[analyzer] Only attempt to get the value of locations of known type

[george.karpenkov]

Summary

Fixes https://bugs.llvm.org/show_bug.cgi?id=36474

In general, getSVal API should be changed so that it does not crash on some non-obvious conditions.
It should either be updated to require a type, or to return Optional<SVal>.

[NoQ]

lib/StaticAnalyzer/Checkers/NonnullGlobalConstantsChecker.cpp

78 ↗

(On Diff #136027)

Pls explain why it would work correctly now?

test/Analysis/novoidtypecrash.c

1 ↗

(On Diff #136027)

Add -verify just in case someone wants to add more checks into this file and doesn't notice that they don't fail before the patch?

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

 void NonnullGlobalConstantsChecker::checkLocation(SVal location, bool isLoad,
                                                  const Stmt *S,
                                                  CheckerContext &C) const {
   initIdentifierInfo(C.getASTContext());
   if (!isLoad || !location.isValid())
     return;
 
   ProgramStateRef State = C.getState();
-  SVal V = State->getSVal(location.castAs<Loc>());
 
   if (isGlobalConstString(location)) {
+    SVal V = State->getSVal(location.castAs<Loc>());
     Optional<DefinedOrUnknownSVal> Constr = V.getAs<DefinedOrUnknownSVal>();
 
     if (Constr) {
 
       // Assume that the variable is non-null.
       ProgramStateRef OutputState = State->assume(*Constr, true);
       C.addTransition(OutputState);
     }

cfe/trunk/test/Analysis/novoidtypecrash.c

+// RUN: %clang_analyze_cc1 -analyzer-checker=core %s
+a;
+b(void **c) { // no-crash
+  *c = a;
+  int *d;
+  b(&d);
+  *d;
+}