Constant expression evaluation: although we don't know whether a literal will

be at the same address as another object, we do know it won't alias a null
pointer.

llvm-svn: 143674

clang/lib/AST/ExprConstant.cpp

@@ -1970,8 +1970,10 @@ bool IntExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) {
           return false;
         // It's implementation-defined whether distinct literals will have
         // distinct addresses. In clang, we do not guarantee the addresses are
-        // distinct.
-        if (IsLiteralLValue(LHSValue) || IsLiteralLValue(RHSValue))
+        // distinct. However, we do know that the address of a literal will be
+        // non-null.
+        if ((IsLiteralLValue(LHSValue) || IsLiteralLValue(RHSValue)) &&
+            LHSValue.Base && RHSValue.Base)
           return false;
         // We can't tell whether weak symbols will end up pointing to the same
         // object.

clang/test/Sema/const-eval.c

@@ -99,3 +99,6 @@ char c = ((union u)(123456)).b[0]; // expected-error {{not a compile-time consta
 extern const int weak_int __attribute__((weak));
 const int weak_int = 42;
 int weak_int_test = weak_int; // expected-error {{not a compile-time constant}}
+
+int literalVsNull1 = "foo" == 0;
+int literalVsNull2 = 0 == "foo";