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Re: Unreviewed patch (expand_expr:MINUS_EXPR)

From: Richard Henderson <rth at redhat dot com>
To: Geoff Keating <geoffk at geoffk dot org>
Cc: Ulrich Weigand <Ulrich dot Weigand at de dot ibm dot com>, jason at redhat dot com, gcc-patches at gcc dot gnu dot org
Date: Mon, 16 Sep 2002 20:17:33 -0700
Subject: Re: Unreviewed patch (expand_expr:MINUS_EXPR)
References: <OF8FFE2FB3.329A18C8-ONC1256C2F.005CDA97@de.ibm.com> <jmadmhxywk.fsf@desire.geoffk.org>

On Mon, Sep 16, 2002 at 05:06:35PM -0700, Geoff Keating wrote:
> 2. I don't understand Jason's original patch.  If you negate something
>    in a POINTER_TYPE, it should be what you'd expect: the value which,
>    when added to another POINTER_TYPE value, is equivalent to
>    subtracting the original thing.  If that doesn't happen then negation
>    is broken.

Consider when ptr_mode is SImode and Pmode is DImode.  If you do the
negation in POINTER_TYPE (which is unsigned), you wind up with "x - 4"
turning into "x + 0x00000000fffffffc".

r~

References:
- Unreviewed patch (expand_expr:MINUS_EXPR)
  - From: Ulrich Weigand
- Re: Unreviewed patch (expand_expr:MINUS_EXPR)
  - From: Geoff Keating

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