Add VIEW_CONVERT_EXPR to operand_equal_p
diff mbox

Message ID CAFiYyc1-g-gJ1hB2k0045QL+B5fTrgP=EzhPak-7tufdS60brQ@mail.gmail.com
State New
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Commit Message

Richard Biener Oct. 19, 2015, 12:30 p.m. UTC
On Sun, Oct 18, 2015 at 7:14 PM, Jan Hubicka <hubicka@ucw.cz> wrote:
>>
>> Adding back the mode check is fine if all types with the same TYPE_CANONICAL have the same mode.  Otherwise we'd regress here.  I thought we do for
>>
>> Struct x { int i; };
>> Typedef y x __attribute__((packed));
>>
>> And then doing
>>
>> X x;
>> Y y;
>> X = y;
>
> Do you have any idea how to turn this into a testcase? I don't think we could
> add packed attribute to typedef. Even in
> gimple_canonical_types_compatible_p
>   /* Can't be the same type if they have different mode.  */
>   if (TYPE_MODE (t1) != TYPE_MODE (t2))
>     return false;
> (which IMO may be wrong WRT -mavx flags where modes of same types may be different
> in different TUs)

Ok, so the following works:

struct x { int i; };
typedef struct x y __attribute__((aligned(1)));

void foo (void)
{
  struct x X;
  y Y;
  X = Y;
}

but we use SImode for y as well even though it's alignment is just one byte ...

Not sure what happens on strict-align targets for this and not sure how this
cannot be _not_ a problem.  Consider

void bar (struct x);

and

bar (Y);

or using y *Y and X = *Y or bar (*Y).

> Therefore I would say that TYPE_CANONICAL determine mode modulo the fact that
> incoplete variant of a complete type will have VOIDmode instead of complete
> type's mode (during non-LTO).  That is why I allow mode changes for casts from
> complete to incomplete.

Incomplete have VOIDmode, right?

> In longer run I think that every query to useless_type_conversion_p that
> contains incomplete types is a confused query.  useless_type_conversion_p is
> about operations on the value and there are no operations for incomplete type
> (and function types).  I know that ipa-icf-gimple and the following code in
> gimplify-stmt checks this frequently:
>       /* The FEs may end up building ADDR_EXPRs early on a decl with
>          an incomplete type.  Re-build ADDR_EXPRs in canonical form
>          here.  */
>       if (!types_compatible_p (TREE_TYPE (op0), TREE_TYPE (TREE_TYPE (expr))))
>         *expr_p = build_fold_addr_expr (op0);
> Taking address of incomplete type or functions, naturally, makes sense.  We may
> want to check something else here, like simply
>        TREE_TYPE (op0) != TREE_TYPE (TREE_TYPE (expr))
> and once ipa-icf is cleanded up start sanity checking in usless_type_conversion
> that we use it to force equality only on types that do have values.
>
> We also can trip it when checking TYPE_METHOD_BASETYPE which may be incomplete.
> This is in the code checking useless_type_conversion on functions that I think
> are confused querries anyway - we need the ABI matcher, I am looking into that.

Ok, so given we seem to be fine in practive with TYPE_MODE (type) ==
TYPE_MODE (TYPE_CANONICAL (type))
(whether that's a but or not ...) I'm fine with re-instantiating the
mode check for
aggregate types.  Please do that with


Can we asses equal sizes when modes are non-BLKmode then?  Thus

@@ -270,10 +269,9 @@ useless_type_conversion_p (tree outer_ty
      use the types in move operations.  */
   else if (AGGREGATE_TYPE_P (inner_type)
           && TREE_CODE (inner_type) == TREE_CODE (outer_type))
-    return (!TYPE_SIZE (outer_type)
-           || (TYPE_SIZE (inner_type)
-               && operand_equal_p (TYPE_SIZE (inner_type),
-                                   TYPE_SIZE (outer_type), 0)));
+    return (TYPE_MODE (outer_type) != BLKmode
+           || operand_equal_p (TYPE_SIZE (inner_type),
+                               TYPE_SIZE (outer_type), 0));

   else if (TREE_CODE (inner_type) == OFFSET_TYPE
           && TREE_CODE (outer_type) == OFFSET_TYPE)

?  Hoping for VOIDmode incomplete case.

Richard.

> Honza
>>
>> Richard.
>>
>>
>> >Honza
>> >>
>> >> --
>> >> Eric Botcazou
>>

Comments

Jan Hubicka Oct. 19, 2015, 8:47 p.m. UTC | #1
Richard,
I missed your reply earlier today.
> > Therefore I would say that TYPE_CANONICAL determine mode modulo the fact that
> > incoplete variant of a complete type will have VOIDmode instead of complete
> > type's mode (during non-LTO).  That is why I allow mode changes for casts from
> > complete to incomplete.
> 
> Incomplete have VOIDmode, right?

