[dev.typeparams] cmd/compile: functions to create GC shape types/names for a concrete type

Created functions to create GC shape type and names, based on a proposal
from Keith. Kept unsigned and signed integer types as different, since
they have different shift operations.

Included adding in alignment fields where padding is
required between fields, even though that seems like it will be fairly
uncommon to use.

Added some extra unusual struct typeparams (for testing the gcshape
names/types) in index.go test.

Change-Id: I8132bbd28098bd933435b8972ac5cc0b39f4c0df
Reviewed-on: https://go-review.googlesource.com/c/go/+/329921
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

2 files changed, 234 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/noder/stencil.go b/src/cmd/compile/internal/noder/stencil.go
index 29ee863a71..b228e40258 100644
--- a/src/cmd/compile/internal/noder/stencil.go
+++ b/src/cmd/compile/internal/noder/stencil.go
@@ -8,6 +8,7 @@
 package noder
 
 import (
+	"bytes"
 	"cmd/compile/internal/base"
 	"cmd/compile/internal/ir"
 	"cmd/compile/internal/objw"
@@ -18,6 +19,7 @@ import (
 	"cmd/internal/src"
 	"fmt"
 	"go/constant"
+	"strconv"
 )
 
 func assert(p bool) {
@@ -490,6 +492,195 @@ func (g *irgen) getInstantiationForNode(inst *ir.InstExpr) (*ir.Func, ir.Node) {
 	}
 }
 
