This introduces a WIP lowering operation, abstracting away quite a bit of
the manual wiring work, which is really important to providing an API that
provides the proper level of abstraction for actually understanding what the
system is doing.
This does not yet have tests associated with it---I had started, but it's a
lot of work and boilerplate for something that is going to
evolve. Generally, I wouldn't use that as an excuse, but the robust type
definitions in play, combined with the tiny amount of actual logic, provide
a pretty high level of confidence. It's very difficult to wire these types
together and produce something incorrect without doing something obviously
bad.
Similarly, I'm holding off on proper docs too, though I did write some
information here.
More to come, after I actually get to work on the XmloReader.
On a side note: I'm happy to have made progress on this, since this wiring
is something I've been dreading and wondering about since before the Parser
abstraction even existed.
Note also that this makes parser::feed_toks private again---I don't intend
to support push parsers yet, since they're only needed internally. Maybe
for error recovery, but I'll wait to decide until it's actually needed.
DEV-10863
This begins to transition XmloReader into a ParseState. Unlike previous
changes where ParseStates were composed into a single ParseState, this is
instead a lowering operation that will take the output of one Parser and
provide it to another.
The mess in ld::poc (...which still needs to be refactored and removed)
shows the concept, which will be abstracted away. This won't actually get
to the ASG in order to test that that this works with the
wip-xmlo-xir-reader flag on (development hasn't gotten that far yet), but
since it type-checks, it should conceptually work.
Wiring lowering operations together is something that I've been dreading for
months, but my approach of only abstracting after-the-fact has helped to
guide a sane approach for this. For some definition of "sane".
It's also worth noting that AsgBuilder will too become a ParseState
implemented as another lowering operation, so:
XIR -> XIRF -> XMLO -> ASG
These steps will all be streaming, with iteration happening only at the
topmost level. For this reason, it's important that ASG not be responsible
for doing that pull, and further we should propagate Parsed::Incomplete
rather than filtering it out and looping an indeterminate number of times
outside of the toplevel.
One final note: the choice of 64 for the maximum depth is entirely
arbitrary and should be more than generous; it'll be finalized at some point
in the future once I actually evaluate what maximum depth is reasonable
based on how the system is used, with some added growing room.
DEV-10863
This is simply not worth it; the size is not going to be the bottleneck (at
least any time soon) and the generic not only pollutes all the things that
will use ASG in the near future, but is also incompatible with the SymbolId
default that is used everywhere; if we have to force it to 32 bits anyway,
then we may as well just default it right off the bat.
I thought that this seemed like a good idea at the time, and saving bits is
certainly tempting, but it was premature.
This rewrites a good portion of the previous commit.
Rather than explicitly storing whether a given string has been escaped, we
can instead assume that all SymbolIds leaving or entering XIR are unescaped,
because there is no reason for any other part of the system to deal with
such details of XML documents.
Given that, we need only unescape on read and escape on write. This is
customary, so why didn't I do that to begin with?
The previous commit outlines the reason, mainly being an optimization for
the echo writer that is upcoming. However, this solution will end up being
better---it's not implemented yet, but we can have a caching layer, such
that the Escaper records a mapping between escaped and unescaped SymbolIds
to avoid work the next time around. If we share the Escaper between _all_
readers and the writer, the result is that
1. Duplicate strings between source files and object files (many of which
are read by both the linker and compiler) avoid re-unescaping; and
2. Writers can use this cache to avoid re-escaping when we've already seen
the escaped variant of the string during read.
The alternative would be a global cache, like the internment system, but I
did not find that to be appropriate here, since this is far less
fundamental and is much easier to compose.
DEV-11081
See the previous commit. There is no sense in some common "IR" namespace,
since those IRs should live close to whatever system whose data they
represent.
In the case of these, they are general IRs that can apply to many different
parts of the system. If that proves to be a false statement, they'll be
moved.
DEV-10863
There isn't a whole lot here, but there is additional work needed in various
places to support upcoming changes and so I want to get this commited to
ease the cognitive burden of what I have thusfar. And to stop stashing. We
have a feature flag for a reason.
