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cmd/compile: import/export of alias declarations
This CL completes support for alias declarations in the compiler. Also: - increased export format version - updated various comments For #16339. Fixes #17487. Change-Id: Ic6945fc44c0041771eaf9dcfe973f601d14de069 Reviewed-on: https://go-review.googlesource.com/32090 Run-TryBot: Robert Griesemer <gri@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Matthew Dempsky <mdempsky@google.com>
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Robert Griesemer
parent
81038d2e2b
commit
03d81b5ed9
11 changed files with 291 additions and 61 deletions
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@ -9,10 +9,12 @@
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1) Export data encoding principles:
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The export data is a serialized description of the graph of exported
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"objects": constants, types, variables, and functions. In general,
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types - but also objects referred to from inlined function bodies -
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can be reexported and so we need to know which package they are coming
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from. Therefore, packages are also part of the export graph.
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"objects": constants, types, variables, and functions. Aliases may be
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directly reexported, and unaliased types may be indirectly reexported
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(as part of the type of a directly exorted object). More generally,
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objects referred to from inlined function bodies can be reexported.
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We need to know which package declares these reexported objects, and
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therefore packages are also part of the export graph.
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The roots of the graph are two lists of objects. The 1st list (phase 1,
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see Export) contains all objects that are exported at the package level.
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@ -30,9 +32,9 @@ function bodies. The format of this representation is compiler specific.
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The graph is serialized in in-order fashion, starting with the roots.
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Each object in the graph is serialized by writing its fields sequentially.
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If the field is a pointer to another object, that object is serialized,
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recursively. Otherwise the field is written. Non-pointer fields are all
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encoded as integer or string values.
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If the field is a pointer to another object, that object is serialized in
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place, recursively. Otherwise the field is written in place. Non-pointer
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fields are all encoded as integer or string values.
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Some objects (packages, types) may be referred to more than once. When
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reaching an object that was not serialized before, an integer _index_
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@ -43,7 +45,7 @@ If the object was already serialized, the encoding is simply the object
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index >= 0. An importer can trivially determine if an object needs to
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be read in for the first time (tag < 0) and entered into the respective
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object table, or if the object was seen already (index >= 0), in which
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case the index is used to look up the object in a table.
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case the index is used to look up the object in the respective table.
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Before exporting or importing, the type tables are populated with the
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predeclared types (int, string, error, unsafe.Pointer, etc.). This way
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@ -59,7 +61,7 @@ format. These strings are followed by version-specific encoding options.
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That format encoding is no longer used but is supported to avoid spurious
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errors when importing old installed package files.)
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The header is followed by the package object for the exported package,
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This header is followed by the package object for the exported package,
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two lists of objects, and the list of inlined function bodies.
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The encoding of objects is straight-forward: Constants, variables, and
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@ -69,6 +71,8 @@ same type was imported before via another import, the importer must use
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the previously imported type pointer so that we have exactly one version
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(i.e., one pointer) for each named type (and read but discard the current
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type encoding). Unnamed types simply encode their respective fields.
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Aliases are encoded starting with their name followed by the original
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(aliased) object.
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In the encoding, some lists start with the list length. Some lists are
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terminated with an end marker (usually for lists where we may not know
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@ -101,30 +105,8 @@ compatibility with both the last release of the compiler, and with the
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corresponding compiler at tip. That change is necessarily more involved,
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as it must switch based on the version number in the export data file.
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It is recommended to turn on debugFormat when working on format changes
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as it will help finding encoding/decoding inconsistencies quickly.
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Special care must be taken to update builtin.go when the export format
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changes: builtin.go contains the export data obtained by compiling the
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builtin/runtime.go and builtin/unsafe.go files; those compilations in
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turn depend on importing the data in builtin.go. Thus, when the export
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data format changes, the compiler must be able to import the data in
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builtin.go even if its format has not yet changed. Proceed in several
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steps as follows:
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- Change the exporter to use the new format, and use a different version
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string as well.
