We previously employed a TreeTransform to perform a task that should
have been achieved by RAV. The TreeTransform approach was a bit
wasteful, as we discarded the transform result and incurred some
incorrect semantic analysis.
Fixes https://github.com/llvm/llvm-project/issues/156225
This is a major change on how we represent nested name qualifications in
the AST.
* The nested name specifier itself and how it's stored is changed. The
prefixes for types are handled within the type hierarchy, which makes
canonicalization for them super cheap, no memory allocation required.
Also translating a type into nested name specifier form becomes a no-op.
An identifier is stored as a DependentNameType. The nested name
specifier gains a lightweight handle class, to be used instead of
passing around pointers, which is similar to what is implemented for
TemplateName. There is still one free bit available, and this handle can
be used within a PointerUnion and PointerIntPair, which should keep
bit-packing aficionados happy.
* The ElaboratedType node is removed, all type nodes in which it could
previously apply to can now store the elaborated keyword and name
qualifier, tail allocating when present.
* TagTypes can now point to the exact declaration found when producing
these, as opposed to the previous situation of there only existing one
TagType per entity. This increases the amount of type sugar retained,
and can have several applications, for example in tracking module
ownership, and other tools which care about source file origins, such as
IWYU. These TagTypes are lazily allocated, in order to limit the
increase in AST size.
This patch offers a great performance benefit.
It greatly improves compilation time for
[stdexec](https://github.com/NVIDIA/stdexec). For one datapoint, for
`test_on2.cpp` in that project, which is the slowest compiling test,
this patch improves `-c` compilation time by about 7.2%, with the
`-fsyntax-only` improvement being at ~12%.
This has great results on compile-time-tracker as well:
This patch also further enables other optimziations in the future, and
will reduce the performance impact of template specialization resugaring
when that lands.
It has some other miscelaneous drive-by fixes.
About the review: Yes the patch is huge, sorry about that. Part of the
reason is that I started by the nested name specifier part, before the
ElaboratedType part, but that had a huge performance downside, as
ElaboratedType is a big performance hog. I didn't have the steam to go
back and change the patch after the fact.
There is also a lot of internal API changes, and it made sense to remove
ElaboratedType in one go, versus removing it from one type at a time, as
that would present much more churn to the users. Also, the nested name
specifier having a different API avoids missing changes related to how
prefixes work now, which could make existing code compile but not work.
How to review: The important changes are all in
`clang/include/clang/AST` and `clang/lib/AST`, with also important
changes in `clang/lib/Sema/TreeTransform.h`.
The rest and bulk of the changes are mostly consequences of the changes
in API.
PS: TagType::getDecl is renamed to `getOriginalDecl` in this patch, just
for easier to rebasing. I plan to rename it back after this lands.
Fixes#136624
Fixes https://github.com/llvm/llvm-project/issues/43179
Fixes https://github.com/llvm/llvm-project/issues/68670
Fixes https://github.com/llvm/llvm-project/issues/92757
After the changes to DynamicRecursiveASTVisitor, we started getting
several warnings from MSVC like:
warning C4661: 'bool clang::DynamicRecursiveASTVisitorBase<false>::WalkUpFromNamedDecl(clang::NamedDecl *)':
no suitable definition provided for explicit template instantiation request
These changes silence the warnings by providing a definition for those
functions.
This relands #122991 (eeefa72).
The last attempt at landing this caused some problems; I’m not entirely
sure what happened, but it might have been due to an unnecessary use
of the `template` keyword in a few places. This removes that and attempts
to land the change again.
Reverts llvm/llvm-project#122991
One of the bots is breaking; I’ll have to investigate what the issue is;
this might be because I haven’t updated the branch in a while.
After some discussion around #116823, it was decided that it would be
nice to have a `const` variant of `DynamicRecursiveASTVisitor`, so this
pr does exactly that by making the main DRAV implementation a template
with a single `bool` template parameter that turns several function
parameters from a `T*` or `T&` to a `const T*` or `const T&`.
Since that made the implementation of a bunch of DRAV functions quite a
bit more verbose, I’ve moved most of them to be stamped out by a macro,
which imo makes it easier to understand what’s actually going on there.
For functions which already accepted `const` parameters in the original
RAV implementation, the parameter is `const` in both versions (e.g.
`TraverseTemplateArgument()` always takes a `const TemplateArgument&`);
conversely, parameters that are passed by value (e.g. in
`TraverseType()`, which takes a `QualType` by value) are *not* `const`
in either variant (i.e. the `QualType` argument is always just a
`QualType`, never a `const QualType`).
As a sanity check, I’ve also migrated some random visitor in the static
analyser to the `const` version (and indeed, it ends up simplifying the
code around that particular visitor actually). It would make sense to do
a pass over all visitors and change all which can be `const` use the
`const` version, but that can be done in a follow-up pr.
The [performance
impact](https://llvm-compile-time-tracker.com/compare.php?from=e3cd88a7be1dfd912bb6e7c7e888e7b442ffb5de&to=d55c5afe4a485b6d0431386e6f45cb44c1fc8883&stat=instructions:u)
of this change seems to be negligible. Clang’s binary size went up by
0.5%, but that’s expected considering that this effectively adds an
extra instantiation of `RecursiveASTVisitor`. Fortunately, this is of
course a one-time cost.
