[libclang] Add a flag to create the precompiled preamble on the first parse.

Summary:
The current default is to create the preamble on the first reparse, aka
second parse. This is useful for clients that do not want to block when
opening a file because serializing the preamble takes a bit of time.
However, this makes the reparse much more expensive and that may be on the
critical path as it's the first interaction a user has with the source code.

YouCompleteMe currently optimizes for the first code interaction by parsing
the file twice when loaded. That's just unnecessarily slow and this flag
helps to avoid that.

Reviewers: doug.gregor, klimek

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D15490

llvm-svn: 255635

7 files changed, 70 insertions, 29 deletions

diff --git a/clang/include/clang-c/Index.h b/clang/include/clang-c/Index.h
index e7ba2b26a4b..09e21608263 100644
--- a/clang/include/clang-c/Index.h
+++ b/clang/include/clang-c/Index.h
@@ -1200,7 +1200,15 @@ enum CXTranslationUnit_Flags {
    * included into the set of code completions returned from this translation
    * unit.
    */
-  CXTranslationUnit_IncludeBriefCommentsInCodeCompletion = 0x80
+  CXTranslationUnit_IncludeBriefCommentsInCodeCompletion = 0x80,
+
+  /**
+   * \brief Used to indicate that the precompiled preamble should be created on
+   * the first parse. Otherwise it will be created on the first reparse. This
+   * trades runtime on the first parse (serializing the preamble takes time) for
+   * reduced runtime on the second parse (can now reuse the preamble).
+   */
+  CXTranslationUnit_CreatePreambleOnFirstParse = 0x100
 };
 
 /**
diff --git a/clang/include/clang/Frontend/ASTUnit.h b/clang/include/clang/Frontend/ASTUnit.h
index d326a53dc2a..a5f7af57143 100644
--- a/clang/include/clang/Frontend/ASTUnit.h
+++ b/clang/include/clang/Frontend/ASTUnit.h
@@ -737,14 +737,15 @@ private:
   /// \brief Helper function for \c LoadFromCompilerInvocation() and
   /// \c LoadFromCommandLine(), which loads an AST from a compiler invocation.
   ///
-  /// \param PrecompilePreamble Whether to precompile the preamble of this
-  /// translation unit, to improve the performance of reparsing.
+  /// \param PrecompilePreambleAfterNParses After how many parses the preamble
+  /// of this translation unit should be precompiled, to improve the performance
+  /// of reparsing. Set to zero to disable preambles.
   ///
   /// \returns \c true if a catastrophic failure occurred (which means that the
   /// \c ASTUnit itself is invalid), or \c false otherwise.
   bool LoadFromCompilerInvocation(
       std::shared_ptr<PCHContainerOperations> PCHContainerOps,
-      bool PrecompilePreamble);
+      unsigned PrecompilePreambleAfterNParses);
 
 public:
   
@@ -783,7 +784,8 @@ public:
       ASTFrontendAction *Action = nullptr, ASTUnit *Unit = nullptr,
       bool Persistent = true, StringRef ResourceFilesPath = StringRef(),
       bool OnlyLocalDecls = false, bool CaptureDiagnostics = false,
-      bool PrecompilePreamble = false, bool CacheCodeCompletionResults = false,
+      unsigned PrecompilePreambleAfterNParses = 0,
+      bool CacheCodeCompletionResults = false,
       bool IncludeBriefCommentsInCodeCompletion = false,
       bool UserFilesAreVolatile = false,
       std::unique_ptr<ASTUnit> *ErrAST = nullptr);
@@ -807,7 +809,8 @@ public:
       std::shared_ptr<PCHContainerOperations> PCHContainerOps,
       IntrusiveRefCntPtr<DiagnosticsEngine> Diags, FileManager *FileMgr,
       bool OnlyLocalDecls = false, bool CaptureDiagnostics = false,
-      bool PrecompilePreamble = false, TranslationUnitKind TUKind = TU_Complete,
+      unsigned PrecompilePreambleAfterNParses = 0,
+      TranslationUnitKind TUKind = TU_Complete,
       bool CacheCodeCompletionResults = false,
       bool IncludeBriefCommentsInCodeCompletion = false,
       bool UserFilesAreVolatile = false);
@@ -842,7 +845,8 @@ public:
       bool OnlyLocalDecls = false, bool CaptureDiagnostics = false,
       ArrayRef<RemappedFile> RemappedFiles = None,
       bool RemappedFilesKeepOriginalName = true,
-      bool PrecompilePreamble = false, TranslationUnitKind TUKind = TU_Complete,
+      unsigned PrecompilePreambleAfterNParses = 0,
+      TranslationUnitKind TUKind = TU_Complete,
       bool CacheCodeCompletionResults = false,
       bool IncludeBriefCommentsInCodeCompletion = false,
       bool AllowPCHWithCompilerErrors = false, bool SkipFunctionBodies = false,
diff --git a/clang/lib/Frontend/ASTUnit.cpp b/clang/lib/Frontend/ASTUnit.cpp
index 0d5dd536589..e6ba29201f8 100644
--- a/clang/lib/Frontend/ASTUnit.cpp
+++ b/clang/lib/Frontend/ASTUnit.cpp
@@ -1725,9 +1725,10 @@ ASTUnit *ASTUnit::LoadFromCompilerInvocationAction(
     std::shared_ptr<PCHContainerOperations> PCHContainerOps,
     IntrusiveRefCntPtr<DiagnosticsEngine> Diags, ASTFrontendAction *Action,
     ASTUnit *Unit, bool Persistent, StringRef ResourceFilesPath,
-    bool OnlyLocalDecls, bool CaptureDiagnostics, bool PrecompilePreamble,
-    bool CacheCodeCompletionResults, bool IncludeBriefCommentsInCodeCompletion,
-    bool UserFilesAreVolatile, std::unique_ptr<ASTUnit> *ErrAST) {
+    bool OnlyLocalDecls, bool CaptureDiagnostics,
+    unsigned PrecompilePreambleAfterNParses, bool CacheCodeCompletionResults,
+    bool IncludeBriefCommentsInCodeCompletion, bool UserFilesAreVolatile,
+    std::unique_ptr<ASTUnit> *ErrAST) {
   assert(CI && "A CompilerInvocation is required");
 
