GCC 3.3 compile speed regression - AN ANSWER

[Matt Austern]

On Tuesday, February 11, 2003, at 04:08  PM, Linus Torvalds wrote:

> The thing is, if you want to make gcc faster, you have to bite the
> bullet and throw out code that doesn't perform well.  And you have to
> _remove_ phases of optimization, instead of adding new ones.  Having
> different phases where you operate on different kinds of data 
> structures
> (ie tree -> ssa -> rtl) is just fundamentally slow, as you have to
> marshall the data into the right format for the next phase (which is
> likely bad for caches too).

All of my measurements suggest that improving the speed of optimization
phases is irrelevant.  What's slow is the front end: parsing and 
semantic analysis.  -O0 compilations are slow, not just -O3.

There are compilers that do lots of tricky optimizations, where you pay
in compile speed for that last 0.1% improvement in SPEC numbers.  gcc
is not one of them.

			--Matt