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Re: Question on register renaming in rtl loop unroll pass
- From: Eric Botcazou <ebotcazou at adacore dot com>
- To: "Bin.Cheng" <amker dot cheng at gmail dot com>
- Cc: gcc at gcc dot gnu dot org
- Date: Fri, 28 Jun 2013 12:39:44 +0200
- Subject: Re: Question on register renaming in rtl loop unroll pass
- References: <CAHFci2-8WTRo4rGER6QHEoh_8tL0AXmpZqs4Sovy6OgeG2mm5g at mail dot gmail dot com> <1413819 dot OeunHWRmPy at polaris> <CAHFci2-yytJQe2soOn8avEvX_1_+PKDFgkvjr-iXjUFhRAdECw at mail dot gmail dot com>
> The problem is auto-inc-dec is weak and can only capture
> post-increment in first part of code, generating even worse code for
> RA:
> .L1:
> r197 <- r162
> [r197++] <- x
> ...
> [r162+4] <- y
> r162 <- r197+0x4
> ...
> b .L1
> Now we have two live registers and it seems hard to eliminate.
>
> So could the unrolled codes be like below?
I'd try the opposite first, i.e to do more renaming so as to get smaller live
ranges for the pseudo-registers and thus help the auto-inc-dec and RA passes.
--
Eric Botcazou