Re: [BUG] BINOP_DIV and ptyp command

Doug Evans
2008-01-29T04:53:55Z

On Jan 21, 2008 1:47 AM, Pierre Muller <muller@ics.u-strasbg.fr> wrote:
> The ptyp command returns inconsistent types for the c '/'(BINOP_DIV)
> operator:
>
> (gdb) ptyp 3 / 2
> type = int
> (gdb) p 3 / 2
> $4 = 1
> (gdb) ptyp 3.0 / 2
> type = double
> (gdb) p 3.0 / 2
> $5 = 1.5
> (gdb) ptyp 3 / 2.0
> type = int
> (gdb) p 3 / 2.0
> $6 = 1.5
>
> I suspect that this bug is due to the fact that
> the type of this binary operator is inferred from the
> left node type, but this is wrong in the case '3 / 2.0'
>
>
> Pierre Muller

I may be missing something, but it seems like special casing
EVAL_AVOID_SIDE_EFFECTS for DIV/MOD/REM is no longer useful here (one
can imagine that it was added way back when to avoid division by zero,
but I'm just guessing). I don't see any need to special case this
here, value_binop will catch integer division by zero and doesn't have
any special checks for floating point division by 0 (uses host fp
which can result in +/-inf, and isn't necessarily accurate for the
target at any rate, but that's an orthogonal issue). If it were a
case of wanting to avoid tripping over the call to error("Division by
zero") then I'd expect to also see special casing of "1 >> 3.0" when
EVAL_AVOID_SIDE_EFFECTS. Also note that for integer MOD, "division by
zero" isn't an issue.

So it seems like the following is the correct patch.

2008-01-28 Doug Evans <dje@google.com>

* eval.c (evaluate_subexp_standard): If DIV/REM/MOD and
EVAL_AVOID_SIDE_EFFECTS, remove special case and process normally.

Index: eval.c
===================================================================
RCS file: /cvs/src/src/gdb/eval.c,v
retrieving revision 1.77
diff -u -p -u -p -r1.77 eval.c
--- eval.c 18 Jan 2008 17:07:39 -0000 1.77
+++ eval.c 29 Jan 2008 04:37:52 -0000
@@ -1509,9 +1509,6 @@ evaluate_subexp_standard (struct type *e
goto nosideret;
if (binop_user_defined_p (op, arg1, arg2))
return value_x_binop (arg1, arg2, op, OP_NULL, noside);
- else if (noside == EVAL_AVOID_SIDE_EFFECTS
- && (op == BINOP_DIV || op == BINOP_REM || op == BINOP_MOD))
- return value_zero (value_type (arg1), not_lval);
else
return value_binop (arg1, arg2, op);