On Wed, Jun 12, 2013 at 6:04 PM, Jeff Law <l...@redhat.com> wrote:
>
> On 06/07/13 03:14, Richard Biener wrote:
>
>>> +/* Given SSA_NAMEs NAME1 and NAME2, return true if they are candidates
>>> for
>>> + coalescing together, false otherwise.
>>> +
>>> + This must stay consistent with the code in tree-ssa-live.c which
>>> + sets up base values in the var map. */
>>> +
>>> +bool
>>> +gimple_can_coalesce_p (tree name1, tree name2)
>>> +{
>>> + /* First check the SSA_NAME's associated DECL. We only want to
>>> + coalesce if they have the same DECL or both have no associated
>>> DECL.
>>> */
>>> + if (SSA_NAME_VAR (name1) != SSA_NAME_VAR (name2))
>>> + return false;
>>> +
>>> + /* Now check the types. If the types are the same, then we should
>>> + try to coalesce V1 and V2. */
>>> + tree t1 = TREE_TYPE (name1);
>>> + tree t2 = TREE_TYPE (name2);
>>> + if (t1 == t2)
>>> + return true;
>>> +
>>> + /* If the types are not the same, check for a canonical type match.
>>> This
>>> + (for example) allows coalescing when the types are fundamentally
>>> the
>>> + same, but just have different names. */
>>> + if (TYPE_CANONICAL (t1) && TYPE_CANONICAL (t1) == TYPE_CANONICAL (t2))
>>
>>
>> Please use types_compatible_p (t1, t2) here, that's the correct API to use
>> here.
>>
>>> + return true;
>>> +
>>> + return false;
>>> +}
>>> diff --git a/gcc/tree-ssa-live.c b/gcc/tree-ssa-live.c
>>> index 83a52a0..a624d00 100644
>>> --- a/gcc/tree-ssa-live.c
>>> +++ b/gcc/tree-ssa-live.c
>>> @@ -111,8 +111,12 @@ var_map_base_init (var_map map)
>>> as it restricts the sets we compute conflicts for.
>>> Using TREE_TYPE to generate sets is the easies as
>>> type equivalency also holds for SSA names with the same
>>> - underlying decl. */
>>> - m->base.from = TREE_TYPE (var);
>>> + underlying decl.
>>> +
>>> + Check gimple_can_coalesce_p when changing this code. */
>>> + m->base.from = (TYPE_CANONICAL (TREE_TYPE (var))
>>> + ? TYPE_CANONICAL (TREE_TYPE (var))
>>> + : TREE_TYPE (var));
>>
>>
>> eh, but it's made complicated here ... so above do
>>
>>
>> if (TYPE_CANONICAL (t1) && TYPE_CANONICAL (t1) == TYPE_CANONICAL (t2)
>> && types_compatible_p (t1, t2))
>>
>> because looking at useless_type_conversion_p it looks like pointer types
>> with different address-spaces may have the same canonical type. A comment
>> on why we check both, refering to var_map_base_init should also be added.
>
> Reading this again after a night of sleep, it appears you're agreeing that
> we can't just use types_compatible_p to drive what objects are put on the
> coalesce list. The only code change you're asking for is to make sure we
> properly reject pointer types with different address spaces (which can be
> done via types_compatible_p).
>
>
> Right?
Yes, if I remember correctly after this long time ;)
Richard.
> jeff
>
>
