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

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

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On Wednesday, October 13, 2010 9:00:28 pm Tom Tromey wrote:
> Ken> I don't see how to control the type of the result of an operator
> Ken> there. I'm still quite new to the GDB parsing internals and would
> Ken> appreciate any insights.
> 
> It is probably a bit of a pain, since the IR generated by the parser is
> a bit unusual (as compilers go).
> 
> However, it seems to me that it would be much friendlier for users to
> report this as a parse error rather than a runtime error.
> 
> One option would be to write a C/C++ implementation of the language_defn
> la_post_parser method, which would look at the expression to see if this
> constraint is violated.
> 
> Another option would be to try to implement it in the grammar.

Ok - I see. Thanks for your suggestions. This seems to be something bigger and 
could be implemented as part of a future patch :). I think for now the non-
language dependent parts of the patch would be sufficient.
The attached patch only contains the fix for the post in-/decrement operators 
as this is what the vec_unop patch (http://sourceware.org/ml/gdb-
patches/2010-10/msg00031.html) prevents from going upstream.
Tested on i686-*-linux-gnu with no regressions.
OK to apply?

Regards
Ken

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ChangeLog:

2010-10-18  Ken Werner  <ken.werner@de.ibm.com>

	* value.h (value_non_lval): Declare.
	* value.c (value_non_lval): New function.
	* eval.c (evaluate_subexp_standard) <UNOP_POSTINCREMENT,
	UNOP_POSTDECREMENT>: Call value_non_lval to ensure to return a
	non-lvalue.

testsuite/ChangeLog:

2010-10-18  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	18 Oct 2010 17:43:52 -0000
@@ -2739,6 +2739,8 @@ evaluate_subexp_standard (struct type *e
 	}
       else
 	{
+	  arg3 = value_non_lval (arg1);
+
 	  if (ptrmath_type_p (exp->language_defn, value_type (arg1)))
 	    arg2 = value_ptradd (arg1, 1);
 	  else
@@ -2751,7 +2753,7 @@ evaluate_subexp_standard (struct type *e
 	    }
 
 	  value_assign (arg1, arg2);
-	  return arg1;
+	  return arg3;
 	}
 
     case UNOP_POSTDECREMENT:
@@ -2764,6 +2766,8 @@ evaluate_subexp_standard (struct type *e
 	}
       else
 	{
+	  arg3 = value_non_lval (arg1);
+
 	  if (ptrmath_type_p (exp->language_defn, value_type (arg1)))
 	    arg2 = value_ptradd (arg1, -1);
 	  else
@@ -2776,7 +2780,7 @@ evaluate_subexp_standard (struct type *e
 	    }
 
 	  value_assign (arg1, arg2);
-	  return arg1;
+	  return arg3;
 	}
 
     case OP_THIS:
Index: gdb/value.c
===================================================================
RCS file: /cvs/src/src/gdb/value.c,v
retrieving revision 1.113
diff -p -u -r1.113 value.c
--- gdb/value.c	30 Sep 2010 18:58:07 -0000	1.113
+++ gdb/value.c	18 Oct 2010 17:43:52 -0000
@@ -826,6 +826,26 @@ value_copy (struct value *arg)
   return val;
 }
 
+/* Return a version of ARG that is non-lvalue.  */
+
+struct value *
+value_non_lval (struct value *arg)
+{
+  if (VALUE_LVAL (arg) != not_lval)
+    {
+      struct type *enc_type = value_enclosing_type (arg);
+      struct value *val = allocate_value (enc_type);
+
+      memcpy (value_contents_all_raw (val), value_contents_all (arg),
+	      TYPE_LENGTH (enc_type));
+      val->type = arg->type;
+      set_value_embedded_offset (val, value_embedded_offset (arg));
+      set_value_pointed_to_offset (val, value_pointed_to_offset (arg));
+      return val;
+    }
+   return arg;
+}
+
 void
 set_value_component_location (struct value *component,
 			      const struct value *whole)
Index: gdb/value.h
===================================================================
RCS file: /cvs/src/src/gdb/value.h,v
retrieving revision 1.162
diff -p -u -r1.162 value.h
--- gdb/value.h	15 Oct 2010 18:54:13 -0000	1.162
+++ gdb/value.h	18 Oct 2010 17:43:52 -0000
@@ -711,6 +711,8 @@ extern void preserve_values (struct objf
 
 extern struct value *value_copy (struct value *);
 
+extern struct value *value_non_lval (struct value *);
+
 extern void preserve_one_value (struct value *, struct objfile *, htab_t);
 
 /* From valops.c */
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	18 Oct 2010 17:43:52 -0000
@@ -253,3 +253,12 @@ 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."