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Re: [PATCH] Use -frounding-math for math testsuite
On Wed, 2 May 2012, Andreas Jaeger wrote:
> On Wednesday, May 02, 2012 16:32:23 Joseph S. Myers wrote:
> > On Wed, 2 May 2012, Joseph S. Myers wrote:
> > > Please commit this. Strictly we should compile all the libraries with
> > > -frounding-math as well, since library functions may be called in any
> > > rounding mode (and without -frounding-math, round-to-nearest is
> > > assumed); the only things for which it's not needed are the
> > > miscellaneous executables, and those testcases (i.e. all except the
> > > ones this patch addresses) that don't change the rounding mode.
> >
> > Incidentally, compiling libraries with -frounding-math should fix bugs
> > such as <http://sourceware.org/bugzilla/show_bug.cgi?id=10846> with
> > missing underflow exceptions (it's still a GCC bug that it folds these
> > underflowing operations with -ftrapping-math -fno-rounding-math, but
> > -frounding-math works around the GCC bug by disabling that folding since
> > the result is inexact).
>
> Do you really mean all libraries - or just the math subdirectory?
I mean all libraries - every shared object that glibc installs, as opposed
to ones built only as part of the testsuite (for which it is unnecessary,
if harmless). For most of them it won't make a practical difference (code
generated ought to be unchanged), in that they don't actually do floating
point, but there's the odd bit outside libm where rounding modes are
relevant (there are open bugs about strtod and printf not respecting them
... although since those work with integer operations, it's likely
-frounding-math won't actually affect the code generated for them).
--
Joseph S. Myers
joseph@codesourcery.com