On Tue, Jul 05, 2016 at 08:31:24AM +0200, Mathieu Malaterre wrote: > I cannot see the builtin mentionned anywhere other than on the X86 page: > > X86 (ok): > https://gcc.gnu.org/onlinedocs/gcc-6.1.0/gcc/x86-Built-in-Functions.html#index-g_t_005f_005fbuiltin_005fcpu_005finit-4335 > > PowerPC (nothing found): > https://gcc.gnu.org/onlinedocs/gcc-6.1.0/gcc/PowerPC-Built-in-Functions.html#PowerPC-Built-in-Functions
It's in the third dash point: # — Built-in Function: int __builtin_cpu_supports (const char *feature) # # This function returns a value of 1 if the run-time CPU supports the # HWCAP feature feature and returns 0 otherwise. The following features # can be detected: # # ‘4xxmac’ # 4xx CPU has a Multiply Accumulator. # ‘altivec’ # CPU has a SIMD/Vector Unit. ... # ‘ppc32’ # CPU supports 32-bit mode execution. > There is an equivalent issue with -march=native on PowerPC, which is > also not mentioned (and does not work): > https://gcc.gnu.org/onlinedocs/gcc/RS_002f6000-and-PowerPC-Options.html#RS_002f6000-and-PowerPC-Options Programs that use detection specifically don't want -mfoo, as those options either require or optimize for such a subtarget only. On the other hand, using __builtin_cpu_supports() means you have two code paths, one optimized for the given feature and one without. > I suspect this is instead a minor formatting issue in the gcc > documentation as shipped in Debian (could not double check): > # reassign -1 gcc-6-doc It's not only in the documentation (both on the webpage and gcc-6-doc), but also in the code: ./gcc/config/rs6000/rs6000.c line 320 lists available arguments to __builtin_cpu_supports(). ./gcc/testsuite/gcc.target/powerpc/cpu-builtin-1.c runs it. I'm afraid I'm terribad about debugging gcc, so I couldn't tell more. At least, the amount of documentation for this and related functions is big enough that it's something more than a "minor formatting issue". If indeed this function is not supposed to be working in gcc-6, then it needs to be clarified and removed from the documentation. Should I try asking upstream? Meow! -- An imaginary friend squared is a real enemy.
