C++ PATCH for c++/84938, ICE dividing by ~-1

[Jason Merrill]

set_up_extended_ref_temp does an abbreviated version of
cp_finish_decl, which didn't include the call to cp_fully_fold that
store_init_value does for user-declared variables.  Adding that fixes
this bug.

Tested x86_64-pc-linux-gnu, applying to trunk.

commit 03b96c95fd7b27fa99964741bd9cb771ad56c882
Author: Jason Merrill <ja...@redhat.com>
Date:   Wed Apr 4 17:18:28 2018 -0400

            PR c++/84938 - ICE with division by ~-1.
    
            * call.c (set_up_extended_ref_temp): Call cp_fully_fold.

diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index f81773157b6..7c99e8ad910 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -10869,6 +10869,8 @@ set_up_extended_ref_temp (tree decl, tree expr, vec<tree, va_gc> **cleanups,
   /* If the initializer is constant, put it in DECL_INITIAL so we get
      static initialization and use in constant expressions.  */
   init = maybe_constant_init (expr);
+  /* As in store_init_value.  */
+  init = cp_fully_fold (init);
   if (TREE_CONSTANT (init))
     {
       if (literal_type_p (type) && CP_TYPE_CONST_NON_VOLATILE_P (type))
diff --git a/gcc/testsuite/g++.dg/expr/div-by-zero1.C b/gcc/testsuite/g++.dg/expr/div-by-zero1.C
new file mode 100644
index 00000000000..63bef406408
--- /dev/null
+++ b/gcc/testsuite/g++.dg/expr/div-by-zero1.C
@@ -0,0 +1,3 @@
+// PR c++/84938
+
+const int &a = 1 / ~-1;		// { dg-warning "division by zero" }