GMP 6.1.2 t-count_zeros failure on ARM with assertions

[Torbjörn Granlund]

nisse at lysator.liu.se (Niels Möller) writes:

  Using inline asm instead has the drawback that it leaves a little less
  opportunity for the compiler to schedule this instructions optimally. No
  idea if that matters in practice. Since it seems we don't really need
  count_*_zeros to support zero input, is there any advantage in using
  inline asm?
  
Sure, and that matters chiefly if the instructions have a long latency.
(Now, it is quite likely that CLZ and RBIT didn't get described to the
compiler scheduler, as they are usually not used.)

  (Related, I wonder what the effect would be of redefining umul_ppmm as C
  expressions involving __uint128_t on compilers that support that).
  
We do that already for some CPUs, but this has proven to be somewhat
fragile, and in unexpected cases lead to libgcc calls.

-- 
Torbjörn
Please encrypt, key id 0xC8601622