input mem, t is the type in question, and offArg and offStore are the offsets from the respective bases.
+func storeOneArg(x *expandState, pos src.XPos, b *Block, locs []*LocalSlot, suffix string, source, mem *Value, t *types.Type, argOffset, storeOffset int64, loadRegOffset Abi1RO, storeRc registerCursor) *Value {
+	if x.debug > 1 {
+		x.indent(3)
+		defer x.indent(-3)
+		x.Printf("storeOneArg(%s;  %s;  %s; aO=%d; sO=%d; lrO=%d; %s)\n", source.LongString(), mem.String(), t.String(), argOffset, storeOffset, loadRegOffset, storeRc.String())
+	}
+
+	w := x.commonArgs[selKey{source, argOffset, t.Size(), t}]
+	if w == nil {
+		w = x.newArgToMemOrRegs(source, w, argOffset, loadRegOffset, t, pos)
+		x.splitSlotsIntoNames(locs, suffix, argOffset, t, w)
+	}
+	return x.storeArgOrLoad(pos, b, w, mem, t, storeOffset, loadRegOffset, storeRc)
+}
+
+// storeOneLoad creates a decomposed (one step) load that is then stored.
+func storeOneLoad(x *expandState, pos src.XPos, b *Block, source, mem *Value, t *types.Type, offArg, offStore int64, loadRegOffset Abi1RO, storeRc registerCursor) *Value {
+	from := x.offsetFrom(source.Block, source.Args[0], offArg, types.NewPtr(t))
+	w := b.NewValue2(source.Pos, OpLoad, t, from, mem)
+	return x.storeArgOrLoad(pos, b, w, mem, t, offStore, loadRegOffset, storeRc)
+}
+
+func storeTwoArg(x *expandState, pos src.XPos, b *Block, locs []*LocalSlot, suffix1 string, suffix2 string, source, mem *Value, t1, t2 *types.Type, offArg, offStore int64, loadRegOffset Abi1RO, storeRc registerCursor) *Value {
+	mem = storeOneArg(x, pos, b, locs, suffix1, source, mem, t1, offArg, offStore, loadRegOffset, storeRc.next(t1))
+	pos = pos.WithNotStmt()
+	t1Size := t1.Size()
+	return storeOneArg(x, pos, b, locs, suffix2, source, mem, t2, offArg+t1Size, offStore+t1Size, loadRegOffset+1, storeRc)
+}
+
+// storeTwoLoad creates a pair of decomposed (one step) loads that are then stored.
+// the elements of the pair must not require any additional alignment.
+func storeTwoLoad(x *expandState, pos src.XPos, b *Block, source, mem *Value, t1, t2 *types.Type, offArg, offStore int64, loadRegOffset Abi1RO, storeRc registerCursor) *Value {
+	mem = storeOneLoad(x, pos, b, source, mem, t1, offArg, offStore, loadRegOffset, storeRc.next(t1))
+	pos = pos.WithNotStmt()
+	t1Size := t1.Size()
+	return storeOneLoad(x, pos, b, source, mem, t2, offArg+t1Size, offStore+t1Size, loadRegOffset+1, storeRc)
+}
+
+// storeArgOrLoad converts stores of SSA-able potentially aggregatable arguments (passed to a call) into a series of primitive-typed
+// stores of non-aggregate types.  It recursively walks up a chain of selectors until it reaches a Load or an Arg.
+// If it does not reach a Load or an Arg, nothing happens; this allows a little freedom in phase ordering.
+func (x *expandState) storeArgOrLoad(pos src.XPos, b *Block, source, mem *Value, t *types.Type, storeOffset int64, loadRegOffset Abi1RO, storeRc registerCursor) *Value {
+	if x.debug > 1 {
+		x.indent(3)
+		defer x.indent(-3)
+		x.Printf("storeArgOrLoad(%s;  %s;  %s; %d; %s)\n", source.LongString(), mem.String(), t.String(), storeOffset, storeRc.String())
+	}
+
+	// Start with Opcodes that can be disassembled
+	switch source.Op {
+	case OpCopy:
+		return x.storeArgOrLoad(pos, b, source.Args[0], mem, t, storeOffset, loadRegOffset, storeRc)
+
+	case OpLoad, OpDereference:
+		ret := x.decomposeLoad(pos, b, source, mem, t, storeOffset, loadRegOffset, storeRc)
+		if ret != nil {
+			return ret
+		}
+
+	case OpArg:
+		ret := x.decomposeArg(pos, b, source, mem, t, storeOffset, loadRegOffset, storeRc)
+		if ret != nil {
+			return ret
+		}
+
+	case OpArrayMake0, OpStructMake0:
+		// TODO(register args) is this correct for registers?
