gcc-2.7 creates faster code than pgcc-1.1.1

[Joe Buck]

> None of the papers discussed it in a floating point context, merely from an
> integer context.  The basics were you had a range [min,max] and a bit which
> indicated that the value was in or out of the range which was built up on a
> basic block level for each expression.
> ...
> As you mention it could be used to detect and eliminate things like domain
> checks which depend solely on the range, not the precision.

There's been work on fixed point optimization for embedded DSP that also
propagates precision information.  e.g. we have [min,max,prec] which means
that the value is known to be a multiple of pow(2,prec), as well as being
in [min,max].  The idea is that we want to eliminate both the
overflow-check operations and the rounding operations in generated code.