DWARF: fix stack usage assessment for DW_OP_neg

When the DWARF back-end generates DW_OP_neg operations in DWARF
procedures, we get an ICE because of inconsistent stack usage
computation for the embedding expression. This is because
resolve_args_picking_1 thinks DW_OP_neg is a binary operation (pops 2
stack slots, pushes 1) whereas it really is an unary one (one pop, one
push).

This change fixes resolve_args_picking_1 and adds a regression testcase
(which crashes with the current trunk).  Bootstrapped and regtested
without regression on x86_64-linux.

gcc/

	* dwarf2out.c (resolve_args_picking_1): Consider DW_OP_neg as an
	unary operation, not a binary one.

gcc/testsuite/

	* gnat.dg/debug6.adb, gnat.dg/debug6_pkg.ads: New testcase.

From-SVN: r236087

gcc/ChangeLog

+2016-05-10  Pierre-Marie de Rodat  <derodat@adacore.com>
+
+	* dwarf2out.c (resolve_args_picking_1): Consider DW_OP_neg as an
+	unary operation, not a binary one.
+
 2016-05-10  Ilya Enkovich  <ilya.enkovich@intel.com>
 
 	PR tree-optimization/70786

gcc/dwarf2out.c

@@ -15407,6 +15407,7 @@ resolve_args_picking_1 (dw_loc_descr_ref loc, unsigned initial_frame_offset,
 	case DW_OP_swap:
 	case DW_OP_rot:
 	case DW_OP_abs:
+	case DW_OP_neg:
 	case DW_OP_not:
 	case DW_OP_plus_uconst:
 	case DW_OP_skip:
@@ -15543,7 +15544,6 @@ resolve_args_picking_1 (dw_loc_descr_ref loc, unsigned initial_frame_offset,
 	case DW_OP_minus:
 	case DW_OP_mod:
 	case DW_OP_mul:
-	case DW_OP_neg:
 	case DW_OP_or:
 	case DW_OP_plus:
 	case DW_OP_shl:

gcc/testsuite/ChangeLog

+2016-05-10  Pierre-Marie de Rodat  <derodat@adacore.com>
+
+	* gnat.dg/debug6.adb, gnat.dg/debug6_pkg.ads: New testcase.
+
 2016-05-10  Ilya Enkovich  <ilya.enkovich@intel.com>
 
 	PR tree-optimization/70786

gcc/testsuite/gnat.dg/debug6.adb

+-- { dg-do compile }
+-- { dg-options "-g" }
+
+with Debug6_Pkg; use Debug6_Pkg;
+
+procedure Debug6 is
+   V : Value := (Kind => Undefined);
+begin
+   Process (V);
+end Debug6;

gcc/testsuite/gnat.dg/debug6_pkg.ads

+package Debug6_Pkg is
+
+   type Vkind is (Int, Undefined);
+   for Vkind use (Int => -2 ** 31, Undefined => 0);
+
+    type Value (Kind : Vkind) is record
+       case Kind is
+          when Undefined => null;
+          when Int       => Value : Integer;
+          when others    => null;
+       end case;
+    end record;
+
+    procedure Process (V : Value);
+
+end Debug6_Pkg;