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- Update the importer accordingly, but accept both the old and the new
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format depending on the version string.
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- all.bash should pass at this point.
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- Run mkbuiltin.go: this will create a new builtin.go using the new
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export format.
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- go test -run Builtin should pass at this point.
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- Remove importer support for the old export format and (maybe) revert
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the version string again (it's only needed to mark the transition).
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- all.bash should still pass.
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Don't forget to set debugFormat to false.
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It is recommended to turn on debugFormat temporarily when working on format
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changes as it will help finding encoding/decoding inconsistencies quickly.
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*/
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package gc
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@ -158,7 +140,11 @@ const debugFormat = false // default: false
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const forceObjFileStability = true
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// Current export format version. Increase with each format change.
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const exportVersion = 2
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// 3: added aliasTag and export of aliases
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// 2: removed unused bool in ODCL export
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// 1: header format change (more regular), export package for _ struct fields
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// 0: Go1.7 encoding
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const exportVersion = 3
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// exportInlined enables the export of inlined function bodies and related
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// dependencies. The compiler should work w/o any loss of functionality with
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@ -364,6 +350,11 @@ func export(out *bufio.Writer, trace bool) int {
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if p.trace {
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p.tracef("\n")
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}
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if sym.Flags&SymAlias != 0 {
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Fatalf("exporter: unexpected alias %v in inlined function body", sym)
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}
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p.obj(sym)
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objcount++
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}
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@ -455,16 +446,44 @@ func unidealType(typ *Type, val Val) *Type {
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}
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func (p *exporter) obj(sym *Sym) {
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if sym.Flags&SymAlias != 0 {
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p.tag(aliasTag)
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p.pos(nil) // TODO(gri) fix position information
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// Aliases can only be exported from the package that
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// declares them (aliases to aliases are resolved to the
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// original object, and so are uses of aliases in inlined
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// exported function bodies). Thus, we only need the alias
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// name without package qualification.
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if sym.Pkg != localpkg {
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Fatalf("exporter: export of non-local alias: %v", sym)
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}
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p.string(sym.Name)
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sym = sym.Def.Sym // original object
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// fall through to export original
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// Multiple aliases to the same original will cause that
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// original to be exported multiple times (issue #17636).
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// TODO(gri) fix this
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}
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if sym != sym.Def.Sym {
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Fatalf("exporter: exported object %v is not original %v", sym, sym.Def.Sym)
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}
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if sym.Flags&SymAlias != 0 {
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Fatalf("exporter: original object %v marked as alias", sym)
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}
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// Exported objects may be from different packages because they
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// may be re-exported as depencies when exporting inlined function
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// bodies. Thus, exported object names must be fully qualified.
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// may be re-exported via an exported alias or as dependencies in
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// exported inlined function bodies. Thus, exported object names
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// must be fully qualified.
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//
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// TODO(gri) This can only happen if exportInlined is enabled
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// (default), and during phase 2 of object export. Objects exported
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// in phase 1 (compiler-indendepent objects) are by definition only
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// the objects from the current package and not pulled in via inlined
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// function bodies. In that case the package qualifier is not needed.
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// Possible space optimization.
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// (This can only happen for aliased objects or during phase 2
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// (exportInlined enabled) of object export. Unaliased Objects
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// exported in phase 1 (compiler-indendepent objects) are by
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// definition only the objects from the current package and not
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// pulled in via inlined function bodies. In that case the package
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// qualifier is not needed. Possible space optimization.)
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n := sym.Def
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switch n.Op {
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@ -1780,6 +1799,9 @@ const (
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stringTag
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nilTag
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unknownTag // not used by gc (only appears in packages with errors)
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// Aliases
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aliasTag
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)
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// Debugging support.
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@ -1815,6 +1837,9 @@ var tagString = [...]string{
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-stringTag: "string",
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-nilTag: "nil",
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-unknownTag: "unknown",
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// Aliases
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-aliasTag: "alias",
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}
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// untype returns the "pseudo" untyped type for a Ctype (import/export use only).
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