Index: cfe/trunk/lib/StaticAnalyzer/Checkers/BuiltinFunctionChecker.cpp
===================================================================
--- cfe/trunk/lib/StaticAnalyzer/Checkers/BuiltinFunctionChecker.cpp
+++ cfe/trunk/lib/StaticAnalyzer/Checkers/BuiltinFunctionChecker.cpp
@@ -100,17 +100,25 @@
   case Builtin::BI__builtin_constant_p: {
     // This must be resolvable at compile time, so we defer to the constant
     // evaluator for a value.
+    SValBuilder &SVB = C.getSValBuilder();
     SVal V = UnknownVal();
     Expr::EvalResult EVResult;
     if (CE->EvaluateAsInt(EVResult, C.getASTContext(), Expr::SE_NoSideEffects)) {
       // Make sure the result has the correct type.
       llvm::APSInt Result = EVResult.Val.getInt();
-      SValBuilder &SVB = C.getSValBuilder();
       BasicValueFactory &BVF = SVB.getBasicValueFactory();
       BVF.getAPSIntType(CE->getType()).apply(Result);
       V = SVB.makeIntVal(Result);
     }
 
+    if (FD->getBuiltinID() == Builtin::BI__builtin_constant_p) {
+      // If we didn't manage to figure out if the value is constant or not,
+      // it is safe to assume that it's not constant and unsafe to assume
+      // that it's constant.
+      if (V.isUnknown())
+        V = SVB.makeIntVal(0, CE->getType());
+    }
+
     C.addTransition(state->BindExpr(CE, LCtx, V));
     return true;
   }
Index: cfe/trunk/test/Analysis/builtin-functions.cpp
===================================================================
--- cfe/trunk/test/Analysis/builtin-functions.cpp
+++ cfe/trunk/test/Analysis/builtin-functions.cpp
@@ -65,19 +65,20 @@
   }
 }
 
-void test_constant_p() {
+void test_constant_p(void *ptr) {
   int i = 1;
   const int j = 2;
   constexpr int k = 3;
   clang_analyzer_eval(__builtin_constant_p(42) == 1); // expected-warning {{TRUE}}
-  clang_analyzer_eval(__builtin_constant_p(i) == 0); // expected-warning {{UNKNOWN}}
+  clang_analyzer_eval(__builtin_constant_p(i) == 0); // expected-warning {{TRUE}}
   clang_analyzer_eval(__builtin_constant_p(j) == 1); // expected-warning {{TRUE}}
   clang_analyzer_eval(__builtin_constant_p(k) == 1); // expected-warning {{TRUE}}
-  clang_analyzer_eval(__builtin_constant_p(i + 42) == 0); // expected-warning {{UNKNOWN}}
+  clang_analyzer_eval(__builtin_constant_p(i + 42) == 0); // expected-warning {{TRUE}}
   clang_analyzer_eval(__builtin_constant_p(j + 42) == 1); // expected-warning {{TRUE}}
   clang_analyzer_eval(__builtin_constant_p(k + 42) == 1); // expected-warning {{TRUE}}
   clang_analyzer_eval(__builtin_constant_p(" ") == 1); // expected-warning {{TRUE}}
-  clang_analyzer_eval(__builtin_constant_p(test_constant_p) == 0); // expected-warning {{UNKNOWN}}
+  clang_analyzer_eval(__builtin_constant_p(test_constant_p) == 0); // expected-warning {{TRUE}}
   clang_analyzer_eval(__builtin_constant_p(k - 3) == 0); // expected-warning {{FALSE}}
   clang_analyzer_eval(__builtin_constant_p(k - 3) == 1); // expected-warning {{TRUE}}
+  clang_analyzer_eval(__builtin_constant_p(ptr == 0)); // expected-warning {{FALSE}}
 }