+		return mem
+
+	case OpStructMake1, OpStructMake2, OpStructMake3, OpStructMake4:
+		for i := 0; i < t.NumFields(); i++ {
+			fld := t.Field(i)
+			mem = x.storeArgOrLoad(pos, b, source.Args[i], mem, fld.Type, storeOffset+fld.Offset, 0, storeRc.next(fld.Type))
+			pos = pos.WithNotStmt()
+		}
+		return mem
+
+	case OpArrayMake1:
+		return x.storeArgOrLoad(pos, b, source.Args[0], mem, t.Elem(), storeOffset, 0, storeRc.at(t, 0))
+
+	case OpInt64Make:
+		tHi, tLo := x.intPairTypes(t.Kind())
+		mem = x.storeArgOrLoad(pos, b, source.Args[0], mem, tHi, storeOffset+x.hiOffset, 0, storeRc.next(tHi))
+		pos = pos.WithNotStmt()
+		return x.storeArgOrLoad(pos, b, source.Args[1], mem, tLo, storeOffset+x.lowOffset, 0, storeRc)
+
+	case OpComplexMake:
+		tPart := x.typs.Float32
+		wPart := t.Size() / 2
+		if wPart == 8 {
+			tPart = x.typs.Float64
+		}
+		mem = x.storeArgOrLoad(pos, b, source.Args[0], mem, tPart, storeOffset, 0, storeRc.next(tPart))
+		pos = pos.WithNotStmt()
+		return x.storeArgOrLoad(pos, b, source.Args[1], mem, tPart, storeOffset+wPart, 0, storeRc)
+
+	case OpIMake:
+		mem = x.storeArgOrLoad(pos, b, source.Args[0], mem, x.typs.Uintptr, storeOffset, 0, storeRc.next(x.typs.Uintptr))
+		pos = pos.WithNotStmt()
+		return x.storeArgOrLoad(pos, b, source.Args[1], mem, x.typs.BytePtr, storeOffset+x.ptrSize, 0, storeRc)
+
+	case OpStringMake:
+		mem = x.storeArgOrLoad(pos, b, source.Args[0], mem, x.typs.BytePtr, storeOffset, 0, storeRc.next(x.typs.BytePtr))
+		pos = pos.WithNotStmt()
+		return x.storeArgOrLoad(pos, b, source.Args[1], mem, x.typs.Int, storeOffset+x.ptrSize, 0, storeRc)
+
+	case OpSliceMake:
+		mem = x.storeArgOrLoad(pos, b, source.Args[0], mem, x.typs.BytePtr, storeOffset, 0, storeRc.next(x.typs.BytePtr))
+		pos = pos.WithNotStmt()
+		mem = x.storeArgOrLoad(pos, b, source.Args[1], mem, x.typs.Int, storeOffset+x.ptrSize, 0, storeRc.next(x.typs.Int))
+		return x.storeArgOrLoad(pos, b, source.Args[2], mem, x.typs.Int, storeOffset+2*x.ptrSize, 0, storeRc)
+	}
+
+	// For nodes that cannot be taken apart -- OpSelectN, other structure selectors.
+	switch t.Kind() {
+	case types.TARRAY:
+		elt := t.Elem()
+		if source.Type != t && t.NumElem() == 1 && elt.Size() == t.Size() && t.Size() == x.regSize {
+			t = removeTrivialWrapperTypes(t)
+			// it could be a leaf type, but the "leaf" could be complex64 (for example)
+			return x.storeArgOrLoad(pos, b, source, mem, t, storeOffset, loadRegOffset, storeRc)
+		}
+		eltRO := x.regWidth(elt)
+		source.Type = t
+		for i := int64(0); i < t.NumElem(); i++ {
+			sel := b.NewValue1I(pos, OpArraySelect, elt, i, source)
+			mem = x.storeArgOrLoad(pos, b, sel, mem, elt, storeOffset+i*elt.Size(), loadRegOffset, storeRc.at(t, 0))
+			loadRegOffset += eltRO
+			pos = pos.WithNotStmt()
+		}
+		return mem
+
+	case types.TSTRUCT:
+		if source.Type != t && t.NumFields() == 1 && t.Field(0).Type.Size() == t.Size() && t.Size() == x.regSize {
+			// This peculiar test deals with accesses to immediate interface data.
+			// It works okay because everything is the same size.
+			// Example code that triggers this can be found in go/constant/value.go, function ToComplex
+			// v119 (+881) = IData <intVal> v6
+			// v121 (+882) = StaticLECall <floatVal,mem> {AuxCall{"".itof([intVal,0])[floatVal,8]}} [16] v119 v1
+			// This corresponds to the generic rewrite rule "(StructSelect [0] (IData x)) => (IData x)"
+			// Guard against "struct{struct{*foo}}"
+			// Other rewriting phases create minor glitches when they transform IData, for instance the
+			// interface-typed Arg "x" of ToFloat in go/constant/value.go
+			//   v6 (858) = Arg <Value> {x} (x[Value], x[Value])
+			// is rewritten by decomposeArgs into
+			//   v141 (858) = Arg <uintptr> {x}
+			//   v139 (858) = Arg <*uint8> {x} [8]
+			// because of a type case clause on line 862 of go/constant/value.go
+			//  	case intVal:
+			//		   return itof(x)
+			// v139 is later stored as an intVal == struct{val *big.Int} which naively requires the fields of
+			// of a *uint8, which does not succeed.
