[patch] fix pre-/post- in-/decrement

[Ken Werner <ken@linux.vnet.ibm.com>]

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On Thursday, September 30, 2010 8:56:34 pm Joel Brobecker wrote:
> Would you mind if we treated this as a separate patch, on top of
> the current patch? I'd also like to add a test that verifies this,
> hopefully not involving vector types.

The attached patch prevents the pre-/post- in-/decrement operators from 
returning  lvalues.  The following gdb command for example should not assign a 
value to the result of the post increment operation but throw an error:
  print i++ = 3;
I've added a few tests to the testsuite. Please let me know if there is a 
better place to put them.
Tested on i686-*-linux-gnu with no regressions. OK to apply?

Thanks
-ken

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ChangeLog:

2010-10-01  Ken Werner  <ken.werner@de.ibm.com>

	* eval.c evaluate_subexp_standard) <UNOP_PREINCREMENT,
	UNOP_PREDECREMENT> Set VALUE_LVAL of the result to not_lval.
	<UNOP_POSTINCREMENT, UNOP_POSTDECREMENT>: Copy arg1 to prevent
	returning a lvalue.

testsuite/ChangeLog:

2010-10-01  Ken Werner  <ken.werner@de.ibm.com>

	* gdb.base/exprs.exp: Add tests for pre-/post- in-/decrement operators.


Index: gdb/eval.c
===================================================================
RCS file: /cvs/src/src/gdb/eval.c,v
retrieving revision 1.139
diff -p -u -r1.139 eval.c
--- gdb/eval.c	11 Aug 2010 16:48:26 -0000	1.139
+++ gdb/eval.c	1 Oct 2010 17:31:16 -0000
@@ -2702,7 +2702,10 @@ evaluate_subexp_standard (struct type *e
 	      arg2 = value_binop (tmp, arg2, BINOP_ADD);
 	    }
 
-	  return value_assign (arg1, arg2);
+	  /* Prevent to return a lvalue.  */
+	  arg3 = value_assign (arg1, arg2);
+	  VALUE_LVAL (arg3) = not_lval;
+	  return arg3;
 	}
 
     case UNOP_PREDECREMENT:
@@ -2726,7 +2729,10 @@ evaluate_subexp_standard (struct type *e
 	      arg2 = value_binop (tmp, arg2, BINOP_SUB);
 	    }
 
-	  return value_assign (arg1, arg2);
+	  /* Prevent to return a lvalue.  */
+	  arg3 = value_assign (arg1, arg2);
+	  VALUE_LVAL (arg3) = not_lval;
+	  return arg3;
 	}
 
     case UNOP_POSTINCREMENT:
@@ -2739,7 +2745,14 @@ evaluate_subexp_standard (struct type *e
 	}
       else
 	{
-	  if (ptrmath_type_p (exp->language_defn, value_type (arg1)))
+	  type = value_type (arg1);
+	  arg3 = allocate_value (type);
+
+	  /* Copy the value to prevent to return a lvalue.  */
+	  memcpy (value_contents_raw (arg3), value_contents (arg1),
+		  TYPE_LENGTH (type));
+
+	  if (ptrmath_type_p (exp->language_defn, type))
 	    arg2 = value_ptradd (arg1, 1);
 	  else
 	    {
@@ -2751,7 +2764,7 @@ evaluate_subexp_standard (struct type *e
 	    }
 
 	  value_assign (arg1, arg2);
-	  return arg1;
+	  return arg3;
 	}
 
     case UNOP_POSTDECREMENT:
@@ -2764,7 +2777,14 @@ evaluate_subexp_standard (struct type *e
 	}
       else
 	{
-	  if (ptrmath_type_p (exp->language_defn, value_type (arg1)))
+	  type = value_type (arg1);
+	  arg3 = allocate_value (type);
+
+	  /* Copy the value to prevent to return a lvalue.  */
+	  memcpy (value_contents_raw (arg3), value_contents (arg1),
+		  TYPE_LENGTH (type));
+
+	  if (ptrmath_type_p (exp->language_defn, type))
 	    arg2 = value_ptradd (arg1, -1);
 	  else
 	    {
@@ -2776,7 +2796,7 @@ evaluate_subexp_standard (struct type *e
 	    }
 
 	  value_assign (arg1, arg2);
-	  return arg1;
+	  return arg3;
 	}
 
     case OP_THIS:
Index: gdb/testsuite/gdb.base/exprs.exp
===================================================================
RCS file: /cvs/src/src/gdb/testsuite/gdb.base/exprs.exp,v
retrieving revision 1.19
diff -p -u -r1.19 exprs.exp
--- gdb/testsuite/gdb.base/exprs.exp	10 Jun 2010 19:48:19 -0000	1.19
+++ gdb/testsuite/gdb.base/exprs.exp	1 Oct 2010 17:31:16 -0000
@@ -253,3 +253,14 @@ gdb_test "set output-radix 8" ".*"
 test_expr "print red" "\\$\[0-9\]* = red"
 test_expr "print/d red" "\\$\[0-9\]* = 0"
 gdb_test "set output-radix 10" ".*"
+
+# Pre-/post in-/decrement tests.
+gdb_test "set variable v_int = 1" ""
+gdb_test "print v_int++" "\\$\[0-9\]* = 1"
+gdb_test "print ++v_int" "\\$\[0-9\]* = 3"
+gdb_test "print v_int--" "\\$\[0-9\]* = 3"
+gdb_test "print --v_int" "\\$\[0-9\]* = 1"
+gdb_test "print v_int++ = 5" "Left operand of assignment is not an lvalue."
+gdb_test "print ++v_int = 5" "Left operand of assignment is not an lvalue."
+gdb_test "print v_int-- = 5" "Left operand of assignment is not an lvalue."
+gdb_test "print --v_int = 5" "Left operand of assignment is not an lvalue."