Commit Graph

11 Commits

Author SHA1 Message Date
Aaron Ballman 22db4824b9 Use functions with prototypes when appropriate; NFC
A significant number of our tests in C accidentally use functions
without prototypes. This patch converts the function signatures to have
a prototype for the situations where the test is not specific to K&R C
declarations. e.g.,

  void func();

becomes

  void func(void);

This is the third batch of tests being updated (there are a significant
number of other tests left to be updated).
2022-02-07 09:25:01 -05:00
Richard Smith 08c8d5bc51 Properly track whether a variable is constant-initialized.
This fixes miscomputation of __builtin_constant_evaluated in the
initializer of a variable that's not usable in constant expressions, but
is readable when constant-folding.

If evaluation of a constant initializer fails, we throw away the
evaluated result instead of keeping it as a non-constant-initializer
value for the variable, because it might not be a correct value.
To avoid regressions for initializers that are foldable but not formally
constant initializers, we now try constant-evaluating some globals in
C++ twice: once to check for a constant initializer (in an mode where
is_constannt_evaluated returns true) and again to determine the runtime
value if the initializer is not a constant initializer.
2020-10-19 23:59:11 -07:00
Richard Smith 96c899449b C++ DR2026: static storage duration variables are not zeroed before
constant initialization.

Removing this zeroing regressed our code generation in a few cases, also
fixed here. We now compute whether a variable has constant destruction
even if it doesn't have a constant initializer, by trying to destroy a
default-initialized value, and skip emitting a trivial default
constructor for a variable even if it has non-trivial (but perhaps
constant) destruction.
2020-02-06 16:37:22 -08:00
Richard Smith 457226e02a For P0784R7: add support for constexpr destructors, and call them as
appropriate during constant evaluation.

Note that the evaluator is sometimes invoked on incomplete expressions.
In such cases, if an object is constructed but we never reach the point
where it would be destroyed (and it has non-trivial destruction), we
treat the expression as having an unmodeled side-effect.

llvm-svn: 372538
2019-09-23 03:48:44 +00:00
Richard Smith a6e8b685e1 [c++20] P1143R2: Add support for the C++20 'constinit' keyword.
This is mostly the same as the
[[clang::require_constant_initialization]] attribute, but has a couple
of additional syntactic and semantic restrictions.

In passing, I added a warning for the attribute form being added after
we have already seen the initialization of the variable (but before we
see the definition); that case previously slipped between the cracks and
the attribute was silently ignored.

llvm-svn: 370972
2019-09-04 20:30:37 +00:00
Aaron Ballman adf66b6174 Determine the attribute subject for diagnostics based on declarative information in DeclNodes.td. This greatly reduces the number of enumerated values used for more complex diagnostics; these are now only required when the "attribute only applies to" diagnostic needs to be generated manually as part of semantic processing.
This also clarifies some terminology used by the diagnostic (methods -> Objective-C methods, fields -> non-static data members, etc).

Many of the tests needed to be updated in multiple places for the diagnostic wording tweaks. The first instance of the diagnostic for that attribute is fully specified and subsequent instances cut off the complete list (to make it easier if additional subjects are added in the future for the attribute).

llvm-svn: 319002
2017-11-26 20:01:12 +00:00
Keno Fischer 4792222fb5 [SemaCXX] Add diagnostics to require_constant_initialization
Summary:
This hooks up the detailed diagnostics of why constant initialization was
not possible if require_constant_initialization reports an error.
I have updated the test to account for the new notes.

Reviewed By: EricWF
Subscribers: cfe-commits
Differential Revision: https://reviews.llvm.org/D24371

llvm-svn: 304451
2017-06-01 18:54:16 +00:00
Richard Smith 9ff61776df Fix attribute name in diagnostic message to match actual attribute name.
llvm-svn: 293853
2017-02-02 01:50:47 +00:00
Eric Fiselier 341e825eae Implement __attribute__((require_constant_initialization)) for safe static initialization.
Summary:
This attribute specifies expectations about the initialization of static and
thread local variables. Specifically that the variable has a
[constant initializer](http://en.cppreference.com/w/cpp/language/constant_initialization)
according to the rules of [basic.start.static]. Failure to meet this expectation
will result in an error.

Static objects with constant initializers avoid hard-to-find bugs caused by
the indeterminate order of dynamic initialization. They can also be safely
used by other static constructors across translation units.

This attribute acts as a compile time assertion that the requirements
for constant initialization have been met. Since these requirements change
between dialects and have subtle pitfalls it's important to fail fast instead
of silently falling back on dynamic initialization.

```c++
  // -std=c++14
  #define SAFE_STATIC __attribute__((require_constant_initialization)) static
  struct T {
    constexpr T(int) {}
    ~T();
  };
  SAFE_STATIC T x = {42}; // OK.
  SAFE_STATIC T y = 42; // error: variable does not have a constant initializer
  // copy initialization is not a constant expression on a non-literal type.
```
This attribute can only be applied to objects with static or thread-local storage
duration.

Reviewers: majnemer, rsmith, aaron.ballman

Subscribers: jroelofs, cfe-commits

Differential Revision: https://reviews.llvm.org/D23385

llvm-svn: 280525
2016-09-02 18:53:31 +00:00
Eric Fiselier bcdcbd11ba Revert r280516 since it contained accidental changes.
llvm-svn: 280521
2016-09-02 18:43:25 +00:00
Eric Fiselier 92f8935e63 Implement __attribute__((require_constant_initialization)) for safe static initialization.
Summary:
This attribute specifies expectations about the initialization of static and
thread local variables. Specifically that the variable has a
[constant initializer](http://en.cppreference.com/w/cpp/language/constant_initialization)
according to the rules of [basic.start.static]. Failure to meet this expectation
will result in an error.

Static objects with constant initializers avoid hard-to-find bugs caused by
the indeterminate order of dynamic initialization. They can also be safely
used by other static constructors across translation units.

This attribute acts as a compile time assertion that the requirements
for constant initialization have been met. Since these requirements change
between dialects and have subtle pitfalls it's important to fail fast instead
of silently falling back on dynamic initialization.

```c++
  // -std=c++14
  #define SAFE_STATIC __attribute__((require_constant_initialization)) static
  struct T {
    constexpr T(int) {}
    ~T();
  };
  SAFE_STATIC T x = {42}; // OK.
  SAFE_STATIC T y = 42; // error: variable does not have a constant initializer
  // copy initialization is not a constant expression on a non-literal type.
```
This attribute can only be applied to objects with static or thread-local storage
duration.

Reviewers: majnemer, rsmith, aaron.ballman

Subscribers: jroelofs, cfe-commits

Differential Revision: https://reviews.llvm.org/D23385

llvm-svn: 280516
2016-09-02 18:25:29 +00:00