DEV-10863
In particular, `name` needn't return an `Option`. `fragment` also returns a
copy, since it's just a `SymbolId`. (It really ought to be a newtype rather
than an alias, but we'll worry about that some other time.)
These changes allow us to remove some runtime panics.
DEV-10859
This moves the logic that sorts identifiers into sections into Sections
itself, and introduces XmleSections to allow for mocking for testing.
This then allows us to narrow the types significantly, eliminating some
runtime checks. The types can be narrowed further, but I'll be limiting the
work I'll be doing now; this'll be inevitably addressed as we use the ASG
for the compiler.
This also handles moving Sections tests, which was a TODO from the previous
commit.
DEV-10859
xmle sections will only ever contain an object of one type, so there is no
use in making this generic.
I think the original plan was to have this represent, generically, sections
of some object file (like ELF), but doing so would require a significant
redesign anyway, so it makes no sense. This is easier to reason about.
DEV-10859
This has always been a lowering operation, but it was not phrased in terms
of it, which made the process a bit more confusing to understand.
The implementation hasn't changed, but this is an incremental refactoring
and so exposes BaseAsg and its `graph` field temporarily.
DEV-10859
Sections, as written, are specific to xmle files.
I think the intent originally was to have this be more generic, but that
doesn't really make sense.
By explicitly coupling it with `xmle` files, that will allow us to turn this
into a proper lowering operation with its own validations that will allow
`xmle::xir` to do its job without having to validate anything itself.
This removes `SymbolStr` in favor of, simply, `&'static str`.
The abstraction provided no additional safety since the slice was trivially
extracted (and commonly, in practice), and was inconvenient to work with.
This is part of a process of relaxing lookups so that symbols can be
conveniently displayed in errors; rather than trying to prevent the
developer from doing something bad, we'll just rely on conventions, hope
that it doesn't happen, and if it does, address it either at that time or
when it shows up in the profiler.
The new writer has reached parity of the old, with the exception of some
edge case explicit error handling that should never occur (which will be
added), and cleanup/docs.
Removing this flag now allows me to perform that cleanup without having to
worry about updating the now-old implementation.
I ran `tameld` with the new writer against our production system with
numerous programs and a significant number of test cases, and diff'd the old
and new xmle files, and everything looks good.
`IdentKind` needs to be written to `xmle` files and displayed in error
messages. String slices were used when quick-xml was used for writing,
which will be going away with the new writer.
This has been a long time coming, and has been repeatedly stashed as other
parts of the system have evolved to support it. The introduction of the XIR
tree was to write tests for this (which are sloppy atm).
This currently writes out the `xmle` header and _most_ of the `l:dep`
section; it's missing the object-type-specific attributes. There is,
relatively speaking, not much more work to do here.
The feature flag `wip-xir-xmle-writer` was introduced to toggle this system
in place of `XmleWriter`. Initial benchmarks show that it will be
competitive with the quick-xml-based writer, but remember that is not the
goal: the purpose of this is to test XIR in a production system before we
continue to implement it for a frontend, and to refactor so that we do not
have multiple implementations writing XML files (once we echo the source XML
files).
I'm excited to get this done with so that I can move on. This has been
rather exhausting.
This had the writing on the wall all the same as the `'i` interner lifetime
that came before it. It was too much of a maintenance burden trying to
accommodate both 16-bit and 32-bit symbols generically.
There is a situation where we do still want 16-bit symbols---the
`Span`. Therefore, I have left generic support for symbol sizes, as well as
the different global interners, but `SymbolId` now defaults to 32-bit, as
does `Asg`. Further, the size parameter has been removed from the rest of
the code, with the exception of `Span`.
This cleans things up quite a bit, and is much nicer to work with. If we
want 16-bit symbols in the future for packing to increase CPU cache
performance, we can handle that situation then in that specific case; it's a
premature optimization that's not at all worth the effort here.
This is a major change, and I apologize for it all being in one commit. I
had wanted to break it up, but doing so would have required a significant
amount of temporary work that was not worth doing while I'm the only one
working on this project at the moment.
