On Mon, 20 Nov 2023, Jakub Jelinek wrote: > On Mon, Nov 20, 2023 at 04:03:07PM +0100, Jakub Jelinek wrote: > > > Note that stdc_bit_ceil now has defined behavior (return 0) on overflow: > > > CD2 comment FR-135 was accepted for the DIS at the June WG14 meeting. > > > This affects both the documentation and the implementation, as they need > > > to avoid an undefined shift by the width of the type. That's why my > > > stdbit.h implementations have two shifts (not claiming that's necessarily > > > the optimal way of ensuring the correct result in the overflow case). > > > > > > return __x <= 1 ? 1 : ((uint64_t) 1) << (__bw64_inline (__x - 1) - 1) > > > << 1; > > > > Given the feedback from Richi I've in the meantime reworked the patch to > > add all 14 builtins (but because the enum rid is very close to 256 values > > and with 14 new ones was already 7 too many, used one RID value for all 14 > > builtins (different spellings)). > > > > Will need to rework it for CD2 FR-135 then... > > Here it is updated to use that > x <= 1 ? 1 : ((type) 2) << (prec - 1 - __builtin_clzg ((type) (x - 1))) > I've mentioned. > > 2023-11-20 Jakub Jelinek <ja...@redhat.com> > > gcc/ > * doc/extend.texi (__builtin_stdc_bit_ceil, __builtin_stdc_bit_floor, > __builtin_stdc_bit_width, __builtin_stdc_count_ones, > __builtin_stdc_count_zeros, __builtin_stdc_first_leading_one, > __builtin_stdc_first_leading_zero, __builtin_stdc_first_trailing_one, > __builtin_stdc_first_trailing_zero, __builtin_stdc_has_single_bit, > __builtin_stdc_leading_ones, __builtin_stdc_leading_zeros, > __builtin_stdc_trailing_ones, __builtin_stdc_trailing_zeros): Document. > gcc/c-family/ > * c-common.h (enum rid): Add RID_BUILTIN_STDC: New. > * c-common.cc (c_common_reswords): Add __builtin_stdc_bit_ceil, > __builtin_stdc_bit_floor, __builtin_stdc_bit_width, > __builtin_stdc_count_ones, __builtin_stdc_count_zeros, > __builtin_stdc_first_leading_one, __builtin_stdc_first_leading_zero, > __builtin_stdc_first_trailing_one, __builtin_stdc_first_trailing_zero, > __builtin_stdc_has_single_bit, __builtin_stdc_leading_ones, > __builtin_stdc_leading_zeros, __builtin_stdc_trailing_ones and > __builtin_stdc_trailing_zeros. Move __builtin_assoc_barrier > alphabetically earlier. > gcc/c/ > * c-parser.cc (c_parser_postfix_expression): Handle RID_BUILTIN_STDC. > * c-decl.cc (names_builtin_p): Likewise. > gcc/testsuite/ > * gcc.dg/builtin-stdc-bit-1.c: New test. > * gcc.dg/builtin-stdc-bit-2.c: New test.
OK with tests added for unsigned _BitInt(1). Specifically, unsigned _BitInt(1) is a bit of a degenerate case for stdc_bit_ceil (always returning 1 after evaluating the argument's side effects); I think the code that builds of constant 2 of that type (a constant only used in dead code) should still work (and produce a constant 0), and that the documentation is also still correct in the case where converting 2 to the type produces 0, but given those degeneracies I think it's worth testing unsigned _BitInt(1) with these functions to make sure they do behave as expected. -- Joseph S. Myers jos...@codesourcery.com
