[Bug tree-optimization/108341] argument to `__builtin_ctz` should be assumed non-zero

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108341

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Not always.
It depends on the definition of CTZ_DEFINED_VALUE_AT_ZERO.

/* The value at zero is only defined for the BMI instructions
   LZCNT and TZCNT, not the BSR/BSF insns in the original isa.  */
#define CTZ_DEFINED_VALUE_AT_ZERO(MODE, VALUE) \
        ((VALUE) = GET_MODE_BITSIZE (MODE), TARGET_BMI ? 2 : 0)
#define CLZ_DEFINED_VALUE_AT_ZERO(MODE, VALUE) \
        ((VALUE) = GET_MODE_BITSIZE (MODE), TARGET_LZCNT ? 2 : 0)



So assuming !=0 with -mbmi would be an invalid assumitation.