[Bug libitm/53113] Build fails in x86_avx.cc if AVX disabled but supported by as (Solaris & Linux)

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53113

--- Comment #16 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to David Kredba from comment #15)
> For me it looks like that GCC build process is taking from some internal
> definition that AVX should be present on Core2 and enables it for libitm.
> Patch attached in this bug report works for gcc-4.9-20131222 fine too.
> 
> "Known to fail" can contain 4.8.2 (and 4.9.0 branch too if possible).
> 
> Gcc knows that there is no AVX, both for 4.8.2 and 4.9.0 snapshot but both

What is exactly the problem? How can I reproduce it?

> versions enable AVX for libitim for me:
> 

That is intentional.  AVX is always compiled in if your binutils supports
it.  When you copy the same GCC run-time library binaries you built on
non-AVX machine, including libitm, to an AVX machine, the AVX functions
are checked and used at the run-time if OS/HW support AVX.