Frontend: Sink named pipe logic from CompilerInstance down to FileManager

Remove compilicated logic from CompilerInstance::InitializeSourceManager
to deal with named pipes, updating FileManager::getBufferForFile to
handle it in a more straightforward way. The existing test at
clang/test/Misc/dev-fd-fs.c covers the new behaviour (just like it did
the old behaviour).

Differential Revision: https://reviews.llvm.org/D90733

Author: dexonsmith

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();

clang/lib/Frontend/CompilerInstance.cpp

@@ -858,30 +858,8 @@ bool CompilerInstance::InitializeSourceManager(const FrontendInputFile &Input,
     }
     FileEntryRef File = *FileOrErr;
 
-    // The natural SourceManager infrastructure can't currently handle named
-    // pipes, but we would at least like to accept them for the main
-    // file. Detect them here, read them with the volatile flag so FileMgr will
-    // pick up the correct size, and simply override their contents as we do for
-    // STDIN.
-    if (File.getFileEntry().isNamedPipe()) {
-      auto MB =
-          FileMgr.getBufferForFile(&File.getFileEntry(), /*isVolatile=*/true);
-      if (MB) {
-        // Create a new virtual file that will have the correct size.
-        const FileEntry *FE =
-            FileMgr.getVirtualFile(InputFile, (*MB)->getBufferSize(), 0);
-        SourceMgr.overrideFileContents(FE, std::move(*MB));
-        SourceMgr.setMainFileID(
-            SourceMgr.createFileID(FE, SourceLocation(), Kind));
-      } else {
-        Diags.Report(diag::err_cannot_open_file) << InputFile
-                                                 << MB.getError().message();
-        return false;
-      }
-    } else {
-      SourceMgr.setMainFileID(
-          SourceMgr.createFileID(File, SourceLocation(), Kind));
-    }
+    SourceMgr.setMainFileID(
+        SourceMgr.createFileID(File, SourceLocation(), Kind));
   } else {
     llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> SBOrErr =
         llvm::MemoryBuffer::getSTDIN();