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Polly was accidently modifying a debug info metadata node when attempting to generate a new unique metadata node for the loop id. The problem was that we had dwarf metadata that referred to a metadata node with a null value, like this: !6 = ... some dwarf metadata referring to !7 ... !7 = {null} When we attempt to generate a new metadata node, we reserve the first space for self-referential node by setting the first argument to null and then mutating the node later to refer to itself. However, because the nodes are uniqued based on pointer values, when we get the new metadata node it actually referred to an existing node (!7 in the example). When we went to modify the metadata to point to itself, we were accidently mutating the dwarf metatdata. We ended up in this situation: !6 = ... some dwarf metadata referring to !7 ... !7 = {!7} and this causes an assert when generating the debug info. The fix is simple, we just need to use a unique value when getting a new metadata node. The MDNode::getTemporary() provides exactly the API we need (and it is used in clang to generate the unique nodes). Differential Revision: http://reviews.llvm.org/D6174 llvm-svn: 221550
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.