On Sat, Nov 21, 2015 at 12:46 AM, H.J. Lu <hjl.to...@gmail.com> wrote: > On Fri, Nov 20, 2015 at 2:17 PM, Jason Merrill <ja...@redhat.com> wrote: >> On 11/20/2015 01:52 PM, H.J. Lu wrote: >>> >>> On Tue, Nov 17, 2015 at 4:22 AM, Richard Biener >>> <richard.guent...@gmail.com> wrote: >>>> >>>> On Tue, Nov 17, 2015 at 12:01 PM, H.J. Lu <hjl.to...@gmail.com> wrote: >>>>> >>>>> Empty record should be returned and passed the same way in C and C++. >>>>> This patch adds LANG_HOOKS_EMPTY_RECORD_P for C++ empty class, which >>>>> defaults to return false. For C++, LANG_HOOKS_EMPTY_RECORD_P is defined >>>>> to is_really_empty_class, which returns true for C++ empty classes. For >>>>> LTO, we stream out a bit to indicate if a record is empty and we store >>>>> it in TYPE_LANG_FLAG_0 when streaming in. get_ref_base_and_extent is >>>>> changed to set bitsize to 0 for empty records. Middle-end and x86 >>>>> backend are updated to ignore empty records for parameter passing and >>>>> function value return. Other targets may need similar changes. >>>> >>>> >>>> Please avoid a new langhook for this and instead claim a bit in >>>> tree_type_common >>>> like for example restrict_flag (double-check it is unused for >>>> non-pointers). >>> >>> >>> There is no bit in tree_type_common I can overload. restrict_flag is >>> checked for non-pointers to issue an error when it is used on >>> non-pointers: >>> >>> >>> /export/gnu/import/git/sources/gcc/gcc/testsuite/g++.dg/template/qualttp20.C:19:38: >>> error: ‘__restrict__’ qualifiers cannot be applied to ‘AS::L’ >>> typedef typename T::L __restrict__ r;// { dg-error "'__restrict__' >>> qualifiers cannot" "" } >> >> >> The C++ front end only needs to check TYPE_RESTRICT for this purpose on >> front-end-specific type codes like TEMPLATE_TYPE_PARM; cp_type_quals could >> handle that specifically if you change TYPE_RESTRICT to only apply to >> pointers. >> > > restrict_flag is also checked in this case: > > [hjl@gnu-6 gcc]$ cat x.i > struct dummy { }; > > struct dummy > foo (struct dummy __restrict__ i) > { > return i; > } > [hjl@gnu-6 gcc]$ gcc -S x.i -Wall > x.i:4:13: error: invalid use of ‘restrict’ > foo (struct dummy __restrict__ i) > ^ > x.i:4:13: error: invalid use of ‘restrict’ > [hjl@gnu-6 gcc]$ > > restrict_flag can't also be used to indicate `i' is an empty record.
I'm sure this error can be done during parsing w/o relying on TYPE_RESTRICT. But well, use any other free bit (but do not enlarge tree_type_common). Eventually you can free up a bit by putting sth into type_lang_specific currently using bits in tree_type_common. Richard. > > H.J.