   std::unique_ptr<ASTUnit> OwnAST;
@@ -1746,8 +1747,8 @@ ASTUnit *ASTUnit::LoadFromCompilerInvocationAction(
   }
   AST->OnlyLocalDecls = OnlyLocalDecls;
   AST->CaptureDiagnostics = CaptureDiagnostics;
-  if (PrecompilePreamble)
-    AST->PreambleRebuildCounter = 2;
+  if (PrecompilePreambleAfterNParses > 0)
+    AST->PreambleRebuildCounter = PrecompilePreambleAfterNParses;
   AST->TUKind = Action ? Action->getTranslationUnitKind() : TU_Complete;
   AST->ShouldCacheCodeCompletionResults = CacheCodeCompletionResults;
   AST->IncludeBriefCommentsInCodeCompletion
@@ -1864,7 +1865,7 @@ ASTUnit *ASTUnit::LoadFromCompilerInvocationAction(
 
 bool ASTUnit::LoadFromCompilerInvocation(
     std::shared_ptr<PCHContainerOperations> PCHContainerOps,
-    bool PrecompilePreamble) {
+    unsigned PrecompilePreambleAfterNParses) {
   if (!Invocation)
     return true;
   
@@ -1874,8 +1875,8 @@ bool ASTUnit::LoadFromCompilerInvocation(
   ProcessWarningOptions(getDiagnostics(), Invocation->getDiagnosticOpts());
 
   std::unique_ptr<llvm::MemoryBuffer> OverrideMainBuffer;
-  if (PrecompilePreamble) {
-    PreambleRebuildCounter = 2;
+  if (PrecompilePreambleAfterNParses > 0) {
+    PreambleRebuildCounter = PrecompilePreambleAfterNParses;
     OverrideMainBuffer =
         getMainBufferWithPrecompiledPreamble(PCHContainerOps, *Invocation);
   }
@@ -1894,9 +1895,10 @@ std::unique_ptr<ASTUnit> ASTUnit::LoadFromCompilerInvocation(
     CompilerInvocation *CI,
     std::shared_ptr<PCHContainerOperations> PCHContainerOps,
     IntrusiveRefCntPtr<DiagnosticsEngine> Diags, FileManager *FileMgr,
-    bool OnlyLocalDecls, bool CaptureDiagnostics, bool PrecompilePreamble,
-    TranslationUnitKind TUKind, bool CacheCodeCompletionResults,
-    bool IncludeBriefCommentsInCodeCompletion, bool UserFilesAreVolatile) {
+    bool OnlyLocalDecls, bool CaptureDiagnostics,
+    unsigned PrecompilePreambleAfterNParses, TranslationUnitKind TUKind,
+    bool CacheCodeCompletionResults, bool IncludeBriefCommentsInCodeCompletion,
+    bool UserFilesAreVolatile) {
   // Create the AST unit.
   std::unique_ptr<ASTUnit> AST(new ASTUnit(false));
   ConfigureDiags(Diags, *AST, CaptureDiagnostics);
@@ -1919,7 +1921,8 @@ std::unique_ptr<ASTUnit> ASTUnit::LoadFromCompilerInvocation(
     llvm::CrashRecoveryContextReleaseRefCleanup<DiagnosticsEngine> >
     DiagCleanup(Diags.get());
 
