[clang] Add tests for statement expression in initializers

The commit 683e83c5
  [Clang][C++2b] P2242R3: Non-literal variables [...] in constexpr
fixed a code generation bug when using (C-extension) statement
expressions inside initializer expressions.

Before that commit a nested static initializer inside the statement
expression would not be emitted, causing it to be zero initialized.

It is a bit surprising (at least to me) that a commit implementing a new
C++ feature would fix this code generation bug. Zooming in it is the
change done in ExprConstant.cpp that helps. That changes so that
"ESR_Failed" is returned in more cases, causing the expression to not be
deemed constant. This fixes the code generation as instead the compiler
has to resort to generating a dynamic initializer.

That commit also meant that some statement expressions (in particular
the ones using static variables) that previously were accepted now are
errors due to not being constant (matching GCC behavior).

Given how a seemingly unrelated change caused this behavior to change,
it is probably a good thing to add at least some rudimentary tests for
these kind expressions.

Differential Revision: https://reviews.llvm.org/D127201

clang/docs/ReleaseNotes.rst

@@ -170,6 +170,11 @@ Bug Fixes
   fixes `Issue 48230 <https://github.com/llvm/llvm-project/issues/48230>`_.
 - Fixed memory leak due to ``VarTemplateSpecializationDecl`` using
   ``TemplateArgumentListInfo`` instead of ``ASTTemplateArgumentListInfo``.
+- An initializer for a static variable declaration, which is nested
+  inside a statement expression in an aggregate initializer, is now
+  emitted as a dynamic initializer. Previously the variable would
+  incorrectly be zero-initialized. In contexts where a dynamic
+  initializer is not allowed this is now diagnosed as an error.
 
 Improvements to Clang's diagnostics
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/test/CodeGen/stmtexpr-init.c

@@ -0,0 +1,37 @@
+// RUN: %clang_cc1 %s -emit-llvm -o - | FileCheck %s
+
+void escape(const void *);
+
+// CHECK-DAG: internal global i8 99
+
+void T1(void) {
+  const char *x[1] = {({static char _x = 99; &_x; })};
+  escape(x);
+}
+
+struct sized_array {
+  int count;
+  int entries[];
+};
+
+#define N_ARGS(...) (sizeof((int[]){__VA_ARGS__}) / sizeof(int))
+
+#define ARRAY_PTR(...) ({                                                    \
+  static const struct sized_array _a = {N_ARGS(__VA_ARGS__), {__VA_ARGS__}}; \
+  &_a;                                                                       \
+})
+
+struct outer {
+  const struct sized_array *a;
+};
+
+void T2(void) {
+  // CHECK-DAG: internal constant { i32, [2 x i32] } { i32 2, [2 x i32] [i32 50, i32 60] }
+  const struct sized_array *A = ARRAY_PTR(50, 60);
+
+  // CHECK-DAG: internal constant { i32, [3 x i32] } { i32 3, [3 x i32] [i32 10, i32 20, i32 30] }
+  struct outer X = {ARRAY_PTR(10, 20, 30)};
+
+  escape(A);
+  escape(&X);
+}

clang/test/Sema/stmtexpr-init.c

@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -verify -fsyntax-only %s
+
+static int *z[1] = {({ static int _x = 70; &_x; })}; // expected-error {{statement expression not allowed at file scope}}
+
+void T1(void) {
+  int *x[1] = {({ static int _x = 10; &_x; })}; // expected-no-error
+
+  /* Before commit
+     683e83c5 [Clang][C++2b] P2242R3: Non-literal variables [...] in constexpr
+     (i.e in clang-14 and earlier)
+     this was silently accepted, but generated incorrect code.
+  */
+  static int *y[1] = {({ static int _x = 20; &_x; })}; // expected-error {{initializer element is not a compile-time constant}}
+}