[StaticAnalyzer] Fix FP in UnreachableCodeChecker

[danielmarjamaki]

Summary

This fixes a FP. Without the fix, the checker says that "static int x;" is unreachable.

[xazax.hun]

LGTM!

cfe/trunk/lib/StaticAnalyzer/Checkers/UnreachableCodeChecker.cpp

for (CFG::const_iterator I = C->begin(), E = C->end(); I != E; ++I) {
     if (!visited.count(CB->getBlockID()))
       FindUnreachableEntryPoints(CB, reachable, visited);
 
     // This block may have been pruned; check if we still want to report it
     if (reachable.count(CB->getBlockID()))
       continue;
 
     // Check for false positives
-    if (CB->size() > 0 && isInvalidPath(CB, *PM))
+    if (isInvalidPath(CB, *PM))
       continue;
 
     // It is good practice to always have a "default" label in a "switch", even
     // if we should never get there. It can be used to detect errors, for
     // instance. Unreachable code directly under a "default" label is therefore
     // likely to be a false positive.
     if (const Stmt *label = CB->getLabel())
       if (label->getStmtClass() == Stmt::DefaultStmtClass)

cfe/trunk/test/Analysis/unreachable-code-path.c

 }
 
 // Don't warn in a macro
 #define RETURN(X)  do { return; } while (0)
 void macro(void) {
   RETURN(1); // no-warning
 }
 
+// Avoid FP when macro argument is known
+void writeSomething(int *x);
+#define MACRO(C)        \
+  if (!C) {             \
+    static int x;       \
+    writeSomething(&x); \
+  }
+void macro2(void) {
+  MACRO(1);
+}