[analyzer] RetainCount: Allow offsets in return values.

Because RetainCountChecker has custom "local" reasoning about escapes,
it has a separate facility to deal with tracked symbols at end of analysis
and check them for leaks regardless of whether they're dead or not.
This facility iterates over the list of tracked symbols and reports
them as leaks, but it needs to treat the return value specially.

Some custom allocators tend to return the value with an offset, storing
extra metadata at the beginning of the buffer. In this case the return value
would be a non-base region. In order to avoid false positives, we still need to
find the original symbol within the return value, otherwise it'll be unable
to match it to the item in the list of tracked symbols.

Differential Revision: https://reviews.llvm.org/D60991

llvm-svn: 359263

clang/lib/StaticAnalyzer/Checkers/RetainCountChecker/RetainCountChecker.cpp

@@ -970,8 +970,10 @@ ExplodedNode * RetainCountChecker::processReturn(const ReturnStmt *S,
     return Pred;
 
   ProgramStateRef state = C.getState();
-  SymbolRef Sym =
-    state->getSValAsScalarOrLoc(RetE, C.getLocationContext()).getAsLocSymbol();
+  // We need to dig down to the symbolic base here because various
+  // custom allocators do sometimes return the symbol with an offset.
+  SymbolRef Sym = state->getSValAsScalarOrLoc(RetE, C.getLocationContext())
+                      .getAsLocSymbol(/*IncludeBaseRegions=*/true);
   if (!Sym)
     return Pred;
 

clang/test/Analysis/retain-release.mm

@@ -515,3 +515,35 @@ void foo() {
 }
 
 }
+
+namespace reinterpret_casts {
+
+void *foo() {
+  void *p = const_cast<void *>(
+      reinterpret_cast<const void *>(CFArrayCreate(0, 0, 0, 0)));
+  void *q = reinterpret_cast<void *>(
+      reinterpret_cast<char *>(p) + 1);
+  // FIXME: Should warn about a leak here. The function should return at +0,
+  // but it returns at +1 instead.
+  return q;
+}
+
+void *fooCreate() {
+  void *p = const_cast<void *>(
+      reinterpret_cast<const void *>(CFArrayCreate(0, 0, 0, 0)));
+  void *q = reinterpret_cast<void *>(
+      reinterpret_cast<char *>(p) + 1);
+  // The function follows the Create Rule.
+  return q; // no-warning
+}
+
+void *fooBar() CF_RETURNS_RETAINED {
+  void *p = const_cast<void *>(
+      reinterpret_cast<const void *>(CFArrayCreate(0, 0, 0, 0)));
+  void *q = reinterpret_cast<void *>(
+      reinterpret_cast<char *>(p) + 1);
+  // The function follows the Create Rule.
+  return q; // no-warning
+}
+
+}