[PATCH] New pass: inductive range check elimination

[Sanjoy Das]

Hi reames, atrick, hfinkel,

The inductive range check elimination pass eliminates range checks from within loops by splitting the iteration space into three segments in a way that the range check is fully redundant in one of the segments.  As an example, it will convert


   len = < known positive >
   for (i = 0; i < n; i++) {
     if (0 <= i && i < len) {
       do_something();
     } else {
       throw_out_of_bounds();
     }
   }

to

   len = < known positive >
   limit = smin(n, len)
   // no first segment
   for (i = 0; i < limit; i++) {
     if (0 <= i && i < len) { // this check is fully redundant
       do_something();
     } else {
       throw_out_of_bounds();
     }
   }
   for (i = limit; i < n; i++) {
     if (0 <= i && i < len) {
       do_something();
     } else {
       throw_out_of_bounds();
     }
   }


This is very close to the now removed LoopIndexSplit pass in spirit.

I believe the pass is correct (i.e. running it should not change the meaning of the program) but there still remains a considerable amount of work left to make it actually effective.  I'd like to do as much of that work as possible in-tree.

http://reviews.llvm.org/D6693

Files:
  include/llvm/InitializePasses.h
  include/llvm/LinkAllPasses.h
  include/llvm/Transforms/Scalar.h
  lib/Transforms/Scalar/CMakeLists.txt
  lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
  lib/Transforms/Scalar/Scalar.cpp
  test/Transforms/InductiveRangeCheckElimination/single.ll

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  http://reviews.llvm.org/settings/panel/emailpreferences/
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