[Bug target/64379] VFP register restore in ARM epilogue can break indirect tailcalls

["ramana at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64379

Ramana Radhakrishnan <ramana at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P4
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-01-13
                 CC|                            |ramana at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #8 from Ramana Radhakrishnan <ramana at gcc dot gnu.org> ---
(In reply to Donn Seeley from comment #7)
> Re -mapcs-frame:  Yes, the failure is due to code in
> arm_expand_epilogue_apcs_frame() that explicitly requires / stomps on IP in
> order to restore VFP/NEON registers.  Sorry, I should have mentioned that. 
> The indirect tailcall register is chosen from CALLER_SAVE_REGS via the "Cs"
> constraint, and CALLER_SAVE_REGS contains the arg regs plus IP; if the arg
> regs are in use, then the tailcall register ends up being IP.  Hence the
> conflict.


Uggh - these ancient options in the backend. mapcs-frame is quite ancient and
isn't really something that's tested very often, no wonder it's rotting. In
this case we seem to have regressed something that worked earlier, I do wonder
if the fix here is to just turn IP regnum into a fixed register in the presence
of mapcs-frame.


regards
Ramana