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
This corrects the codegen for the final class optimization to
correct handle the case where there is no path to perform the
cast, and also corrects the codegen to handle ptrauth protected
vtable pointers.
As part of this fix we separate out the path computation as
that makes it easier to reason about the failure code paths
and more importantly means we can know what the type of the
this object is during the cast.
The allows us to use the GetVTablePointer interface which
correctly performs the authentication operations required when
pointer authentication is enabled. This still leaves incorrect
authentication behavior in the multiple inheritance case but
currently the optimization is disabled entirely if pointer
authentication is enabled.
Fixes#137518
The codegen for the final class dynamic_cast optimization fails to
consider pointer authentication. This change resolves this be simply
disabling the optimization when pointer authentication enabled.
CodeGenFunction::EmitCXXDeleteExpr contains logic to go from a pointer
to an array to a pointer to the first element of the array using a
getelementptr LLVM IR instruction. This was done for pointers that were
not variable length arrays, as pointers to variable length arrays never
existed in LLVM IR, but rather than checking for arrays that were not
variable length arrays, it checked for arrays that had a constant bound.
This caused incomplete arrays to be inadvertently omitted.
This getelementptr was necessary back when LLVM IR used typed pointers,
but they have been gone for a while, a gep with a constant zero offset
does nothing now, so we can simplify the code by removing that.
It isn't used and is redundant with the result pointer type argument.
A more reasonable API would only have LangAS parameters, or IR parameters,
not both. Not all values have a meaningful value for this. I'm also
not sure why we have this at all, it's not overridden by any targets and
further simplification is possible.
Finding operator delete[] is still problematic, without it the extension
is a security hazard, so reverting until the problem with operator
delete[] is figured out.
This reverts the following PRs:
Reland [MS][clang] Add support for vector deleting destructors (llvm#133451)
[MS][clang] Make sure vector deleting dtor calls correct operator delete (llvm#133950)
[MS][clang] Fix crash on deletion of array of pointers (llvm#134088)
[clang] Do not diagnose unused deleted operator delete[] (llvm#134357)
[MS][clang] Error about ambiguous operator delete[] only when required (llvm#135041)
This is a basic implementation of P2719: "Type-aware allocation and
deallocation functions" described at http://wg21.link/P2719
The proposal includes some more details but the basic change in
functionality is the addition of support for an additional implicit
parameter in operators `new` and `delete` to act as a type tag. Tag is
of type `std::type_identity<T>` where T is the concrete type being
allocated. So for example, a custom type specific allocator for `int`
say can be provided by the declaration of
void *operator new(std::type_identity<int>, size_t, std::align_val_t);
void operator delete(std::type_identity<int>, void*, size_t, std::align_val_t);
However this becomes more powerful by specifying templated declarations,
for example
template <typename T> void *operator new(std::type_identity<T>, size_t, std::align_val_t);
template <typename T> void operator delete(std::type_identity<T>, void*, size_t, std::align_val_t););
Where the operators being resolved will be the concrete type being
operated over (NB. A completely unconstrained global definition as above
is not recommended as it triggers many problems similar to a general
override of the global operators).
These type aware operators can be declared as either free functions or
in class, and can be specified with or without the other implicit
parameters, with overload resolution performed according to the existing
standard parameter prioritisation, only with type parameterised
operators having higher precedence than non-type aware operators. The
only exception is destroying_delete which for reasons discussed in the
paper we do not support type-aware variants by default.
Whereas it is UB in terms of the standard to delete an array of objects
via pointer whose static type doesn't match its dynamic type, MSVC
supports an extension allowing to do it.
Aside from array deletion not working correctly in the mentioned case,
currently not having this extension implemented causes clang to generate
code that is not compatible with the code generated by MSVC, because
clang always puts scalar deleting destructor to the vftable. This PR
aims to resolve these problems.
It was reverted due to link time errors in chromium with sanitizer
coverage enabled,
which is fixed by https://github.com/llvm/llvm-project/pull/131929 .
The second commit of this PR also contains a fix for a runtime failure
in chromium reported
in
https://github.com/llvm/llvm-project/pull/126240#issuecomment-2730216384
.
Fixes https://github.com/llvm/llvm-project/issues/19772
This caused link errors when building with sancov. See comment on the PR.
