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69774fa1c4
querying of the pass registry. The pass manager relies on the static registry of PassInfo objects to perform all manner of its functionality. I don't understand why it does much of this. My very vague understanding is that this registry is touched both during static initialization *and* while each pass is being constructed. As a consequence it is hard to make accessing it not require a acquiring some lock. This lock ends up in the hot path of setting up, tearing down, and invaliditing analyses in the legacy pass manager. On most systems you can observe this as a non-trivial % of the time spent in 'ninja check-llvm'. However, I haven't really seen it be more than 1% in extreme cases of compiling more real-world software, including LTO. Unfortunately, some of the GPU JITs are seeing this taking essentially all of their time because they have very small IR running through a small pass pipeline very many times (at least, this is the vague understanding I have of it). This patch tries to minimize the cost of looking up PassInfo objects by leveraging the fact that the objects themselves are immutable and they are allocated separately on the heap and so don't have their address change. It also requires a change I made the last time I tried to debug this problem which removed the ability to de-register a pass from the registry. This patch creates a single access path to these objects inside the PMTopLevelManager which memoizes the result of querying the registry. This is somewhat gross as I don't really know if PMTopLevelManager is the *right* place to put it, and I dislike using a mutable member to memoize things, but it seems to work. For long-lived pass managers this should completely eliminate the cost of acquiring locks to look into the pass registry once the memoized cache is warm. For 'ninja check' I measured about 1.5% reduction in CPU time and in total time on a machine with 32 hardware threads. For normal compilation, I don't know how much this will help, sadly. We will still pay the cost while we populate the memoized cache. I don't think it will hurt though, and for LTO or compiles with many small functions it should still be a win. However, for tight loops around a pass manager with many passes and small modules, this will help tremendously. On the AArch64 backend I saw nearly 50% reductions in time to complete 2000 cycles of spinning up and tearing down the pipeline. Measurements from Owen of an actual long-lived pass manager show more along the lines of 10% improvements. Differential Revision: http://reviews.llvm.org/D7213 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227299 91177308-0d34-0410-b5e6-96231b3b80d8 |
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| .. | ||
| Analysis | ||
| AsmParser | ||
| Bitcode | ||
| CodeGen | ||
| DebugInfo | ||
| ExecutionEngine | ||
| Fuzzer | ||
| IR | ||
| IRReader | ||
| LineEditor | ||
| Linker | ||
| LTO | ||
| MC | ||
| Object | ||
| Option | ||
| ProfileData | ||
| Support | ||
| TableGen | ||
| Target | ||
| Transforms | ||
| CMakeLists.txt | ||
| LLVMBuild.txt | ||
| Makefile | ||