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55d678e697
This CL adds three new functions to determine the SSA Value
for a given syntactic var, func or const object:
Program.{Const,Func,Var}Value.
Since constants and functions are immutable, the first
two only need a types.Object; but each distinct
reference to a var may return a distinct Value, so the third
requires an ast.Ident parameter too.
Debug information for local vars is encoded in the
instruction stream in the form of DebugRef instructions,
which are a no-op but relate their operand to a particular
ident in the AST. The beauty of this approach is that it
naturally stays consistent during optimisation passes
(e.g. lifting) without additional bookkeeping.
DebugRef instructions are only generated if the DebugMode
builder flag is set; I plan to make the policy more fine-
grained (per function).
DebugRef instructions are inserted for:
- expr(Ident) for rvalue idents
- address.store() for idents that update an lvalue
- address.address() for idents that take address of lvalue
(this new method replaces all uses of lval.(address).addr)
- expr() for all constant expressions
- local ValueSpecs with implicit zero initialization (no RHS)
(this case doesn't call store() or address())
To ensure we don't forget to emit debug info for uses of Idents,
we must use the lvalue mechanism consistently. (Previously,
many simple cases had effectively inlined these functions.)
Similarly setCallFunc no longer inlines expr(Ident).
Also:
- Program.Value() has been inlined & specialized.
- Program.Package() has moved nearer the new lookup functions.
- refactoring: funcSyntax has lost paramFields, resultFields;
gained funcType, which provides access to both.
- add package-level constants to Package.values map.
- opt: don't call localValueSpec for constants.
(The resulting code is always optimised away.)
There are a number of comments asking whether Literals
should have positions. Will address in a follow-up.
Added tests of all interesting cases.
R=gri
CC=golang-dev
https://golang.org/cl/11259044
117 lines
2.8 KiB
Go
117 lines
2.8 KiB
Go
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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id *ast.Ident // source syntax, if from *ast.Ident
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object types.Object // source var, if from *ast.Ident
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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.id != nil {
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// store.Val is v converted for assignability.
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emitDebugRef(fn, a.id, store.Val)
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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.id != nil {
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// NB: this kind of DebugRef yields the object's address.
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emitDebugRef(fn, a.id, a.addr)
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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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}
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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.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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fn.emit(&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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}
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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 blanks 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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