> Whereas it is UB in terms of the standard to delete an array of objects
> via pointer whose static type doesn't match its dynamic type, MSVC
> supports an extension allowing to do it.
> Aside from array deletion not working correctly in the mentioned case,
> currently not having this extension implemented causes clang to generate
> code that is not compatible with the code generated by MSVC, because
> clang always puts scalar deleting destructor to the vftable. This PR
> aims to resolve these problems.
>
> Fixes https://github.com/llvm/llvm-project/issues/19772
This reverts commit d6942d54f677000cf713d2b0eba57b641452beb4.
Whereas it is UB in terms of the standard to delete an array of objects
via pointer whose static type doesn't match its dynamic type, MSVC
supports an extension allowing to do it.
Aside from array deletion not working correctly in the mentioned case,
currently not having this extension implemented causes clang to generate
code that is not compatible with the code generated by MSVC, because
clang always puts scalar deleting destructor to the vftable. This PR
aims to resolve these problems.
Fixes https://github.com/llvm/llvm-project/issues/19772
In EmitCXXNewAllocSize, when handling a constant array size, we were
calling tryEmitAbstract with the type of the object being allocated rather
than the expected type of the array size. This worked out because the
allocated type was always a pointer and tryEmitAbstract only ends up
using the size of the type to extend or truncate the constant, and in this
case the destination type should be size_t, which is usually the same
width as the pointer. This change fixes the type, but it makes no
functional difference with the current constant emitter implementation.
This patch is the frontend implementation of the coroutine elide
improvement project detailed in this discourse post:
https://discourse.llvm.org/t/language-extension-for-better-more-deterministic-halo-for-c-coroutines/80044
This patch proposes a C++ struct/class attribute
`[[clang::coro_await_elidable]]`. This notion of await elidable task
gives developers and library authors a certainty that coroutine heap
elision happens in a predictable way.
Originally, after we lower a coroutine to LLVM IR, CoroElide is
responsible for analysis of whether an elision can happen. Take this as
an example:
```
Task foo();
Task bar() {
co_await foo();
}
```
For CoroElide to happen, the ramp function of `foo` must be inlined into
`bar`. This inlining happens after `foo` has been split but `bar` is
usually still a presplit coroutine. If `foo` is indeed a coroutine, the
inlined `coro.id` intrinsics of `foo` is visible within `bar`. CoroElide
then runs an analysis to figure out whether the SSA value of
`coro.begin()` of `foo` gets destroyed before `bar` terminates.
`Task` types are rarely simple enough for the destroy logic of the task
to reference the SSA value from `coro.begin()` directly. Hence, the pass
is very ineffective for even the most trivial C++ Task types. Improving
CoroElide by implementing more powerful analyses is possible, however it
doesn't give us the predictability when we expect elision to happen.
The approach we want to take with this language extension generally
originates from the philosophy that library implementations of `Task`
types has the control over the structured concurrency guarantees we
demand for elision to happen. That is, the lifetime for the callee's
frame is shorter to that of the caller.
The ``[[clang::coro_await_elidable]]`` is a class attribute which can be
applied to a coroutine return type.
When a coroutine function that returns such a type calls another
coroutine function, the compiler performs heap allocation elision when
the following conditions are all met:
- callee coroutine function returns a type that is annotated with
``[[clang::coro_await_elidable]]``.
- In caller coroutine, the return value of the callee is a prvalue that
is immediately `co_await`ed.
From the C++ perspective, it makes sense because we can ensure the
lifetime of elided callee cannot exceed that of the caller if we can
guarantee that the caller coroutine is never destroyed earlier than the
callee coroutine. This is not generally true for any C++ programs.
However, the library that implements `Task` types and executors may
provide this guarantee to the compiler, providing the user with
certainty that HALO will work on their programs.
After this patch, when compiling coroutines that return a type with such
attribute, the frontend checks that the type of the operand of
`co_await` expressions (not `operator co_await`). If it's also
attributed with `[[clang::coro_await_elidable]]`, the FE emits metadata
on the call or invoke instruction as a hint for a later middle end pass
to elide the elision.
The original patch version is
https://github.com/llvm/llvm-project/pull/94693 and as suggested, the
patch is split into frontend and middle end solutions into stacked PRs.
