On Wed, Sep 30, 2015 at 6:43 PM, Jeff Law <l...@redhat.com> wrote:
> On 09/30/2015 01:48 AM, Richard Biener wrote:
>>
>> On Tue, Sep 29, 2015 at 6:55 PM, Jeff Law <l...@redhat.com> wrote:
>>>
>>> The pdp11 port fails to build with the trunk because of a warning.
>>> Essentially VRP determines that the result of using BRANCH_COST is a
>>> constant with the range [0..1]. That's always less than 4, 3 and the
>>> various other magic constants used with BRANCH_COST and VRP issues a
>>> warning
>>> about that comparison.
>>
>>
>> It does? Huh. Is it about undefined overflow which is the only thing
>> VRP should end up
>> warning about? If so I wonder how that happens, at least I can't
>> reproduce it for
>> --target=pdp11 --enable-werror build of cc1.
>
> You have to use a trunk compiler to build the pdp11 cross. You'll bump into
> this repeatedly:
>
> if (warn_type_limits
> && ret && only_ranges
> && TREE_CODE_CLASS (code) == tcc_comparison
> && TREE_CODE (op0) == SSA_NAME)
> {
> /* If the comparison is being folded and the operand on the LHS
> is being compared against a constant value that is outside of
> the natural range of OP0's type, then the predicate will
> always fold regardless of the value of OP0. If -Wtype-limits
> was specified, emit a warning. */
> tree type = TREE_TYPE (op0);
> value_range_t *vr0 = get_value_range (op0);
>
> if (vr0->type == VR_RANGE
> && INTEGRAL_TYPE_P (type)
> && vrp_val_is_min (vr0->min)
> && vrp_val_is_max (vr0->max)
> && is_gimple_min_invariant (op1))
> {
> location_t location;
>
> if (!gimple_has_location (stmt))
> location = input_location;
> else
> location = gimple_location (stmt);
>
> warning_at (location, OPT_Wtype_limits,
> integer_zerop (ret)
> ? G_("comparison always false "
> "due to limited range of data type")
> : G_("comparison always true "
> "due to limited range of data type"));
> }
> }
Oh, I didn't remember we have this kind of warning in VRP ... it's
bound to trigger
for example after jump-threading. So I'm not sure it's useful.
Richard.
> return ret;
> }
>
>
> Jeff
