[LLVMbugs] [Bug 2377] New: SCEV should be a loop pass

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=2377

           Summary: SCEV should be a loop pass
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Loop Optimizer
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: resistor at mac.com
                CC: llvmbugs at cs.uiuc.edu


Because ScalarEvolution is a FunctionPass, it kills the LoopPassManager when it
is run.  This creates overhead because it require the re-instantiation of the
LPM, as well as forcing LCSSA to be recomputed repeatedly.  As of right now, we
compute LCSSA no less than five times in -std-compile-opts, mostly because of
this.  If SCEV were a loop pass, this could probably be reduced to one or two.


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