[analyzer] Be less pessimistic about invalidation of global variables

as a result of a call.

Problem:
Global variables, which come in from system libraries should not be
invalidated by all calls. Also, non-system globals should not be
invalidated by system calls.

Solution:
The following solution to invalidation of globals seems flexible enough
for taint (does not invalidate stdin) and should not lead to too
many false positives. We split globals into 3 classes:

* immutable - values are preserved by calls (unless the specific
global is passed in as a parameter):
     A :  Most system globals and const scalars

* invalidated by functions defined in system headers:
     B: errno

* invalidated by all other functions (note, these functions may in
turn contain system calls):
     B: errno
     C: all other globals (which are not in A nor B)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@147569 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 10 insertions, 0 deletions

diff --git a/test/Analysis/system-header-simulator.h b/test/Analysis/system-header-simulator.h
new file mode 100644
index 0000000000..68c66574df
--- /dev/null
+++ b/test/Analysis/system-header-simulator.h
@@ -0,0 +1,10 @@
+#pragma clang system_header
+
+typedef struct _FILE FILE;
+extern FILE *stdin;
+int fscanf(FILE *restrict stream, const char *restrict format, ...);
+
+// Note, on some platforms errno macro gets replaced with a function call.
+extern int errno;
+
+unsigned long strlen(const char *);