PR c++/79533 - C++17 ICE with temporary cast to reference

	* call.c (build_over_call): Conversion to a reference prevents copy
	elision.

From-SVN: r245538

gcc/cp/ChangeLog

+2017-02-17  Jason Merrill  <jason@redhat.com>
+
+	PR c++/79533 - C++17 ICE with temporary cast to reference
+	* call.c (build_over_call): Conversion to a reference prevents copy
+	elision.
+
 2017-02-16  Jakub Jelinek  <jakub@redhat.com>
 	    Jason Merrill  <jason@redhat.com>
 

gcc/cp/call.c

@@ -7955,7 +7955,14 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
 
       /* Pull out the real argument, disregarding const-correctness.  */
       targ = arg;
-      while (CONVERT_EXPR_P (targ)
+      /* Strip the reference binding for the constructor parameter.  */
+      if (CONVERT_EXPR_P (targ)
+	  && TREE_CODE (TREE_TYPE (targ)) == REFERENCE_TYPE)
+	targ = TREE_OPERAND (targ, 0);
+      /* But don't strip any other reference bindings; binding a temporary to a
+	 reference prevents copy elision.  */
+      while ((CONVERT_EXPR_P (targ)
+	      && TREE_CODE (TREE_TYPE (targ)) != REFERENCE_TYPE)
 	     || TREE_CODE (targ) == NON_LVALUE_EXPR)
 	targ = TREE_OPERAND (targ, 0);
       if (TREE_CODE (targ) == ADDR_EXPR)

gcc/testsuite/g++.dg/init/elide6.C

+// PR c++/79533
+
+struct S {
+  S();
+  S(const S&);
+};
+S f();
+S s(static_cast<S const &>(f()));
+
+// The static_cast prevents copy elision.
+// { dg-final { scan-assembler "_ZN1SC1ERKS_" } }