This accomplishes a number of important things, now that I'm preparing to
write the first compiler frontend for TAMER:
1. `Symbol` has been removed; `SymbolId` is used in its place.
2. Consequently, symbols use 16 or 32 bits, rather than a 64-bit pointer.
3. Using symbols no longer requires dereferencing.
4. **Lifetimes no longer pollute the entire system! (`'i`)**
5. Two global interners are offered to produce `SymbolStr` with `'static`
lifetimes, simplfiying lifetime management and borrowing where strings
are still needed.
6. A nice API is provided for interning and lookups (e.g. "foo".intern())
which makes this look like a core feature of Rust.
Unfortunately, making this change required modifications to...virtually
everything. And that serves to emphasize why this change was needed:
_everything_ used symbols, and so there's no use in not providing globals.
I implemented this in a way that still provides for loose coupling through
Rust's trait system. Indeed, Rustc offers a global interner, and I decided
not to go that route initially because it wasn't clear to me that such a
thing was desirable. It didn't become apparent to me, in fact, until the
recent commit where I introduced `SymbolIndexSize` and saw how many things
had to be touched; the linker evolved so rapidly as I was trying to learn
Rust that I lost track of how bad it got.
Further, this shows how the design of the internment system was a bit
naive---I assumed certain requirements that never panned out. In
particular, everything using symbols stored `&'i Symbol<'i>`---that is, a
reference (usize) to an object containing an index (32-bit) and a string
slice (128-bit). So it was a reference to a pretty large value, which was
allocated in the arena alongside the interned string itself.
But, that was assuming that something would need both the symbol index _and_
a readily available string. That's not the case. In fact, it's pretty
clear that interning happens at the beginning of execution, that `SymbolId`
is all that's needed during processing (unless an error occurs; more on that
below); and it's not until _the very end_ that we need to retrieve interned
strings from the pool to write either to a file or to display to the
user. It was horribly wasteful!
So `SymbolId` solves the lifetime issue in itself for most systems, but it
still requires that an interner be available for anything that needs to
create or resolve symbols, which, as it turns out, is still a lot of
things. Therefore, I decided to implement them as thread-local static
variables, which is very similar to what Rustc does itself (Rustc's are
scoped). TAMER does not use threads, so the resulting `'static` lifetime
should be just fine for now. Eventually I'd like to implement `!Send` and
`!Sync`, though, to prevent references from escaping the thread (as noted in
the patch); I can't do that yet, since the feature has not yet been
stabalized.
In the end, this leaves us with a system that's much easier to use and
maintain; hopefully easier for newcomers to get into without having to deal
with so many complex lifetimes; and a nice API that makes it a pleasure to
work with symbols.
Admittedly, the `SymbolIndexSize` adds some complexity, and we'll see if I
end up regretting that down the line, but it exists for an important reason:
the `Span` and other structures that'll be introduced need to pack a lot of
data into 64 bits so they can be freely copied around to keep lifetimes
simple without wreaking havoc in other ways, but a 32-bit symbol size needed
by the linker is too large for that. (Actually, the linker doesn't yet need
32 bits for our systems, but it's going to in the somewhat near future
unless we optimize away a bunch of symbols...but I'd really rather not have
the linker hit a limit that requires a lot of code changes to resolve).
Rustc uses interned spans when they exceed 8 bytes, but I'd prefer to avoid
that for now. Most systems can just use on of the `PkgSymbolId` or
`ProgSymbolId` type aliases and not have to worry about it. Systems that
are actually shared between the compiler and the linker do, though, but it's
not like we don't already have a bunch of trait bounds.
Of course, as we implement link-time optimizations (LTO) in the future, it's
possible most things will need the size and I'll grow frustrated with that
and possibly revisit this. We shall see.
Anyway, this was exhausting...and...onward to the first frontend!
Oh boy. What a mess of a change.
This demonstrates some significant issues we have with Symbol. I had
originally modelled the system a bit after Rustc's, but deviated in certain
regards:
1. This has a confurable base type to enable better packing without bit
twiddling and potentially unsafe tricks I'd rather avoid unless
necessary; and
2. The lifetime is not static, and there is no global, singleton interner;
and
3. I pass around references to a Symbol rather than passing around an
index into an interner.
