[LLVMbugs] [Bug 415] NEW: [ipcp] Sparse conditional IP constant propagation

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=415

           Summary: [ipcp] Sparse conditional IP constant propagation
           Product: libraries
           Version: 1.0
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Interprocedural Optimizations
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: sabre at nondot.org


Brian pointed out that the Olden/mst benchmark has code that basically looks
like this:

main() {
  Do_all_BlueRule(..., 1, 0);
}

void Do_all_BlueRule(..., int nproc, int pn) {
  if (nproc > 1) {
    Do_all_BlueRule(nproc/2, nproc/2+pn);
    ... A BUNCH OF OTHER STUFF ...
  }

  bar();
}

The observation is that Do_all_BlueRule contains a bunch of code that is
dynamically dead, but it requires a smarter IPCP algorithm to notice it (the
unreachable recursive call causes us to miss this).

It seems like an aggressive IPCP coupled with SCCP'y techniques could solve this
pretty easily.

-Chris



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