+			t = removeTrivialWrapperTypes(t)
+			// it could be a leaf type, but the "leaf" could be complex64 (for example)
+			return x.storeArgOrLoad(pos, b, source, mem, t, storeOffset, loadRegOffset, storeRc)
+		}
+
+		source.Type = t
+		for i := 0; i < t.NumFields(); i++ {
+			fld := t.Field(i)
+			sel := b.NewValue1I(pos, OpStructSelect, fld.Type, int64(i), source)
+			mem = x.storeArgOrLoad(pos, b, sel, mem, fld.Type, storeOffset+fld.Offset, loadRegOffset, storeRc.next(fld.Type))
+			loadRegOffset += x.regWidth(fld.Type)
+			pos = pos.WithNotStmt()
+		}
+		return mem
+
+	case types.TINT64, types.TUINT64:
+		if t.Size() == x.regSize {
+			break
+		}
+		tHi, tLo := x.intPairTypes(t.Kind())
+		sel := b.NewValue1(pos, OpInt64Hi, tHi, source)
+		mem = x.storeArgOrLoad(pos, b, sel, mem, tHi, storeOffset+x.hiOffset, loadRegOffset+x.hiRo, storeRc.plus(x.hiRo))
+		pos = pos.WithNotStmt()
+		sel = b.NewValue1(pos, OpInt64Lo, tLo, source)
+		return x.storeArgOrLoad(pos, b, sel, mem, tLo, storeOffset+x.lowOffset, loadRegOffset+x.loRo, storeRc.plus(x.hiRo))
+
+	case types.TINTER:
+		sel := b.NewValue1(pos, OpITab, x.typs.BytePtr, source)
+		mem = x.storeArgOrLoad(pos, b, sel, mem, x.typs.BytePtr, storeOffset, loadRegOffset, storeRc.next(x.typs.BytePtr))
+		pos = pos.WithNotStmt()
+		sel = b.NewValue1(pos, OpIData, x.typs.BytePtr, source)
+		return x.storeArgOrLoad(pos, b, sel, mem, x.typs.BytePtr, storeOffset+x.ptrSize, loadRegOffset+RO_iface_data, storeRc)
+
+	case types.TSTRING:
+		sel := b.NewValue1(pos, OpStringPtr, x.typs.BytePtr, source)
+		mem = x.storeArgOrLoad(pos, b, sel, mem, x.typs.BytePtr, storeOffset, loadRegOffset, storeRc.next(x.typs.BytePtr))
+		pos = pos.WithNotStmt()
+		sel = b.NewValue1(pos, OpStringLen, x.typs.Int, source)
+		return x.storeArgOrLoad(pos, b, sel, mem, x.typs.Int, storeOffset+x.ptrSize, loadRegOffset+RO_string_len, storeRc)
+
+	case types.TSLICE:
+		et := types.NewPtr(t.Elem())
+		sel := b.NewValue1(pos, OpSlicePtr, et, source)
+		mem = x.storeArgOrLoad(pos, b, sel, mem, et, storeOffset, loadRegOffset, storeRc.next(et))
+		pos = pos.WithNotStmt()
+		sel = b.NewValue1(pos, OpSliceLen, x.typs.Int, source)
+		mem = x.storeArgOrLoad(pos, b, sel, mem, x.typs.Int, storeOffset+x.ptrSize, loadRegOffset+RO_slice_len, storeRc.next(x.typs.Int))
+		sel = b.NewValue1(pos, OpSliceCap, x.typs.Int, source)
+		return x.storeArgOrLoad(pos, b, sel, mem, x.typs.Int, storeOffset+2*x.ptrSize, loadRegOffset+RO_slice_cap, storeRc)
+
+	case types.TCOMPLEX64:
+		sel := b.NewValue1(pos, OpComplexReal, x.typs.Float32, source)
+		mem = x.storeArgOrLoad(pos, b, sel, mem, x.typs.Float32, storeOffset, loadRegOffset, storeRc.next(x.typs.Float32))
+		pos = pos.WithNotStmt()
+		sel = b.NewValue1(pos, OpComplexImag, x.typs.Float32, source)
+		return x.storeArgOrLoad(pos, b, sel, mem, x.typs.Float32, storeOffset+4, loadRegOffset+RO_complex_imag, storeRc)
+
+	case types.TCOMPLEX128:
+		sel := b.NewValue1(pos, OpComplexReal, x.typs.Float64, source)
+		mem = x.storeArgOrLoad(pos, b, sel, mem, x.typs.Float64, storeOffset, loadRegOffset, storeRc.next(x.typs.Float64))
+		pos = pos.WithNotStmt()
+		sel = b.NewValue1(pos, OpComplexImag, x.typs.Float64, source)
+		return x.storeArgOrLoad(pos, b, sel, mem, x.typs.Float64, storeOffset+8, loadRegOffset+RO_complex_imag, storeRc)
+	}
+
+	s := mem
+	if source.Op == OpDereference {
+		source.Op = OpLoad // For purposes of parameter passing expansion, a Dereference is a Load.
+	}
+	if storeRc.hasRegs() {
+		storeRc.addArg(source)
+	} else {
+		dst := x.offsetFrom(b, storeRc.storeDest, storeOffset, types.NewPtr(t))
+		s = b.NewValue3A(pos, OpStore, types.TypeMem, t, dst, source, mem)
+	}
+	if x.debug > 1 {
+		x.Printf("-->storeArg returns %s, storeRc=%s\n", s.LongString(), storeRc.String())
+	}
+	return s
+}
+
+// rewriteArgs replaces all the call-parameter Args to a call with their register translation (if any).
+// Preceding parameters (code pointers, closure pointer) are preserved, and the memory input is modified
+// to account for any parameter stores required.
+// Any of the old Args that have their use count fall to zero are marked OpInvalid.
+func (x *expandState) rewriteArgs(v *Value, firstArg int) {
+	if x.debug > 1 {
+		x.indent(3)
+		defer x.indent(-3)
+		x.Printf("rewriteArgs(%s; %d)\n", v.LongString(), firstArg)
+	}
+	// Thread the stores on the memory arg
+	aux := v.Aux.(*AuxCall)
+	m0 := v.MemoryArg()
+	mem := m0
+	newArgs := []*Value{}
+	oldArgs := []*Value{}
+	sp := x.sp
+	if v.Op == OpTailLECall {
+		// For tail call, we unwind the frame before the call so we'll use the caller's
+		// SP.
+		sp = x.f.Entry.NewValue0(src.NoXPos, OpGetCallerSP, x.typs.Uintptr)
+	}
+	for i, a := range v.Args[firstArg : len(v.Args)-1] { // skip leading non-parameter SSA Args and trailing mem SSA Arg.
