[dev.regabi] cmd/compile: separate dowidth better

Having a global MaxWidth lets us avoid needing to
refer to thearch from split-out packages when all
they need is thearch.MAXWIDTH.

And make a couple interface changes to let dowidth
avoid importing package ir directly.
Then it can move into package types.

Change-Id: I2c12e8e22252597530e648848320e19bdd490a01
Reviewed-on: https://go-review.googlesource.com/c/go/+/279302
Trust: Russ Cox <rsc@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -29,6 +29,7 @@ func TestMain(m *testing.M) {
 	thearch.LinkArch = &x86.Linkamd64
 	thearch.REGSP = x86.REGSP
 	thearch.MAXWIDTH = 1 << 50
+	MaxWidth = thearch.MAXWIDTH
 	base.Ctxt = obj.Linknew(thearch.LinkArch)
 	base.Ctxt.DiagFunc = base.Errorf
 	base.Ctxt.DiagFlush = base.FlushErrors

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

@@ -7,12 +7,14 @@ package gc
 import (
 	"bytes"
 	"cmd/compile/internal/base"
-	"cmd/compile/internal/ir"
 	"cmd/compile/internal/types"
 	"fmt"
 	"sort"
 )
 
+// MaxWidth is the maximum size of a value on the target architecture.
+var MaxWidth int64
+
 // sizeCalculationDisabled indicates whether it is safe
 // to calculate Types' widths and alignments. See dowidth.
 var sizeCalculationDisabled bool
@@ -84,7 +86,7 @@ func expandiface(t *types.Type) {
 
 	sort.Sort(methcmp(methods))
 
-	if int64(len(methods)) >= thearch.MAXWIDTH/int64(Widthptr) {
+	if int64(len(methods)) >= MaxWidth/int64(Widthptr) {
 		base.ErrorfAt(typePos(t), "interface too large")
 	}
 	for i, m := range methods {
@@ -118,8 +120,7 @@ func widstruct(errtype *types.Type, t *types.Type, o int64, flag int) int64 {
 			o = Rnd(o, int64(f.Type.Align))
 		}
 		f.Offset = o
-		if n := ir.AsNode(f.Nname); n != nil {
-			n := n.Name()
+		if f.Nname != nil {
 			// addrescapes has similar code to update these offsets.
 			// Usually addrescapes runs after widstruct,
 			// in which case we could drop this,
@@ -127,12 +128,7 @@ func widstruct(errtype *types.Type, t *types.Type, o int64, flag int) int64 {
 			// NOTE(rsc): This comment may be stale.
 			// It's possible the ordering has changed and this is
 			// now the common case. I'm not sure.
-			if n.Name().Stackcopy != nil {
-				n.Name().Stackcopy.SetFrameOffset(o)
-				n.SetFrameOffset(0)
-			} else {
-				n.SetFrameOffset(o)
-			}
+			f.Nname.(types.VarObject).RecordFrameOffset(o)
 		}
 
 		w := f.Type.Width
@@ -143,7 +139,7 @@ func widstruct(errtype *types.Type, t *types.Type, o int64, flag int) int64 {
 			lastzero = o
 		}
 		o += w
-		maxwidth := thearch.MAXWIDTH
+		maxwidth := MaxWidth
 		// On 32-bit systems, reflect tables impose an additional constraint
 		// that each field start offset must fit in 31 bits.
 		if maxwidth < 1<<32 {
@@ -206,7 +202,7 @@ func findTypeLoop(t *types.Type, path *[]*types.Type) bool {
 		}
 