Yes
> 
> > In longer run I think that every query to useless_type_conversion_p that
> > contains incomplete types is a confused query.  useless_type_conversion_p is
> > about operations on the value and there are no operations for incomplete type
> > (and function types).  I know that ipa-icf-gimple and the following code in
> > gimplify-stmt checks this frequently:
> >       /* The FEs may end up building ADDR_EXPRs early on a decl with
> >          an incomplete type.  Re-build ADDR_EXPRs in canonical form
> >          here.  */
> >       if (!types_compatible_p (TREE_TYPE (op0), TREE_TYPE (TREE_TYPE (expr))))
> >         *expr_p = build_fold_addr_expr (op0);
> > Taking address of incomplete type or functions, naturally, makes sense.  We may
> > want to check something else here, like simply
> >        TREE_TYPE (op0) != TREE_TYPE (TREE_TYPE (expr))
> > and once ipa-icf is cleanded up start sanity checking in usless_type_conversion
> > that we use it to force equality only on types that do have values.
> >
> > We also can trip it when checking TYPE_METHOD_BASETYPE which may be incomplete.
> > This is in the code checking useless_type_conversion on functions that I think
> > are confused querries anyway - we need the ABI matcher, I am looking into that.
> 
> Ok, so given we seem to be fine in practive with TYPE_MODE (type) ==
> TYPE_MODE (TYPE_CANONICAL (type))

Witht the exception of incopmlete variants a type. Then TYPE_CANONICAL may
be complete and !VOIDmode.  
But sure, i believe we ought to chase away the calls to useless_type_conversion
when one of types in incomplete.
> (whether that's a but or not ...) I'm fine with re-instantiating the
> mode check for
> aggregate types.  Please do that with
> 
> Index: gcc/gimple-expr.c
> ===================================================================
> --- gcc/gimple-expr.c   (revision 228963)
> +++ gcc/gimple-expr.c   (working copy)
> @@ -89,8 +89,7 @@ useless_type_conversion_p (tree outer_ty
> 
>    /* Changes in machine mode are never useless conversions unless we
>       deal with aggregate types in which case we defer to later checks.  */
> -  if (TYPE_MODE (inner_type) != TYPE_MODE (outer_type)
> -      && !AGGREGATE_TYPE_P (inner_type))
> +  if (TYPE_MODE (inner_type) != TYPE_MODE (outer_type))
>      return false;

OK, that is variant of the patch I had at beggining.  I will test it.
> 
>    /* If both the inner and outer types are integral types, then the
> 
> Can we asses equal sizes when modes are non-BLKmode then?  Thus
> 
> @@ -270,10 +269,9 @@ useless_type_conversion_p (tree outer_ty
>       use the types in move operations.  */
>    else if (AGGREGATE_TYPE_P (inner_type)
>            && TREE_CODE (inner_type) == TREE_CODE (outer_type))
> -    return (!TYPE_SIZE (outer_type)
> -           || (TYPE_SIZE (inner_type)
> -               && operand_equal_p (TYPE_SIZE (inner_type),
> -                                   TYPE_SIZE (outer_type), 0)));
> +    return (TYPE_MODE (outer_type) != BLKmode
> +           || operand_equal_p (TYPE_SIZE (inner_type),
> +                               TYPE_SIZE (outer_type), 0));
> 
>    else if (TREE_CODE (inner_type) == OFFSET_TYPE
>            && TREE_CODE (outer_type) == OFFSET_TYPE)
> 
> ?  Hoping for VOIDmode incomplete case.
Don't see why this would be a problem either.  I am going to start the testing of this variant.

Honza
> 
> Richard.
> 
> > Honza
> >>
> >> Richard.
> >>
> >>
> >> >Honza
> >> >>
> >> >> --
> >> >> Eric Botcazou
> >>

Patch
diff mbox

Index: gcc/gimple-expr.c
===================================================================
--- gcc/gimple-expr.c   (revision 228963)
+++ gcc/gimple-expr.c   (working copy)
@@ -89,8 +89,7 @@  useless_type_conversion_p (tree outer_ty

   /* Changes in machine mode are never useless conversions unless we
      deal with aggregate types in which case we defer to later checks.  */
-  if (TYPE_MODE (inner_type) != TYPE_MODE (outer_type)
-      && !AGGREGATE_TYPE_P (inner_type))
+  if (TYPE_MODE (inner_type) != TYPE_MODE (outer_type))
     return false;

   /* If both the inner and outer types are integral types, then the