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Re: Speed up RTL CPROP

On Wed, 2005-02-02 at 11:26 -0500, Ian Lance Taylor wrote:
> Jeffrey A Law <> writes:
> > The sole remaining purpose of the reg_set_table is to allow us to know
> > what blocks a particular pseudo register is set in.  Rather than store
> > the insn which sets the pseudo, we can just as easily store the block
> > index of the block containing the insn which sets the pseudo.  That
> > allows us to remove two memory loads from the loop.
> Don't you know have duplicate information in reg_set_table,
Yes.  Note that we effectively had duplicate information before
even if the entries weren't exact duplicates.

>  in that a
> single basic block index may appear in the list multiple times?

>   That
> shouldn't break anything, but is it wasteful?
It's rare.
> In particular, what if you make the simple optimization that
> record_one_set only adds a new entry if
>     reg_set_table[regno] != NULL
>     && reg_set_table[regno]->bb_index != BLOCK_NUM (insn)
> ?  I would imagine that that would cut down on the number of entries
> considerably in some types of code, given that compute_sets() just
> walks down the insn chain in order.
I can do some experiments with it.  


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