[LLVMbugs] [Bug 3170] New: loop unswitch never unswitches any loops

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=3170

           Summary: loop unswitch never unswitches any loops
           Product: new-bugs
           Version: unspecified
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: sharparrow1 at yahoo.com
                CC: dpatel at apple.com, llvmbugs at cs.uiuc.edu


Take even the most trivial loop to unswitch:
int a(int x, int y) {
  for (unsigned i = 0; i < y; i++) {
    if (x) {
      b();
    }
  }return 0;
}

Loop unswitch somehow can't manage to unswitch it.

The cause here is r58631; it changed FindLIVLoopCondition so that it always
returns null, which means the unswitcher can never find any conditions to
unswitch on.  I somehow doubt that was the intention, but I can't figure out
what it was trying to do.


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