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Re: MIPS tests (nan-legacy.c and nans-legacy.c) failing
- From: "Maciej W. Rozycki" <macro at codesourcery dot com>
- To: Richard Sandiford <rdsandiford at googlemail dot com>
- Cc: Steve Ellcey <sellcey at mips dot com>, <gcc-patches at gcc dot gnu dot org>
- Date: Tue, 13 Aug 2013 22:53:00 +0100
- Subject: Re: MIPS tests (nan-legacy.c and nans-legacy.c) failing
- References: <9f69a43f-c31f-4c49-aaa0-b022fd602f52 at BAMAIL02 dot ba dot imgtec dot org> <87fvul5k37 dot fsf at talisman dot default> <alpine dot DEB dot 1 dot 10 dot 1308130002260 dot 8514 at tp dot orcam dot me dot uk> <87ioz9iju3 dot fsf at talisman dot default>
On Tue, 13 Aug 2013, Richard Sandiford wrote:
> > I've had a look now and that is related to the width of `long' on the
> > host -- encode_ieee_double returns its output 32-bit bit patterns in a
> > buffer of signed longs. The arithmetic value of these patterns therefore
> > depends on whether the width of `long' is 32 bits or wider.
> >
> > Here, in the case of nan-legacy.c, we have:
> >
> > image_hi <- 0x7ff7ffff
> > image_lo <- 0xffffffff
> >
> > so the returned pair of long values will be:
> >
> > 2146959359, -1
> >
> > on a host where the width of `long' is 32 bits and:
> >
> > 2146959359, 4294967295
> >
> > on a host where the width of `long' is 64 bits. Then when supplied as the
> > argument to the assembly-language .word pseudo-op, the two sets of values
> > produce the same bit patterns in the object file produced.
> >
> > It's not clear to me if this dependency on the width of `long' is a bug
> > or feature, but a path-of-least-resistance fix is as follows.
>
> IMO a bug. If we're sure 32 bits is enough then we should use "int".
> If we're not sure we should use HOST_WIDE_INT. The only thing using
> "long" is going to do is create this kind of weird host dependence.
Since encode_ieee_double will always return 32-bit chunks I think these
days this should really use explicit `int32_t' rather than `long' or
trying to guess what `int' or HOST_WIDE_INT might be. The type can be
easily autoconf'ed if missing on pre-C99 hosts.
Of course all the real.c handlers would have to be reviewed and adjusted
accordingly, as would the callers, e.g. assemble_real in varasm.c which is
where the buffer in this particular case comes from (`data').
> > gcc/testsuite/
> > * gcc.target/mips/nan-legacy.c: Accept 4294967295 as an
> > alternative to -1.
> > * gcc.target/mips/nans-legacy.c: Likewise.
>
> OK, thanks.
Thanks for review, applied. Steve, thanks for verifying.
Maciej