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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 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.
Ah, yea, that makes sense.

jeff


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