This CL is for discussion how to better fix bit-filed layout compatibility issue with GCC (see PR25575 for test case and more details). Current clang behavior is compatible with GCC 4.1-4.3 series but it was fixed in 4.4+. Ignoring packed attribute looks very odd and because it was also fixed in GCC 4.4+, it makes sense also fix it in clang.
Differential Revision: http://reviews.llvm.org/D14872
llvm-svn: 254596
The GCC construct __attribute__((aligned)) is defined to set alignment
to "the default alignment for the target architecture" according to
the GCC documentation:
The default alignment is sufficient for all scalar types, but may not be
enough for all vector types on a target that supports vector operations.
The default alignment is fixed for a particular target ABI.
clang currently hard-coded an alignment of 16 bytes for that construct,
which is correct on some platforms (including X86), but wrong on others
(including SystemZ). Since this value is ABI-relevant, it is important
to get correct for compatibility purposes.
This patch adds a new TargetInfo member "DefaultAlignForAttributeAligned"
that targets can set to the appropriate default __attribute__((aligned))
value.
Note that I'm deliberately *not* using the existing "SuitableAlign"
value, which is used to set the pre-defined macro __BIGGEST_ALIGNMENT__,
since those two values may not be the same on all platforms. In fact,
on X86, __attribute__((aligned)) always uses 16-byte alignment, while
__BIGGEST_ALIGNMENT__ may be larger if AVX-2 or AVX-512 are supported.
(This is actually not yet correctly implemented in clang either.)
The patch provides a value for DefaultAlignForAttributeAligned only for
SystemZ, and leaves the default for all other targets at 16, which means
no visible change in behavior on all other targets. (The value is still
wrong for some other targets, but I'd prefer to leave it to the target
maintainers for those platforms to fix.)
llvm-svn: 235397
Also, revert a couple of suppressions.
r214298, "Suppress clang/test/Sema/struct-packed-align.c for targeting LLP64."
r214301, "Suppress clang/test/Sema/struct-packed-align.c also on msvc for investigating."
llvm-svn: 214794
- This is designed to make it obvious that %clang_cc1 is a "test variable"
which is substituted. It is '%clang_cc1' instead of '%clang -cc1' because it
can be useful to redefine what gets run as 'clang -cc1' (for example, to set
a default target).
llvm-svn: 91446
and union codepaths and fixes some minor bugs.
I'm reasonably confident this is accurate, at least for X86. I'll
correct any bugs as I find them; I haven't found any for a while,
though.
llvm-svn: 51762
NAKAMURA Takumi