Should -fcross-jumping be part of -O1?

[Scott Robert Ladd]

Robert Dewar wrote:
> You make the mistake of assuming that accurate floating-point is 
> well-defined. That's far from the case. There are many possible 
> interpretations.

> Indeed often the issue is that optimization *increases* accuracy, for 
> example by using 80-bit intermediate results on the x86.

And then you have the IEEE-754/IEC-60559 purists who insistent that 
using the 80-bit registers is a platform-specific optimization that 
destroys reproducibility.

> Different motivations here are:
> 
> 1. Keep the results the same when optimized
> 
> 2. Don't worry too much about precise fpt semantics, do things fast
> 
> 3. Optimize as much as you can, but respecting language semantics (for
> example Ada specifically allows the extra precision mentioned above).

Different programming languages -- even different *versions* of the same 
language -- may differ in their requirements for floating-point.

> Nothing is simple in this area :-)

Tell me about it! I'm trying to develop an accuracy benchmark, after 
perusing what's available and finding nothing truly satisfactory. Even 
Kahan's old paranoia benchmark is lacking in many ways.

-- 
Scott Robert Ladd
Coyote Gulch Productions (http://www.coyotegulch.com)
Software Invention for High-Performance Computing