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Date: Thu, 22 Nov 2007 11:32:00 -0000
From: Aldy Hernandez <aldyh@redhat.com>
To: Richard Guenther <richard.guenther@gmail.com>
Cc: Diego Novillo <dnovillo@google.com>, gcc-patches@gcc.gnu.org
Subject: Re: [tuples] dereference POINTER_PLUS_EXPR check
Message-ID: <20071122005837.GA7171@redhat.com>
References: <20071121204635.GA7204@redhat.com> <4744A197.1060701@google.com> <20071121215235.GA11077@redhat.com> <84fc9c000711211357w7a2587d2n663dd561845e4e1c@mail.gmail.com> <20071121225800.GA5508@redhat.com> <84fc9c000711211525h37554477yf567a8265f09d59@mail.gmail.com>
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> now due to the transitiveness of u_t_c, we now simply need to check
> 
>   useless_type_conversion (lhs, op0)
> 
> which in your notation is lhs and rhs1.  Which is exactly what the code did
> before your patch.

...

> Why are the pointed-to types relevant at all?  Type relations for the
> pointed-to types don't necessary translate to the relations of the
> pointer types.
> For example useless_type_conversion (void *, int *) == true but
> useless_type_conversion (void, int) is certainly not true.

This is the failed testcase that prompted the patch:

(gdb) ptt lhs_type
 <pointer_type 0x2aaaaf571600
    type <integer_type 0x2aaaaf559240 character(kind=1) public unsigned string-flag QI

...

(gdb) ptt rhs1_type
 <reference_type 0x2aaaaf5e6240
    type <array_type 0x2aaaaf5e6180
        type <integer_type 0x2aaaaf559240 character(kind=1) public unsigned string-flag QI

u_t_c(lhs_type, rhs1_type) fails because it doesn't look far enough
down, but you're saying it shouldn't.  Is u_t_c wrong then?

Aldy