Add LTO support (full and thin), with -flto=thin|full.
#1840
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Yes, using clang's options seems like the obvious choice. Only have a vague idea what this fthinlto-index option is, also see [ThinLTO] Option to invoke ThinLTO backend passes and importing. |
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| unsigned char opt = optLevel(); | ||
| static char optChars[15] = "-plugin-opt=O0"; | ||
| optChars[13] = '0' + (opt & 0x03); // the plugin O-level ranges from 0 to 3 |
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Have you considered just making this min(optLevel(), 3)? -O4 and -O5 are currently documented as being equal to -O3, and it doesn't seem like resetting to 0 resp. 1 would be intuitive for these.
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How stupid, thanks for catching this bug. Trying to optimize something that doesn't need optimizing.
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| std::string getLTOGoldPluginPath() { | ||
| // TODO: cmdline option for plugin path, or in ldc.conf? |
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Command-line option which can then be set from ldc2.conf? ;)
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Note to self: the plugin path is also useful for OS X.
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@MartinNowak See http://blog.llvm.org/2016/06/thinlto-scalable-and-incremental-lto.html for -fthinlto-index . I'm leaving that out for now. |
JohanEngelen
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Bug : When there are module ctors/dtors in different modules, not all of them are run :( Edit: I think I found the cause. There is a latent bug in our llvm.used emission. ThinLTO is very aggressively optimizing and thus things break. Working on a fix. (edit: #1855) Edit2: nice! With that fix, I managed to build LDC with LTO, mixing C++ and D LTO! In other words: cross-language cross-module inlining. |
Pretty cool. :) |
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LTO testing is now enabled on CircleCI |
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Any concerns before I merge this? |
LTO needs linker support: I am only aware of support on OS X and Linux (through the LLVMgold plugin). Resolves ldc-developers#693
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Merging when green. |
LTO needs linker support: I am only aware of support on OS X and Linux (through the LLVMgold plugin).
I chose the cmdline option
flto=thin|fullthat mimics Clang's option (also Martin was looking forfltoin the issue #693 he reported).Resolves #693 .
For OS X, additional logic could be added later to point to a newer libLTO.dylib (see clang'sDone: addeddarwin::Linker::AddLinkArgs).flto-binaryfor that purpose. Also, CMake installs LLVM's LTO libs when it can find them; the LTO lib is installed in LDC's /lib/, and that's the first path searched when adding LTO linker flags.