Skip NonNull sema checks in unevaluated contexts.

Summary:
Currently when a function annotated with __attribute__((nonnull)) is called in an unevaluated context with a null argument a -Wnonnull warning is emitted. 
This warning seems like a false positive unless the call expression is potentially evaluated. Change this behavior so that the non-null warnings use DiagRuntimeBehavior so they wont emit when they won't be evaluated.

Reviewers: majnemer, rsmith

Subscribers: mclow.lists, cfe-commits

Differential Revision: http://reviews.llvm.org/D13408

llvm-svn: 249787

clang/lib/Sema/SemaChecking.cpp

@@ -1151,7 +1151,8 @@ static void CheckNonNullArgument(Sema &S,
                                  const Expr *ArgExpr,
                                  SourceLocation CallSiteLoc) {
   if (CheckNonNullExpr(S, ArgExpr))
-    S.Diag(CallSiteLoc, diag::warn_null_arg) << ArgExpr->getSourceRange();
+    S.DiagRuntimeBehavior(CallSiteLoc, ArgExpr,
+           S.PDiag(diag::warn_null_arg) << ArgExpr->getSourceRange());
 }
 
 bool Sema::GetFormatNSStringIdx(const FormatAttr *Format, unsigned &Idx) {

clang/test/Sema/non-null-warning.c

@@ -37,6 +37,9 @@ int * ret_nonnull() {
   return 0; // expected-warning {{null returned from function that requires a non-null return value}}
 }
 
+#define SAFE_CALL(X) if (X) foo(X)
 int main () {
   foo(0); // expected-warning {{null passed to a callee that requires a non-null argument}}
+  (void)sizeof(foo(0)); // expect no diagnostic in unevaluated context.
+  SAFE_CALL(0); // expect no diagnostic for unreachable code.
 }