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using GEPs. Previously, it used a number of different heuristics for analyzing the GEPs. Several of these were conservatively correct, but failed to fall back to SCEV even when SCEV might have given a reasonable answer. One was simply incorrect in how it was formulated. There was good code already to recursively evaluate the constant offsets in GEPs, look through pointer casts, etc. I gathered this into a form code like the SLP code can use in a previous commit, which allows all of this code to become quite simple. There is some performance (compile time) concern here at first glance as we're directly attempting to walk both pointers constant GEP chains. However, a couple of thoughts: 1) The very common cases where there is a dynamic pointer, and a second pointer at a constant offset (usually a stride) from it, this code will actually not do any unnecessary work. 2) InstCombine and other passes work very hard to collapse constant GEPs, so it will be rare that we iterate here for a long time. That said, if there remain performance problems here, there are some obvious things that can improve the situation immensely. Doing a vectorizer-pass-wide memoizer for each individual layer of pointer values, their base values, and the constant offset is likely to be able to completely remove redundant work and strictly limit the scaling of the work to scrape these GEPs. Since this optimization was not done on the prior version (which would still benefit from it), I've not done it here. But if folks have benchmarks that slow down it should be straight forward for them to add. I've added a test case, but I'm not really confident of the amount of testing done for different access patterns, strides, and pointer manipulation. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189007 91177308-0d34-0410-b5e6-96231b3b80d8 |
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Low Level Virtual Machine (LLVM) ================================ This directory and its subdirectories contain source code for the Low Level Virtual Machine, a toolkit for the construction of highly optimized compilers, optimizers, and runtime environments. LLVM is open source software. You may freely distribute it under the terms of the license agreement found in LICENSE.txt. Please see the documentation provided in docs/ for further assistance with LLVM, and in particular docs/GettingStarted.rst for getting started with LLVM and docs/README.txt for an overview of LLVM's documentation setup. If you're writing a package for LLVM, see docs/Packaging.rst for our suggestions.