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Re: GCC 4.1: Problem with old-loop and REG_EQUAL notes

From: Eric Botcazou <ebotcazou at libertysurf dot fr>
To: Andreas Krebbel <Andreas dot Krebbel at de dot ibm dot com>
Cc: gcc at gcc dot gnu dot org
Date: Fri, 4 May 2007 19:08:36 +0200
Subject: Re: GCC 4.1: Problem with old-loop and REG_EQUAL notes
References: <20070503123322.GA3309@blc4eb430604175.ibm.com> <200705041455.52736.ebotcazou@libertysurf.fr> <20070504161831.GA21783@blc4eb430604175.ibm.com>

> Sure, that would be an alternative compared to always removing the
> REG_EQUAL notes when hoisting an insn and it would fix my particular
> testcase as well.

Then it's pre-approved for the branch if your testcase exhibits a regression.

> But I don't see why this can't happen with unconditional loop invariants?
> Maybe it can be consider safe since loop.c is *always* able to hoist
> unconditional loop invariants?!

I guess that real loop invariants are not supposed to be modified in the loop 
at all, so it's OK to move up insns consuming them to the loop pre-header.

-- 
Eric Botcazou

References:
- GCC 4.1: Problem with old-loop and REG_EQUAL notes
  - From: Andreas Krebbel
- Re: GCC 4.1: Problem with old-loop and REG_EQUAL notes
  - From: Eric Botcazou
- Re: GCC 4.1: Problem with old-loop and REG_EQUAL notes
  - From: Andreas Krebbel

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