-  if (AST->LoadFromCompilerInvocation(PCHContainerOps, PrecompilePreamble))
+  if (AST->LoadFromCompilerInvocation(PCHContainerOps,
+                                      PrecompilePreambleAfterNParses))
     return nullptr;
   return AST;
 }
@@ -1930,12 +1933,11 @@ ASTUnit *ASTUnit::LoadFromCommandLine(
     IntrusiveRefCntPtr<DiagnosticsEngine> Diags, StringRef ResourceFilesPath,
     bool OnlyLocalDecls, bool CaptureDiagnostics,
     ArrayRef<RemappedFile> RemappedFiles, bool RemappedFilesKeepOriginalName,
-    bool PrecompilePreamble, TranslationUnitKind TUKind,
+    unsigned PrecompilePreambleAfterNParses, TranslationUnitKind TUKind,
     bool CacheCodeCompletionResults, bool IncludeBriefCommentsInCodeCompletion,
     bool AllowPCHWithCompilerErrors, bool SkipFunctionBodies,
     bool UserFilesAreVolatile, bool ForSerialization,
-    llvm::Optional<StringRef> ModuleFormat,
-    std::unique_ptr<ASTUnit> *ErrAST) {
+    llvm::Optional<StringRef> ModuleFormat, std::unique_ptr<ASTUnit> *ErrAST) {
   assert(Diags.get() && "no DiagnosticsEngine was provided");
 
   SmallVector<StoredDiagnostic, 4> StoredDiagnostics;
@@ -2002,7 +2004,8 @@ ASTUnit *ASTUnit::LoadFromCommandLine(
   llvm::CrashRecoveryContextCleanupRegistrar<ASTUnit>
     ASTUnitCleanup(AST.get());
 
-  if (AST->LoadFromCompilerInvocation(PCHContainerOps, PrecompilePreamble)) {
+  if (AST->LoadFromCompilerInvocation(PCHContainerOps,
+                                      PrecompilePreambleAfterNParses)) {
     // Some error occurred, if caller wants to examine diagnostics, pass it the
     // ASTUnit.
     if (ErrAST) {
diff --git a/clang/test/Index/complete-preamble.cpp b/clang/test/Index/complete-preamble.cpp
index c57c88ab330..15720f9a297 100644
--- a/clang/test/Index/complete-preamble.cpp
+++ b/clang/test/Index/complete-preamble.cpp
@@ -3,6 +3,15 @@ void f() {
   std::
 }
 
-// RUN: env CINDEXTEST_EDITING=1 c-index-test -code-completion-at=%s:3:8 %s -o - | FileCheck -check-prefix=CHECK-CC1 %s
-// CHECK-CC1: {ResultType void}{TypedText wibble}{LeftParen (}{RightParen )} (50)
+// RUN: env CINDEXTEST_EDITING=1 LIBCLANG_TIMING=1 c-index-test -code-completion-at=%s:3:8 %s -o - 2>&1 | FileCheck -check-prefix=CHECK-CC1 -check-prefix=SECOND %s
+// RUN: env CINDEXTEST_EDITING=1 CINDEXTEST_CREATE_PREAMBLE_ON_FIRST_PARSE=1 LIBCLANG_TIMING=1 c-index-test -code-completion-at=%s:3:8 %s -o - 2>&1 | FileCheck -check-prefix=CHECK-CC1 -check-prefix=FIRST %s
+
+// FIRST: Precompiling preamble
+// FIRST: Parsing
+// FIRST: Reparsing
 
+// SECOND: Parsing
+// SECOND: Precompiling preamble
+// SECOND: Reparsing
+
+// CHECK-CC1: {ResultType void}{TypedText wibble}{LeftParen (}{RightParen )} (50)
diff --git a/clang/tools/c-index-test/c-index-test.c b/clang/tools/c-index-test/c-index-test.c
index 948195debae..48f22eb4bbf 100644
--- a/clang/tools/c-index-test/c-index-test.c
+++ b/clang/tools/c-index-test/c-index-test.c
@@ -76,7 +76,9 @@ static unsigned getDefaultParsingOptions() {
     options |= CXTranslationUnit_SkipFunctionBodies;
   if (getenv("CINDEXTEST_COMPLETION_BRIEF_COMMENTS"))
     options |= CXTranslationUnit_IncludeBriefCommentsInCodeCompletion;
-  
+  if (getenv("CINDEXTEST_CREATE_PREAMBLE_ON_FIRST_PARSE"))
+    options |= CXTranslationUnit_CreatePreambleOnFirstParse;
+
   return options;
 }
 
diff --git a/clang/tools/libclang/CIndex.cpp b/clang/tools/libclang/CIndex.cpp
index 768cd6a5b23..5022417d9af 100644
--- a/clang/tools/libclang/CIndex.cpp
+++ b/clang/tools/libclang/CIndex.cpp
@@ -3083,6 +3083,8 @@ clang_parseTranslationUnit_Impl(CXIndex CIdx, const char *source_filename,
     setThreadBackgroundPriority();
 
