Re: [PATCH] C++: Do not try to re-fold a CONSTRUCTOR in a template [PR126811].

[Jason Merrill]

On 9/12/26 3:08 PM, Iain Sandoe wrote:

Tested on x86_64-linux, x86_64-darwin (where it fixes the ICEs in 14
simd cases).  OK for trunk/backports?

OK.

--- 8< ---

In a similar manner to PR102990, we are encountering a call to fold
an expression in a template where the NSDMI has already been folded
and, as a result, produces expressions which are not handled by the
tsubst machinery.

        PR c++/126811

gcc/cp/ChangeLog:

        * typeck2.cc (store_init_value): Skip folding CONSTRUCTORs
        when handling template decls.

gcc/testsuite/ChangeLog:

        * g++.dg/cpp0x/nsdmi-template27.C: New test.

Signed-off-by: Iain Sandoe <i...@sandoe.co.uk>
---
  gcc/cp/typeck2.cc                             | 11 +++++---
  gcc/testsuite/g++.dg/cpp0x/nsdmi-template27.C | 25 +++++++++++++++++++
  2 files changed, 32 insertions(+), 4 deletions(-)
  create mode 100644 gcc/testsuite/g++.dg/cpp0x/nsdmi-template27.C

diff --git a/gcc/cp/typeck2.cc b/gcc/cp/typeck2.cc
index 62f583dcf40..f0f59b3b1a3 100644
--- a/gcc/cp/typeck2.cc
+++ b/gcc/cp/typeck2.cc
@@ -456,7 +456,7 @@ cxx_incomplete_type_inform (const_tree type)
                    else
                      cand = TYPE_NAME (t);
                  }
-               
+
                if (!COMPLETE_TYPE_P (TREE_TYPE (cand)))
                  continue;

@@ -1076,9 +1076,12 @@ store_init_value (tree decl, tree init, vec<tree, va_gc>** cleanups, int flags)

          || (DECL_IN_AGGR_P (decl)
              && DECL_INITIALIZED_IN_CLASS_P (decl)))
        {
-         value = fold_non_dependent_expr (value, tf_warning_or_error,
-                                          /*manifestly_const_eval=*/true,
-                                          decl);
+         /* As in massage_init_elt, do not fold a CONSTRUCTOR in a template
+            it has already been folded c++/126811.  */
+         if (!(processing_template_decl && TREE_CODE (value) == CONSTRUCTOR))
+           value = fold_non_dependent_expr (value, tf_warning_or_error,
+                                            /*manifestly_const_eval=*/true,
+                                            decl);
          if (value == error_mark_node)
            ;
          /* Diagnose a non-constant initializer for constexpr variable or
diff --git a/gcc/testsuite/g++.dg/cpp0x/nsdmi-template27.C 
b/gcc/testsuite/g++.dg/cpp0x/nsdmi-template27.C
new file mode 100644
index 00000000000..8c2197a7b51
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/nsdmi-template27.C
@@ -0,0 +1,25 @@
+// PR c++/126811
+// { dg-do compile { target c++11 } }
+
+struct M { constexpr M () : x (0) {} int x; };
+
+struct A { double m = 1; };                    // FLOAT_EXPR
+struct B { int m = 1.0; };                     // FIX_TRUNC_EXPR
+struct C { __complex__ double c = 1; };                // COMPLEX_EXPR
+struct D { double a = 1; double m = a; };      // PLACEHOLDER_EXPR
+struct E { M m = M (); };                      // TARGET_EXPR
+
+// The initializers must still be constant-evaluated.
+template<class T> void g ()
+{
+  constexpr A a = {};
+  static_assert (a.m == 1.0, "");
+  constexpr B b = {};
+  static_assert (b.m == 1, "");
+  constexpr C c = {};
+  static_assert (__real__ c.c == 1.0, "");
+  constexpr D d = {};
+  static_assert (d.m == 1.0, "");
+  constexpr E e = {};
+  static_assert (e.m.x == 0, "");
+}