[LLVMbugs] [Bug 1160] x86 backend misses read-modify-write opportunity

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=1160


Chris Lattner <sabre at nondot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
         Resolution|                            |LATER




--- Comment #9 from Chris Lattner <sabre at nondot.org>  2007-09-26 01:31:45 ---
Some progress on this bug.  With -static, we now produce pretty nice code for
the first loop, but we still don't get the RMW thing correct:

LBB1_1: # bb
        movl    _huge(,%eax,4), %ecx
        orl     _target(,%eax,4), %ecx
        movl    %ecx, _target(,%eax,4)
        incl    %eax
        cmpl    $2048, %eax
        jne     LBB1_1  # bb

I entered the reduced testcase into the README.txt file here:
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20070924/053908.html

In the second loop, we are now producing nice simple code with no branches in
it:

 LBB1_3: # bb18
        addl    _target(,%ecx,4), %eax
        incl    %ecx
        cmpl    $2048, %ecx
        jne     LBB1_3  # bb18

Thus this bug is subsumed by the readme entry.  Closing.

-Chris


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