+		oldArgs = append(oldArgs, a)
+		auxI := int64(i)
+		aRegs := aux.RegsOfArg(auxI)
+		aType := aux.TypeOfArg(auxI)
+		if len(aRegs) == 0 && a.Op == OpDereference {
+			aOffset := aux.OffsetOfArg(auxI)
+			if a.MemoryArg() != m0 {
+				x.f.Fatalf("Op...LECall and OpDereference have mismatched mem, %s and %s", v.LongString(), a.LongString())
+			}
+			if v.Op == OpTailLECall {
+				// It's common for a tail call passing the same arguments (e.g. method wrapper),
+				// so this would be a self copy. Detect this and optimize it out.
+				a0 := a.Args[0]
+				if a0.Op == OpLocalAddr {
+					n := a0.Aux.(*ir.Name)
+					if n.Class == ir.PPARAM && n.FrameOffset()+x.f.Config.ctxt.Arch.FixedFrameSize == aOffset {
+						continue
+					}
+				}
+			}
+			if x.debug > 1 {
+				x.Printf("...storeArg %s, %v, %d\n", a.LongString(), aType, aOffset)
+			}
+			// "Dereference" of addressed (probably not-SSA-eligible) value becomes Move
+			// TODO(register args) this will be more complicated with registers in the picture.
+			mem = x.rewriteDereference(v.Block, sp, a, mem, aOffset, aux.SizeOfArg(auxI), aType, a.Pos)
+		} else {
+			var rc registerCursor
+			var result *[]*Value
+			var aOffset int64
+			if len(aRegs) > 0 {
+				result = &newArgs
+			} else {
+				aOffset = aux.OffsetOfArg(auxI)
+			}
+			if v.Op == OpTailLECall && a.Op == OpArg && a.AuxInt == 0 {
+				// It's common for a tail call passing the same arguments (e.g. method wrapper),
+				// so this would be a self copy. Detect this and optimize it out.
+				n := a.Aux.(*ir.Name)
+				if n.Class == ir.PPARAM && n.FrameOffset()+x.f.Config.ctxt.Arch.FixedFrameSize == aOffset {
+					continue
+				}
+			}
+			if x.debug > 1 {
+				x.Printf("...storeArg %s, %v, %d\n", a.LongString(), aType, aOffset)
+			}
+			rc.init(aRegs, aux.abiInfo, result, sp)
+			mem = x.storeArgOrLoad(a.Pos, v.Block, a, mem, aType, aOffset, 0, rc)
+		}
+	}
+	var preArgStore [2]*Value
+	preArgs := append(preArgStore[:0], v.Args[0:firstArg]...)
+	v.resetArgs()
+	v.AddArgs(preArgs...)
+	v.AddArgs(newArgs...)
+	v.AddArg(mem)
+	for _, a := range oldArgs {
+		if a.Uses == 0 {
+			x.invalidateRecursively(a)
+		}
+	}
+
+	return
+}
+
+func (x *expandState) invalidateRecursively(a *Value) {
+	var s string
+	if x.debug > 0 {
+		plus := " "
+		if a.Pos.IsStmt() == src.PosIsStmt {
+			plus = " +"
+		}
+		s = a.String() + plus + a.Pos.LineNumber() + " " + a.LongString()
+		if x.debug > 1 {
+			x.Printf("...marking %v unused\n", s)
+		}
+	}
+	lost := a.invalidateRecursively()
+	if x.debug&1 != 0 && lost { // For odd values of x.debug, do this.
+		x.Printf("Lost statement marker in %s on former %s\n", base.Ctxt.Pkgpath+"."+x.f.Name, s)
+	}
+}
+
+// expandCalls converts LE (Late Expansion) calls that act like they receive value args into a lower-level form
+// that is more oriented to a platform's ABI.  The SelectN operations that extract results are rewritten into
+// more appropriate forms, and any StructMake or ArrayMake inputs are decomposed until non-struct values are
+// reached.  On the callee side, OpArg nodes are not decomposed until this phase is run.
+// TODO results should not be lowered until this phase.
+func expandCalls(f *Func) {
+	// Calls that need lowering have some number of inputs, including a memory input,
+	// and produce a tuple of (value1, value2, ..., mem) where valueK may or may not be SSA-able.
+
+	// With the current ABI those inputs need to be converted into stores to memory,
+	// rethreading the call's memory input to the first, and the new call now receiving the last.
+
+	// With the current ABI, the outputs need to be converted to loads, which will all use the call's
+	// memory output as their input.
+	sp, _ := f.spSb()
+	x := &expandState{
+		f:                  f,
+		abi1:               f.ABI1,
+		debug:              f.pass.debug,
+		canSSAType:         f.fe.CanSSA,
+		regSize:            f.Config.RegSize,
+		sp:                 sp,
+		typs:               &f.Config.Types,
+		ptrSize:            f.Config.PtrSize,
+		namedSelects:       make(map[*Value][]namedVal),
+		sdom:               f.Sdom(),
+		commonArgs:         make(map[selKey]*Value),
+		memForCall:         make(map[ID]*Value),
+		transformedSelects: make(map[ID]bool),
+	}
+
+	// For 32-bit, need to deal with decomposition of 64-bit integers, which depends on endianness.
+	if f.Config.BigEndian {
+		x.lowOffset, x.hiOffset = 4, 0
+		x.loRo, x.hiRo = 1, 0
+	} else {
+		x.lowOffset, x.hiOffset = 0, 4
+		x.loRo, x.hiRo = 0, 1
+	}
+
+	if x.debug > 1 {
+		x.Printf("\nexpandsCalls(%s)\n", f.Name)
+	}
+
+	for i, name := range f.Names {
+		t := name.Type
+		if x.isAlreadyExpandedAggregateType(t) {
+			for j, v := range f.NamedValues[*name] {
+				if v.Op == OpSelectN || v.Op == OpArg && x.isAlreadyExpandedAggregateType(v.Type) {
+					ns := x.namedSelects[v]
+					x.namedSelects[v] = append(ns, namedVal{locIndex: i, valIndex: j})
+				}
+			}
+		}
+	}
+
+	// TODO if too slow, whole program iteration can be replaced w/ slices of appropriate values, accumulated in first loop here.
