[Bug c/97445] Some fonctions marked static inline in Linux kernel are not inlined

[christophe.leroy at csgroup dot eu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97445

--- Comment #42 from Christophe Leroy <christophe.leroy at csgroup dot eu> ---
(In reply to Jakub Jelinek from comment #41)
> It is documented to be undefined:
>  -- Built-in Function: int __builtin_clz (unsigned int x)
>      Returns the number of leading 0-bits in X, starting at the most
>      significant bit position.  If X is 0, the result is undefined.
> Especially GCC 11 (but e.g. clang too) will e.g. during value range
> propagation assume that e.g. the builtin return value will be only 0 to 31,
> not to 32, etc.
> The portable way how to write this is x ? __builtin_clz (x) :
> whatever_value_you_want_for_clz_0;
> and the compiler should recognize that and if the instruction is well
> defined for 0 and matches your choice, use optimal sequence.

int f(int x)
{
        return x ? __builtin_clz(x) : 32;
}

Is compiled into (with -O2):

00000000 <f>:
   0:   2c 03 00 00     cmpwi   r3,0
   4:   40 82 00 0c     bne     10 <f+0x10>
   8:   38 60 00 20     li      r3,32
   c:   4e 80 00 20     blr
  10:   7c 63 00 34     cntlzw  r3,r3
  14:   4e 80 00 20     blr



Allthough

int g(void)
{