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From: Toon Moene <toon@moene.indiv.nluug.nl>
To: law@cygnus.com
Cc: egcs@cygnus.com
Subject: Re: Fortran array indexing on 64-bit targets & snapshot 971023
Date: Sun, 26 Oct 1997 05:26:00 -0000	[thread overview]
Message-ID: <9710261322.AA08510@moene.indiv.nluug.nl> (raw)
In-Reply-To: <11138.877705479@hurl.cygnus.com>

> I believe Jim is referring to this:

[ In expand_expr, case ARRAY_REF: ]

[ ... ]

        /* Optimize the special-case of a zero lower bound.

           We convert the low_bound to sizetype to avoid some problems
           with constant folding.  (E.g. suppose the lower bound is 1,
           and its mode is QI.  Without the conversion,  (ARRAY
           +(INDEX-(unsigned char)1)) becomes ((ARRAY+(-(unsigned  
char)1))
           +INDEX), which becomes (ARRAY+255+INDEX).  Oops!)

           But sizetype isn't quite right either (especially if
           the lowbound is negative).  FIXME */

[ ... ]

The problem is that you cannot be sure that sizetype is signed (see  
functions `make_signed_type' and `make_unsigned_type' in  
stor-layout.c).

Why it's done this way is beyond me ...

HTH,
Toon.

  parent reply	other threads:[~1997-10-26  5:26 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
1997-10-24  5:26 Toon Moene
1997-10-24  8:03 ` Jeffrey A Law
1997-10-24 11:21   ` Toon Moene
1997-10-26  5:26   ` Toon Moene [this message]
1997-10-26  8:09     ` Jeffrey A Law
1997-10-26 10:31       ` Per Bothner
1997-10-27 14:46       ` Jim Wilson

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