Introduce basic support for loading a precompiled preamble while

reparsing an ASTUnit. When saving a preamble, create a buffer larger
than the actual file we're working with but fill everything from the
end of the preamble to the end of the file with spaces (so the lexer
will quickly skip them). When we load the file, create a buffer of the
same size, filling it with the file and then spaces. Then, instruct
the lexer to start lexing after the preamble, therefore continuing the
parse from the spot where the preamble left off.

It's now possible to perform a simple preamble build + parse (+
reparse) with ASTUnit. However, one has to disable a bunch of checking
in the PCH reader to do so. That part isn't committed; it will likely
be handled with some other kind of flag (e.g., -fno-validate-pch).

As part of this, fix some issues with null termination of the memory
buffers created for the preamble; we were trying to explicitly
NULL-terminate them, even though they were also getting implicitly
NULL terminated, leading to excess warnings about NULL characters in
source files.

llvm-svn: 109445

1 files changed, 56 insertions, 16 deletions

diff --git a/clang/lib/Frontend/ASTUnit.cpp b/clang/lib/Frontend/ASTUnit.cpp
index 77a414772af..7ff3cdc5b9a 100644
--- a/clang/lib/Frontend/ASTUnit.cpp
+++ b/clang/lib/Frontend/ASTUnit.cpp
@@ -46,6 +46,20 @@ ASTUnit::~ASTUnit() {
   CleanTemporaryFiles();
   if (!PreambleFile.empty())
     PreambleFile.eraseFromDisk();
+  
+  // Free the buffers associated with remapped files. We are required to
+  // perform this operation here because we explicitly request that the
+  // compiler instance *not* free these buffers for each invocation of the
+  // parser.
+  if (Invocation.get()) {
+    PreprocessorOptions &PPOpts = Invocation->getPreprocessorOpts();
+    for (PreprocessorOptions::remapped_file_buffer_iterator
+           FB = PPOpts.remapped_file_buffer_begin(),
+           FBEnd = PPOpts.remapped_file_buffer_end();
+         FB != FBEnd;
+         ++FB)
+      delete FB->second;
+  }
 }
 
 void ASTUnit::CleanTemporaryFiles() {
@@ -371,6 +385,17 @@ bool ASTUnit::Parse(llvm::MemoryBuffer *OverrideMainBuffer) {
   // Create the source manager.
   Clang.setSourceManager(&getSourceManager());
   
+  // If the main file has been overridden due to the use of a preamble,
+  // make that override happen and introduce the preamble.
+  PreprocessorOptions &PreprocessorOpts = Clang.getPreprocessorOpts();
+  if (OverrideMainBuffer) {
+    PreprocessorOpts.addRemappedFile(OriginalSourceFile, OverrideMainBuffer);
+    PreprocessorOpts.PrecompiledPreambleBytes.first = Preamble.size();
+    PreprocessorOpts.PrecompiledPreambleBytes.second
+                                                    = PreambleEndsAtStartOfLine;
+    PreprocessorOpts.ImplicitPCHInclude = PreambleFile.str();
+  }
+  
   llvm::OwningPtr<TopLevelDeclTrackerAction> Act;
   Act.reset(new TopLevelDeclTrackerAction(*this));
   if (!Act->BeginSourceFile(Clang, Clang.getFrontendOpts().Inputs[0].second,
@@ -388,6 +413,11 @@ bool ASTUnit::Parse(llvm::MemoryBuffer *OverrideMainBuffer) {
   Target.reset(Clang.takeTarget());
   
   Act->EndSourceFile();
+
+  // Remove the overridden buffer we used for the preamble.
+  if (OverrideMainBuffer)
+    PreprocessorOpts.eraseRemappedFile(
+                               PreprocessorOpts.remapped_file_buffer_end() - 1);
   
   Clang.takeDiagnosticClient();
   
@@ -395,6 +425,11 @@ bool ASTUnit::Parse(llvm::MemoryBuffer *OverrideMainBuffer) {
   return false;
   
 error:
+  // Remove the overridden buffer we used for the preamble.
+  if (OverrideMainBuffer)
+    PreprocessorOpts.eraseRemappedFile(
+                               PreprocessorOpts.remapped_file_buffer_end() - 1);
+  
   Clang.takeSourceManager();
   Clang.takeFileManager();
   Clang.takeDiagnosticClient();
@@ -424,8 +459,10 @@ static std::string GetPreamblePCHPath() {
   return P.str();
 }
 
-/// \brief Compute the preamble for the main file, providing
-std::pair<llvm::MemoryBuffer *, unsigned> 
+/// \brief Compute the preamble for the main file, providing the source buffer
+/// that corresponds to the main file along with a pair (bytes, start-of-line)
+/// that describes the preamble.
+std::pair<llvm::MemoryBuffer *, std::pair<unsigned, bool> > 
 ASTUnit::ComputePreamble(CompilerInvocation &Invocation, bool &CreatedBuffer) {
   FrontendOptions &FrontendOpts = Invocation.getFrontendOpts();
   PreprocessorOptions &PreprocessorOpts
@@ -455,7 +492,8 @@ ASTUnit::ComputePreamble(CompilerInvocation &Invocation, bool &CreatedBuffer) {
           
           Buffer = llvm::MemoryBuffer::getFile(M->second);
           if (!Buffer)
-            return std::make_pair((llvm::MemoryBuffer*)0, 0);
+            return std::make_pair((llvm::MemoryBuffer*)0, 
+                                  std::make_pair(0, true));
           CreatedBuffer = true;
           
