Re: for information, gcc-4.2.3 miscompiles musl math

[Rich Felker <dalias@libc.org>]

On Sat, Nov 21, 2015 at 09:11:22PM +0100, u-uy74@aetey.se wrote:
> On Sat, Nov 21, 2015 at 02:25:48PM -0500, Rich Felker wrote:
> > > like "sin(8.000000) = 21.709544".
> > > Looks like the argument reduction logic has changed in a way
> > > which is not compatible with gcc-4.2.3.
> > 
> > Are you using configure or a hand-written config.mak? configure sets
> > up a big hammer, -ffloat-store, when -fexcess-precision=standard is
> > not supported (i.e. on old gcc), which hopefully suffices to make this
> > code work, but it's possible it doesn't always do the job.
> 
> I was using configure.
> 
> Here are the compilation flags which were used while building with 4.2.3:
> (the command line has been run through "fmt" here)

OK. It looks like we've tracked down the problem anyway and have a
viable fix already, anyway.

> > > I do not notice any problems while compiling musl with gcc-5.2, nor
> > > have a compelling reason to insist on using gcc-4.2.3 (somebody else
> > > might have though, gcc-4.2.3 is the last one under gpl 2).
> > 
> > I thought 4.2.1 was the last.
> 
> I think Wikipedia says so as well but The Source is the truth. It is
> 4.2.3 and nothing else. It is also in fact remarkably better than 4.2.1
> and I could build with it mostly everything I needed, modulo features
> newer than the compiler.

This sounds interesting. Do you have any details beyond "remarkably
better"? If you're right and the benefits are significant maybe Rob
could update Aboriginal to this version.

Rich