Re: MIPS tests (nan-legacy.c and nans-legacy.c) failing

["Maciej W. Rozycki" <macro@codesourcery.com>]

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