[PR 79905] ICE with vector_type

[Nathan Sidwell]

On 04/04/2017 04:27 AM, Richard Biener wrote:
> On Mon, Apr 3, 2017 at 9:03 PM, Nathan Sidwell <nathan@acm.org> wrote:

>> However, as you can see there's already a get-out for COMPLEX_TYPE, and I
>> think the same is needed for VECTOR_TYPE.
>
> Hmm, but that is essentially a hack given that build_complex_type does things
> it shouldn't (assign a name to the type).

Oh, didn't know that.

>> Both set_underlying_type and rs6000 set the builtin vector type's TYPE_NAME,
>> and so one constructed via applying __attribute__((vector_size(16))) will
>> never match.   And it should.
>
> why?  They only need to share the canonical type not the type node itself
> (unless their name is the same, of course).

Correct, that's what I meant.  the canonical type equal function must 
match a just-consed vector with the already-hashed builtin.

> Now -- that name comparing is somewhat odd.  We hash type "variants"
> with different names the same (so setting the name after inserting sth into
> the hash is allowed, but it will overwrite the old entry so any unnamed uses
> up to now get a type with a name...).  I guess we'd be better off leaving
> only unnamed types in the hash and building a type variant whenever we
> add a name to such type.

Right, the name matching surprised me, and my first attempt was to 
remove it.  but that breaks wchar_t.  wchar_t is the same representation 
as int (pedantically, some integral type), but is a distinct type (in 
C++ at least, I don't think C cares).  The canonical type system records 
language-level distinctness, not representation distinctness.

The difference between wchar_t and vector types is the only way to get a 
type the same as wchar_t is to use 'wchar_t' (so we have to start with a 
type at least as canonical as what we want).  Whereas vector types are 
constructed via applying attributes to some underlying scalar type (so 
we have to go find the canonical type).

It would therefore seem that this code in set_underlying_type 
(c-common.c) is wrong:
   if (DECL_IS_BUILTIN (x) && TREE_CODE (TREE_TYPE (x)) != ARRAY_TYPE)
     {
       if (TYPE_NAME (TREE_TYPE (x)) == 0)
	TYPE_NAME (TREE_TYPE (x)) = x;
     }

And this rs6000.c code is totally bogus:
   tdecl = add_builtin_type ("__vector unsigned int", 
unsigned_V4SI_type_node);
   TYPE_NAME (unsigned_V4SI_type_node) = tdecl; <-- this line

(note that at this point, add_builtin_type has already set the TYPE_NAME 
via set_underlying type)

For C++'s creation of the wchar_t node, we'd need to special case 
setting the node's name in some way?

[char16_t and char32_t have the same distinctness property as wchar_t. 
I think that's the complete set]

nathan

-- 
Nathan Sidwell