[clang][Sema, Lex, Parse] Preprocessor embed in C and C++ (and Obj-C and Obj-C++ by-proxy) (#68620)

This commit implements the entirety of the now-accepted [N3017 -
Preprocessor
Embed](https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3017.htm) and
its sister C++ paper [p1967](https://wg21.link/p1967). It implements
everything in the specification, and includes an implementation that
drastically improves the time it takes to embed data in specific
scenarios (the initialization of character type arrays). The mechanisms
used to do this are used under the "as-if" rule, and in general when the
system cannot detect it is initializing an array object in a variable
declaration, will generate EmbedExpr AST node which will be expanded
by AST consumers (CodeGen or constant expression evaluators) or
expand embed directive as a comma expression.

---------

Co-authored-by: Aaron Ballman <aaron@aaronballman.com>
Co-authored-by: cor3ntin <corentinjabot@gmail.com>
Co-authored-by: H. Vetinari <h.vetinari@gmx.com>
Co-authored-by: Podchishchaeva, Mariya <mariya.podchishchaeva@intel.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/clang/lib/Basic/FileManager.cpp b/clang/lib/Basic/FileManager.cpp
index 1dc51de..4509cee 100644
--- a/clang/lib/Basic/FileManager.cpp
+++ b/clang/lib/Basic/FileManager.cpp
@@ -530,13 +530,18 @@ void FileManager::fillRealPathName(FileEntry *UFE, llvm::StringRef FileName) {
 
 llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>>
 FileManager::getBufferForFile(FileEntryRef FE, bool isVolatile,
-                              bool RequiresNullTerminator) {
+                              bool RequiresNullTerminator,
+                              std::optional<int64_t> MaybeLimit) {
   const FileEntry *Entry = &FE.getFileEntry();
   // If the content is living on the file entry, return a reference to it.
   if (Entry->Content)
     return llvm::MemoryBuffer::getMemBuffer(Entry->Content->getMemBufferRef());
 
   uint64_t FileSize = Entry->getSize();
+
+  if (MaybeLimit)
+    FileSize = *MaybeLimit;
+
   // 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 || Entry->isNamedPipe())