C++ PATCH for c++/78244 - narrowing conversion in template not detected

[Marek Polacek]

While looking into 88815, a 9 regression, I realized we'll have to fix 78244
first.  This patch fixes one half of 78244.  The problem was that we never
detected narrowing conversion in a template, because the IMPLICIT_CONV_EXPR
template code doesn't have the information whether it was initialized by a
braced-init-list.  This patch adds such a bit, which works much like
IMPLICIT_CONV_EXPR_DIRECT_INIT.

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

2019-01-16  Marek Polacek  <pola...@redhat.com>

        PR c++/78244 - narrowing conversion in template not detected.
        * call.c (perform_implicit_conversion_flags): Set
        IMPLICIT_CONV_EXPR_BRACED_INIT.
        * cp-tree.h (IMPLICIT_CONV_EXPR_BRACED_INIT): New.
        * pt.c (tsubst_copy_and_build): Use it.

        * g++.dg/cpp0x/Wnarrowing13.C: New test.
        * g++.dg/cpp0x/Wnarrowing14.C: New test.

diff --git gcc/cp/call.c gcc/cp/call.c
index 8bc8566e8d6..4f04b610004 100644
--- gcc/cp/call.c
+++ gcc/cp/call.c
@@ -11018,6 +11018,8 @@ perform_implicit_conversion_flags (tree type, tree expr,
       expr = build1 (IMPLICIT_CONV_EXPR, type, expr);
       if (!(flags & LOOKUP_ONLYCONVERTING))
        IMPLICIT_CONV_EXPR_DIRECT_INIT (expr) = true;
+      if (flags & LOOKUP_NO_NARROWING)
+       IMPLICIT_CONV_EXPR_BRACED_INIT (expr) = true;
     }
   else
     expr = convert_like (conv, expr, complain);
diff --git gcc/cp/cp-tree.h gcc/cp/cp-tree.h
index 6a2004330d2..1c85b37ba7f 100644
--- gcc/cp/cp-tree.h
+++ gcc/cp/cp-tree.h
@@ -442,6 +442,7 @@ extern GTY(()) tree cp_global_trees[CPTI_MAX];
       OVL_HIDDEN_P (in OVERLOAD)
       SWITCH_STMT_NO_BREAK_P (in SWITCH_STMT)
       LAMBDA_EXPR_CAPTURE_OPTIMIZED (in LAMBDA_EXPR)
+      IMPLICIT_CONV_EXPR_BRACED_INIT (in IMPLICIT_CONV_EXPR)
    3: (TREE_REFERENCE_EXPR) (in NON_LVALUE_EXPR) (commented-out).
       ICS_BAD_FLAG (in _CONV)
       FN_TRY_BLOCK_P (in TRY_BLOCK)
@@ -4229,6 +4230,11 @@ more_aggr_init_expr_args_p (const 
aggr_init_expr_arg_iterator *iter)
 #define IMPLICIT_CONV_EXPR_NONTYPE_ARG(NODE) \
   (TREE_LANG_FLAG_1 (IMPLICIT_CONV_EXPR_CHECK (NODE)))
 
+/* True if NODE represents a conversion for braced-init-list in a
+   template.  Set by perform_implicit_conversion_flags.  */
+#define IMPLICIT_CONV_EXPR_BRACED_INIT(NODE) \
+  (TREE_LANG_FLAG_2 (IMPLICIT_CONV_EXPR_CHECK (NODE)))
+
 /* Nonzero means that an object of this type cannot be initialized using
    an initializer list.  */
 #define CLASSTYPE_NON_AGGREGATE(NODE) \
diff --git gcc/cp/pt.c gcc/cp/pt.c
index c6fc1cfeffb..83bceb26474 100644
--- gcc/cp/pt.c
+++ gcc/cp/pt.c
@@ -18210,6 +18210,8 @@ tsubst_copy_and_build (tree t,
        int flags = LOOKUP_IMPLICIT;
        if (IMPLICIT_CONV_EXPR_DIRECT_INIT (t))
          flags = LOOKUP_NORMAL;
+       if (IMPLICIT_CONV_EXPR_BRACED_INIT (t))
+         flags |= LOOKUP_NO_NARROWING;
        RETURN (perform_implicit_conversion_flags (type, expr, complain,
                                                  flags));
       }
diff --git gcc/testsuite/g++.dg/cpp0x/Wnarrowing13.C 
gcc/testsuite/g++.dg/cpp0x/Wnarrowing13.C
new file mode 100644
index 00000000000..3750f293df3
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp0x/Wnarrowing13.C
@@ -0,0 +1,8 @@
+// PR c++/78244
+// { dg-do compile { target c++11 } }
+
+template<typename>
+struct S {
+  static const int i{1.1}; // { dg-error "narrowing conversion" }
+  static const int i2 = {1.1}; // { dg-error "narrowing conversion" }
+};
diff --git gcc/testsuite/g++.dg/cpp0x/Wnarrowing14.C 
gcc/testsuite/g++.dg/cpp0x/Wnarrowing14.C
new file mode 100644
index 00000000000..1aa22196f33
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp0x/Wnarrowing14.C
@@ -0,0 +1,17 @@
+// PR c++/78244
+// { dg-do compile { target c++11 } }
+
+using Number = unsigned int;
+
+template <int>
+struct S {
+  S() {
+    const Number x = {-1}; // { dg-error "narrowing conversion" }
+    (void)x;
+  }
+};
+
+int main()
+{
+  S<1> s;
+}