+func addGcType(fl []*types.Field, t *types.Type) []*types.Field {
+	return append(fl, types.NewField(base.Pos, typecheck.Lookup("F"+strconv.Itoa(len(fl))), t))
+}
+
+const INTTYPE = types.TINT64   // XX fix for 32-bit arch
+const UINTTYPE = types.TUINT64 // XX fix for 32-bit arch
+const INTSTRING = "i8"         // XX fix for 32-bit arch
+const UINTSTRING = "u8"        // XX fix for 32-bit arch
+
+// accumGcshape adds fields to fl resulting from the GCshape transformation of
+// type t. The string associated with the GCshape transformation of t is added to
+// buf. fieldSym is the sym of the field associated with type t, if it is in a
+// struct. fieldSym could be used to have special naming for blank fields, etc.
+func accumGcshape(fl []*types.Field, buf *bytes.Buffer, t *types.Type, fieldSym *types.Sym) []*types.Field {
+
+	// t.Kind() is already the kind of the underlying type, so no need to
+	// reference t.Underlying() to reference the underlying type.
+	assert(t.Kind() == t.Underlying().Kind())
+
+	switch t.Kind() {
+	case types.TINT8:
+		fl = addGcType(fl, types.Types[types.TINT8])
+		buf.WriteString("i1")
+
+	case types.TUINT8:
+		fl = addGcType(fl, types.Types[types.TUINT8])
+		buf.WriteString("u1")
+
+	case types.TINT16:
+		fl = addGcType(fl, types.Types[types.TINT16])
+		buf.WriteString("i2")
+
+	case types.TUINT16:
+		fl = addGcType(fl, types.Types[types.TUINT16])
+		buf.WriteString("u2")
+
+	case types.TINT32:
+		fl = addGcType(fl, types.Types[types.TINT32])
+		buf.WriteString("i4")
+
+	case types.TUINT32:
+		fl = addGcType(fl, types.Types[types.TUINT32])
+		buf.WriteString("u4")
+
+	case types.TINT64:
+		fl = addGcType(fl, types.Types[types.TINT64])
+		buf.WriteString("i8")
+
+	case types.TUINT64:
+		fl = addGcType(fl, types.Types[types.TUINT64])
+		buf.WriteString("u8")
+
+	case types.TINT:
+		fl = addGcType(fl, types.Types[INTTYPE])
+		buf.WriteString(INTSTRING)
+
+	case types.TUINT, types.TUINTPTR:
+		fl = addGcType(fl, types.Types[UINTTYPE])
+		buf.WriteString(UINTSTRING)
+
+	case types.TCOMPLEX64:
+		fl = addGcType(fl, types.Types[types.TFLOAT32])
+		fl = addGcType(fl, types.Types[types.TFLOAT32])
+		buf.WriteString("f4")
+		buf.WriteString("f4")
+
+	case types.TCOMPLEX128:
+		fl = addGcType(fl, types.Types[types.TFLOAT64])
+		fl = addGcType(fl, types.Types[types.TFLOAT64])
+		buf.WriteString("f8")
+		buf.WriteString("f8")
+
+	case types.TFLOAT32:
+		fl = addGcType(fl, types.Types[types.TFLOAT32])
+		buf.WriteString("f4")
+
+	case types.TFLOAT64:
+		fl = addGcType(fl, types.Types[types.TFLOAT64])
+		buf.WriteString("f8")
+
+	case types.TBOOL:
+		fl = addGcType(fl, types.Types[types.TINT8])
+		buf.WriteString("i1")
+
+	case types.TPTR:
+		fl = addGcType(fl, types.Types[types.TUNSAFEPTR])
+		buf.WriteString("p")
+
+	case types.TFUNC:
+		fl = addGcType(fl, types.Types[types.TUNSAFEPTR])
+		buf.WriteString("p")
+
+	case types.TSLICE:
+		fl = addGcType(fl, types.Types[types.TUNSAFEPTR])
+		fl = addGcType(fl, types.Types[INTTYPE])
+		fl = addGcType(fl, types.Types[INTTYPE])
+		buf.WriteString("p")
+		buf.WriteString(INTSTRING)
+		buf.WriteString(INTSTRING)
+
+	case types.TARRAY:
+		n := t.NumElem()
+		if n == 1 {
+			fl = accumGcshape(fl, buf, t.Elem(), nil)
+		} else if n > 0 {
+			// Represent an array with more than one element as its
+			// unique type, since it must be treated differently for
+			// regabi.
+			fl = addGcType(fl, t)
+			buf.WriteByte('[')
+			buf.WriteString(strconv.Itoa(int(n)))
+			buf.WriteString("](")
+			var ignore []*types.Field
+			// But to determine its gcshape name, we must call
+			// accumGcShape() on t.Elem().
+			accumGcshape(ignore, buf, t.Elem(), nil)
+			buf.WriteByte(')')
+		}
+
+	case types.TSTRUCT:
+		nfields := t.NumFields()
+		for i, f := range t.Fields().Slice() {
+			fl = accumGcshape(fl, buf, f.Type, f.Sym)
+
+			// Check if we need to add an alignment field.
+			var pad int64
+			if i < nfields-1 {
+				pad = t.Field(i+1).Offset - f.Offset - f.Type.Width
+			} else {
+				pad = t.Width - f.Offset - f.Type.Width
+			}
+			if pad > 0 {
+				// There is padding between fields or at end of
+				// struct. Add an alignment field.
+				fl = addGcType(fl, types.NewArray(types.Types[types.TUINT8], pad))
+				buf.WriteString("a")
+				buf.WriteString(strconv.Itoa(int(pad)))
+			}
+		}
+
+	case types.TCHAN:
+		fl = addGcType(fl, types.Types[types.TUNSAFEPTR])
+		buf.WriteString("p")
+
+	case types.TMAP:
+		fl = addGcType(fl, types.Types[types.TUNSAFEPTR])
+		buf.WriteString("p")
+
+	case types.TINTER:
+		fl = addGcType(fl, types.Types[types.TUNSAFEPTR])
+		fl = addGcType(fl, types.Types[types.TUNSAFEPTR])
+		buf.WriteString("pp")
+
+	case types.TFORW, types.TANY:
+		assert(false)
+
+	case types.TSTRING:
+		fl = addGcType(fl, types.Types[types.TUNSAFEPTR])
+		fl = addGcType(fl, types.Types[INTTYPE])
+		buf.WriteString("p")
+		buf.WriteString(INTSTRING)
+
+	case types.TUNSAFEPTR:
+		fl = addGcType(fl, types.Types[types.TUNSAFEPTR])
+		buf.WriteString("p")
+
+	default: // Everything TTYPEPARAM and below in list of Kinds
+		assert(false)
+	}
+
+	return fl
+}
+
+// gcshapeType returns the GCshape type and name corresponding to type t.
+func gcshapeType(t *types.Type) (*types.Type, string) {
+	var fl []*types.Field
+	buf := bytes.NewBufferString("")
+
+	// Call CallSize so type sizes and field offsets are available.
+	types.CalcSize(t)
+	fl = accumGcshape(fl, buf, t, nil)
+	// TODO: Should gcshapes be in a global package, so we don't have to
+	// duplicate in each package? Or at least in the specified source package
+	// of a function/method instantiation?
+	gcshape := types.NewStruct(types.LocalPkg, fl)
+	assert(gcshape.Size() == t.Size())
+	return gcshape, buf.String()
+}
+
 // getInstantiation gets the instantiantion and dictionary of the function or method nameNode
 // with the type arguments targs. If the instantiated function is not already
 // cached, then it calls genericSubst to create the new instantiation.
@@ -506,6 +697,13 @@ func (g *irgen) getInstantiation(nameNode *ir.Name, targs []*types.Type, isMeth
 	sym := typecheck.MakeInstName(nameNode.Sym(), targs, isMeth)
 	st := g.target.Stencils[sym]
 	if st == nil {
+		if false {
+			// Testing out gcshapeType() and gcshapeName()
+			for i, t := range targs {
+				gct, gcs := gcshapeType(t)
+				fmt.Printf("targ %d: %v %v\n", i, gct, gcs)
+			}
+		}
 		// If instantiation doesn't exist yet, create it and add
 		// to the list of decls.
 		st = g.genericSubst(sym, nameNode, targs, isMeth)
diff --git a/test/typeparam/index.go b/test/typeparam/index.go
index cb9b2613c3..80824efac3 100644
--- a/test/typeparam/index.go
+++ b/test/typeparam/index.go
@@ -26,6 +26,26 @@ type obj struct {
 	x int
 }
 
+type obj2 struct {
+	x int8
+	y float64
+}
+
+type obj3 struct {
+	x int64
+	y int8
+}
+
+type inner struct {
+	y int64
+	z int32
+}
+
+type obj4 struct {
+	x int32
+	s inner
+}
+
 func main() {
 	want := 2
 
@@ -43,4 +63,20 @@ func main() {
 	if got := Index(vec3, vec3[2]); got != want {
 		panic(fmt.Sprintf("got %d, want %d", got, want))
 	}
+
+	vec4 := []obj2{obj2{2, 3.0}, obj2{3, 4.0}, obj2{4, 5.0}}
+	if got := Index(vec4, vec4[2]); got != want {
+		panic(fmt.Sprintf("got %d, want %d", got, want))
+	}
+
+	vec5 := []obj3{obj3{2, 3}, obj3{3, 4}, obj3{4, 5}}
+	if got := Index(vec5, vec5[2]); got != want {
+		panic(fmt.Sprintf("got %d, want %d", got, want))
+	}
+
+	vec6 := []obj4{obj4{2, inner{3, 4}}, obj4{3, inner{4, 5}}, obj4{4, inner{5, 6}}}
+	if got := Index(vec6, vec6[2]); got != want {
+		panic(fmt.Sprintf("got %d, want %d", got, want))
+	}
 }
+