   bool PrecompilePreamble = options & CXTranslationUnit_PrecompiledPreamble;
+  bool CreatePreambleOnFirstParse =
+      options & CXTranslationUnit_CreatePreambleOnFirstParse;
   // FIXME: Add a flag for modules.
   TranslationUnitKind TUKind
     = (options & CXTranslationUnit_Incomplete)? TU_Prefix : TU_Complete;
@@ -3157,13 +3159,18 @@ clang_parseTranslationUnit_Impl(CXIndex CIdx, const char *source_filename,
   
   unsigned NumErrors = Diags->getClient()->getNumErrors();
   std::unique_ptr<ASTUnit> ErrUnit;
+  // Unless the user specified that they want the preamble on the first parse
+  // set it up to be created on the first reparse. This makes the first parse
+  // faster, trading for a slower (first) reparse.
+  unsigned PrecompilePreambleAfterNParses =
+      !PrecompilePreamble ? 0 : 2 - CreatePreambleOnFirstParse;
   std::unique_ptr<ASTUnit> Unit(ASTUnit::LoadFromCommandLine(
       Args->data(), Args->data() + Args->size(),
       CXXIdx->getPCHContainerOperations(), Diags,
       CXXIdx->getClangResourcesPath(), CXXIdx->getOnlyLocalDecls(),
       /*CaptureDiagnostics=*/true, *RemappedFiles.get(),
-      /*RemappedFilesKeepOriginalName=*/true, PrecompilePreamble, TUKind,
-      CacheCodeCompletionResults, IncludeBriefCommentsInCodeCompletion,
+      /*RemappedFilesKeepOriginalName=*/true, PrecompilePreambleAfterNParses,
+      TUKind, CacheCodeCompletionResults, IncludeBriefCommentsInCodeCompletion,
       /*AllowPCHWithCompilerErrors=*/true, SkipFunctionBodies,
       /*UserFilesAreVolatile=*/true, ForSerialization,
       CXXIdx->getPCHContainerOperations()->getRawReader().getFormat(),
diff --git a/clang/tools/libclang/Indexing.cpp b/clang/tools/libclang/Indexing.cpp
index d198f404a08..5bfc4245eac 100644
--- a/clang/tools/libclang/Indexing.cpp
+++ b/clang/tools/libclang/Indexing.cpp
@@ -601,6 +601,7 @@ static CXErrorCode clang_indexSourceFile_Impl(
   bool Persistent = requestedToGetTU;
   bool OnlyLocalDecls = false;
   bool PrecompilePreamble = false;
+  bool CreatePreambleOnFirstParse = false;
   bool CacheCodeCompletionResults = false;
   PreprocessorOptions &PPOpts = CInvok->getPreprocessorOpts(); 
   PPOpts.AllowPCHWithCompilerErrors = true;
@@ -608,6 +609,8 @@ static CXErrorCode clang_indexSourceFile_Impl(
   if (requestedToGetTU) {
     OnlyLocalDecls = CXXIdx->getOnlyLocalDecls();
     PrecompilePreamble = TU_options & CXTranslationUnit_PrecompiledPreamble;
+    CreatePreambleOnFirstParse =
+        TU_options & CXTranslationUnit_CreatePreambleOnFirstParse;
     // FIXME: Add a flag for modules.
     CacheCodeCompletionResults
       = TU_options & CXTranslationUnit_CacheCompletionResults;
@@ -620,11 +623,16 @@ static CXErrorCode clang_indexSourceFile_Impl(
   if (!requestedToGetTU && !CInvok->getLangOpts()->Modules)
     PPOpts.DetailedRecord = false;
 
+  // Unless the user specified that they want the preamble on the first parse
+  // set it up to be created on the first reparse. This makes the first parse
+  // faster, trading for a slower (first) reparse.
+  unsigned PrecompilePreambleAfterNParses =
+      !PrecompilePreamble ? 0 : 2 - CreatePreambleOnFirstParse;
   DiagnosticErrorTrap DiagTrap(*Diags);
   bool Success = ASTUnit::LoadFromCompilerInvocationAction(
       CInvok.get(), CXXIdx->getPCHContainerOperations(), Diags,
       IndexAction.get(), Unit, Persistent, CXXIdx->getClangResourcesPath(),
-      OnlyLocalDecls, CaptureDiagnostics, PrecompilePreamble,
+      OnlyLocalDecls, CaptureDiagnostics, PrecompilePreambleAfterNParses,
       CacheCodeCompletionResults,
       /*IncludeBriefCommentsInCodeCompletion=*/false,
       /*UserFilesAreVolatile=*/true);