Author: Reid Kleckner Date: 2019-11-19T12:42:33-08:00 New Revision: 586f65d31f32ca6bc8cfdb8a4f61bee5057bf6c8
URL: https://github.com/llvm/llvm-project/commit/586f65d31f32ca6bc8cfdb8a4f61bee5057bf6c8 DIFF: https://github.com/llvm/llvm-project/commit/586f65d31f32ca6bc8cfdb8a4f61bee5057bf6c8.diff LOG: Add a key method to Sema to optimize debug info size It turns out that the debug info describing the Sema class is an appreciable percentage of the total object file size of objects in Sema. By adding a key function, clang is able to optimize the debug info size by emitting a forward declaration in TUs that do not define the key function. On Windows, with clang-cl, these are the total sizes of object files in Sema before and after this change, compiling with optimizations and debug info: before: 335,012 KB after: 278,116 KB delta: -56,896 KB percent: -17.0% The effect on link time was negligible, despite having ~56MB less input. On Linux, with clang, these are the same sizes using DWARF -g and optimizations: before: 603,756 KB after: 515,340 KB delta: -88,416 KB percent: -14.6% I didn't use type units, DWARF-5, fission, or any other special flags. Reviewed By: thakis Differential Revision: https://reviews.llvm.org/D70340 Added: Modified: clang/include/clang/Sema/Sema.h clang/lib/Sema/Sema.cpp Removed: ################################################################################ diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h index 220b6c17835d..7d8ab59fe900 100644 --- a/clang/include/clang/Sema/Sema.h +++ b/clang/include/clang/Sema/Sema.h @@ -328,10 +328,13 @@ class PreferredTypeBuilder { }; /// Sema - This implements semantic analysis and AST building for C. -class Sema { +class Sema final { Sema(const Sema &) = delete; void operator=(const Sema &) = delete; + /// A key method to reduce duplicate debug info from Sema. + virtual void anchor(); + ///Source of additional semantic information. ExternalSemaSource *ExternalSource; diff --git a/clang/lib/Sema/Sema.cpp b/clang/lib/Sema/Sema.cpp index bedea2167950..c3c6cad277ff 100644 --- a/clang/lib/Sema/Sema.cpp +++ b/clang/lib/Sema/Sema.cpp @@ -189,6 +189,9 @@ Sema::Sema(Preprocessor &pp, ASTContext &ctxt, ASTConsumer &consumer, SemaPPCallbackHandler->set(*this); } +// Anchor Sema's type info to this TU. +void Sema::anchor() {} + void Sema::addImplicitTypedef(StringRef Name, QualType T) { DeclarationName DN = &Context.Idents.get(Name); if (IdResolver.begin(DN) == IdResolver.end()) _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
