Hi Tom
What's the behavior of your patch to the following case
typedef int int_unaligned __attribute__((aligned(1)));
int foo (int_unaligned *p)
{
return *p;
}
thanks
Carrot
On Tue, Sep 20, 2011 at 7:13 PM, Tom de Vries <[email protected]> wrote:
> Hi Richard,
>
> I have a patch for PR43814. It introduces an option that assumes that function
> arguments of pointer type are aligned, and uses that information in
> tree-ssa-ccp. This enables the memcpy in pr43814-2.c to be inlined.
>
> I tested the patch successfully on-by-default on x86_64 and i686 (both gcc
> only
> builds).
>
> I also tested the patch on-by-default for ARM (gcc/glibc build). The patch
> generated wrong code for uselocale.c:
> ...
> glibc/locale/locale.h:
> ...
> /* This value can be passed to `uselocale' and may be returned by
> it. Passing this value to any other function has undefined behavior. */
> # define LC_GLOBAL_LOCALE ((__locale_t) -1L)
> ...
> glibc/locale/uselocale.c:
> ...
> locale_t
> __uselocale (locale_t newloc)
> {
> locale_t oldloc = _NL_CURRENT_LOCALE;
>
> if (newloc != NULL)
> {
> const locale_t locobj
> = newloc == LC_GLOBAL_LOCALE ? &_nl_global_locale : newloc;
>
> ...
> The assumption that function arguments of pointer type are aligned, allowed
> the
> test 'newloc == LC_GLOBAL_LOCALE' to evaluate to false.
> But the usage of ((__locale_t) -1L) as function argument in uselocale violates
> that assumption.
>
> Fixing the definition of LC_GLOBAL_LOCALE allowed the gcc tests to run without
> regressions for ARM.
>
> Furthermore, the patch fixes ipa-sra-2.c and ipa-sra-6.c regressions on ARM,
> discussed here:
> - http://gcc.gnu.org/ml/gcc-patches/2011-08/msg00930.html
> - http://gcc.gnu.org/ml/gcc-patches/2011-09/msg00459.html
>
> But, since glibc uses this construct currently, the option is off-by-default
> for
> now.
>
> OK for trunk?
>
> Thanks,
> - Tom
>
> 2011-09-20 Tom de Vries <[email protected]>
>
> PR target/43814
> * tree-ssa-ccp.c (get_align_value): New function, factored out of
> get_value_from_alignment.
> (get_value_from_alignment): Use get_align_value.
> (get_value_for_expr): Use get_align_value to handle alignment of
> function argument pointers.
> * common.opt (faligned-pointer-argument): New option.
> * doc/invoke.texi (Optimization Options): Add
> -faligned-pointer-argument.
> (-faligned-pointer-argument): New item.
>
> * gcc/testsuite/gcc.dg/pr43814.c: New test.
> * gcc/testsuite/gcc.target/arm/pr43814-2.c: New test.
>
