[Bug target/40503] DEC_EVAL_METHOD not match operators

[joseph at codesourcery dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=40503

--- Comment #10 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
I was not attempting to confirm that GCC had a particular bug.

In this case: as I said, no excess precision support is hooked up for 
decimal floating point (i.e., whatever the back end does, the front end 
behaves as if DEC_EVAL_METHOD is 0; but the back end could still do things 
like x87 excess precision where it hides that from the front end, although 
that doesn't apply in this case).

The problem in the case of this bug looks like it's actually in 
convert_to_real_1 where it attempts to optimize conversions applied to the 
results of arithmetic (e.g. changing (float)((double)float + (double)float 
into plain float arithmetic).  See 
<https://gcc.gnu.org/ml/gcc-patches/2008-10/msg01221.html>, point (a), 
where I fixed cases involving loss of precision for DFP and left it to the 
DFP maintainers to deal with getting it completely correct for DFP.