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Date: Wed, 27 Aug 2003 20:44:00 -0000
From: "yuri at tsoft dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Message-ID: <20030827204425.12083.yuri@tsoft.com>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug c/12083] New: [IMPROVEMENT PROPOSITION] To have builtin function comparing memory backwards
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X-SW-Source: 2003-08/txt/msg03090.txt.bz2
List-Id: <gcc-bugs.sourceware.org>

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12083

           Summary: [IMPROVEMENT PROPOSITION] To have builtin function
                    comparing memory backwards
           Product: gcc
           Version: 3.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: yuri at tsoft dot com
                CC: gcc-bugs at gcc dot gnu dot org

Right now if code has function "memcmp" compiler will inline/optimize it into
"cld; repz cmpsb" - type of code inassembly on i386.

But if the problem is to compare backwards, assembly still can do it efficiently
just replacing cld with std and moving pointers to the end of block.

But from C this efficiency is unavailable.

I propose to add GCC-extention: add builtin function "gcc_rmemcmp" which
will compare memory in reverse direction.

Yuri (yuri at tsoft dot com).

PS: I will try to work on such patch myself once I have time.