This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
Re: [PATCH] Add X86_TUNE_AVOID_LEA_FOR_ADDR
- From: Uros Bizjak <ubizjak at gmail dot com>
- To: Jakub Jelinek <jakub at redhat dot com>
- Cc: "H.J. Lu" <hjl dot tools at gmail dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Fri, 17 Jan 2014 16:33:24 +0100
- Subject: Re: [PATCH] Add X86_TUNE_AVOID_LEA_FOR_ADDR
- Authentication-results: sourceware.org; auth=none
- References: <20140117141937 dot GA1174 at intel dot com> <20140117143031 dot GI892 at tucnak dot redhat dot com> <CAMe9rOo+_sEh9=-MRK41ErB9+KFRvJnSoUPGG-OC+HZK_hrMVQ at mail dot gmail dot com> <CAFULd4ZF0Z3caJhJxuNw5B4+H8+Kkwq0fXw0-PFaaR=y+f1fXg at mail dot gmail dot com> <20140117152633 dot GJ892 at tucnak dot redhat dot com>
On Fri, Jan 17, 2014 at 4:26 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> On Fri, Jan 17, 2014 at 04:24:50PM +0100, Uros Bizjak wrote:
>> On Fri, Jan 17, 2014 at 3:50 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> >
>> > Wrong example. It should be
>> >
>> > lea 0x400(%edx, %ecx, 8), %edx
>> >
>> > we get
>> >
>> > add %ecx, %edx
>> > add %ecx, %edx
>> > add %ecx, %edx
>> > add %ecx, %edx
>> > add %ecx, %edx
>> > add %ecx, %edx
>> > add %ecx, %edx
>> > add %ecx, %edx
>> > add $0x400, %edx
>>
>> Even for this example, the code can be substantially improved:
>>
>> shl $3, %ecx
>> add %ecx, %edx
>> add $0x400, %edx
>
> Only if ecx is dead after the statement.
True. Do we have this information at the point transformation is performed?
Uros.