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Re: Where does the time go?
Steven Bosscher <stevenb.gcc@gmail.com> writes:
> And finally: expand. This should be just a change of IR format, from
> GIMPLE to RTL. I have no idea why this pass always shows up in the top
> 10 of slowest parts of GCC. Lowering passes on e.g. WHIRL, or GENERIC
> lowering to GIMPLE, never show up in the compile time overviews.
expand unfortunately does more than just convert IR. It also does
things like changing division by a constant into multiplication by a
constant, and changing multiplication by a constant into a set of
shifts and adds. It does various optimizations involving store flags
(a = b == c;). When expanding function calls, it generates
instructions to put arguments in the right place in registers and on
the stack. Etc.
Ian