cmd/compile: use new runtime type mechanism for type switches and asserts

Change-Id: Ife7d6d6d773ac0d8ac38dbd2da7dccc519998b63
Reviewed-on: https://go-review.googlesource.com/c/go/+/534816
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>

src/cmd/compile/internal/rttype/rttype.go

@@ -38,6 +38,10 @@ var Method *types.Type
 var StructField *types.Type
 var UncommonType *types.Type
 
+// Type switches and asserts
+var InterfaceSwitch *types.Type
+var TypeAssert *types.Type
+
 func Init() {
 	// Note: this has to be called explicitly instead of being
 	// an init function so it runs after the types package has
@@ -57,6 +61,9 @@ func Init() {
 	StructField = fromReflect(reflect.TypeOf(abi.StructField{}))
 	UncommonType = fromReflect(reflect.TypeOf(abi.UncommonType{}))
 
+	InterfaceSwitch = fromReflect(reflect.TypeOf(abi.InterfaceSwitch{}))
+	TypeAssert = fromReflect(reflect.TypeOf(abi.TypeAssert{}))
+
 	// Make sure abi functions are correct. These functions are used
 	// by the linker which doesn't have the ability to do type layout,
 	// so we check the functions it uses here.
@@ -87,6 +94,8 @@ func fromReflect(rt reflect.Type) *types.Type {
 // must be CalcSize'd before using.
 func reflectToType(rt reflect.Type) *types.Type {
 	switch rt.Kind() {
+	case reflect.Bool:
+		return types.Types[types.TBOOL]
 	case reflect.Int:
 		return types.Types[types.TINT]
 	case reflect.Int32:
@@ -181,6 +190,12 @@ func (c Cursor) WriteInt32(val int32) {
 	}
 	objw.Uint32(c.lsym, int(c.offset), uint32(val))
 }
+func (c Cursor) WriteBool(val bool) {
+	if c.typ.Kind() != types.TBOOL {
+		base.Fatalf("can't write bool, it has kind %s", c.typ.Kind())
+	}
+	objw.Bool(c.lsym, int(c.offset), val)
+}
 
 // WriteSymPtrOff writes a "pointer" to the given symbol. The symbol
 // is encoded as a uint32 offset from the start of the section.
@@ -255,3 +270,14 @@ func (a ArrayCursor) Elem(i int) Cursor {
 	}
 	return Cursor{lsym: a.c.lsym, offset: a.c.offset + int64(i)*a.c.typ.Size(), typ: a.c.typ}
 }
+
+// ModifyArray converts a cursor pointing at a type [k]T to a cursor pointing
+// at a type [n]T.
+// Also returns the size delta, aka (n-k)*sizeof(T).
+func (c Cursor) ModifyArray(n int) (ArrayCursor, int64) {
+	if c.typ.Kind() != types.TARRAY {
+		base.Fatalf("can't call ModifyArray on non-array %v", c.typ)
+	}
+	k := c.typ.NumElem()
+	return ArrayCursor{c: Cursor{lsym: c.lsym, offset: c.offset, typ: c.typ.Elem()}, n: n}, (int64(n) - k) * c.typ.Elem().Size()
+}

src/cmd/compile/internal/walk/expr.go

@@ -14,6 +14,7 @@ import (
 	"cmd/compile/internal/ir"
 	"cmd/compile/internal/objw"
 	"cmd/compile/internal/reflectdata"
+	"cmd/compile/internal/rttype"
 	"cmd/compile/internal/staticdata"
 	"cmd/compile/internal/typecheck"
 	"cmd/compile/internal/types"
@@ -738,15 +739,12 @@ func makeTypeAssertDescriptor(target *types.Type, canFail bool) *obj.LSym {
 	// Allocate an internal/abi.TypeAssert descriptor for that call.
 	lsym := types.LocalPkg.Lookup(fmt.Sprintf(".typeAssert.%d", typeAssertGen)).LinksymABI(obj.ABI0)
 	typeAssertGen++
-	off := 0
+	c := rttype.NewCursor(lsym, 0, rttype.TypeAssert)
-	off = objw.SymPtr(lsym, off, typecheck.LookupRuntimeVar("emptyTypeAssertCache"), 0)
+	c.Field("Cache").WritePtr(typecheck.LookupRuntimeVar("emptyTypeAssertCache"))
-	off = objw.SymPtr(lsym, off, reflectdata.TypeSym(target).Linksym(), 0)
+	c.Field("Inter").WritePtr(reflectdata.TypeSym(target).Linksym())
-	off = objw.Bool(lsym, off, canFail)
+	c.Field("CanFail").WriteBool(canFail)
-	off += types.PtrSize - 1
+	objw.Global(lsym, int32(rttype.TypeAssert.Size()), obj.LOCAL)
-	objw.Global(lsym, int32(off), obj.LOCAL)
+	lsym.Gotype = reflectdata.TypeLinksym(rttype.TypeAssert)
-	// Set the type to be just a single pointer, as the cache pointer is the
-	// only one that GC needs to see.
-	lsym.Gotype = reflectdata.TypeLinksym(types.Types[types.TUINT8].PtrTo())
 	return lsym
 }
 

src/cmd/compile/internal/walk/switch.go

@@ -527,16 +527,18 @@ func walkSwitchType(sw *ir.SwitchStmt) {
 			// Build an internal/abi.InterfaceSwitch descriptor to pass to the runtime.
 			lsym := types.LocalPkg.Lookup(fmt.Sprintf(".interfaceSwitch.%d", interfaceSwitchGen)).LinksymABI(obj.ABI0)
 			interfaceSwitchGen++
-			off := 0
+			c := rttype.NewCursor(lsym, 0, rttype.InterfaceSwitch)
-			off = objw.SymPtr(lsym, off, typecheck.LookupRuntimeVar("emptyInterfaceSwitchCache"), 0)
+			c.Field("Cache").WritePtr(typecheck.LookupRuntimeVar("emptyInterfaceSwitchCache"))
-			off = objw.Uintptr(lsym, off, uint64(len(interfaceCases)))
+			c.Field("NCases").WriteInt(int64(len(interfaceCases)))
-			for _, c := range interfaceCases {
+			array, sizeDelta := c.Field("Cases").ModifyArray(len(interfaceCases))
-				off = objw.SymPtr(lsym, off, reflectdata.TypeSym(c.typ.Type()).Linksym(), 0)
+			for i, c := range interfaceCases {
+				array.Elem(i).WritePtr(reflectdata.TypeSym(c.typ.Type()).Linksym())
 			}
-			objw.Global(lsym, int32(off), obj.LOCAL)
+			objw.Global(lsym, int32(rttype.InterfaceSwitch.Size()+sizeDelta), obj.LOCAL)
-			// Set the type to be just a single pointer, as the cache pointer is the
+			// The GC only needs to see the first pointer in the structure (all the others
-			// only one that GC needs to see.
+			// are to static locations). So the InterfaceSwitch type itself is fine, even
-			lsym.Gotype = reflectdata.TypeLinksym(types.Types[types.TUINT8].PtrTo())
+			// though it might not cover the whole array we wrote above.
+			lsym.Gotype = reflectdata.TypeLinksym(rttype.InterfaceSwitch)
 
 			// Call runtime to do switch
 			// case, itab = runtime.interfaceSwitch(&descriptor, typeof(arg))