[patch] Reduce memory overhead for build_insn_chain

[Vladimir Makarov]

On 08/07/2012 02:22 AM, Steven Bosscher wrote:
> Hello,
>
> In the test case for PR54146, build_insn_chain spends almost all its
> time in this loop:
>
>    FOR_EACH_BB_REVERSE (bb)
>      {
>        bitmap_iterator bi;
>        rtx insn;
>
>        CLEAR_REG_SET (live_relevant_regs);
> -->   memset (live_subregs_used, 0, max_regno * sizeof (int));
>
> The test case has >400,000 basic blocks and >1,000,000 regs...
>
> Fortunately this can be done much more efficiently if one realizes
> that an sbitmap knows its own size (using SBITMAP_SIZE that I
> introduced recently). With that, live_subregs_used can be a sparse
> bitmap.
>
> Bootstrapped&tested on x86_64-unknown-linux-gnu. OK for trunk?
>
>
Ok.  Thanks for the patch, Steven.