>Submitter-Id:  net
>Originator:    [EMAIL PROTECTED]
>Organization:  The Debian project
>Confidential:  no
>Synopsis:      builtin memcmp() could be optimised
>Severity:       non-critical
>Priority:       low
>Category:      optimization
>Class:         sw-bug
>Release:       3.0 (Debian GNU/Linux) and HEAD 20010701
>Environment:
System: Debian GNU/Linux (testing/unstable)
Architecture: i686
        
host: i386-linux
build: i386-linux
target: i386-linux
configured with: ../src/configure -v 
--enable-languages=c,c++,java,f77,proto,objc --prefix=/usr 
--infodir=/share/info --mandir=/share/man --enable-shared --with-gnu-as 
--with-gnu-ld --with-system-zlib --enable-long-long --enable-nls 
--without-included-gettext --disable-checking --enable-threads=posix 
--enable-java-gc=boehm --with-cpp-install-dir=bin --enable-objc-gc i386-linux
>Description:
[ Reported to the Debian BTS as report #85535.
  Please CC [EMAIL PROTECTED] on replies.
  Log of report can be found at http://bugs.debian.org/85535 ]
        

int main() {
        return !memcmp("abcd", "efgh", 4);
}

produces the assembly (-S -g -O2),

        movl    $.LC1, %edi
        movl    $.LC0, %esi
        movl    $4, %ecx
        cld
        repz
        cmpsb
        seta    %cl
        setb    %dl
        popl    %esi
        xorl    %eax, %eax
        popl    %edi
        cmpb    %dl, %cl
        sete    %al

which is a waste because it could've simply loaded the two objects into
registers and compared them.  The same is true on other architectures as
well.

>How-To-Repeat:
        
>Fix:
        


Reply via email to