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Summary: Third part in series to support Safe Whole Program Devirtualization Enablement, see RFC here: http://lists.llvm.org/pipermail/llvm-dev/2019-December/137543.html This patch adds type test metadata under -fwhole-program-vtables, even for classes without hidden visibility. It then changes WPD to skip devirtualization for a virtual function call when any of the compatible vtables has public vcall visibility. Additionally, internal LLVM options as well as lld and gold-plugin options are added which enable upgrading all public vcall visibility to linkage unit (hidden) visibility during LTO. This enables the more aggressive WPD to kick in based on LTO time knowledge of the visibility guarantees. Support was added to all flavors of LTO WPD (regular, hybrid and index-only), and to both the new and old LTO APIs. Unfortunately it was not simple to split the first and second parts of this part of the change (the unconditional emission of type tests and the upgrading of the vcall visiblity) as I needed a way to upgrade the public visibility on legacy WPD llvm assembly tests that don't include linkage unit vcall visibility specifiers, to avoid a lot of test churn. I also added a mechanism to LowerTypeTests that allows dropping type test assume sequences we now aggressively insert when we invoke distributed ThinLTO backends with null indexes, which is used in testing mode, and which doesn't invoke the normal ThinLTO backend pipeline. Depends on D71907 and D71911. Reviewers: pcc, evgeny777, steven_wu, espindola Subscribers: emaste, Prazek, inglorion, arichardson, hiraditya, MaskRay, dexonsmith, dang, davidxl, cfe-commits, llvm-commits Tags: #clang, #llvm Differential Revision: https://reviews.llvm.org/D71913 |
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| CMakeLists.txt | ||
| gold-plugin.cpp | ||
| gold.exports | ||
| README.txt | ||
The LLVM Gold LTO Plugin ======================== This directory contains a plugin that is designed to work with binutils gold linker. At present time, this is not the default linker in binutils, and the default build of gold does not support plugins. See docs/GoldPlugin.html for complete build and usage instructions. NOTE: libLTO and LLVMgold aren't built without PIC because they would fail to link on x86-64 with a relocation error: PIC and non-PIC can't be combined. As an alternative to passing --enable-pic, you can use 'make ENABLE_PIC=1' in your entire LLVM build.