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List:       llvm-bugs
Subject:    [LLVMbugs] [Bug 187] NEW: [loopsimplify, code quality] Many pointless phi nodes are created
From:       bugzilla-daemon () zion ! cs ! uiuc ! edu
Date:       2003-12-16 21:57:27
Message-ID: 200312162157.PAA18401 () zion ! cs ! uiuc ! edu
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http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=187

           Summary: [loopsimplify, code quality] Many pointless phi nodes
                    are created
           Product: libraries
           Version: 1.0
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Scalar Optimizations
        AssignedTo: sabre@nondot.org
        ReportedBy: sabre@nondot.org


In .general_ci_points_4 function of 177.mesa, for example, the following
preheader block is created by the loop simplify pass:

no_exit.0.preheader:
%iy.2.ph = phi int [ 0, %cond_true.0 ], [ 0, %cond_true.1 ], [ 0, %cond_false.1
]             
%ix.4.ph = phi int [ 0, %cond_true.0 ], [ 0, %cond_true.1 ], [ 0, %cond_false.1
]             
%y1.1.ph = phi int [ 0, %cond_true.0 ], [ 0, %cond_true.1 ], [ 0, %cond_false.1
]             
%y0.1.ph = phi int [ 0, %cond_true.0 ], [ 0, %cond_true.1 ], [ 0, %cond_false.1
]             
%x1.1.ph = phi int [ 0, %cond_true.0 ], [ 0, %cond_true.1 ], [ 0, %cond_false.1
]             
%x0.1.ph = phi int [ 0, %cond_true.0 ], [ 0, %cond_true.1 ], [ 0, %cond_false.1
]             
%z.0.ph = phi int [ 0, %cond_true.0 ], [ 0, %cond_true.1 ], [ 0, %cond_false.1 ]
             
%y.0.ph = phi int [ 0, %cond_true.0 ], [ 0, %cond_true.1 ], [ 0, %cond_false.1 ]
             
%x.0.ph = phi int [ 0, %cond_true.0 ], [ 0, %cond_true.1 ], [ 0, %cond_false.1 ]
             

This is a common occurance, so the loop simplify pass should try a bit harder to
clean things up for subsequent loop optimization passes.

-Chris



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