[analyzer] NFC: CallDescription: Implement describing C library functions.

When matching C standard library functions in the checker, it's easy to forget
that they are often implemented as macros that are expanded to builtins.

Such builtins would have a different name, so matching the callee identifier
would fail, or may sometimes have more arguments than expected, so matching
the exact number of arguments would fail, but this is fine as long as we have
all the arguments that we need in their respective places.

This patch adds a set of flags to the CallDescription class so that to handle
various special matching rules, and adds the first flag into this set,
which enables a more fuzzy matching for functions that
may be implemented as compiler builtins.

Differential Revision: https://reviews.llvm.org/D62556

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@364867 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h

@@ -1044,6 +1044,14 @@ public:
   }
 };
 
+enum CallDescriptionFlags : int {
+  /// Describes a C standard function that is sometimes implemented as a macro
+  /// that expands to a compiler builtin with some __builtin prefix.
+  /// The builtin may as well have a few extra arguments on top of the requested
+  /// number of arguments.
+  CDF_MaybeBuiltin = 1 << 0,
+};
+
 /// This class represents a description of a function call using the number of
 /// arguments and the name of the function.
 class CallDescription {
@@ -1055,6 +1063,7 @@ class CallDescription {
   // e.g. "{a, b}" represent the qualified names, like "a::b".
   std::vector<const char *> QualifiedName;
   Optional<unsigned> RequiredArgs;
+  int Flags;
 
 public:
   /// Constructs a CallDescription object.
@@ -1067,9 +1076,15 @@ public:
   /// @param RequiredArgs The number of arguments that is expected to match a
   /// call. Omit this parameter to match every occurrence of call with a given
   /// name regardless the number of arguments.
+  CallDescription(int Flags, ArrayRef<const char *> QualifiedName,
+                  Optional<unsigned> RequiredArgs = None)
+      : QualifiedName(QualifiedName), RequiredArgs(RequiredArgs),
+        Flags(Flags) {}
+
+  /// Construct a CallDescription with default flags.
   CallDescription(ArrayRef<const char *> QualifiedName,
                   Optional<unsigned> RequiredArgs = None)
-      : QualifiedName(QualifiedName), RequiredArgs(RequiredArgs) {}
+      : CallDescription(0, QualifiedName, RequiredArgs) {}
 
   /// Get the name of the function that this object matches.
   StringRef getFunctionName() const { return QualifiedName.back(); }

lib/StaticAnalyzer/Core/CallEvent.cpp

@@ -356,20 +356,32 @@ bool CallEvent::isCalled(const CallDescription &CD) const {
   // FIXME: Add ObjC Message support.
   if (getKind() == CE_ObjCMessage)
     return false;
+
+  const IdentifierInfo *II = getCalleeIdentifier();
+  if (!II)
+    return false;
+  const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(getDecl());
+  if (!FD)
+    return false;
+
+  if (CD.Flags & CDF_MaybeBuiltin) {
+    return CheckerContext::isCLibraryFunction(FD, CD.getFunctionName()) &&
+           (!CD.RequiredArgs || CD.RequiredArgs <= getNumArgs());
+  }
+
   if (!CD.IsLookupDone) {
     CD.IsLookupDone = true;
     CD.II = &getState()->getStateManager().getContext().Idents.get(
         CD.getFunctionName());
   }
-  const IdentifierInfo *II = getCalleeIdentifier();
-  if (!II || II != CD.II)
+
+  if (II != CD.II)
     return false;
 
-  const Decl *D = getDecl();
   // If CallDescription provides prefix names, use them to improve matching
   // accuracy.
-  if (CD.QualifiedName.size() > 1 && D) {
-    const DeclContext *Ctx = D->getDeclContext();
+  if (CD.QualifiedName.size() > 1 && FD) {
+    const DeclContext *Ctx = FD->getDeclContext();
     // See if we'll be able to match them all.
     size_t NumUnmatched = CD.QualifiedName.size() - 1;
     for (; Ctx && isa<NamedDecl>(Ctx); Ctx = Ctx->getParent()) {

unittests/StaticAnalyzer/CallDescriptionTest.cpp

@@ -143,6 +143,18 @@ TEST(CallEvent, CallDescription) {
           {{{"bar", "foo"}}, false},
           {{"foo"}, true},
       }), "void foo(); struct bar { void foo(); }; void test() { foo(); }"));
+
+  // Test CDF_MaybeBuiltin - a flag that allows matching weird builtins.
+  EXPECT_TRUE(tooling::runToolOnCode(
+      new CallDescriptionAction({
+          {{"memset", 3}, false},
+          {{CDF_MaybeBuiltin, "memset", 3}, true}
+      }),
+      "void foo() {"
+      "  int x;"
+      "  __builtin___memset_chk(&x, 0, sizeof(x),"
+      "                         __builtin_object_size(&x, 0));"
+      "}"));
 }
 
 } // namespace