[PATCH] c++: ICE with IMPLICIT_CONV_EXPR in array subscript [PR95508]

[Marek Polacek via Gcc-patches]

Since r10-7096 convert_like, when called in a template, creates an
IMPLICIT_CONV_EXPR when we're converting to/from array type.

In this test, we have e[f], and we're converting f (of type class A) to
int, so convert_like in build_new_op_1 created the IMPLICIT_CONV_EXPR
that got into cp_build_array_ref which calls maybe_constant_value.  My
patch above failed to adjust this spot to call fold_non_dependent_expr
instead, which can handle codes like I_C_E in a template.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/10?

gcc/cp/ChangeLog:

        PR c++/95508
        * typeck.c (cp_build_array_ref): Call fold_non_dependent_expr instead
        of maybe_constant_value.

gcc/testsuite/ChangeLog:

        PR c++/95508
        * g++.dg/template/conv16.C: New test.
---
 gcc/cp/typeck.c                        |  2 +-
 gcc/testsuite/g++.dg/template/conv16.C | 17 +++++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/template/conv16.C

diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
index f01ae656254..07144d4c1fc 100644
--- a/gcc/cp/typeck.c
+++ b/gcc/cp/typeck.c
@@ -3565,7 +3565,7 @@ cp_build_array_ref (location_t loc, tree array, tree idx,
         pointer arithmetic.)  */
       idx = cp_perform_integral_promotions (idx, complain);
 
-      idx = maybe_constant_value (idx);
+      idx = fold_non_dependent_expr (idx, complain);
 
       /* An array that is indexed by a non-constant
         cannot be stored in a register; we must be able to do
diff --git a/gcc/testsuite/g++.dg/template/conv16.C 
b/gcc/testsuite/g++.dg/template/conv16.C
new file mode 100644
index 00000000000..c0843efdf9d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/conv16.C
@@ -0,0 +1,17 @@
+// PR c++/95508
+// { dg-do compile }
+
+template <typename>
+struct A;
+template <typename>
+struct B {
+  operator int () { return 0; }
+};
+template <>
+struct A<unsigned> : B<int> {};
+struct D {
+  template <typename>
+  int foo () { return e[f]; }
+  int e[6];
+  A<unsigned> f;
+};

base-commit: a2c2cee92e5defff9bf23d3b1184ee96e57e5fdd
-- 
Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA