Re: [PATCH 1/2] soft-fp: Fix overwritten issue for division in op-4.h

[Joseph Myers <joseph at codesourcery dot com>]

On Tue, 23 Oct 2018, Zong Li wrote:

> > I think it would be less disruptive to allow exact overlap between
> > corresponding elements of R and Y.  Then __FP_FRAC_SUB_3 and
> > __FP_FRAC_SUB_4 would be fixed to use temporaries to follow that
> > interface, while _FP_DIV_MEAT_4_udiv and _FP_DIV_MEAT_N_loop would also be
> > made to use temporaries so their calls to the FRAC_SUB macros follow that
> > restriction on overlap.  (It's true that the current sfp-machine.h files
> > only use _FP_DIV_MEAT_1_loop, not _FP_DIV_MEAT_2_loop or
> > _FP_DIV_MEAT_4_loop, but it's still appropriate to fix _FP_DIV_MEAT_N_loop
> > to follow the FRAC_SUB interface properly.)
> >
> > The compiler should have no difficulty optimizing out the temporaries in
> > cases where they end up not being needed.
> >
> > In all cases, names of temporary variables in soft-fp macros should start
> > with the full name of the macro (so __FP_FRAC_SUB_3_* for temporaries
> > inside __FP_FRAC_SUB_3, for example), to avoid the risk of bugs resulting
> > from shadowing when one macro calls another macro with the same variable
> > name.
> 
> I see, I would change the __FP_FRAC_SUB_3, __FP_FRAC_SUB_4,
> __FP_FRAC_ADD_3 and __FP_FRAC_ADD_4 implementation, let the interface
> is identical for users.

My expectation is that __FP_FRAC_ADD_3 and __FP_FRAC_ADD_4 don't need to 
change (because they are already valid for exact overlap between the 
result and the second input).

-- 
Joseph S. Myers
joseph@codesourcery.com