[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

1 files changed, 3 insertions, 3 deletions

diff --git a/clang/lib/Lex/Preprocessor.cpp b/clang/lib/Lex/Preprocessor.cpp
index e1294994df5..1f9a469bc59 100644
--- a/clang/lib/Lex/Preprocessor.cpp
+++ b/clang/lib/Lex/Preprocessor.cpp
@@ -516,9 +516,9 @@ void Preprocessor::EnterMainSourceFile() {
     // If we've been asked to skip bytes in the main file (e.g., as part of a
     // precompiled preamble), do so now.
     if (SkipMainFilePreamble.first > 0)
-      CurLexer->SkipBytes(SkipMainFilePreamble.first, 
-                          SkipMainFilePreamble.second);
-    
+      CurLexer->SetByteOffset(SkipMainFilePreamble.first,
+                              SkipMainFilePreamble.second);
+
     // Tell the header info that the main file was entered.  If the file is later
     // #imported, it won't be re-entered.
     if (const FileEntry *FE = SourceMgr.getFileEntryForID(MainFileID))