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Re: Simple Value Range Propagation


Josef Zlomek <zlomj9am@artax.karlin.mff.cuni.cz> writes:

> > 	I would like GCC to have a VRP optimization, but I still do not
> > understand why the proposals always record such detailed, accurate
> > information, which requires a slow, heavy-weight implementation.  I do not
> > see it in other production compilers.
> 
> I do not see why my VRP is heavy-weight, it really is very simple.
> Is 2% of compile time (measured on combine.c and insn-attrtab.c) too much?
> It takes as much time as any data-flow problem using fast "hybrid search"
> algorithm (faster than iterative dataflow).

You're not going to better than 2% if you keep it as a separate pass;
I expect most of that time is spent getting RTL into cache.

-- 
- Geoffrey Keating <geoffk@geoffk.org>


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