[LLVMbugs] [Bug 14703] New: ScalarEvolution cannot detect the iteration count of a simple reverse loop.

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=14703

             Bug #: 14703
           Summary: ScalarEvolution cannot detect the iteration count of a
                    simple reverse loop.
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Loop Optimizer
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: nrotem at apple.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


SCEV can't detect the iteration count of the following loop (example21 from
gcc-loops). As a result the loop vectorizer can't vectorize it. It can handle
reverse loops that end at zero.

for (i = n-1; i >= 0; i--)
     a += b[i];

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