+
+	// Step 0: rewrite the calls to convert args to calls into stores/register movement.
+	for _, b := range f.Blocks {
+		for _, v := range b.Values {
+			firstArg := 0
+			switch v.Op {
+			case OpStaticLECall, OpTailLECall:
+			case OpInterLECall:
+				firstArg = 1
+			case OpClosureLECall:
+				firstArg = 2
+			default:
+				continue
+			}
+			x.rewriteArgs(v, firstArg)
+		}
+		if isBlockMultiValueExit(b) {
+			x.indent(3)
+			// Very similar to code in rewriteArgs, but results instead of args.
+			v := b.Controls[0]
+			m0 := v.MemoryArg()
+			mem := m0
+			aux := f.OwnAux
+			allResults := []*Value{}
+			if x.debug > 1 {
+				x.Printf("multiValueExit rewriting %s\n", v.LongString())
+			}
+			var oldArgs []*Value
+			for j, a := range v.Args[:len(v.Args)-1] {
+				oldArgs = append(oldArgs, a)
+				i := int64(j)
+				auxType := aux.TypeOfResult(i)
+				auxBase := b.NewValue2A(v.Pos, OpLocalAddr, types.NewPtr(auxType), aux.NameOfResult(i), x.sp, mem)
+				auxOffset := int64(0)
+				auxSize := aux.SizeOfResult(i)
+				aRegs := aux.RegsOfResult(int64(j))
+				if len(aRegs) == 0 && a.Op == OpDereference {
+					// Avoid a self-move, and if one is detected try to remove the already-inserted VarDef for the assignment that won't happen.
+					if dAddr, dMem := a.Args[0], a.Args[1]; dAddr.Op == OpLocalAddr && dAddr.Args[0].Op == OpSP &&
+						dAddr.Args[1] == dMem && dAddr.Aux == aux.NameOfResult(i) {
+						if dMem.Op == OpVarDef && dMem.Aux == dAddr.Aux {
+							dMem.copyOf(dMem.MemoryArg()) // elide the VarDef
+						}
+						continue
+					}
+					mem = x.rewriteDereference(v.Block, auxBase, a, mem, auxOffset, auxSize, auxType, a.Pos)
+				} else {
+					if a.Op == OpLoad && a.Args[0].Op == OpLocalAddr {
+						addr := a.Args[0] // This is a self-move. // TODO(register args) do what here for registers?
+						if addr.MemoryArg() == a.MemoryArg() && addr.Aux == aux.NameOfResult(i) {
+							continue
+						}
+					}
+					var rc registerCursor
+					var result *[]*Value
+					if len(aRegs) > 0 {
+						result = &allResults
+					}
+					rc.init(aRegs, aux.abiInfo, result, auxBase)
+					mem = x.storeArgOrLoad(v.Pos, b, a, mem, aux.TypeOfResult(i), auxOffset, 0, rc)
+				}
+			}
+			v.resetArgs()
+			v.AddArgs(allResults...)
+			v.AddArg(mem)
+			v.Type = types.NewResults(append(abi.RegisterTypes(aux.abiInfo.OutParams()), types.TypeMem))
+			b.SetControl(v)
+			for _, a := range oldArgs {
+				if a.Uses == 0 {
+					if x.debug > 1 {
+						x.Printf("...marking %v unused\n", a.LongString())
+					}
+					x.invalidateRecursively(a)
+				}
+			}
+			if x.debug > 1 {
+				x.Printf("...multiValueExit new result %s\n", v.LongString())
+			}
+			x.indent(-3)
+		}
+	}
+
+	// Step 1: any stores of aggregates remaining are believed to be sourced from call results or args.
+	// Decompose those stores into a series of smaller stores, adding selection ops as necessary.
+	for _, b := range f.Blocks {
+		for _, v := range b.Values {
+			if v.Op == OpStore {
+				t := v.Aux.(*types.Type)
+				source := v.Args[1]
+				tSrc := source.Type
+				iAEATt := x.isAlreadyExpandedAggregateType(t)
+
+				if !iAEATt {
+					// guarding against store immediate struct into interface data field -- store type is *uint8
+					// TODO can this happen recursively?
+					iAEATt = x.isAlreadyExpandedAggregateType(tSrc)
+					if iAEATt {
+						t = tSrc
+					}
+				}
+				dst, mem := v.Args[0], v.Args[2]
+				mem = x.storeArgOrLoad(v.Pos, b, source, mem, t, 0, 0, registerCursor{storeDest: dst})
+				v.copyOf(mem)
+			}
+		}
+	}
+
+	val2Preds := make(map[*Value]int32) // Used to accumulate dependency graph of selection operations for topological ordering.
+
+	// Step 2: transform or accumulate selection operations for rewrite in topological order.
+	//
+	// Aggregate types that have already (in earlier phases) been transformed must be lowered comprehensively to finish
+	// the transformation (user-defined structs and arrays, slices, strings, interfaces, complex, 64-bit on 32-bit architectures),
+	//
+	// Any select-for-addressing applied to call results can be transformed directly.
