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57b40ea3a5
Merging two type streams is one of the most time consuming parts of generating a PDB, and as such it needs to be as fast as possible. The visitor abstractions used for interoperating nicely with many different types of inputs and outputs have been used widely and help greatly for testability and implementing tools, but the abstractions build up and get in the way of performance. This patch removes all of the visitation stuff from the type stream merger, essentially re-inventing the leaf / member switch and loop, but at a very low level. This allows us many other optimizations, such as not actually deserializing *any* records (even member records which don't describe their own length), as the operation of "figure out how long this record is" is somewhat faster than "figure out how long this record *and* get all its fields out". Furthermore, whereas before we had to deserialize, re-write type indices, then re-serialize, now we don't have to do any of those 3 steps. We just find out where the type indices are and pull them directly out of the byte stream and re-write them. This is worth a 50-60% performance increase. On top of all other optimizations that have been applied this week, I now get the following numbers when linking lld.exe and lld.pdb MSVC: 25.67s Before This Patch: 18.59s After This Patch: 8.92s So this is a huge performance win. Differential Revision: https://reviews.llvm.org/D33564 llvm-svn: 303935 |
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