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https://github.com/golang/go
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9f640c2abb
A DebugRef associates a source expression E with an ssa.Value
V, but until now did not record whether V was the value or the
address of E. So, we would guess from the "pointerness" of
the Value, leading to confusion in some cases, e.g.
type N *N
var n N
n = &n // lvalue and rvalue are both pointers
Now we explicitly record 'IsAddress bool' in DebugRef, and
plumb this everywhere: through (*Function).ValueForExpr and
(*Program).VarValue, all the way to forming the pointer
analysis query.
Also:
- VarValue now treats each reference to a global distinctly,
just like it does for other vars. So:
var g int
func f() {
g = 1 // VarValue(g) == Const(1:int), !isAddress
print(g) // VarValue(g) == Global(g), isAddress
}
- DebugRefs are not emitted for references to predeclared
identifiers (nil, built-in).
- DebugRefs no longer prevent lifting of an Alloc var into a
register; now we update or discard the debug info.
- TestValueForExpr: improve coverage of ssa.EnclosingFunction
by putting expectations in methods and init funcs, not just
normal funcs.
- oracle: fix golden file broken by recent
(*types.Var).IsField change.
R=gri
CC=golang-dev
https://golang.org/cl/16610045
123 lines
3.0 KiB
Go
123 lines
3.0 KiB
Go
// 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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"code.google.com/p/go.tools/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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starPos token.Pos // source position, if from explicit *addr
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expr ast.Expr // source syntax [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.starPos
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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)
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store.pos = a.starPos
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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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