[Patch][LoopInfo] Use CGLoopInfo to generate loop hints

[Tyler Nowicki]

Hi,

Recent changes to OpenMP conflicted with the original patch. Here is the updated patch.

Any comments are much appreciated!

Tyler

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> On Jun 13, 2015, at 6:36 PM, Tyler Nowicki <tnowicki at apple.com> wrote:
> 
> Hello,
> 
> I noticed a problem with my implementation of #pragma clang loop vectorize(assume_safety). When it was specified on a loop other loop hints were lost. The problem is that CGLoopInfo attaches metadata a little bit differently than EmitCondBrHints in CGStmt. For do-loops CGLoopInfo attaches metadata to the br in the body block and for while and for loops, the inc block. EmitCondBrHints on the other hand always attaches data to the br in the cond block. When specifying assume_safety CGLoopInfo emits an empty llvm.loop metadata shadowing the metadata in the cond block. Loop transformations like rotate and unswitch would then eliminate the cond block.
> 
> This patch unifies both approaches for adding metadata and modifies the existing safety tests to include non-assume_safety loop hints.
> 
> Thanks,
> 
> Tyler
> 
> 
> <0001-Use-CGLoopInfo-to-insert-loop-hints-to-fix-conflict-.patch>