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Re: Enable EBX for x86 in 32bits PIC code
- From: Uros Bizjak <ubizjak at gmail dot com>
- To: Ilya Enkovich <enkovich dot gnu at gmail dot com>
- Cc: gcc at gnu dot org, "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>, Evgeny Stupachenko <evstupac at gmail dot com>, Richard Biener <richard dot guenther at gmail dot com>, Jeff Law <law at redhat dot com>, Vladimir Makarov <vmakarov at redhat dot com>
- Date: Thu, 28 Aug 2014 15:01:17 +0200
- Subject: Re: Enable EBX for x86 in 32bits PIC code
- Authentication-results: sourceware.org; auth=none
- References: <CAOvf_xxsQ_oYGqNAVQ1+BW+CuD3mzebZ2xma0jpF=WfyZMCRCA at mail dot gmail dot com> <CAFiYyc1mFtTezkTJORmJJq+yht=qPSwiN7KDn19+bSuSdaqvMQ at mail dot gmail dot com> <CAOvf_xyeVeg2oB9Xxz8RMEQ6gyfJY5whd9s4ygoAAEaMU9efnA at mail dot gmail dot com> <20140707114750 dot GB31640 at tucnak dot redhat dot com> <CAMbmDYZV_fx0jxmKHhLsC2pJ7pDzuu6toEAH72izOdpq6KGyfg at mail dot gmail dot com> <20140822121151 dot GA60032 at msticlxl57 dot ims dot intel dot com>
On Fri, Aug 22, 2014 at 2:21 PM, Ilya Enkovich <firstname.lastname@example.org> wrote:
> On Cauldron 2014 we had a couple of talks about relaxation of ebx usage in 32bit PIC mode. It was decided that the best approach would be to not fix ebx register, use speudo register for GOT base address and let allocator do the rest. This should be similar to how clang and icc work with GOT base address. I've been working for some time on such patch and now want to share my results.
+ ((TARGET_64BIT && (ix86_cmodel == CM_SMALL_PIC \
+ || TARGET_PECOFF))
+ || !flag_pic ? INVALID_REGNUM \
+ : X86_TUNE_RELAX_PIC_REG ? (pic_offset_table_rtx ? INVALID_REGNUM \
+ : REAL_PIC_OFFSET_TABLE_REGNUM) \
+ : reload_completed ? REGNO (pic_offset_table_rtx) \
I'd like to avoid X86_TUNE_RELAX_PIC_REG and always treat EBX as an
allocatable register. This way, we can avoid all mess with implicit
xchgs in atomic_compare_and_swap<dwi>_doubleword. Also, having
allocatable EBX would allow us to introduce __builtin_cpuid builtin
and cleanup cpiud.h.