[gcc r11-8151] c++: constexpr, inheritance, and local class [PR91933]

[Jason Merrill <jason@gcc.gnu.org>]

https://gcc.gnu.org/g:0851ac6df0596df1e3b640e58094cf94ebb790b8

commit r11-8151-g0851ac6df0596df1e3b640e58094cf94ebb790b8
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Apr 12 17:43:51 2021 -0400

    c++: constexpr, inheritance, and local class [PR91933]
    
    Here we complained about referring to nm3 from the local class member
    function because referring to the base class subobject involved taking the
    variable's address.  Let's shortcut this case to avoid that.
    
    gcc/cp/ChangeLog:
    
            PR c++/91933
            * class.c (build_base_path): Shortcut simple non-pointer case.
    
    gcc/testsuite/ChangeLog:
    
            PR c++/91933
            * g++.dg/cpp0x/constexpr-base7.C: New test.

Diff:
---
 gcc/cp/class.c                               | 13 ++++++++++---
 gcc/testsuite/g++.dg/cpp0x/constexpr-base7.C | 15 +++++++++++++++
 2 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/gcc/cp/class.c b/gcc/cp/class.c
index 4bffec4a707..90b343803a0 100644
--- a/gcc/cp/class.c
+++ b/gcc/cp/class.c
@@ -330,6 +330,15 @@ build_base_path (enum tree_code code,
       return error_mark_node;
     }
 
+  bool uneval = (cp_unevaluated_operand != 0
+		 || processing_template_decl
+		 || in_template_function ());
+
+  /* For a non-pointer simple base reference, express it as a COMPONENT_REF
+     without taking its address (and so causing lambda capture, 91933).  */
+  if (code == PLUS_EXPR && !v_binfo && !want_pointer && !has_empty && !uneval)
+    return build_simple_base_path (expr, binfo);
+
   if (!want_pointer)
     {
       rvalue = !lvalue_p (expr);
@@ -357,9 +366,7 @@ build_base_path (enum tree_code code,
      template (even in instantiate_non_dependent_expr), we don't have vtables
      set up properly yet, and the value doesn't matter there either; we're
      just interested in the result of overload resolution.  */
-  if (cp_unevaluated_operand != 0
-      || processing_template_decl
-      || in_template_function ())
+  if (uneval)
     {
       expr = build_nop (ptr_target_type, expr);
       goto indout;
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-base7.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-base7.C
new file mode 100644
index 00000000000..14e026ec202
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-base7.C
@@ -0,0 +1,15 @@
+// PR c++/91933
+// { dg-do compile { target c++11 } }
+
+struct NoMut1 { int a, b; };
+struct NoMut3 : NoMut1 {
+  constexpr NoMut3(int a, int b) : NoMut1{a, b} {}
+};
+void mutable_subobjects() {
+  constexpr NoMut3 nm3 = {1, 2};
+  struct A {
+    void f() {
+      static_assert(nm3.a == 1, "");
+    }
+  };
+}