Re: Add VIEW_CONVERT_EXPR to operand_equal_p

[Jan Hubicka <hubicka@ucw.cz>]

> > Added and comitted now.
> 
> Thanks.  Now on to the wrong code issues. :-)
> 
> Up to the change, the useless_type_conversion_p predicate was relying on 
> structural equivalence via the TYPE_CANONICAL check, now it only looks at the 
> outermost level (size, mode).  Now some back-ends, most notably x86-64, do a 
> deep structural scan to determine the calling conventions (classify_argument) 
> instead of just looking at the size and the mode, so consistency dictates that 
> the type of the argument and that of the parameter be structurally equivalent 
> and this sometimes can only be achieved by a VCE... which is now deleted. :-(
> See the call to derivedIP in the attached testcase which now fails on x86-64.
> 
> How do we get away from here?

Hmm, I noticed this in ipa-icf context and wrote checker that two functions are ABI
compatile (did not pushed it out yet), but of course this is nastier.

I think the problem exists before my patch with LTO - it is just matter of
doing two types which will be considered equivalent by
gimple_canonical_types_compatible_p but have different type conversion.  An
example of such type would be:

struct a {
  int a[4];
};
struct b {
  int a[4];
} __attribute__ ((__aligned__(16)));

I tried to turn this into an testcase, the problem is that I don't know of a way
to obtain VIEW_CONVERT_EXPR between the two types out of C or C++ frontend and we
don't seem to synthetize these in middle end (even in cases it would make sense).
I will try to play with it more - would be nice to have a C reproducer.

We may be safe before my patch from wrong code issues if there is no way to 
rpduce VIEW_CONVERT_EXPR between types like this in languages that support
aligned attribute.

I think the problem is generally similar to memory references - the gimple type
compatibility should not be tied to ABI details.  Probably most consistent
solution would be to extend GIMPLE_CALL to also list types of parameters and do
not rely on whatever type the operand have....

Richard, any ideas?

Honza
> 
> 
> 	* gnat.dg/discr44.adb: New test.
> 
> -- 
> Eric Botcazou

> -- { dg-do run }
> -- { dg-options "-gnatws" }
> 
> procedure Discr44 is
> 
>   function Ident (I : Integer) return Integer is
>   begin
>     return I;
>   end;
> 
>   type Int is range 1 .. 10;
> 
>   type Str is array (Int range <>) of Character;
> 
>   type Parent (D1, D2 : Int; B : Boolean) is record
>     S : Str (D1 .. D2);
>   end record;
> 
>   type Derived (D : Int) is new Parent (D1 => D, D2 => D, B => False);
> 
>   X1 : Derived (D => Int (Ident (7)));
> 
> begin
>   if X1.D /= 7 then
>     raise Program_Error;
>   end if;
> end;