Re: [PATCH] PR fortran/63797 - Bogus ambiguous reference to 'sqrt'

[Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>]

On Fri, 16 Apr 2021 09:38:27 +0200
Tobias Burnus <tobias@codesourcery.com> wrote:

> On 16.04.21 09:06, Bernhard Reutner-Fischer via Fortran wrote:
> 
> > Does this change the module format in an incompatible way, i.e. does
> > this require a module format version bump?  
> Not having looked it in detail but I doubt it – it is just a symbol
> which is not output.
> > What happens when we read an existing module that names an intrinsic?
> > Without bumping the module version, we'd run into the same issue as
> > before, don't we?  
> ...
> > Even if we'd skip reading existing intrinsic now, we'd break interop
> > with older compiler versions if we would stop writing them without
> > bumping the module format, i think?  
> 
>  From the function name ("write_symtree"), gfortran only skips writing it;
> it still reads all symtrees which are in the .mod file.
> As this is the only change of Harald's patch, it should be:
> 
> * .mod by old compiler → used by new/old compiler: bogus error for 'sqrt'.
> 
> * .mod by new compiler → used by new/old compiler: works after the patch
> 
> Thus, from that side there should be no issue.

So we'd need to skip (intrinsic) when reading existing modules written
by an older compiler to fix the issue for good, as said.
But maybe that's overkill.

> And I see no point in bumping the .mod version to force the recompilation;
> those running into the corner case can still do 'make clean && make' and
> all others can keep using the old version.

That might not always be possible but admittedly that's a corner case,
yes.