 		*path = append(*path, t)
-		if findTypeLoop(t.Obj().(*ir.Name).Ntype.Type(), path) {
+		if findTypeLoop(t.Obj().(types.TypeObject).TypeDefn(), path) {
 			return true
 		}
 		*path = (*path)[:len(*path)-1]
@@ -419,7 +415,7 @@ func dowidth(t *types.Type) {
 
 		dowidth(t.Elem())
 		if t.Elem().Width != 0 {
-			cap := (uint64(thearch.MAXWIDTH) - 1) / uint64(t.Elem().Width)
+			cap := (uint64(MaxWidth) - 1) / uint64(t.Elem().Width)
 			if uint64(t.NumElem()) > cap {
 				base.ErrorfAt(typePos(t), "type %L larger than address space", t)
 			}
@@ -479,6 +475,13 @@ func dowidth(t *types.Type) {
 	resumecheckwidth()
 }
 
+// CalcStructSize calculates the size of s,
+// filling in s.Width and s.Align,
+// even if size calculation is otherwise disabled.
+func CalcStructSize(s *types.Type) {
+	s.Width = widstruct(s, s, 0, 1) // sets align
+}
+
 // when a type's width should be known, we call checkwidth
 // to compute it.  during a declaration like
 //

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

@@ -208,6 +208,7 @@ func Main(archInit func(*Arch)) {
 
 	Widthptr = thearch.LinkArch.PtrSize
 	Widthreg = thearch.LinkArch.RegSize
+	MaxWidth = thearch.MAXWIDTH
 
 	Target = new(ir.Package)
 

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

@@ -164,7 +164,7 @@ func (s *ssafn) AllocFrame(f *ssa.Func) {
 
 		dowidth(n.Type())
 		w := n.Type().Width
-		if w >= thearch.MAXWIDTH || w < 0 {
+		if w >= MaxWidth || w < 0 {
 			base.Fatalf("bad width")
 		}
 		if w == 0 && lastHasPtr {

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

@@ -331,8 +331,7 @@ func deferstruct(stksize int64) *types.Type {
 	// build struct holding the above fields
 	s := types.NewStruct(types.NoPkg, fields)
 	s.SetNoalg(true)
-	s.Width = widstruct(s, s, 0, 1)
-	s.Align = uint8(Widthptr)
+	CalcStructSize(s)
 	return s
 }
 

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

@@ -1019,7 +1019,7 @@ func stataddr(n ir.Node) (name *ir.Name, offset int64, ok bool) {
 		}
 
 		// Check for overflow.
-		if n.Type().Width != 0 && thearch.MAXWIDTH/n.Type().Width <= int64(l) {
+		if n.Type().Width != 0 && MaxWidth/n.Type().Width <= int64(l) {
 			break
 		}
 		offset += int64(l) * n.Type().Width

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

@@ -147,6 +147,24 @@ func (n *Name) isExpr() {}
 // Callers must use n.CloneName to make clear they intend to create a separate name.
 func (n *Name) CloneName() *Name { c := *n; return &c }
 
+// TypeDefn returns the type definition for a named OTYPE.
+// That is, given "type T Defn", it returns Defn.
+// It is used by package types.
+func (n *Name) TypeDefn() *types.Type {
+	return n.Ntype.Type()
+}
+
+// RecordFrameOffset records the frame offset for the name.
+// It is used by package types when laying out function arguments.
+func (n *Name) RecordFrameOffset(offset int64) {
+	if n.Stackcopy != nil {
+		n.Stackcopy.SetFrameOffset(offset)
+		n.SetFrameOffset(0)
+	} else {
+		n.SetFrameOffset(offset)
+	}
+}
+
 // NewNameAt returns a new ONAME Node associated with symbol s at position pos.
 // The caller is responsible for setting Curfn.
 func NewNameAt(pos src.XPos, sym *types.Sym) *Name {

src/cmd/compile/internal/types/type.go

@@ -20,6 +20,18 @@ type Object interface {
 	Type() *Type
 }
 
+// A TypeObject is an Object representing a named type.
+type TypeObject interface {
+	Object
+	TypeDefn() *Type // for "type T Defn", returns Defn
+}
+
+// A VarObject is an Object representing a function argument, variable, or struct field.
+type VarObject interface {
+	Object
+	RecordFrameOffset(int64) // save frame offset
+}
+
 //go:generate stringer -type EType -trimprefix T
 
 // EType describes a kind of type.