The middle end CoroSplit patch can be found at
https://github.com/llvm/llvm-project/pull/99283
The middle end transformation that performs the elide can be found at
https://github.com/llvm/llvm-project/pull/99285
Used to implement CWG2191 where `typeid` for a polymorphic glvalue only
becomes potentially-throwing if the `typeid` operand was already
potentially throwing or a `nullptr` check was inserted:
https://cplusplus.github.io/CWG/issues/2191.html
Also change `Expr::hasSideEffects` for `CXXTypeidExpr` to check the
operand for side-effects instead of always reporting that there are
side-effects
Remove `IsDeref` parameter of `CGCXXABI::shouldTypeidBeNullChecked`
because it should never return `true` if `!IsDeref` (we shouldn't add a
null check that wasn't there in the first place)
This is in effect a revert of f139ae3d93797, as we have since gained a
more sophisticated way of doing extra IRGen with the addition of
RawAddress in #86923.
At the moment, Clang is rather liberal in assuming that 0 (and by extension unqualified) is always a safe default. This does not work for targets that actually use a different value for the default / generic AS (for example, the SPIRV that obtains from HIPSPV or SYCL). This patch is a first, fairly safe step towards trying to clear things up by querying a modules' default AS from the target, rather than assuming it's 0, alongside fixing a few places where things break / we encode the 0 == DefaultAS assumption. A bunch of existing tests are extended to check for non-zero default AS usage.
Latest diff:
f1ab4c2677..adf9bc902b
We address two additional bugs here:
### Problem 1: Deactivated normal cleanup still runs, leading to
double-free
Consider the following:
```cpp
struct A { };
struct B { B(const A&); };
struct S {
A a;
B b;
};
int AcceptS(S s);
void Accept2(int x, int y);
void Test() {
Accept2(AcceptS({.a = A{}, .b = A{}}), ({ return; 0; }));
}
```
We add cleanups as follows:
1. push dtor for field `S::a`
2. push dtor for temp `A{}` (used by ` B(const A&)` in `.b = A{}`)
3. push dtor for field `S::b`
4. Deactivate 3 `S::b`-> This pops the cleanup.
5. Deactivate 1 `S::a` -> Does not pop the cleanup as *2* is top. Should
create _active flag_!!
6. push dtor for `~S()`.
7. ...
It is important to deactivate **5** using active flags. Without the
active flags, the `return` will fallthrough it and would run both `~S()`
and dtor `S::a` leading to **double free** of `~A()`.
In this patch, we unconditionally emit active flags while deactivating
normal cleanups. These flags are deleted later by the `AllocaTracker` if
the cleanup is not emitted.
### Problem 2: Missing cleanup for conditional lifetime extension
We push 2 cleanups for lifetime-extended cleanup. The first cleanup is
useful if we exit from the middle of the expression (stmt-expr/coro
suspensions). This is deactivated after full-expr, and a new cleanup is
pushed, extending the lifetime of the temporaries (to the scope of the
reference being initialized).
If this lifetime extension happens to be conditional, then we use active
flags to remember whether the branch was taken and if the object was
initialized.
Previously, we used a **single** active flag, which was used by both
cleanups. This is wrong because the first cleanup will be forced to
deactivate after the full-expr and therefore this **active** flag will
always be **inactive**. The dtor for the lifetime extended entity would
not run as it always sees an **inactive** flag.
In this patch, we solve this using two separate active flags for both
cleanups. Both of them are activated if the conditional branch is taken,
but only one of them is deactivated after the full-expr.
---
Fixes https://github.com/llvm/llvm-project/issues/63818
Fixes https://github.com/llvm/llvm-project/issues/88478
---
Previous PR logs:
1. https://github.com/llvm/llvm-project/pull/85398
2. https://github.com/llvm/llvm-project/pull/88670
3. https://github.com/llvm/llvm-project/pull/88751
4. https://github.com/llvm/llvm-project/pull/88884
The original change caused widespread breakages in msan/ubsan tests and
causes `use-after-free`. Most likely we are adding more cleanups than
necessary.
Fixes https://github.com/llvm/llvm-project/issues/63818 for control flow
out of an expressions.
#### Background
A control flow could happen in the middle of an expression due to
stmt-expr and coroutine suspensions.
