[Bug target/68081] Cygwin GCC cannot compile program that uses __builtin_ia32_rdseed64_step

["noloader at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68081

--- Comment #3 from Jeffrey Walton <noloader at gmail dot com> ---
(In reply to Jeffrey Walton from comment #2)
> (In reply to Andrew Pinski from comment #1)
> > Why are you using the builtin directly?  You should be using the intrinsics
> > form instead.
> 
> Its a cross product of (1) that's what the docs tell me to use for RDRAND
> and (2) lack of documentation for RDSEED.
> 
> The doc I am referring to is
> http://gcc.gnu.org/onlinedocs/gcc/x86-Built-in-Functions.html#x86-Built-in-
> Functions lists. It tells me to use "__builtin_ia32_rdrand{16|32|64}_step"
> for RDRAND. But it does not tell me what to use for RDSEED. I made the leap
> I should use the *_rdseed variants for RDSEED.
> 
> (My apologies for the literal read. If I should be doing something
> different, then I need to be told to do so :)

By the way, I tried to find RDRAND and RDSEED intrinsic functions in the past:
http://www.google.com/search?q=RDRAND+intrinsic+site:gnu.org . The best I can
tell, they are undocumented.

I did find H.J. Lu's patches that provide __builtin_ia32_rdseed{X}_step, so I
used them instead. They are documented, so I used them.

Its very important (to me) to find provenance in vendor documentation.