[clang][analyzer] Fix alpha.unix.BlockInCriticalSection

When analyzing C code with function pointers the checker crashes because
of how the implementation extracts IdentifierInfo. Without the fix, this
test crashes.

Add crashing test

Author: gamesh411

clang/lib/StaticAnalyzer/Checkers/BlockInCriticalSectionChecker.cpp

@@ -14,6 +14,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "clang/Analysis/AnalysisDeclContext.h"
 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
 #include "clang/StaticAnalyzer/Core/Checker.h"
@@ -103,9 +104,10 @@ class RAIIMutexDescriptor {
       // this function is called instead of early returning it. To avoid this, a
       // bool variable (IdentifierInfoInitialized) is used and the function will
       // be run only once.
-      Guard = &Call.getCalleeAnalysisDeclContext()->getASTContext().Idents.get(
-          GuardName);
-      IdentifierInfoInitialized = true;
+      if (AnalysisDeclContext *CalleCtx = Call.getCalleeAnalysisDeclContext()) {
+        Guard = &CalleCtx->getASTContext().Idents.get(GuardName);
+        IdentifierInfoInitialized = true;
+      }
     }
   }
 

clang/test/Analysis/block-in-critical-section.c

@@ -0,0 +1,6 @@
+// RUN: %clang_analyze_cc1 -analyzer-checker=core,alpha.unix.BlockInCriticalSection -verify %s
+// expected-no-diagnostics
+
+// This should not crash
+int (*a)(void);
+void b(void) { a(); }