Commit Graph

6 Commits

Author SHA1 Message Date
Richard Smith 5030928d60 [c++20] Implement semantic restrictions for C++20 designated
initializers.

This has some interesting interactions with our existing extensions to
support C99 designated initializers as an extension in C++. Those are
resolved as follows:

 * We continue to permit the full breadth of C99 designated initializers
   in C++, with the exception that we disallow a partial overwrite of an
   initializer with a non-trivially-destructible type. (Full overwrite
   is OK, because we won't run the first initializer at all.)

 * The C99 extensions are disallowed in SFINAE contexts and during
   overload resolution, where they could change the meaning of valid
   programs.

 * C++20 disallows reordering of initializers. We only check for that for
   the simple cases that the C++20 rules permit (designators of the form
   '.field_name =' and continue to allow reordering in other cases).
   It would be nice to improve this behavior in future.

 * All C99 designated initializer extensions produce a warning by
   default in C++20 mode. People are going to learn the C++ rules based
   on what Clang diagnoses, so it's important we diagnose these properly
   by default.

 * In C++ <= 17, we apply the C++20 rules rather than the C99 rules, and
   so still diagnose C99 extensions as described above. We continue to
   accept designated C++20-compatible initializers in C++ <= 17 silently
   by default (but naturally still reject under -pedantic-errors).

This is not a complete implementation of P0329R4. In particular, that
paper introduces new non-C99-compatible syntax { .field { init } }, and
we do not support that yet.

This is based on a previous patch by Don Hinton, though I've made
substantial changes when addressing the above interactions.

Differential Revision: https://reviews.llvm.org/D59754

llvm-svn: 370544
2019-08-30 22:52:55 +00:00
Richard Smith afe48f9d68 Fold -Wreturn-stack-address into general initialization lifetime
checking.

llvm-svn: 337743
2018-07-23 21:21:22 +00:00
Richard Smith d87aab939a Restructure checking for, and warning on, lifetime extension.
This change implements C++ DR1696, which makes initialization of a
reference member of a class from a temporary object ill-formed. The
standard wording here is imprecise, but we interpret it as meaning that
any time a mem-initializer would result in lifetime extension, the
program is ill-formed.

This reinstates r337226, reverted in r337255, with a fix for the
InitializedEntity alignment problem that was breaking ARM buildbots.

llvm-svn: 337329
2018-07-17 22:24:09 +00:00
Florian Hahn 0aa117dd2c Temporarily revert r337226 "Restructure checking for, and warning on, lifetime extension."
This change breaks on ARM because pointers to clang::InitializedEntity are only
4 byte aligned and do not have 3 bits to store values. A possible solution
would be to change the fields in clang::InitializedEntity to enforce a bigger
alignment requirement.

The error message is

llvm/include/llvm/ADT/PointerIntPair.h:132:3: error: static_assert failed "PointerIntPair with integer size too large for pointer"
  static_assert(IntBits <= PtrTraits::NumLowBitsAvailable,
include/llvm/ADT/PointerIntPair.h:73:13: note: in instantiation of template class 'llvm::PointerIntPairInfo<const clang::InitializedEntity *, 3, llvm::PointerLikeTypeTraits<const clang::InitializedEntity *> >' requested here
    Value = Info::updateInt(Info::updatePointer(0, PtrVal),
llvm/include/llvm/ADT/PointerIntPair.h:51:5: note: in instantiation of member function 'llvm::PointerIntPair<const clang::InitializedEntity *, 3, (anonymous namespace)::LifetimeKind, llvm::PointerLikeTypeTraits<const clang::InitializedEntity *>, llvm::PointerIntPairInfo<const clang::InitializedEntity *, 3, llvm::PointerLikeTypeTraits<const clang::InitializedEntity *> > >::setPointerAndInt' requested here
    setPointerAndInt(PtrVal, IntVal);
    ^
llvm/tools/clang/lib/Sema/SemaInit.cpp:6237:12: note: in instantiation of member function 'llvm::PointerIntPair<const clang::InitializedEntity *, 3, (anonymous namespace)::LifetimeKind, llvm::PointerLikeTypeTraits<const clang::InitializedEntity *>, llvm::PointerIntPairInfo<const clang::InitializedEntity *, 3, llvm::PointerLikeTypeTraits<const clang::InitializedEntity *> > >::PointerIntPair' requested here
    return {Entity, LK_Extended};

Full log here:
http://lab.llvm.org:8011/builders/clang-cmake-armv7-global-isel/builds/1330
http://lab.llvm.org:8011/builders/clang-cmake-armv7-full/builds/1394

llvm-svn: 337255
2018-07-17 09:23:31 +00:00
Richard Smith 0a9969b36b Restructure checking for, and warning on, lifetime extension.
This change implements C++ DR1696, which makes initialization of a
reference member of a class from a temporary object ill-formed. The
standard wording here is imprecise, but we interpret it as meaning that
any time a mem-initializer would result in lifetime extension, the
program is ill-formed.

llvm-svn: 337226
2018-07-17 00:11:41 +00:00
Richard Smith 9f7df0c068 Revert r301742, which caused us to try to evaluate all full-expressions.
Also add testcases for a bunch of expression forms that cause our evaluator to
crash. See PR33140 and PR32864 for crashes that this was causing.

This reverts r305287, which reverted r305239, which reverted r301742. The
previous revert claimed that buildbots were broken, but did not add any
testcases and the buildbots have lost all memory of what was wrong here.

Changes to test/OpenMP are not reverted; another change has triggered those
tests to change their output in the same way that r301742 did.

llvm-svn: 306346
2017-06-26 23:19:32 +00:00