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Re: [patch] Reduce memory overhead for build_insn_chain

From: Vladimir Makarov <vmakarov at redhat dot com>
To: Steven Bosscher <stevenb dot gcc at gmail dot com>
Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>
Date: Tue, 07 Aug 2012 13:02:31 -0400
Subject: Re: [patch] Reduce memory overhead for build_insn_chain
References: <CABu31nOQHXLMNmf9FC8tvEUo3B7h8Ci+jGFhCcJEUC_e7ofCzQ@mail.gmail.com>

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.

References:
- [patch] Reduce memory overhead for build_insn_chain
  - From: Steven Bosscher

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