rework the stat cache, pulling it out of FileManager.h into

its own header and giving it some more structure.  No 
functionality change.

llvm-svn: 120030

clang/lib/Basic/FileSystemStatCache.cpp

@@ -0,0 +1,40 @@
+//===--- FileSystemStatCache.cpp - Caching for 'stat' calls ---------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file defines the FileSystemStatCache interface.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Basic/FileSystemStatCache.h"
+#include "llvm/System/Path.h"
+using namespace clang;
+
+MemorizeStatCalls::LookupResult
+MemorizeStatCalls::getStat(const char *Path, struct stat &StatBuf) {
+  LookupResult Result = statChained(Path, StatBuf);
+  
+  // If the chained cache didn't know anything about the file, do the stat now
+  // so we can record the result.
+  if (Result == CacheMiss)
+    Result = ::stat(Path, &StatBuf) ? CacheHitMissing : CacheHitExists;
+  
+  
+  // Do not cache failed stats, it is easy to construct common inconsistent
+  // situations if we do, and they are not important for PCH performance (which
+  // currently only needs the stats to construct the initial FileManager
+  // entries).
+  if (Result == CacheHitMissing)
+    return Result;
+  
+  // Cache file 'stat' results and directories with absolutely paths.
+  if (!S_ISDIR(StatBuf.st_mode) || llvm::sys::Path(Path).isAbsolute())
+    StatCalls[Path] = StatResult(Result, StatBuf);
+  
+  return Result;
+}