forked from OSchip/llvm-project
37f1f12226
of, and I misdiagnosed for months and months. Andrea has had a patch for this forever, but I just couldn't see how it was fixing the root cause of the problem. It didn't make sense to me, even though the patch was perfectly good and the analysis of the actual failure event was *fantastic*. Well, I came back to it today because the patch has sat for *far* too long and needs attention and decided I wouldn't let it go until I really understood what was going on. After quite some time in the debugger, I finally realized that in fact I had just missed an important case with my previous attempt to fix PR22093 in r225149. Not only do we need to handle loads that won't be split, but stores-of-loads that we won't split. We *do* actually have enough logic in the presplitting to form new slices for split stores.... *unless* we decided not to split them! I'm so sorry that it took me this long to come to the realization that this is the issue. It seems so obvious in hind sight (of course). Anyways, the fix becomes *much* smaller and more focused. The fact that we're left doing integer smashing is related to the FIXME in my original commit: fundamentally, we're not aggressive about pre-splitting for loads and stores to the same alloca. If we want to get aggressive about this, it'll need both what Andrea had put into the proposed fix, but also a *lot* more logic to essentially iteratively pre-split the alloca until we can't do any more. As I said in that commit log, its really unclear that this is the right call. Instead, the integer blending and letting targets lower this to narrower stores seems slightly better. But we definitely shouldn't really go down that path just to fix this bug. Again, tons of thanks are owed to Andrea and others at Sony for working on this bug. I really should have seen what was going on here and re-directed them sooner. =//// llvm-svn: 263121 |
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README.txt
Low Level Virtual Machine (LLVM) ================================ This directory and its subdirectories contain source code for LLVM, 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 are writing a package for LLVM, see docs/Packaging.rst for our suggestions.