+	for _, b := range f.Blocks {
+		for _, v := range b.Values {
+			// Accumulate chains of selectors for processing in topological order
+			switch v.Op {
+			case OpStructSelect, OpArraySelect,
+				OpIData, OpITab,
+				OpStringPtr, OpStringLen,
+				OpSlicePtr, OpSliceLen, OpSliceCap, OpSlicePtrUnchecked,
+				OpComplexReal, OpComplexImag,
+				OpInt64Hi, OpInt64Lo:
+				w := v.Args[0]
+				switch w.Op {
+				case OpStructSelect, OpArraySelect, OpSelectN, OpArg:
+					val2Preds[w] += 1
+					if x.debug > 1 {
+						x.Printf("v2p[%s] = %d\n", w.LongString(), val2Preds[w])
+					}
+				}
+				fallthrough
+
+			case OpSelectN:
+				if _, ok := val2Preds[v]; !ok {
+					val2Preds[v] = 0
+					if x.debug > 1 {
+						x.Printf("v2p[%s] = %d\n", v.LongString(), val2Preds[v])
+					}
+				}
+
+			case OpArg:
+				if !x.isAlreadyExpandedAggregateType(v.Type) {
+					continue
+				}
+				if _, ok := val2Preds[v]; !ok {
+					val2Preds[v] = 0
+					if x.debug > 1 {
+						x.Printf("v2p[%s] = %d\n", v.LongString(), val2Preds[v])
+					}
+				}
+
+			case OpSelectNAddr:
+				// Do these directly, there are no chains of selectors.
+				call := v.Args[0]
+				which := v.AuxInt
+				aux := call.Aux.(*AuxCall)
+				pt := v.Type
+				off := x.offsetFrom(x.f.Entry, x.sp, aux.OffsetOfResult(which), pt)
+				v.copyOf(off)
+			}
+		}
+	}
+
+	// Step 3: Compute topological order of selectors,
+	// then process it in reverse to eliminate duplicates,
+	// then forwards to rewrite selectors.
+	//
+	// All chains of selectors end up in same block as the call.
+
+	// Compilation must be deterministic, so sort after extracting first zeroes from map.
+	// Sorting allows dominators-last order within each batch,
+	// so that the backwards scan for duplicates will most often find copies from dominating blocks (it is best-effort).
+	var toProcess []*Value
+	less := func(i, j int) bool {
+		vi, vj := toProcess[i], toProcess[j]
+		bi, bj := vi.Block, vj.Block
+		if bi == bj {
+			return vi.ID < vj.ID
+		}
+		return x.sdom.domorder(bi) > x.sdom.domorder(bj) // reverse the order to put dominators last.
+	}
+
+	// Accumulate order in allOrdered
+	var allOrdered []*Value
+	for v, n := range val2Preds {
+		if n == 0 {
+			allOrdered = append(allOrdered, v)
+		}
+	}
+	last := 0 // allOrdered[0:last] has been top-sorted and processed
+	for len(val2Preds) > 0 {
+		toProcess = allOrdered[last:]
+		last = len(allOrdered)
+		sort.SliceStable(toProcess, less)
+		for _, v := range toProcess {
+			delete(val2Preds, v)
+			if v.Op == OpArg {
+				continue // no Args[0], hence done.
+			}
+			w := v.Args[0]
+			n, ok := val2Preds[w]
+			if !ok {
+				continue
+			}
+			if n == 1 {
+				allOrdered = append(allOrdered, w)
+				delete(val2Preds, w)
+				continue
+			}
+			val2Preds[w] = n - 1
+		}
+	}
+
+	x.commonSelectors = make(map[selKey]*Value)
+	// Rewrite duplicate selectors as copies where possible.
+	for i := len(allOrdered) - 1; i >= 0; i-- {
+		v := allOrdered[i]
+		if v.Op == OpArg {
+			continue
+		}
+		w := v.Args[0]
+		if w.Op == OpCopy {
+			for w.Op == OpCopy {
+				w = w.Args[0]
+			}
+			v.SetArg(0, w)
+		}
+		typ := v.Type
+		if typ.IsMemory() {
+			continue // handled elsewhere, not an indexable result
+		}
+		size := typ.Size()
+		offset := int64(0)
+		switch v.Op {
+		case OpStructSelect:
+			if w.Type.Kind() == types.TSTRUCT {
+				offset = w.Type.FieldOff(int(v.AuxInt))
+			} else { // Immediate interface data artifact, offset is zero.
+				f.Fatalf("Expand calls interface data problem, func %s, v=%s, w=%s\n", f.Name, v.LongString(), w.LongString())
+			}
+		case OpArraySelect:
+			offset = size * v.AuxInt
+		case OpSelectN:
+			offset = v.AuxInt // offset is just a key, really.
+		case OpInt64Hi:
+			offset = x.hiOffset
+		case OpInt64Lo:
+			offset = x.lowOffset
+		case OpStringLen, OpSliceLen, OpIData:
+			offset = x.ptrSize
+		case OpSliceCap:
+			offset = 2 * x.ptrSize
+		case OpComplexImag:
+			offset = size
+		}
+		sk := selKey{from: w, size: size, offsetOrIndex: offset, typ: typ}
+		dupe := x.commonSelectors[sk]
+		if dupe == nil {
+			x.commonSelectors[sk] = v
+		} else if x.sdom.IsAncestorEq(dupe.Block, v.Block) {
+			if x.debug > 1 {
+				x.Printf("Duplicate, make %s copy of %s\n", v, dupe)
+			}
+			v.copyOf(dupe)
+		} else {
+			// Because values are processed in dominator order, the old common[s] will never dominate after a miss is seen.
+			// Installing the new value might match some future values.
+			x.commonSelectors[sk] = v
+		}
+	}
+
+	// Indices of entries in f.Names that need to be deleted.
+	var toDelete []namedVal
+
+	// Rewrite selectors.
