[PCH] Fixed preamble breaking with BOM presence (and particularly, fluctuating BOM presence)

This patch fixes broken preamble-skipping when the preamble region includes a byte order mark (BOM). Previously, parsing would fail if preamble PCH generation was enabled and a BOM was present.

This also fixes preamble invalidation when a BOM appears or disappears. This may seem to be an obscure edge case, but it happens regularly with IDEs that pass buffer overrides that never (or always) have a BOM, yet the underlying file from the initial parse that generated a PCH might (or might not) have a BOM.

I've included a test case for these scenarios.

Differential Revision: https://reviews.llvm.org/D37491

llvm-svn: 313796

2 files changed, 2 insertions, 3 deletions

diff --git a/clang/lib/Frontend/FrontendActions.cpp b/clang/lib/Frontend/FrontendActions.cpp
index 3e3483d2c6b..86460f17d0f 100644
--- a/clang/lib/Frontend/FrontendActions.cpp
+++ b/clang/lib/Frontend/FrontendActions.cpp
@@ -591,7 +591,7 @@ void PrintPreambleAction::ExecuteAction() {
   auto Buffer = CI.getFileManager().getBufferForFile(getCurrentFile());
   if (Buffer) {
     unsigned Preamble =
-        Lexer::ComputePreamble((*Buffer)->getBuffer(), CI.getLangOpts()).first;
+        Lexer::ComputePreamble((*Buffer)->getBuffer(), CI.getLangOpts()).Size;
     llvm::outs().write((*Buffer)->getBufferStart(), Preamble);
   }
 }
diff --git a/clang/lib/Frontend/PrecompiledPreamble.cpp b/clang/lib/Frontend/PrecompiledPreamble.cpp
index cd7446189cc..bd6770acdff 100644
--- a/clang/lib/Frontend/PrecompiledPreamble.cpp
+++ b/clang/lib/Frontend/PrecompiledPreamble.cpp
@@ -195,8 +195,7 @@ template <class T> bool moveOnNoError(llvm::ErrorOr<T> Val, T &Output) {
 PreambleBounds clang::ComputePreambleBounds(const LangOptions &LangOpts,
                                             llvm::MemoryBuffer *Buffer,
                                             unsigned MaxLines) {
-  auto Pre = Lexer::ComputePreamble(Buffer->getBuffer(), LangOpts, MaxLines);
-  return PreambleBounds(Pre.first, Pre.second);
+  return Lexer::ComputePreamble(Buffer->getBuffer(), LangOpts, MaxLines);
 }
 
 llvm::ErrorOr<PrecompiledPreamble> PrecompiledPreamble::Build(