For #3---this is done because there's no singleton interner and therefore
resolving a symbol requires a direct reference to an available interner. It
also wasn't clear to me (and still isn't, in fact) whether more than one
interner may be used for different contexts.
But, that doesn't preclude removing lifetimes and just passing around
indexes; in fact, I plan to do this in the frontend where the parser and
such will have direct interner access and can therefore just look up based
on a symbol index. We could reserve references for situations where
exposing an interner would be undesirable.
Anyway, more to come...
This will be used for the next commit, but this change has been isolated
both because it distracts from the implementation change in the next commit,
and because it cleans up the code by removing the need for a type parameter
on `AsgError`.
Note that the sort test cases now use `unwrap` instead of having
`{,Sortable}AsgError` support one or the other---this is because that does
not currently happen in practice, and there is not supposed to be a
hierarchy; they are siblings (though perhaps their name may imply otherwise).
We want to be able to build a representation of the dependency graph so
we can easily inspect it.
We do not want to make GraphML by default. It is better to use a tool.
We use "petgraph-graphml".
This is a union (sum type) of three other errors types, plus errors specific
to this builder.
This commit does a good job demonstrating the boilerplate, as well as a need
for additional context (in the case of `IdentKindError`), that we'll want to
work on abstracting away.
This flips the API from using XmloWriter as the context to using Asg and
consuming anything that can produce XmloResults. This not only makes more
sense, but avoids having to create a trait for XmloReader, and simplifies
the trait bounds we have to concern ourselves with.
This abstracts away the canonicalizer and solves the problem whereby
canonicalization was not being performed prior to recording whether a path
has been visited. This ensures that multiple relative paths to the same
file will be properly recognized as visited.
This will be entirely replaced in an upcoming commit. See that for
details. I don't feel like dealing with the conflicts for rearranging and
squashing these commits.
This also includes an implementation to visit paths only once. Note that it
does not yet canonicalize the path before visiting, so relative paths to the
same file can slip through, and relative paths to _different_ files could be
erroneously considered to have been visited.
This will be fixed in an upcoming commit.
This serves as a constructor for the time being, decoupling from POC. We
may do something better once we have a better idea of how the various
abstractions around this will evolve.
This undoes work I did earlier today...but now we'll be able to support a
Source on an extern.
There is duplicate code between `BaseAsg::declare{,_extern}` that will be
resolved in an upcoming commit. Upcoming commits will also simplify
terminology and clean up methods on ObjectState.
There is some duplication here with `declare` that will be cleared up in a
following commit. Reintroducing this method is necessary so that Source can
be used to represent the source location of the extern itself; it's
currently None to indicate an extern in `declare`.
This properly verifies extern types, and cleans up Asg's API a little so
that externs aren't handled much differently than other declarations.
With that said, after making src optional, I realized that we will indeed
want source information for externs themselves so we can direct the user to
what package is expecting that symbol (as the old linker does). So this
approach will not work, and I'll have to undo some of those changes.
This is essential to clarify what exactly the different object types
represent with the new generic abstractions. For example, we will have
expressions as an object type.
There's a lot here to make the object stored on the `Asg` generic. This
introduces `ObjectState` for state transitions and `ObjectData` for pure
data retrieval. This will allow not only for mocking, but will be useful to
enforce compile-time restrictions on the type of objects expected by the
linker vs. the compiler (e.g. the linker will not have expressions).
This commit intentionally leaves the corresponding tests in their original
location to prove that the functionality has not changed; they'll be moved
in a future commit.
This also leaves the names as "Object" to reduce the number the cognative
overhead of this commit. It will be renamed to something like "IdentObject"
in the near future to clarify the intent of the current object type and to
open the way for expressions and a type that marries both of them in the
future.
Once all of this is done, we'll finally be able to make changes to the
compatibility logic in state transitions to implement extern compatibility
checks during resolution.
DEV-7087
Mike Gerwitz
Austin Schaffer