[Bug target/56560] [4.6/4.7 regression] vzeroupper clobbers argument with AVX

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56560

--- Comment #7 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2013-03-12 11:37:27 UTC ---
> This patch adds expand_args to track library calls to
> expend arguments.  We add vzeroupper when expand_args == 1,
> which indicates we are expanding the actual function.

This looks complicated.  A simpler approach could be to record the AVX state in
the CUMULATIVE_ARGS structure and transfer it to cfun->machine only at the end
of the argument processing.  Comments and code in calls.c appear to guarantee
that

  targetm.calls.function_arg (&args_so_far, VOIDmode, void_type_node, true)

is invoked immediately before the call instruction is emitted.