Partially revert Doug's PCH validation patch (r98585).

This patch completely defeated the "passing in a prestat'd size 
to MemoryBuffer" optimization, leading to an extra fstat call for
every buffer opened, in order to find out if the datestamp and size 
of the file on disk matches what is in the stat cache.

I fully admit that I don't completely understand what is going on here:
why punish code when a stat cache isn't in use?  what is the point of a
stat cache if you have to turn around and stat stuff to validate it?

To resolve both these issues, just drop the modtime check and check the
file size, which is the important thing anyway.  This should also resolve
PR6812, because presumably windows is stable when it comes to file sizes.
If the modtime is actually important, we should get it and keep it on the
first stat.

This eliminates 833 fstat syscalls when processing Cocoa.h, speeding up
system time on -Eonly Cocoa.h  from 0.041 to 0.038s.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@120001 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 4 insertions, 14 deletions

diff --git a/lib/Basic/SourceManager.cpp b/lib/Basic/SourceManager.cpp
index 4fa7d1d879..2e47cdc275 100644
--- a/lib/Basic/SourceManager.cpp
+++ b/lib/Basic/SourceManager.cpp
@@ -73,10 +73,9 @@ const llvm::MemoryBuffer *ContentCache::getBuffer(Diagnostic &Diag,
   // Lazily create the Buffer for ContentCaches that wrap files.
   if (!Buffer.getPointer() && Entry) {
     std::string ErrorStr;
-    struct stat FileInfo;
     Buffer.setPointer(SM.getFileManager().getBufferForFile(Entry,
                                                          SM.getFileSystemOpts(),
-                                                         &ErrorStr, &FileInfo));
+                                                         &ErrorStr));
 
     // If we were unable to open the file, then we are in an inconsistent
     // situation where the content cache referenced a file which no longer
@@ -105,17 +104,9 @@ const llvm::MemoryBuffer *ContentCache::getBuffer(Diagnostic &Diag,
 
       Buffer.setInt(Buffer.getInt() | InvalidFlag);
 
-    // FIXME: This conditionalization is horrible, but we see spurious failures
-    // in the test suite due to this warning and no one has had time to hunt it
-    // down. So for now, we just don't emit this diagnostic on Win32, and hope
-    // nothing bad happens.
-    //
-    // PR6812.
-#if !defined(LLVM_ON_WIN32)
-    } else if (FileInfo.st_size != Entry->getSize() ||
-               FileInfo.st_mtime != Entry->getModificationTime()) {
-      // Check that the file's size and modification time are the same
-      // as in the file entry (which may have come from a stat cache).
+    } else if (getRawBuffer()->getBufferSize() != (size_t)Entry->getSize()) {
+      // Check that the file's size is the same as in the file entry (which may
+      // have come from a stat cache).
       if (Diag.isDiagnosticInFlight())
         Diag.SetDelayedDiagnostic(diag::err_file_modified,
                                   Entry->getName());
@@ -124,7 +115,6 @@ const llvm::MemoryBuffer *ContentCache::getBuffer(Diagnostic &Diag,
           << Entry->getName();
 
       Buffer.setInt(Buffer.getInt() | InvalidFlag);
-#endif
     }
     
     // If the buffer is valid, check to see if it has a UTF Byte Order Mark