[PATCH] Use loop unrolling pragma metadata in the loop unroller

[Mark Heffernan]

Hi eliben,

I'm adding loop unrolling pragmas to clang with change (not yet submitted): http://reviews.llvm.org/D4089
This optimizer change consumes the metadata produced from those pragmas and uses them in the loop unroller.

The pragmas must immediately precede a loop statement and take the following forms:

#pragma clang loop unroll(enable)  // unroll the loop completely
#pragma clang loop unroll(disable)  // do not unroll the loop.
#pragma clang loop unroll_count(N)  // unroll the loop N times

These pragmas mirror recently added loop vectorizer pragmas.  If you have comments on the particulars of the syntax and semantics please comment on the clang change.

http://reviews.llvm.org/D4090

Files:
  lib/Transforms/Scalar/LoopUnrollPass.cpp
  test/Transforms/LoopUnroll/unroll-pragmas.ll
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