sammccall created this revision. sammccall added a reviewer: kadircet. Herald added subscribers: usaxena95, arphaman. Herald added a project: All. sammccall requested review of this revision. Herald added subscribers: cfe-commits, MaskRay, ilya-biryukov. Herald added a project: clang-tools-extra.
This is unneccesary work. With this change, we skip generating and lexing ~10k of predefines twice. A dumb benchmark of building a preamble for an empty file in a loop shows: - before: 1.90ms/run - after: 1.36ms/run So this should be worth 0.5ms for each AST build and code completion. There can be a functional difference, but it's very minor. If the preamble contains e.g. `#ifndef __llvm__ ... #endif` then before we would not take it. After this change we will take the branch (single-file mode takes all branches with unknown conditions) and so gather different directives. However I think this is negligible: - this is already true of non-builtin macros (from included headers). We've had no complaints. - this affects the baseline and modified in the same way, so only makes a difference transiently when code guarded by such an #ifdef is being edited Repository: rG LLVM Github Monorepo https://reviews.llvm.org/D125179 Files: clang-tools-extra/clangd/Preamble.cpp Index: clang-tools-extra/clangd/Preamble.cpp =================================================================== --- clang-tools-extra/clangd/Preamble.cpp +++ clang-tools-extra/clangd/Preamble.cpp @@ -302,6 +302,7 @@ return error("compiler instance had no inputs"); // We are only interested in main file includes. Clang->getPreprocessorOpts().SingleFileParseMode = true; + Clang->getPreprocessorOpts().UsePredefines = false; PreprocessOnlyAction Action; if (!Action.BeginSourceFile(*Clang, Clang->getFrontendOpts().Inputs[0])) return error("failed BeginSourceFile");
Index: clang-tools-extra/clangd/Preamble.cpp =================================================================== --- clang-tools-extra/clangd/Preamble.cpp +++ clang-tools-extra/clangd/Preamble.cpp @@ -302,6 +302,7 @@ return error("compiler instance had no inputs"); // We are only interested in main file includes. Clang->getPreprocessorOpts().SingleFileParseMode = true; + Clang->getPreprocessorOpts().UsePredefines = false; PreprocessOnlyAction Action; if (!Action.BeginSourceFile(*Clang, Clang->getFrontendOpts().Inputs[0])) return error("failed BeginSourceFile");
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