Use __builtin_tgmath in tgmath.h with GCC 8 (bug 21660) [committed]

[Florian Weimer]

On 11/17/2017 01:11 PM, Szabolcs Nagy wrote:
>> +/* There are two variant implementations of type-generic macros in
>> +   this file: one for GCC 8 and later, using __builtin_tgmath and
>> +   where each macro expands each of its arguments only once, and one
>> +   for older GCC, using other compiler extensions but with macros
>> +   expanding their arguments many times (so resulting in exponential
>> +   blowup of the size of expansions when calls to such macros are
>> +   nested inside arguments to such macros).  */
>> +
>> +#define __HAVE_BUILTIN_TGMATH __GNUC_PREREQ (8, 0)
> 
> this breaks the build on trunk toolchains that
> lack __builtin_tgmath

Short of getting GCC to adopt something similar to the Clang 
__has_builtin pseudo-macro, I don't see any solution other that 
requiring those who are affected by such issues to update.

Considering that this only affects an unreleased toolchain, I don't 
think the upgrade requirement is unreasonably onerous.

Thanks,
Florian