+	for i, v := range allOrdered {
+		if x.debug > 1 {
+			b := v.Block
+			x.Printf("allOrdered[%d] = b%d, %s, uses=%d\n", i, b.ID, v.LongString(), v.Uses)
+		}
+		if v.Uses == 0 {
+			x.invalidateRecursively(v)
+			continue
+		}
+		if v.Op == OpCopy {
+			continue
+		}
+		locs := x.rewriteSelect(v, v, 0, 0)
+		// Install new names.
+		if v.Type.IsMemory() {
+			continue
+		}
+		// Leaf types may have debug locations
+		if !x.isAlreadyExpandedAggregateType(v.Type) {
+			for _, l := range locs {
+				if _, ok := f.NamedValues[*l]; !ok {
+					f.Names = append(f.Names, l)
+				}
+				f.NamedValues[*l] = append(f.NamedValues[*l], v)
+			}
+			continue
+		}
+		if ns, ok := x.namedSelects[v]; ok {
+			// Not-leaf types that had debug locations need to lose them.
+
+			toDelete = append(toDelete, ns...)
+		}
+	}
+
+	deleteNamedVals(f, toDelete)
+
+	// Step 4: rewrite the calls themselves, correcting the type.
+	for _, b := range f.Blocks {
+		for _, v := range b.Values {
+			switch v.Op {
+			case OpArg:
+				x.rewriteArgToMemOrRegs(v)
+			case OpStaticLECall:
+				v.Op = OpStaticCall
+				rts := abi.RegisterTypes(v.Aux.(*AuxCall).abiInfo.OutParams())
+				v.Type = types.NewResults(append(rts, types.TypeMem))
+			case OpTailLECall:
+				v.Op = OpTailCall
+				rts := abi.RegisterTypes(v.Aux.(*AuxCall).abiInfo.OutParams())
+				v.Type = types.NewResults(append(rts, types.TypeMem))
+			case OpClosureLECall:
+				v.Op = OpClosureCall
+				rts := abi.RegisterTypes(v.Aux.(*AuxCall).abiInfo.OutParams())
+				v.Type = types.NewResults(append(rts, types.TypeMem))
+			case OpInterLECall:
+				v.Op = OpInterCall
+				rts := abi.RegisterTypes(v.Aux.(*AuxCall).abiInfo.OutParams())
+				v.Type = types.NewResults(append(rts, types.TypeMem))
+			}
+		}
+	}
+
+	// Step 5: dedup OpArgXXXReg values. Mostly it is already dedup'd by commonArgs,
+	// but there are cases that we have same OpArgXXXReg values with different types.
+	// E.g. string is sometimes decomposed as { *int8, int }, sometimes as { unsafe.Pointer, uintptr }.
+	// (Can we avoid that?)
+	var IArg, FArg [32]*Value
+	for _, v := range f.Entry.Values {
+		switch v.Op {
+		case OpArgIntReg:
+			i := v.AuxInt
+			if w := IArg[i]; w != nil {
+				if w.Type.Size() != v.Type.Size() {
+					f.Fatalf("incompatible OpArgIntReg [%d]: %s and %s", i, v.LongString(), w.LongString())
+				}
+				if w.Type.IsUnsafePtr() && !v.Type.IsUnsafePtr() {
+					// Update unsafe.Pointer type if we know the actual pointer type.
+					w.Type = v.Type
+				}
+				// TODO: don't dedup pointer and scalar? Rewrite to OpConvert? Can it happen?
+				v.copyOf(w)
+			} else {
+				IArg[i] = v
+			}
+		case OpArgFloatReg:
+			i := v.AuxInt
+			if w := FArg[i]; w != nil {
+				if w.Type.Size() != v.Type.Size() {
+					f.Fatalf("incompatible OpArgFloatReg [%d]: %v and %v", i, v, w)
+				}
+				v.copyOf(w)
+			} else {
+				FArg[i] = v
+			}
+		}
+	}
+
+	// Step 6: elide any copies introduced.
+	// Update named values.
+	for _, name := range f.Names {
+		values := f.NamedValues[*name]
+		for i, v := range values {
+			if v.Op == OpCopy {
+				a := v.Args[0]
+				for a.Op == OpCopy {
+					a = a.Args[0]
+				}
+				values[i] = a
+			}
+		}
+	}
+	for _, b := range f.Blocks {
+		for _, v := range b.Values {
+			for i, a := range v.Args {
+				if a.Op != OpCopy {
+					continue
+				}
+				aa := copySource(a)
+				v.SetArg(i, aa)
+				for a.Uses == 0 {
+					b := a.Args[0]
+					x.invalidateRecursively(a)
+					a = b
+				}
+			}
+		}
+	}
+
+	// Rewriting can attach lines to values that are unlikely to survive code generation, so move them to a use.
+	for _, b := range f.Blocks {
+		for _, v := range b.Values {
+			for _, a := range v.Args {
+				if a.Pos.IsStmt() != src.PosIsStmt {
+					continue
+				}
+				if a.Type.IsMemory() {
+					continue
+				}
+				if a.Pos.Line() != v.Pos.Line() {
+					continue
+				}
+				if !a.Pos.SameFile(v.Pos) {
+					continue
+				}
+				switch a.Op {
+				case OpArgIntReg, OpArgFloatReg, OpSelectN:
+					v.Pos = v.Pos.WithIsStmt()
+					a.Pos = a.Pos.WithDefaultStmt()
+				}
+			}
+		}
+	}
+}
+
+// rewriteArgToMemOrRegs converts OpArg v in-place into the register version of v,
+// if that is appropriate.
