Should -fcross-jumping be part of -O1?

[Robert Dewar]

Ian Lance Taylor wrote:

> No, I do mean what I am saying.  Of course C doesn't give you any
> useful guarantees (I haven't looked at the latest standard).

You should :-)

> But you
> can prove the algorithm in the abstract.  Then you can use gcc
> -fno-fast-math -ffloat-store and get what you want--you don't even
> need -ffloat-store if you are using software floating point.

Of course you still need to understand the C rules for intermediate
values ... and you are still talking in a very C specific universe.
GCC is not only a C compiler :-)

> So to me
> accurate floating point means -fno-fast-math -ffloat-store

Well you can use words anyway you want, but this is an odd definition 
for most people, so you had better always define what you mean :-)

> But you are quite right that that is not what most people want, and
> probably not what many people would expect.

Right, such as those folks interested in performance, of whom there are
one or two in the fpt world :-)

Also note that your description of what you are doing is *precisely* 
what I referred to in my message. You are not relying only on the IEEE
standard, but on an auxiliary "standard" which is the behavior of GCC
when compiling C using -fno-fast-math -ffloat-store. That was my point.
You can't just say you are using the IEEE standard, you must always add
the assumptions you are making about the translation of the high level 
language you are using.