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Re: Enable EBX for x86 in 32bits PIC code

On 09/23/14 10:03, Jakub Jelinek wrote:
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 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.
Ah, yea, that makes sense.


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