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[dev.typeparams] cmd/compile: add types2.Sizes implementation
This CL adds an implementation of types2.Sizes that calculates sizes using the same sizing algorithm as cmd/compile. In particular, it matches how cmd/compile pads structures and includes padding in size calculations. Change-Id: I4dd8e51f95c90f9d7bd1e7463e40edcd3955a219 Reviewed-on: https://go-review.googlesource.com/c/go/+/282915 Trust: Matthew Dempsky <mdempsky@google.com> Trust: Robert Griesemer <gri@golang.org> Run-TryBot: Matthew Dempsky <mdempsky@google.com> TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Robert Griesemer <gri@golang.org>
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@ -133,6 +133,7 @@ func ParseFiles(filenames []string) (lines uint) {
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return os.Open(file)
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},
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},
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Sizes: &gcSizes{},
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}
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info := types2.Info{
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Types: make(map[syntax.Expr]types2.TypeAndValue),
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150
src/cmd/compile/internal/noder/sizes.go
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150
src/cmd/compile/internal/noder/sizes.go
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@ -0,0 +1,150 @@
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// Copyright 2021 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package noder
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import (
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"fmt"
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"cmd/compile/internal/types"
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"cmd/compile/internal/types2"
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)
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// Code below based on go/types.StdSizes.
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// Intentional differences are marked with "gc:".
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type gcSizes struct{}
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func (s *gcSizes) Alignof(T types2.Type) int64 {
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// For arrays and structs, alignment is defined in terms
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// of alignment of the elements and fields, respectively.
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switch t := T.Underlying().(type) {
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case *types2.Array:
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// spec: "For a variable x of array type: unsafe.Alignof(x)
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// is the same as unsafe.Alignof(x[0]), but at least 1."
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return s.Alignof(t.Elem())
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case *types2.Struct:
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// spec: "For a variable x of struct type: unsafe.Alignof(x)
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// is the largest of the values unsafe.Alignof(x.f) for each
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// field f of x, but at least 1."
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max := int64(1)
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for i, nf := 0, t.NumFields(); i < nf; i++ {
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if a := s.Alignof(t.Field(i).Type()); a > max {
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max = a
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}
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}
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return max
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case *types2.Slice, *types2.Interface:
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// Multiword data structures are effectively structs
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// in which each element has size PtrSize.
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return int64(types.PtrSize)
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case *types2.Basic:
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// Strings are like slices and interfaces.
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if t.Info()&types2.IsString != 0 {
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return int64(types.PtrSize)
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}
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}
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a := s.Sizeof(T) // may be 0
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// spec: "For a variable x of any type: unsafe.Alignof(x) is at least 1."
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if a < 1 {
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return 1
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}
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// complex{64,128} are aligned like [2]float{32,64}.
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if isComplex(T) {
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a /= 2
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}
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if a > int64(types.RegSize) {
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return int64(types.RegSize)
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}
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return a
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}
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func isComplex(T types2.Type) bool {
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basic, ok := T.Underlying().(*types2.Basic)
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return ok && basic.Info()&types2.IsComplex != 0
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}
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func (s *gcSizes) Offsetsof(fields []*types2.Var) []int64 {
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offsets := make([]int64, len(fields))
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var o int64
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for i, f := range fields {
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typ := f.Type()
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a := s.Alignof(typ)
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o = types.Rnd(o, a)
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offsets[i] = o
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o += s.Sizeof(typ)
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}
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return offsets
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}
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func (s *gcSizes) Sizeof(T types2.Type) int64 {
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switch t := T.Underlying().(type) {
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case *types2.Basic:
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k := t.Kind()
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if int(k) < len(basicSizes) {
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if s := basicSizes[k]; s > 0 {
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return int64(s)
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}
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}
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switch k {
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case types2.String:
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return int64(types.PtrSize) * 2
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case types2.Int, types2.Uint, types2.Uintptr, types2.UnsafePointer:
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return int64(types.PtrSize)
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}
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panic(fmt.Sprintf("unimplemented basic: %v (kind %v)", T, k))
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case *types2.Array:
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n := t.Len()
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if n <= 0 {
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return 0
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}
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// n > 0
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// gc: Size includes alignment padding.
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return s.Sizeof(t.Elem()) * n
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case *types2.Slice:
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return int64(types.PtrSize) * 3
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case *types2.Struct:
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n := t.NumFields()
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if n == 0 {
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return 0
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}
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fields := make([]*types2.Var, n)
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for i := range fields {
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fields[i] = t.Field(i)
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}
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offsets := s.Offsetsof(fields)
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// gc: The last field of a struct is not allowed to
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// have size 0.
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last := s.Sizeof(fields[n-1].Type())
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if last == 0 {
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last = 1
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}
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// gc: Size includes alignment padding.
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return types.Rnd(offsets[n-1]+last, s.Alignof(t))
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case *types2.Interface:
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return int64(types.PtrSize) * 2
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case *types2.Chan, *types2.Map, *types2.Pointer, *types2.Signature:
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return int64(types.PtrSize)
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default:
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panic(fmt.Sprintf("unimplemented type: %T", t))
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}
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}
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var basicSizes = [...]byte{
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types2.Bool: 1,
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types2.Int8: 1,
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types2.Int16: 2,
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types2.Int32: 4,
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types2.Int64: 8,
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types2.Uint8: 1,
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types2.Uint16: 2,
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types2.Uint32: 4,
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types2.Uint64: 8,
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types2.Float32: 4,
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types2.Float64: 8,
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types2.Complex64: 8,
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types2.Complex128: 16,
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}
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