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| author | Jessica Clarke <jrtc27@jrtc27.com> | 2021-03-31 10:12:39 (GMT) |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2021-03-31 10:12:39 (GMT) |
| commit | dec075754960dd85972ce5170df76e862f966132 (patch) | |
| tree | d03d976a2f077f0f07ebfd9ed35f2c91490de89d /configure.ac | |
| parent | cfa176685a5e788bafc7749d7a93f43ea3e4de9f (diff) | |
| download | cpython-dec075754960dd85972ce5170df76e862f966132.zip cpython-dec075754960dd85972ce5170df76e862f966132.tar.gz cpython-dec075754960dd85972ce5170df76e862f966132.tar.bz2 | |
bpo-43179: Generalise alignment for optimised string routines (GH-24624)
* Remove m68k-specific hack from ascii_decode
On m68k, alignments of primitives is more relaxed, with 4-byte and
8-byte types only requiring 2-byte alignment, thus using sizeof(size_t)
does not work. Instead, use the portable alternative.
Note that this is a minimal fix that only relaxes the assertion and the
condition for when to use the optimised version remains overly strict.
Such issues will be fixed tree-wide in the next commit.
NB: In C11 we could use _Alignof(size_t) instead, but for compatibility
we use autoconf.
* Optimise string routines for architectures with non-natural alignment
C only requires that sizeof(x) is a multiple of alignof(x), not that the
two are equal. Thus anywhere where we optimise based on alignment we
should be using alignof(x) not sizeof(x).
This is more annoying than it would be in C11 where we could just use
_Alignof(x) (and alignof(x) in C++11), but since we still require only
C99 we must plumb the information all the way from autoconf through the
various typedefs and defines.
Diffstat (limited to 'configure.ac')
| -rw-r--r-- | configure.ac | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/configure.ac b/configure.ac index 0db7e60..8b3ab1e 100644 --- a/configure.ac +++ b/configure.ac @@ -2354,10 +2354,11 @@ AC_CHECK_TYPE(ssize_t, AC_CHECK_TYPE(__uint128_t, AC_DEFINE(HAVE_GCC_UINT128_T, 1, [Define if your compiler provides __uint128_t]),,) -# Sizes of various common basic types +# Sizes and alignments of various common basic types # ANSI C requires sizeof(char) == 1, so no need to check it AC_CHECK_SIZEOF(int, 4) AC_CHECK_SIZEOF(long, 4) +AC_CHECK_ALIGNOF(long) AC_CHECK_SIZEOF(long long, 8) AC_CHECK_SIZEOF(void *, 4) AC_CHECK_SIZEOF(short, 2) @@ -2365,6 +2366,7 @@ AC_CHECK_SIZEOF(float, 4) AC_CHECK_SIZEOF(double, 8) AC_CHECK_SIZEOF(fpos_t, 4) AC_CHECK_SIZEOF(size_t, 4) +AC_CHECK_ALIGNOF(size_t) AC_CHECK_SIZEOF(pid_t, 4) AC_CHECK_SIZEOF(uintptr_t) |