Enable EBX for x86 in 32bits PIC code

[Jakub Jelinek]

On Tue, Sep 23, 2014 at 10:00:00AM -0600, Jeff Law wrote:
> On 09/23/14 08:34, Jakub Jelinek wrote:
> >On Tue, Sep 23, 2014 at 05:54:37PM +0400, Ilya Enkovich wrote:
> >>use fixed EBX at least until we make sure pseudo PIC doesn't harm debug
> >>info generation.  If we have such option then gcc.target/i386/pic-1.c and
> >
> >For debug info, it seems you are already handling this in
> >delegitimize_address target hook, I'd suggest just building some very large
> >shared library at -O2 -g -fpic on i?86 and either look at the
> >sizes of .debug_info/.debug_loc sections with/without the patch,
> >or use the locstat utility from elfutils (talk to Petr Machata if needed).
> Can't hurt, but I really don't see how changing from a fixed to an
> allocatable register is going to muck up debug info in any significant way.

What matters is if the delegitimize_address target hook is as efficient in
delegitimization as before.  E.g. if it previously matched only when seeing
%ebx + gotoff or similar, and wouldn't match anything now, some vars could
have debug locations including UNSPEC and be dropped on the floor.

	Jakub