From ca37e4fc6c52875fd2dbbf00dac4640288f48b72 Mon Sep 17 00:00:00 2001
From: Ilya Biryukov <ibiryukov@google.com>
Date: Thu, 18 Jan 2018 15:16:53 +0000
Subject: [PATCH] [Frontend] Allow to use PrecompiledPreamble without calling
 CanReuse

Summary:
The new method 'OverridePreamble' allows to override the preamble of
any source file without checking if preamble bounds or dependencies
were changed.

This is used for completion in clangd.

Reviewers: bkramer, sammccall

Reviewed By: sammccall

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D41990

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@322853 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/clang/Frontend/PrecompiledPreamble.h | 22 ++++++++--
 lib/Frontend/PrecompiledPreamble.cpp         | 42 ++++++++++++++------
 2 files changed, 47 insertions(+), 17 deletions(-)

diff --git a/include/clang/Frontend/PrecompiledPreamble.h b/include/clang/Frontend/PrecompiledPreamble.h
index 130fe60704..f1898f573f 100644
--- a/include/clang/Frontend/PrecompiledPreamble.h
+++ b/include/clang/Frontend/PrecompiledPreamble.h
@@ -104,14 +104,22 @@ 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.
+  /// Requires that CanReuse() is true.
+  /// 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;
 
+  /// Configure \p CI to use this preamble.
+  /// Like AddImplicitPreamble, but doesn't assume CanReuse() is true.
+  /// If this preamble does not match the file, it may parse differently.
+  void OverridePreamble(CompilerInvocation &CI,
+                        IntrusiveRefCntPtr<vfs::FileSystem> &VFS,
+                        llvm::MemoryBuffer *MainFileBuffer) const;
+
 private:
   PrecompiledPreamble(PCHStorage Storage, std::vector<char> PreambleBytes,
                       bool PreambleEndsAtStartOfLine,
@@ -222,6 +230,12 @@ private:
     }
   };
 
+  /// Helper function to set up PCH for the preamble into \p CI and \p VFS to
+  /// with the specified \p Bounds.
+  void configurePreamble(PreambleBounds Bounds, CompilerInvocation &CI,
+                         IntrusiveRefCntPtr<vfs::FileSystem> &VFS,
+                         llvm::MemoryBuffer *MainFileBuffer) const;
+
   /// Sets up the PreprocessorOptions and changes VFS, so that PCH stored in \p
   /// Storage is accessible to clang. This method is an implementation detail of
   /// AddImplicitPreamble.
diff --git a/lib/Frontend/PrecompiledPreamble.cpp b/lib/Frontend/PrecompiledPreamble.cpp
index 7e1323fd83..d761f6ee45 100644
--- a/lib/Frontend/PrecompiledPreamble.cpp
+++ b/lib/Frontend/PrecompiledPreamble.cpp
@@ -485,20 +485,15 @@ bool PrecompiledPreamble::CanReuse(const CompilerInvocation &Invocation,
 void PrecompiledPreamble::AddImplicitPreamble(
     CompilerInvocation &CI, IntrusiveRefCntPtr<vfs::FileSystem> &VFS,
     llvm::MemoryBuffer *MainFileBuffer) const {
-  assert(VFS && "VFS must not be null");
-
-  auto &PreprocessorOpts = CI.getPreprocessorOpts();
-
-  // Remap main file to point to MainFileBuffer.
-  auto MainFilePath = CI.getFrontendOpts().Inputs[0].getFile();
-  PreprocessorOpts.addRemappedFile(MainFilePath, MainFileBuffer);
-
-  // Configure ImpicitPCHInclude.
-  PreprocessorOpts.PrecompiledPreambleBytes.first = PreambleBytes.size();
-  PreprocessorOpts.PrecompiledPreambleBytes.second = PreambleEndsAtStartOfLine;
-  PreprocessorOpts.DisablePCHValidation = true;
+  PreambleBounds Bounds(PreambleBytes.size(), PreambleEndsAtStartOfLine);
+  configurePreamble(Bounds, CI, VFS, MainFileBuffer);
+}
 
-  setupPreambleStorage(Storage, PreprocessorOpts, VFS);
+void PrecompiledPreamble::OverridePreamble(
+    CompilerInvocation &CI, IntrusiveRefCntPtr<vfs::FileSystem> &VFS,
+    llvm::MemoryBuffer *MainFileBuffer) const {
+  auto Bounds = ComputePreambleBounds(*CI.getLangOpts(), MainFileBuffer, 0);
+  configurePreamble(Bounds, CI, VFS, MainFileBuffer);
 }
 
 PrecompiledPreamble::PrecompiledPreamble(
@@ -681,6 +676,27 @@ PrecompiledPreamble::PreambleFileHash::createForMemoryBuffer(
   return Result;
 }
 
+void PrecompiledPreamble::configurePreamble(
+    PreambleBounds Bounds, CompilerInvocation &CI,
+    IntrusiveRefCntPtr<vfs::FileSystem> &VFS,
+    llvm::MemoryBuffer *MainFileBuffer) const {
+  assert(VFS);
+
+  auto &PreprocessorOpts = CI.getPreprocessorOpts();
+
+  // Remap main file to point to MainFileBuffer.
+  auto MainFilePath = CI.getFrontendOpts().Inputs[0].getFile();
+  PreprocessorOpts.addRemappedFile(MainFilePath, MainFileBuffer);
+
+  // Configure ImpicitPCHInclude.
+  PreprocessorOpts.PrecompiledPreambleBytes.first = Bounds.Size;
+  PreprocessorOpts.PrecompiledPreambleBytes.second =
+      Bounds.PreambleEndsAtStartOfLine;
+  PreprocessorOpts.DisablePCHValidation = true;
+
+  setupPreambleStorage(Storage, PreprocessorOpts, VFS);
+}
+
 void PrecompiledPreamble::setupPreambleStorage(
     const PCHStorage &Storage, PreprocessorOptions &PreprocessorOpts,
     IntrusiveRefCntPtr<vfs::FileSystem> &VFS) {
-- 
2.40.0