           // Remove this remapping. We've captured the buffer already.
@@ -495,7 +533,7 @@ ASTUnit::ComputePreamble(CompilerInvocation &Invocation, bool &CreatedBuffer) {
   if (!Buffer) {
     Buffer = llvm::MemoryBuffer::getFile(FrontendOpts.Inputs[0].second);
     if (!Buffer)
-      return std::make_pair((llvm::MemoryBuffer*)0, 0);    
+      return std::make_pair((llvm::MemoryBuffer*)0, std::make_pair(0, true));    
     
     CreatedBuffer = true;
   }
@@ -512,9 +550,8 @@ static llvm::MemoryBuffer *CreatePaddedMainFileBuffer(llvm::MemoryBuffer *Old,
   memcpy(const_cast<char*>(Result->getBufferStart()), 
          Old->getBufferStart(), Old->getBufferSize());
   memset(const_cast<char*>(Result->getBufferStart()) + Old->getBufferSize(), 
-         ' ', NewSize - Old->getBufferSize() - 2);
-  const_cast<char*>(Result->getBufferEnd())[-2] = '\n';  
-  const_cast<char*>(Result->getBufferEnd())[-1] = 0;  
+         ' ', NewSize - Old->getBufferSize() - 1);
+  const_cast<char*>(Result->getBufferEnd())[-1] = '\n';  
   
   if (DeleteOld)
     delete Old;
@@ -542,10 +579,10 @@ llvm::MemoryBuffer *ASTUnit::BuildPrecompiledPreamble() {
     = PreambleInvocation.getPreprocessorOpts();
 
   bool CreatedPreambleBuffer = false;
-  std::pair<llvm::MemoryBuffer *, unsigned> NewPreamble 
+  std::pair<llvm::MemoryBuffer *, std::pair<unsigned, bool> > NewPreamble 
     = ComputePreamble(PreambleInvocation, CreatedPreambleBuffer);
 
-  if (!NewPreamble.second) {
+  if (!NewPreamble.second.first) {
     // We couldn't find a preamble in the main source. Clear out the current
     // preamble, if we have one. It's obviously no good any more.
     Preamble.clear();
@@ -564,10 +601,11 @@ llvm::MemoryBuffer *ASTUnit::BuildPrecompiledPreamble() {
     // preamble now that we did before, and that there's enough space in
     // the main-file buffer within the precompiled preamble to fit the
     // new main file.
-    if (Preamble.size() == NewPreamble.second &&
+    if (Preamble.size() == NewPreamble.second.first &&
+        PreambleEndsAtStartOfLine == NewPreamble.second.second &&
         NewPreamble.first->getBufferSize() < PreambleReservedSize-2 &&
         memcmp(&Preamble[0], NewPreamble.first->getBufferStart(),
-               NewPreamble.second) == 0) {
+               NewPreamble.second.first) == 0) {
       // The preamble has not changed. We may be able to re-use the precompiled
       // preamble.
       // FIXME: Check that none of the files used by the preamble have changed.
@@ -593,7 +631,7 @@ llvm::MemoryBuffer *ASTUnit::BuildPrecompiledPreamble() {
   // grows.  
   PreambleReservedSize = NewPreamble.first->getBufferSize();
   if (PreambleReservedSize < 4096)
-    PreambleReservedSize = 8192;
+    PreambleReservedSize = 8191;
   else
     PreambleReservedSize *= 2;
 
@@ -603,14 +641,15 @@ llvm::MemoryBuffer *ASTUnit::BuildPrecompiledPreamble() {
   memcpy(const_cast<char*>(PreambleBuffer->getBufferStart()), 
          NewPreamble.first->getBufferStart(), Preamble.size());
   memset(const_cast<char*>(PreambleBuffer->getBufferStart()) + Preamble.size(), 
-         ' ', PreambleReservedSize - Preamble.size() - 2);
-  const_cast<char*>(PreambleBuffer->getBufferEnd())[-1] = 0;
-  const_cast<char*>(PreambleBuffer->getBufferEnd())[-2] = '\n';  
+         ' ', PreambleReservedSize - Preamble.size() - 1);
+  const_cast<char*>(PreambleBuffer->getBufferEnd())[-1] = '\n';  
 
   // Save the preamble text for later; we'll need to compare against it for
   // subsequent reparses.
   Preamble.assign(NewPreamble.first->getBufferStart(), 
-                  NewPreamble.first->getBufferStart() + NewPreamble.second);
+                  NewPreamble.first->getBufferStart() 
+                                                  + NewPreamble.second.first);
+  PreambleEndsAtStartOfLine = NewPreamble.second.second;
   
   // Remap the main source file to the preamble buffer.
   llvm::sys::PathWithStatus MainFilePath(FrontendOpts.Inputs[0].second);
@@ -734,6 +773,7 @@ ASTUnit *ASTUnit::LoadFromCompilerInvocation(CompilerInvocation *CI,
   AST->CaptureDiagnostics = CaptureDiagnostics;
   AST->OnlyLocalDecls = OnlyLocalDecls;
   AST->Invocation.reset(CI);
+  CI->getPreprocessorOpts().RetainRemappedFileBuffers = true;
   
   llvm::MemoryBuffer *OverrideMainBuffer = 0;
   if (PrecompilePreamble)