2 files changed, 31 insertions, 20 deletions

diff --git a/clang/lib/Basic/FileManager.cpp b/clang/lib/Basic/FileManager.cpp
index c0d3685..f3afe6d 100644
--- a/clang/lib/Basic/FileManager.cpp
+++ b/clang/lib/Basic/FileManager.cpp
@@ -489,7 +489,7 @@ FileManager::getBufferForFile(const FileEntry *Entry, bool isVolatile,
   uint64_t FileSize = Entry->getSize();
   // If there's a high enough chance that the file have changed since we
   // got its size, force a stat before opening it.
-  if (isVolatile)
+  if (isVolatile || Entry->isNamedPipe())
     FileSize = -1;
 
   StringRef Filename = Entry->getName();
diff --git a/clang/lib/Basic/SourceManager.cpp b/clang/lib/Basic/SourceManager.cpp
index b71b2be..d2c0de5 100644
--- a/clang/lib/Basic/SourceManager.cpp
+++ b/clang/lib/Basic/SourceManager.cpp
@@ -115,23 +115,6 @@ ContentCache::getBufferOrNone(DiagnosticsEngine &Diag, FileManager &FM,
   // return paths.
   IsBufferInvalid = true;
 
-  // Check that the file's size fits in an 'unsigned' (with room for a
-  // past-the-end value). This is deeply regrettable, but various parts of
-  // Clang (including elsewhere in this file!) use 'unsigned' to represent file
-  // offsets, line numbers, string literal lengths, and so on, and fail
-  // miserably on large source files.
-  if ((uint64_t)ContentsEntry->getSize() >=
-      std::numeric_limits<unsigned>::max()) {
-    if (Diag.isDiagnosticInFlight())
-      Diag.SetDelayedDiagnostic(diag::err_file_too_large,
-                                ContentsEntry->getName());
-    else
-      Diag.Report(Loc, diag::err_file_too_large)
-        << ContentsEntry->getName();
-
-    return None;
-  }
-
   auto BufferOrError = FM.getBufferForFile(ContentsEntry, IsFileVolatile);
 
   // If we were unable to open the file, then we are in an inconsistent
@@ -153,9 +136,31 @@ ContentCache::getBufferOrNone(DiagnosticsEngine &Diag, FileManager &FM,
 
   Buffer = std::move(*BufferOrError);
 
-  // Check that the file's size is the same as in the file entry (which may
+  // Check that the file's size fits in an 'unsigned' (with room for a
+  // past-the-end value). This is deeply regrettable, but various parts of
+  // Clang (including elsewhere in this file!) use 'unsigned' to represent file
+  // offsets, line numbers, string literal lengths, and so on, and fail
+  // miserably on large source files.
+  //
+  // Note: ContentsEntry could be a named pipe, in which case
+  // ContentsEntry::getSize() could have the wrong size. Use
+  // MemoryBuffer::getBufferSize() instead.
+  if (Buffer->getBufferSize() >= std::numeric_limits<unsigned>::max()) {
+    if (Diag.isDiagnosticInFlight())
+      Diag.SetDelayedDiagnostic(diag::err_file_too_large,
+                                ContentsEntry->getName());
+    else
+      Diag.Report(Loc, diag::err_file_too_large)
+        << ContentsEntry->getName();
+
+    return None;
+  }
+
+  // Unless this is a named pipe (in which case we can handle a mismatch),
+  // check that the file's size is the same as in the file entry (which may
   // have come from a stat cache).
-  if (Buffer->getBufferSize() != (size_t)ContentsEntry->getSize()) {
+  if (!ContentsEntry->isNamedPipe() &&
+      Buffer->getBufferSize() != (size_t)ContentsEntry->getSize()) {
     if (Diag.isDiagnosticInFlight())
       Diag.SetDelayedDiagnostic(diag::err_file_modified,
                                 ContentsEntry->getName());
@@ -541,6 +546,12 @@ FileID SourceManager::createFileID(FileEntryRef SourceFile,
                                    int LoadedID, unsigned LoadedOffset) {
   SrcMgr::ContentCache &IR = getOrCreateContentCache(&SourceFile.getFileEntry(),
                                                      isSystem(FileCharacter));
+
+  // If this is a named pipe, immediately load the buffer to ensure subsequent
+  // calls to ContentCache::getSize() are accurate.
+  if (IR.ContentsEntry->isNamedPipe())
+    (void)IR.getBufferOrNone(Diag, getFileManager(), SourceLocation());
+
   return createFileIDImpl(IR, SourceFile.getName(), IncludePos, FileCharacter,
                           LoadedID, LoadedOffset);
 }