forked from OSchip/llvm-project
1eeedf4829
When performing invariant load hoisting we check that invariant load expressions are not too complex. Up to this commit, we performed this check by counting the sum of dimensions in the access range as a very simple heuristic. This heuristic is a little too conservative, as it prevents hoisting for any scops with a very large number of parameters. Hence, we update the heuristic to only count existentially quantified dimensions and set dimensions. We expect this to still detect the problematic expressions in h264 because of which this check was originally introduced. For some unknown reason, this complexity check was originally committed in IslNodeBuilder. It really belongs in ScopInfo, as there is no point in optimizing a program which we could have known earlier cannot be code generated. The benefit of running the check early is that we can avoid to even hoist checks that are expensive to code generate as invariant loads. This can be seen in the changed tests, where we now indeed detect the scop, but just not invariant load hoist the complicated access. We also improve the formatting of the code, document it, and use isl++ to simplify expressions. llvm-svn: 308659 |
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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.