PR c++/88613 - ICE with use of const var in lambda.

The issue here was that we were cp_folding a location wrapper around a
lambda capture proxy before it had been mark_rvalue_used.  I considered
adding mark_rvalue_use calls to build_new_op_1, but it seems appropriate to
have them in cp_fold_maybe_rvalue when we know we're trying to produce an
rvalue.

The change to mark_use is for a related issue: when we change the operand of
the location wrapper from VAR_DECL to INTEGER_CST, we need the TREE_CODE of
the location wrapper to change as well, from VIEW_CONVERT_EXPR to
NON_LVALUE_EXPR.

	* expr.c (mark_use): Fix location wrapper handling.
	* cp-gimplify.c (cp_fold_maybe_rvalue): Call mark_rvalue_use.

From-SVN: r267859

gcc/cp/ChangeLog

@@ -1,3 +1,9 @@
+2019-01-11  Jason Merrill  <jason@redhat.com>
+
+	PR c++/88613 - ICE with use of const var in lambda.
+	* expr.c (mark_use): Fix location wrapper handling.
+	* cp-gimplify.c (cp_fold_maybe_rvalue): Call mark_rvalue_use.
+
 2019-01-11  Tobias Burnus  <burnus@net-b.de>
 
 	PR C++/88114

gcc/cp/cp-gimplify.c

@@ -2124,6 +2124,8 @@ cp_fold_maybe_rvalue (tree x, bool rval)
   while (true)
     {
       x = cp_fold (x);
+      if (rval)
+	x = mark_rvalue_use (x);
       if (rval && DECL_P (x)
 	  && !TYPE_REF_P (TREE_TYPE (x)))
 	{

gcc/cp/expr.c

@@ -187,10 +187,23 @@ mark_use (tree expr, bool rvalue_p, bool read_p,
 	}
       break;
 
-    CASE_CONVERT:
     case VIEW_CONVERT_EXPR:
       if (location_wrapper_p (expr))
-	loc = EXPR_LOCATION (expr);
+	{
+	  loc = EXPR_LOCATION (expr);
+	  tree op = TREE_OPERAND (expr, 0);
+	  tree nop = RECUR (op);
+	  if (nop == error_mark_node)
+	    return error_mark_node;
+	  TREE_OPERAND (expr, 0) = nop;
+	  /* If we're replacing a DECL with a constant, we also need to change
+	     the TREE_CODE of the location wrapper.  */
+	  if (op != nop && rvalue_p)
+	    TREE_SET_CODE (expr, NON_LVALUE_EXPR);
+	  return expr;
+	}
+      gcc_fallthrough();
+    CASE_CONVERT:
       recurse_op[0] = true;
       break;
 

gcc/testsuite/g++.dg/cpp0x/lambda/lambda-const10.C

@@ -0,0 +1,11 @@
+// PR c++/88613
+// { dg-do compile { target c++11 } }
+// { dg-additional-options -Wtautological-compare }
+
+void a() {
+  const int b = 5;
+  [=] {
+    if (b != 5)
+      ;
+  }();
+}