[LLVMbugs] [Bug 8609] New: SCEV not updated correctly?

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=8609

           Summary: SCEV not updated correctly?
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Loop Optimizer
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: grosser at fim.uni-passau.de
                CC: llvmbugs at cs.uiuc.edu


Created an attachment (id=5775)
 --> (http://llvm.org/bugs/attachment.cgi?id=5775)
Failing testcase (not yet reduced)

For the attached test case I get the correct values, if scalar-evolution is
executed in a separate program. However if it is scheduled right after -O1 it
says it cannot predict some backedge-taken counts.

$opt  -O1 /tmp/unpredictable_exit_count.ll | opt -scalar-evolution -analyze 
[...]
Loop %"4.i.i": backedge-taken count is 1023
Loop %"4.i.i": max backedge-taken count is 1023
Loop %"3.i.i": backedge-taken count is 1023
Loop %"3.i.i": max backedge-taken count is 1023
[...]

$opt  -O1 /tmp/unpredictable_exit_count.ll -scalar-evolution -analyze 
[...]
Determining loop execution counts for: @main
Loop %"4.i.i": backedge-taken count is 1023
Loop %"4.i.i": max backedge-taken count is 1023
Loop %"3.i.i": Unpredictable backedge-taken count. 
Loop %"3.i.i": Unpredictable max backedge-taken count. 
[...]

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