This is the mail archive of the gcc@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: Enable EBX for x86 in 32bits PIC code


2014-08-28 0:19 GMT+04:00 Vladimir Makarov <vmakarov@redhat.com>:
> On 2014-08-26 5:42 PM, Ilya Enkovich wrote:
>>
>> Hi,
>>
>> Here is a patch I tried.  I apply it over revision 214215.  Unfortunately
>> I do not have a small reproducer but the problem can be easily reproduced on
>> SPEC2000 benchmark 175.vpr.  The problem is in read_arch.c:701 where float
>> value is compared with float constant 1.0.  It is inlined into read_arch
>> function and can be easily found in RTL dump of function read_arch as a
>> float comparison with 1.0 after the first call to strtod function.
>>
>> Here is a compilation string I use:
>>
>> gcc -m32 -mno-movbe -g3 -fdump-rtl-all-details -O2 -ffast-math
>> -mfpmath=sse -m32  -march=slm -fPIE -pie -c -o read_arch.o
>> -DSPEC_CPU2000        read_arch.c
>>
>> In my final assembler comparison with 1.0 looks like:
>>
>> comiss  .LC11@GOTOFF(%ebp), %xmm0       # 1101  *cmpisf_sse     [length =
>> 7]
>>
>> and %ebp here doesn't have a proper value.
>>
>> I'll try to make a smaller reproducer if these instructions don't help.
>
>
> I've managed to reproduce it.  Although it would be better to send the patch
> as an attachment.
>
> The problem is actually in IRA not LRA.  IRA splits pseudo used for PIC.
> Then in a region when a *new* pseudo used as PIC we rematerialize a constant
> which transformed in memory addressed through *original* PIC pseudo.
>
> To solve the problem we should prevent such splitting and guarantee that PIC
> pseudo allocnos in different region gets the same hard reg.
>
> The following patch should solve the problem.
>

Thanks for the patch! I'll try it and be back with results.

Ilya
>


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]