121 lines
2.9 KiB
Go
121 lines
2.9 KiB
Go
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// Copyright 2013 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 ssa
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// lvalues are the union of addressable expressions and map-index
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// expressions.
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import (
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"go/ast"
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"go/token"
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"go/types"
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)
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// An lvalue represents an assignable location that may appear on the
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// left-hand side of an assignment. This is a generalization of a
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// pointer to permit updates to elements of maps.
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//
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type lvalue interface {
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store(fn *Function, v Value) // stores v into the location
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load(fn *Function) Value // loads the contents of the location
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address(fn *Function) Value // address of the location
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typ() types.Type // returns the type of the location
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}
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// An address is an lvalue represented by a true pointer.
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type address struct {
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addr Value
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pos token.Pos // source position
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expr ast.Expr // source syntax of the value (not address) [debug mode]
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}
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func (a *address) load(fn *Function) Value {
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load := emitLoad(fn, a.addr)
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load.pos = a.pos
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return load
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}
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func (a *address) store(fn *Function, v Value) {
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store := emitStore(fn, a.addr, v, a.pos)
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if a.expr != nil {
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// store.Val is v, converted for assignability.
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emitDebugRef(fn, a.expr, store.Val, false)
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}
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}
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func (a *address) address(fn *Function) Value {
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if a.expr != nil {
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emitDebugRef(fn, a.expr, a.addr, true)
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}
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return a.addr
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}
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func (a *address) typ() types.Type {
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return deref(a.addr.Type())
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}
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// An element is an lvalue represented by m[k], the location of an
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// element of a map or string. These locations are not addressable
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// since pointers cannot be formed from them, but they do support
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// load(), and in the case of maps, store().
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//
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type element struct {
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m, k Value // map or string
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t types.Type // map element type or string byte type
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pos token.Pos // source position of colon ({k:v}) or lbrack (m[k]=v)
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}
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func (e *element) load(fn *Function) Value {
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l := &Lookup{
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X: e.m,
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Index: e.k,
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}
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l.setPos(e.pos)
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l.setType(e.t)
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return fn.emit(l)
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}
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func (e *element) store(fn *Function, v Value) {
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up := &MapUpdate{
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Map: e.m,
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Key: e.k,
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Value: emitConv(fn, v, e.t),
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}
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up.pos = e.pos
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fn.emit(up)
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}
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func (e *element) address(fn *Function) Value {
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panic("map/string elements are not addressable")
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}
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func (e *element) typ() types.Type {
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return e.t
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}
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// A blank is a dummy variable whose name is "_".
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// It is not reified: loads are illegal and stores are ignored.
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//
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type blank struct{}
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func (bl blank) load(fn *Function) Value {
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panic("blank.load is illegal")
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}
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func (bl blank) store(fn *Function, v Value) {
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// no-op
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}
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func (bl blank) address(fn *Function) Value {
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panic("blank var is not addressable")
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}
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func (bl blank) typ() types.Type {
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// This should be the type of the blank Ident; the typechecker
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// doesn't provide this yet, but fortunately, we don't need it
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// yet either.
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panic("blank.typ is unimplemented")
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}
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