9f6e41cdba
This allows -polly-optree to move instructions that depend on synthesizable values. The difficulty for synthesizable values is that their value depends on the location. When it is moved over a loop header, and the SCEV expression depends on the loop induction variable (SCEVAddRecExpr), it would use the current induction variable instead of the last one. At the moment we cannot forward PHI nodes such that crossing the header of loops referenced by SCEVAddRecExpr is not possible (assuming the loop header has at least two incoming blocks: for entering the loop and the backedge, such any instruction to be forwarded must have a phi between use and definition). A remaining issue is when the forwarded value is used after the loop, but is only synthesizable inside the loop. This happens e.g. if ScalarEvolution is unable to determine the number of loop iterations or the initial loop value. We do not forward in this situation. Differential Revision: https://reviews.llvm.org/D36102 llvm-svn: 309609 |
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README
Polly - Polyhedral optimizations for LLVM ----------------------------------------- http://polly.llvm.org/ Polly uses a mathematical representation, the polyhedral model, to represent and transform loops and other control flow structures. Using an abstract representation it is possible to reason about transformations in a more general way and to use highly optimized linear programming libraries to figure out the optimal loop structure. These transformations can be used to do constant propagation through arrays, remove dead loop iterations, optimize loops for cache locality, optimize arrays, apply advanced automatic parallelization, drive vectorization, or they can be used to do software pipelining.