golang typebits 代码
文件路径：/src/cmd/compile/internal/typebits/typebits.go
/ Copyright 2013 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 typebits
import (
"cmd/compile/internal/base"
"cmd/compile/internal/bitvec"
"cmd/compile/internal/types"
)
/ NOTE: The bitmap for a specific type t could be cached in t after
/ the first run and then simply copied into bv at the correct offset
/ on future calls with the same type t.
func Set(t *types.Type, off int64, bv bitvec.BitVec) {
if uint8(t.Alignment()) > 0 && off&int64(uint8(t.Alignment())-1) != 0 {
base.Fatalf("typebits.Set: invalid initial alignment: type %v has alignment %d, but offset is %v", t, uint8(t.Alignment()), off)
}
if !t.HasPointers() {
/ Note: this case ensures that pointers to go:notinheap types
/ are not considered pointers by garbage collection and stack copying.
return
}
switch t.Kind() {
case types.TPTR, types.TUNSAFEPTR, types.TFUNC, types.TCHAN, types.TMAP:
if off&int64(types.PtrSize-1) != 0 {
base.Fatalf("typebits.Set: invalid alignment, %v", t)
}
bv.Set(int32(off / int64(types.PtrSize))) / pointer
case types.TSTRING:
/ struct { byte *str; intgo len; }
if off&int64(types.PtrSize-1) != 0 {
base.Fatalf("typebits.Set: invalid alignment, %v", t)
}
bv.Set(int32(off / int64(types.PtrSize))) /pointer in first slot
case types.TINTER:
/ struct { Itab *tab; void *data; }
/ or, when isnilinter(t)==true:
/ struct { Type *type; void *data; }
if off&int64(types.PtrSize-1) != 0 {
base.Fatalf("typebits.Set: invalid alignment, %v", t)
}
/ The first word of an interface is a pointer, but we don't
/ treat it as such.
/ 1. If it is a non-empty interface, the pointer points to an itab
/ which is always in persistentalloc space.
/ 2. If it is an empty interface, the pointer points to a _type.
/ a. If it is a compile-time-allocated type, it points into
/ the read-only data section.
/ b. If it is a reflect-allocated type, it points into the Go heap.
/ Reflect is responsible for keeping a reference to
/ the underlying type so it won't be GCd.
/ If we ever have a moving GC, we need to change this for 2b (as
/ well as scan itabs to update their itab._type fields).
bv.Set(int32(off/int64(types.PtrSize) + 1)) / pointer in second slot
case types.TSLICE:
/ struct { byte *array; uintgo len; uintgo cap; }
if off&int64(types.PtrSize-1) != 0 {
base.Fatalf("typebits.Set: invalid TARRAY alignment, %v", t)
}
bv.Set(int32(off / int64(types.PtrSize))) / pointer in first slot (BitsPointer)
case types.TARRAY:
elt := t.Elem()
if elt.Size() == 0 {
/ Short-circuit for #20739.
break
}
for i := int64(0); i < t.NumElem(); i++ {
Set(elt, off, bv)
off += elt.Size()
}
case types.TSTRUCT:
for _, f := range t.Fields().Slice() {
Set(f.Type, off+f.Offset, bv)
}
default:
base.Fatalf("typebits.Set: unexpected type, %v", t)
}
}