The stat cache became essentially useless ever since we started
validating all file entries in the PCH.
But the motivating reason for removing it now is that it also affected
correctness in this situation:
-You have a header without include guards (using "#pragma once" or #import)
-When creating the PCH:
-The same header is referenced in an #include with different filename cases.
-In the PCH, of course, we record only one file entry for the header file
-But we cache in the PCH file the stat info for both filename cases
-Then the source files are updated and the header file is updated in a way that
its size and modification time are the same but its inode changes
-When using the PCH:
-We validate the headers, we check that header file and we create a file entry with its current inode
-There's another #include with a filename with different case than the previously created file entry
-In order to get its stat info we go through the cached stat info of the PCH and we receive the old inode
-because of the different inodes, we think they are different files so we go ahead and include its contents.
Removing the stat cache will potentially break clients that are attempting to use the stat cache
as a way of avoiding having the actual input files available. If that use case is important, patches are welcome
to bring it back in a way that will actually work correctly (i.e., emit a PCH that is self-contained, coping with
literal strings, line/column computations, etc.).
This fixes rdar://5502805
llvm-svn: 167172
Argyrios Kyrtzidis