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| author | Mark Mitchell <mark@codesourcery.com> | 2002-12-23 16:39:36 +0000 |
|---|---|---|
| committer | Mark Mitchell <mmitchel@gcc.gnu.org> | 2002-12-23 16:39:36 +0000 |
| commit | 8dc65b6e6d423750c05dbe4e241556febf84dcca (patch) | |
| tree | 159cad292d86d5201b0631ba807629fb2759076d /gcc/doc | |
| parent | 7c02ae17fed20316d9790f679903b274f6abe77d (diff) | |
| download | gcc-8dc65b6e6d423750c05dbe4e241556febf84dcca.zip gcc-8dc65b6e6d423750c05dbe4e241556febf84dcca.tar.gz gcc-8dc65b6e6d423750c05dbe4e241556febf84dcca.tar.bz2 | |
stor-layout.c (update_alignment_for_field): Correct handling of unnamed bitfields on PCC_BITFIELD_TYPE_MATTERS machines.
* stor-layout.c (update_alignment_for_field): Correct handling of
unnamed bitfields on PCC_BITFIELD_TYPE_MATTERS machines.
* doc/tm.texi (PCC_BITFIELD_TYPE_MATTERS): Note that an unnamed
bitfield does not affect alignment.
* testsuite/gcc.dg/i386-bitfield3.c: New test.
From-SVN: r60439
Diffstat (limited to 'gcc/doc')
| -rw-r--r-- | gcc/doc/tm.texi | 24 |
1 files changed, 13 insertions, 11 deletions
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi index 496a4a2..8436e89 100644 --- a/gcc/doc/tm.texi +++ b/gcc/doc/tm.texi @@ -1181,17 +1181,19 @@ go slower in that case, define this macro as 0. Define this if you wish to imitate the way many other C compilers handle alignment of bit-fields and the structures that contain them. -The behavior is that the type written for a bit-field (@code{int}, -@code{short}, or other integer type) imposes an alignment for the -entire structure, as if the structure really did contain an ordinary -field of that type. In addition, the bit-field is placed within the -structure so that it would fit within such a field, not crossing a -boundary for it. - -Thus, on most machines, a bit-field whose type is written as @code{int} -would not cross a four-byte boundary, and would force four-byte -alignment for the whole structure. (The alignment used may not be four -bytes; it is controlled by the other alignment parameters.) +The behavior is that the type written for a named bit-field (@code{int}, +@code{short}, or other integer type) imposes an alignment for the entire +structure, as if the structure really did contain an ordinary field of +that type. In addition, the bit-field is placed within the structure so +that it would fit within such a field, not crossing a boundary for it. + +Thus, on most machines, a named bit-field whose type is written as +@code{int} would not cross a four-byte boundary, and would force +four-byte alignment for the whole structure. (The alignment used may +not be four bytes; it is controlled by the other alignment parameters.) + +An unnamed bit-field will not affect the alignment of the containing +structure. If the macro is defined, its definition should be a C expression; a nonzero value for the expression enables this behavior. |