Re: [PATCH]: fix conversion of nearbyint/rint -> lrint

["Richard Guenther" <richard dot guenther at gmail dot com>]

On 3/5/07, Kaveh R. GHAZI <ghazi@caip.rutgers.edu> wrote:
> I noticed that the code which converts nearbyint/rint (whose result is
> cast to an int type) into lrint is wrong.  Currently it unconditionally
> converts nearbyint into lrint, and only converts rint into lrint when
> -fno-trapping-math is set.  This is backwards, what it should do is the
> opposite.
>
> The result is that people using nearbyint under the expectation that it
> preserves the exception status are getting lrint which sets fp exceptions.
> Also we're needlessly pessimizing the rint case.
>
> We have a testcase that checks that both nearbyint/rint get converted when
> trapping math is off, and it passes correctly.  However we have nothing
> that checks for nearbyint staying put when trapping math is on.
>
> This bug is present on all active branches.
>
> Patch tested on sparc-sun-solaris2.10, no regressions.
>
> Okay for mainline/4.2/4.1?

I think this is not correct, as lrint will get extra exceptions
compared to using
conversion and rint (the invalid exception in case the result doesn't
fit the integer type).
It looks like now we are only trying to not remove traps and do not
care about introducing
more, which is wrong as you noted.  I fear the only valid solution is
to make both
transformations conditional under flag_no_trapping_math.

Or am I missing something?

Thanks,
Richard.

> 2007-03-04  Kaveh R. Ghazi  <ghazi@caip.rutgers.edu>
>
>         * convert.c (convert_to_integer): Fix nearbyint/rint -> *lrint
>         conversion.
>
> testsuite:
>         * gcc.dg/torture/builtin-convert-4.c: New test.