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Re: Ada subtypes and base types
- From: Jeffrey A Law <law at redhat dot com>
- To: Robert Dewar <dewar at adacore dot com>
- Cc: Richard Kenner <kenner at vlsi1 dot ultra dot nyu dot edu>, gcc at gcc dot gnu dot org
- Date: Wed, 22 Feb 2006 09:55:39 -0700
- Subject: Re: Ada subtypes and base types
- References: <10602212222.AA13983@vlsi1.ultra.nyu.edu> <43FB9E0E.4090200@adacore.com>
- Reply-to: law at redhat dot com
On Tue, 2006-02-21 at 18:11 -0500, Robert Dewar wrote:
> Richard Kenner wrote:
>
> > Let me try again and take a simpler example. If we have
> >
> > subtype T is Integer range 20..50;
> >
> > Y: T;
> >
> > ... Y + 1 ...
> >
> > What the tree looks like is a PLUS_EXPR of type "Integer" (the base type of
> > T), not T, whose first operand is a NOP_EXPR converting Y to Integer and
> > whose second operand is the constant 1 also of type Integer, not T.
>
> Note that this *exactly* reflects the formal Ada semantics ...
And that's not what's at issue here. We agreed on this some time
ago. The nop-conversions are a necessary requirement to implement
Ada semantics and those nop conversions are and need to be explicit
in the IL.
Assuming the NOP conversions are explicit statements in the IL
(as they are by the time VRP runs), then within an expression we
are type consistent. ie, TREE_TYPE (expr) == TREE_TYPE (op0) ==
TREE_TYPE (op1) where op0 & op1 are either SSA_NAMEs or invariants.
Furthermore, the operation specified by expr is to be carried out
in TREE_TYPE (expr).
Jeff