[Sema] Fix -Wuninitialized for struct assignment from GNU C statement expression

Summary:
Do not automatically report self references of structs in statement expression
as warnings. Instead wait for uninitialized cfg analysis.
https://bugs.llvm.org/show_bug.cgi?id=42604

Reviewers: aaron.ballman, rsmith, nickdesaulniers

Reviewed By: aaron.ballman, nickdesaulniers

Subscribers: nathanchance, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D64678

llvm-svn: 367134

clang/lib/Sema/SemaDecl.cpp

@@ -11257,9 +11257,12 @@ void Sema::AddInitializerToDecl(Decl *RealDecl, Expr *Init, bool DirectInit) {
   // Check for self-references within variable initializers.
   // Variables declared within a function/method body (except for references)
   // are handled by a dataflow analysis.
-  if (!VDecl->hasLocalStorage() || VDecl->getType()->isRecordType() ||
-      VDecl->getType()->isReferenceType()) {
-    CheckSelfReference(*this, RealDecl, Init, DirectInit);
+  // This is undefined behavior in C++, but valid in C.
+  if (getLangOpts().CPlusPlus) {
+    if (!VDecl->hasLocalStorage() || VDecl->getType()->isRecordType() ||
+        VDecl->getType()->isReferenceType()) {
+      CheckSelfReference(*this, RealDecl, Init, DirectInit);
+    }
   }
 
   // If the type changed, it means we had an incomplete type that was

clang/test/Sema/warn-uninitialized-statement-expression.c

@@ -0,0 +1,56 @@
+// RUN: %clang_cc1 -fsyntax-only -Wuninitialized -verify %s
+
+void init(int *);
+
+void foo(void) {
+  int i = ({
+    init(&i);
+    i;
+  });
+}
+
+void foo_bad(void) {
+  int i = ({
+    int z = i; // expected-warning{{variable 'i' is uninitialized when used within its own initialization}}
+    init(&i);
+    i;
+  });
+}
+
+struct widget {
+  int x, y;
+};
+void init2(struct widget *);
+
+void bar(void) {
+  struct widget my_widget = ({
+    init2(&my_widget);
+    my_widget;
+  });
+  struct widget a = (init2(&a), a);
+}
+
+void bar_bad(void) {
+  struct widget my_widget = ({
+    struct widget z = my_widget; // expected-warning{{variable 'my_widget' is uninitialized when used within its own initialization}}
+    int x = my_widget.x;         //FIXME: There should be an uninitialized warning here
+    init2(&my_widget);
+    my_widget;
+  });
+}
+
+void baz(void) {
+  struct widget a = ({
+    struct widget b = ({
+      b = a; // expected-warning{{variable 'a' is uninitialized when used within its own initialization}}
+    });
+    a;
+  });
+}
+
+void f(void) {
+  struct widget *a = ({
+    init2(a); // expected-warning{{variable 'a' is uninitialized when used within its own initialization}}
+    a;
+  });
+}