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Re: [patch]: Enhance rtl-dse to remove unaligned read after writes.
- From: "Andrew Pinski" <pinskia at gmail dot com>
- To: "Kenneth Zadeck" <zadeck at naturalbridge dot com>
- Cc: gcc-patches <gcc-patches at gcc dot gnu dot org>, "Ian Lance Taylor" <iant at google dot com>, "Christopher, Eric" <echristo at gmail dot com>
- Date: Mon, 23 Jul 2007 19:22:01 -0700
- Subject: Re: [patch]: Enhance rtl-dse to remove unaligned read after writes.
- References: <468E5141.5080804@naturalbridge.com>
On 7/6/07, Kenneth Zadeck <zadeck@naturalbridge.com> wrote:
These are surprisingly common. While it is understood that such reads
are cheap (because the value is almost certainly in cache), they do take
space for the address as well as inhibit the general code for removing
redundant stores.
One some targets these reads are very expensive :) (Cell's PowerPC unit).
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30271 shows one place
where this patch helps. Though it does not fix up the issue fully as
the store is still there and does not pick up the case where we need a
shift for some reason.
And I have another case with vector modes this patch does not work but
I have not filed a bug report yet and I will try to file one tomorrow.
Thanks,
Andrew Pinski
PS bootstrapped and tested this patch on powerpc64-linux-gnu with no
regressions and also on built for spu-elf with no regressions.