[Bug c++/93620] New: Floating point is broken in C++ on targets with excess precision

[bugdal at aerifal dot cx]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93620

            Bug ID: 93620
           Summary: Floating point is broken in C++ on targets with excess
                    precision
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bugdal at aerifal dot cx
  Target Milestone: ---

Attempting to use -fexcess-precision=standard with g++ produces:

cc1plus: sorry, unimplemented: '-fexcess-precision=standard' for C++

In light of eldritch horrors like pr 85957 this means floating point is
essentially catastrophically broken on i386 and m68k.

This came to my attention while analyzing
https://github.com/OSGeo/PROJ/issues/1906. Most of the problems are g++
incorrectly handling excess precision, and they're having to put awful hacks
with volatile objects in place to work around it.