Due to branch-in-expr, we missed running cleanups for the temporaries
constructed in the expression before the branch.
Previously, these cleanups were only added as `EHCleanup` during the
expression and as normal expression after the full expression.
Examples of such deferred cleanups include:
`ParenList/InitList`: Cleanups for fields are performed by the
destructor of the object being constructed.
`Array init`: Cleanup for elements of an array is included in the array
cleanup.
`Lifetime-extended temporaries`: reference-binding temporaries in
braced-init are lifetime extended to the parent scope.
`Lambda capture init`: init in the lambda capture list is destroyed by
the lambda object.
---
#### In this PR
In this PR, we change some of the `EHCleanups` cleanups to
`NormalAndEHCleanups` to make sure these are emitted when we see a
branch inside an expression (through statement expressions or coroutine
suspensions).
These are supposed to be deactivated after full expression and destroyed
later as part of the destructor of the aggregate or array being
constructed. To simplify deactivating cleanups, we add two utilities as
well:
* `DeferredDeactivationCleanupStack`: A stack to remember cleanups with
deferred deactivation.
* `CleanupDeactivationScope`: RAII for deactivating cleanups added to
the above stack.
---
#### Deactivating normal cleanups
These were previously `EHCleanups` and not `Normal` and **deactivation**
of **required** `Normal` cleanups had some bugs. These specifically
include deactivating `Normal` cleanups which are not the top of
`EHStack`
[source1](92b56011e6/clang/lib/CodeGen/CGCleanup.cpp (L1319)),
[2](92b56011e6/clang/lib/CodeGen/CGCleanup.cpp (L722-L746)).
This has not been part of our test suite (maybe it was never required
before statement expressions). In this PR, we also fix the emission of
required-deactivated-normal cleanups.
To authenticate pointers, CodeGen needs access to the key and
discriminators that were used to sign the pointer. That information is
sometimes known from the context, but not always, which is why `Address`
needs to hold that information.
This patch adds methods and data members to `Address`, which will be
needed in subsequent patches to authenticate signed pointers, and uses
the newly added methods throughout CodeGen. Although this patch isn't
strictly NFC as it causes CodeGen to use different code paths in some
cases (e.g., `mergeAddressesInConditionalExpr`), it doesn't cause any
changes in functionality as it doesn't add any information needed for
authentication.
In addition to the changes mentioned above, this patch introduces class
`RawAddress`, which contains a pointer that we know is unsigned, and
adds several new functions for creating `Address` and `LValue` objects.
This reapplies d9a685a9dd589486e882b722e513ee7b8c84870c, which was
reverted because it broke ubsan bots. There seems to be a bug in
coroutine code-gen, which is causing EmitTypeCheck to use the wrong
alignment. For now, pass alignment zero to EmitTypeCheck so that it can
compute the correct alignment based on the passed type (see function
EmitCXXMemberOrOperatorMemberCallExpr).
To authenticate pointers, CodeGen needs access to the key and
discriminators that were used to sign the pointer. That information is
sometimes known from the context, but not always, which is why `Address`
needs to hold that information.
This patch adds methods and data members to `Address`, which will be
needed in subsequent patches to authenticate signed pointers, and uses
the newly added methods throughout CodeGen. Although this patch isn't
strictly NFC as it causes CodeGen to use different code paths in some
cases (e.g., `mergeAddressesInConditionalExpr`), it doesn't cause any
changes in functionality as it doesn't add any information needed for
authentication.
In addition to the changes mentioned above, this patch introduces class
`RawAddress`, which contains a pointer that we know is unsigned, and
adds several new functions for creating `Address` and `LValue` objects.
This reapplies 8bd1f9116aab879183f34707e6d21c7051d083b6. The commit
broke msan bots because LValue::IsKnownNonNull was uninitialized.
In PR #79382, I need to add a new type that derives from
ConstantArrayType. This means that ConstantArrayType can no longer use
`llvm::TrailingObjects` to store the trailing optional Expr*.
This change refactors ConstantArrayType to store a 60-bit integer and
4-bits for the integer size in bytes. This replaces the APInt field
previously in the type but preserves enough information to recreate it
where needed.
To reduce the number of places where the APInt is re-constructed I've
also added some helper methods to the ConstantArrayType to allow some
common use cases that operate on either the stored small integer or the
APInt as appropriate.
