[PATCH] D40302: Avoid copying the data of in-memory preambles

[Ilya Biryukov via Phabricator via cfe-commits]

ilya-biryukov created this revision.

Preambles are large and we should prefer not to copy it.


https://reviews.llvm.org/D40302

Files:
  include/clang/Frontend/PrecompiledPreamble.h
  lib/Frontend/PrecompiledPreamble.cpp


Index: lib/Frontend/PrecompiledPreamble.cpp
===================================================================
--- lib/Frontend/PrecompiledPreamble.cpp
+++ lib/Frontend/PrecompiledPreamble.cpp
@@ -699,9 +699,7 @@
     StringRef PCHPath = getInMemoryPreamblePath();
     PreprocessorOpts.ImplicitPCHInclude = PCHPath;
 
-    // FIMXE(ibiryukov): Preambles can be large. We should allow shared access
-    // to the preamble data instead of copying it here.
-    auto Buf = llvm::MemoryBuffer::getMemBufferCopy(Storage.asMemory().Data);
+    auto Buf = llvm::MemoryBuffer::getMemBuffer(Storage.asMemory().Data);
     VFS = createVFSOverlayForPreamblePCH(PCHPath, std::move(Buf), VFS);
   }
 }
Index: include/clang/Frontend/PrecompiledPreamble.h
===================================================================
--- include/clang/Frontend/PrecompiledPreamble.h
+++ include/clang/Frontend/PrecompiledPreamble.h
@@ -98,6 +98,10 @@
   /// Changes options inside \p CI to use PCH from this preamble. Also remaps
   /// main file to \p MainFileBuffer and updates \p VFS to ensure the preamble
   /// is accessible.
+  /// For in-memory preambles, PrecompiledPreamble instance continues to owns
+  /// the MemoryBuffer with the Preamble after this method returns. The caller
+  /// is reponsible for making sure the PrecompiledPreamble instance outlives
+  /// the compiler run and the AST that will be using the PCH.
   void AddImplicitPreamble(CompilerInvocation &CI,
                            IntrusiveRefCntPtr<vfs::FileSystem> &VFS,
                            llvm::MemoryBuffer *MainFileBuffer) const;


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