PR c++/89576 - if constexpr of lambda capture.

Now that we're doing implicit lambda capture in templates, we see x here as
the lambda capture.  maybe_convert_cond was doing nothing in a template, so
we never called mark_rvalue_use on x.  As part of the broad move toward
doing more processing of non-dependent expressions, let's do this
conversion.

	* semantics.c (maybe_convert_cond): Do convert a non-dependent
	condition in a template.
	* typeck.c (condition_conversion): Handle being called in a
	template.

From-SVN: r269433

gcc/cp/ChangeLog

+2019-03-06  Jason Merrill  <jason@redhat.com>
+
+	PR c++/89576 - if constexpr of lambda capture.
+	* semantics.c (maybe_convert_cond): Do convert a non-dependent
+	condition in a template.
+	* typeck.c (condition_conversion): Handle being called in a
+	template.
+
 2019-03-06  Marek Polacek  <polacek@redhat.com>
 
 	PR c++/87378 - bogus -Wredundant-move warning.

gcc/cp/semantics.c

@@ -646,10 +646,10 @@ maybe_convert_cond (tree cond)
     return NULL_TREE;
 
   /* Wait until we instantiate templates before doing conversion.  */
-  if (processing_template_decl)
+  if (type_dependent_expression_p (cond))
     return cond;
 
-  if (warn_sequence_point)
+  if (warn_sequence_point && !processing_template_decl)
     verify_sequence_points (cond);
 
   /* Do the conversion.  */

gcc/cp/typeck.c

@@ -5867,17 +5867,16 @@ cp_truthvalue_conversion (tree expr)
     return c_common_truthvalue_conversion (input_location, expr);
 }
 
-/* Just like cp_truthvalue_conversion, but we want a CLEANUP_POINT_EXPR.  */
+/* Just like cp_truthvalue_conversion, but we want a CLEANUP_POINT_EXPR.  This
+   is a low-level function; most callers should use maybe_convert_cond.  */
 
 tree
 condition_conversion (tree expr)
 {
   tree t;
-  /* Anything that might happen in a template should go through
-     maybe_convert_cond.  */
-  gcc_assert (!processing_template_decl);
   t = perform_implicit_conversion_flags (boolean_type_node, expr,
 					 tf_warning_or_error, LOOKUP_NORMAL);
+  if (!processing_template_decl)
     t = fold_build_cleanup_point_expr (boolean_type_node, t);
   return t;
 }

gcc/testsuite/g++.dg/cpp1z/constexpr-if15.C

@@ -7,5 +7,5 @@ constexpr int foo (int) { return 2; }
 template <typename>
 void a()
 {
-  if constexpr(foo) { };
+  if constexpr(foo) { };	// { dg-error "overloaded" }
 }

gcc/testsuite/g++.dg/cpp1z/constexpr-if28.C

+// PR c++/89576
+// { dg-do compile { target c++17 } }
+
+template <class T>
+void foo()
+{
+    constexpr int x = 0;
+    [&] {
+        if constexpr (x) {}
+    };
+}