Resolves#85124.
To authenticate pointers, CodeGen needs access to the key and
discriminators that were used to sign the pointer. That information is
sometimes known from the context, but not always, which is why `Address`
needs to hold that information.
This patch adds methods and data members to `Address`, which will be
needed in subsequent patches to authenticate signed pointers, and uses
the newly added methods throughout CodeGen. Although this patch isn't
strictly NFC as it causes CodeGen to use different code paths in some
cases (e.g., `mergeAddressesInConditionalExpr`), it doesn't cause any
changes in functionality as it doesn't add any information needed for
authentication.
In addition to the changes mentioned above, this patch introduces class
`RawAddress`, which contains a pointer that we know is unsigned, and
adds several new functions for creating `Address` and `LValue` objects.
This bug is caused by parenthesized list initialization not being
implemented in `CodeGenFunction::EmitNewArrayInitializer(...)`.
Parenthesized list initialization of `struct`s with `operator new`
already works in Clang and is not affected by this bug.
Additionally, fix the test new-delete.cpp as it incorrectly assumes that
using parentheses with operator new to initialize arrays is illegal for
C++ versions >= C++17.
Fixes#68198
This patch converts `CXXConstructExpr::ConstructionKind` into a scoped enum in namespace scope, making it eligible for forward declaring. This is useful in cases like annotating bit-fields with `preferred_type`.
After https://reviews.llvm.org/D153092, for targets that use a non-default AS for globals, an "interesting" situation arises around typeid and its paired type, type_info:
- on the AST level, the type_info interface is defined with default / generic addresses, be it for function arguments, or for this;
- in IR, type_info values are globals, and thus pointers to type_info values are pointers to global
This leads to a mismatch between the function signature / formal type of the argument, and its actual type. Currently we try to handle such mismatches via `bitcast`, but that is wrong in this case, since an `ascast` is required. This patch ensures that iff the pointer to `type_info` points to a non-default AS, an ascast is inserted so as to match the `typeid` interface / return value type.
Reviewed by: yaxunl
Differential Revision: https://reviews.llvm.org/D157452
It seems preferable to avoid this optimization under -O0, and we're not
set up to emit speculative references to vtables at -O0 in general
anyway.
For #64088.
- When the destination is a final class type that does not derive from
the source type, the cast always fails and is now emitted as a null
pointer or call to __cxa_bad_cast.
- When the destination is a final class type that does derive from the
source type, emit a direct comparison against the corresponding base
class vptr value(s). There may be more than one such value in the case
of multiple inheritance; check them all.
For now, this is supported only for the Itanium ABI. I expect the same thing is
possible for the MS ABI too, but I don't know what guarantees are made about
vfptr uniqueness.
Reviewed By: rjmccall
Differential Revision: https://reviews.llvm.org/D154658
`CGBuilderTy::CreateElementBitCast()` no longer does what its name suggests.
Remove remaining in-tree uses by one of the following methods.
* drop the call entirely
* fold it to an `Address` construction
* replace it with `Address::withElementType()`
This is a NFC cleanup effort.
Reviewed By: barannikov88, nikic, jrtc27
Differential Revision: https://reviews.llvm.org/D154285
Partial progress towards replacing in-tree uses of `Type::getPointerTo()`.
This needs to be done before deprecating the API.
Reviewed By: nikic, barannikov88
Differential Revision: https://reviews.llvm.org/D152321
With the Microsoft ABI, some destructors need to offset a parameter to
get the derived this pointer, in which case the type of that parameter
should not be a pointer to the derived type.
Fixes#60465
In case of placement new, if we do not know the alignment of the
operand, we can't assume it has the preferred alignment. It might be
e.g. a pointer to a struct member which follows ABI alignment rules.
This makes UBSAN no longer report "constructor call on misaligned
address" when constructing a double into a struct field of type double
on i686. The psABI specifies an alignment of 4 bytes, but the preferred
alignment used by Clang is 8 bytes.
We now use ABI alignment for allocating new as well, as the preferred
alignment should be used for over-aligning e.g. local variables, which
isn't relevant for ABI code dealing with operator new. AFAICT there
wouldn't be problems either way though.
Fixes#54845.
Differential Revision: https://reviews.llvm.org/D124736
