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e56cb5ff31
operations. Specifically, we had code that tried to badly approximate reconstructing all of the possible variations on addressing modes in two x86 instructions based on those in one pseudo instruction. This is not the first bug uncovered with doing this, so stop doing it altogether. Instead generically and pedantically copy every operand from the address over to both new instructions, and strip kill flags from any register operands. This fixes a subtle bug seen in the wild where we would mysteriously drop parts of the addressing mode, causing for example the index argument in the added test case to just be completely ignored. Hypothetically, this was an extremely bad miscompile because it actually caused a predictable and leveragable write of a 64bit quantity to an unintended offset (the first element of the array intead of whatever other element was intended). As a consequence, in theory this could even have introduced security vulnerabilities. However, this was only something that could happen with an atomic floating point add. No other operation could trigger this bug, so it seems extremely unlikely to have occured widely in the wild. But it did in fact occur, and frequently in scientific applications which were using relaxed atomic updates of a floating point value after adding a delta. Those would end up being quite badly miscompiled by LLVM, which is how we found this. Of course, this often looks like a race condition in the code, but it was actually a miscompile. I suspect that this whole RELEASE_FADD thing was a complete mistake. There is no such operation, and I worry that anything other than add will get remarkably worse codegeneration. But that's not for this change.... git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@264845 91177308-0d34-0410-b5e6-96231b3b80d8 |
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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.