[Bug target/68028] [6/7/8 regression] Compilation error "lto1: error: target attribute or pragma changes single precision floating point" with LTO on PowerPC

[nickc at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68028

--- Comment #11 from Nick Clifton <nickc at redhat dot com> ---
Hi Richard,

> If the backend doesn't support mixing of -msingle-float/-mno-single-float
> within a compilation unit then this will only work if the user didn't mix TUs
> with conflicting setting at link-time.  So the following will not be diagnosed
> but will instead have conflicting IL accepted silently with your
> patch (with unknown effect):
> 
>> gcc -c t1.c -flto -msingle-float
>> gcc -c t2.c -flto -mdouble-float
>> gcc t1.o t2.o -flto

But even without the patch, if the user does the above, but leaves out
the final -flto then the problem will still not be diagnosed:

 gcc -c t1.c -flto -msingle-float
 gcc -c t2.c -flto -mdouble-float
 gcc t1.o t2.o 

That is, unless the linker detects and reports this problem.  Which it does.
There are tags recorded in the build notes which specify the precision of
floating point used, and the linker will complain if these do not match.

So, since the linker will report conflicts there is no need for the LTO 
compiler to do so.   Especially when, as this bug report shows, it gets
the warning wrong under some circumstances.

So I still think that my patch is viable.  Comments ?

Cheers
  Nick