07e315e780
After DeLICM, it is possible to have two writes of the same value to the same location in the same statement when it determined that those writes do not conflict (write the same value). Teach -polly-simplify to remove one of the writes. It interferes with the pattern matching of matrix-multiplication kernels and also seem to not be optimized away by LLVM. The algorthm is simple, has O(n^2) behaviour (n = max number of MemoryAccesses in a statement) and only matches the most obvious cases, but seem to be enough to pattern-match Boost ublas gemm. Not handled cases include: - StoreInst instructions (a.k.a. explicit writes), since the value might be loaded or overwritten between the two stores. - PHINode, especially LCSSA, when the PHI value matches with on other's. - Partial writes (in preparation) llvm-svn: 302805 |
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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.