From: Ilya Biryukov <ibiryukov@google.com>
Date: Fri, 24 Nov 2017 13:12:38 +0000 (+0000)
Subject: Avoid copying the data of in-memory preambles
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=e5081fa9ed363e3aafa7bef037bb61bf2472f188;p=clang

Avoid copying the data of in-memory preambles

Summary: Preambles are large and we should avoid copying them.

Reviewers: bkramer, klimek

Reviewed By: bkramer

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D40302

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@318945 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/include/clang/Frontend/PrecompiledPreamble.h b/include/clang/Frontend/PrecompiledPreamble.h
index 28e25bcdb5..13edea09af 100644
--- a/include/clang/Frontend/PrecompiledPreamble.h
+++ b/include/clang/Frontend/PrecompiledPreamble.h
@@ -98,6 +98,10 @@ public:
   /// 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 own
+  /// 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;
diff --git a/lib/Frontend/PrecompiledPreamble.cpp b/lib/Frontend/PrecompiledPreamble.cpp
index 130b9045c8..c6ee4d0289 100644
--- a/lib/Frontend/PrecompiledPreamble.cpp
+++ b/lib/Frontend/PrecompiledPreamble.cpp
@@ -699,9 +699,7 @@ void PrecompiledPreamble::setupPreambleStorage(
     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);
   }
 }