+func (x *expandState) rewriteArgToMemOrRegs(v *Value) *Value {
+	if x.debug > 1 {
+		x.indent(3)
+		defer x.indent(-3)
+		x.Printf("rewriteArgToMemOrRegs(%s)\n", v.LongString())
+	}
+	pa := x.prAssignForArg(v)
+	switch len(pa.Registers) {
+	case 0:
+		frameOff := v.Aux.(*ir.Name).FrameOffset()
+		if pa.Offset() != int32(frameOff+x.f.ABISelf.LocalsOffset()) {
+			panic(fmt.Errorf("Parameter assignment %d and OpArg.Aux frameOffset %d disagree, op=%s",
+				pa.Offset(), frameOff, v.LongString()))
+		}
+	case 1:
+		t := v.Type
+		key := selKey{v, 0, t.Size(), t}
+		w := x.commonArgs[key]
+		if w != nil && w.Uses != 0 { // do not reuse dead value
+			v.copyOf(w)
+			break
+		}
+		r := pa.Registers[0]
+		var i int64
+		v.Op, i = ArgOpAndRegisterFor(r, x.f.ABISelf)
+		v.Aux = &AuxNameOffset{v.Aux.(*ir.Name), 0}
+		v.AuxInt = i
+		x.commonArgs[key] = v
+
+	default:
+		panic(badVal("Saw unexpanded OpArg", v))
+	}
+	if x.debug > 1 {
+		x.Printf("-->%s\n", v.LongString())
+	}
+	return v
+}
+
+// newArgToMemOrRegs either rewrites toReplace into an OpArg referencing memory or into an OpArgXXXReg to a register,
+// or rewrites it into a copy of the appropriate OpArgXXX.  The actual OpArgXXX is determined by combining baseArg (an OpArg)
+// with offset, regOffset, and t to determine which portion of it to reference (either all or a part, in memory or in registers).
+func (x *expandState) newArgToMemOrRegs(baseArg, toReplace *Value, offset int64, regOffset Abi1RO, t *types.Type, pos src.XPos) *Value {
+	if x.debug > 1 {
+		x.indent(3)
+		defer x.indent(-3)
+		x.Printf("newArgToMemOrRegs(base=%s; toReplace=%s; t=%s; memOff=%d; regOff=%d)\n", baseArg.String(), toReplace.LongString(), t.String(), offset, regOffset)
+	}
+	key := selKey{baseArg, offset, t.Size(), t}
+	w := x.commonArgs[key]
+	if w != nil && w.Uses != 0 { // do not reuse dead value
+		if toReplace != nil {
+			toReplace.copyOf(w)
+			if x.debug > 1 {
+				x.Printf("...replace %s\n", toReplace.LongString())
+			}
+		}
+		if x.debug > 1 {
+			x.Printf("-->%s\n", w.LongString())
+		}
+		return w
+	}
+
+	pa := x.prAssignForArg(baseArg)
+	if len(pa.Registers) == 0 { // Arg is on stack
+		frameOff := baseArg.Aux.(*ir.Name).FrameOffset()
+		if pa.Offset() != int32(frameOff+x.f.ABISelf.LocalsOffset()) {
+			panic(fmt.Errorf("Parameter assignment %d and OpArg.Aux frameOffset %d disagree, op=%s",
+				pa.Offset(), frameOff, baseArg.LongString()))
+		}
+		aux := baseArg.Aux
+		auxInt := baseArg.AuxInt + offset
+		if toReplace != nil && toReplace.Block == baseArg.Block {
+			toReplace.reset(OpArg)
+			toReplace.Aux = aux
+			toReplace.AuxInt = auxInt
+			toReplace.Type = t
+			w = toReplace
+		} else {
+			w = baseArg.Block.NewValue0IA(baseArg.Pos, OpArg, t, auxInt, aux)
+		}
+		x.commonArgs[key] = w
+		if toReplace != nil {
+			toReplace.copyOf(w)
+		}
+		if x.debug > 1 {
+			x.Printf("-->%s\n", w.LongString())
+		}
+		return w
+	}
+	// Arg is in registers
+	r := pa.Registers[regOffset]
+	op, auxInt := ArgOpAndRegisterFor(r, x.f.ABISelf)
+	if op == OpArgIntReg && t.IsFloat() || op == OpArgFloatReg && t.IsInteger() {
+		fmt.Printf("pa=%v\nx.f.OwnAux.abiInfo=%s\n",
+			pa.ToString(x.f.ABISelf, true),
+			x.f.OwnAux.abiInfo.String())
+		panic(fmt.Errorf("Op/Type mismatch, op=%s, type=%s", op.String(), t.String()))
+	}
+	if baseArg.AuxInt != 0 {
+		base.Fatalf("BaseArg %s bound to registers has non-zero AuxInt", baseArg.LongString())
+	}
+	aux := &AuxNameOffset{baseArg.Aux.(*ir.Name), offset}
+	if toReplace != nil && toReplace.Block == baseArg.Block {
+		toReplace.reset(op)
+		toReplace.Aux = aux
+		toReplace.AuxInt = auxInt
+		toReplace.Type = t
+		w = toReplace
+	} else {
+		w = baseArg.Block.NewValue0IA(baseArg.Pos, op, t, auxInt, aux)
+	}
+	x.commonArgs[key] = w
+	if toReplace != nil {
+		toReplace.copyOf(w)
+	}
+	if x.debug > 1 {
+		x.Printf("-->%s\n", w.LongString())
+	}
+	return w
+
+}
+
+// ArgOpAndRegisterFor converts an abi register index into an ssa Op and corresponding
+// arg register index.
+func ArgOpAndRegisterFor(r abi.RegIndex, abiConfig *abi.ABIConfig) (Op, int64) {
+	i := abiConfig.FloatIndexFor(r)
+	if i >= 0 { // float PR
+		return OpArgFloatReg, i
+	}
+	return OpArgIntReg, int64(r)
+}