This is the mail archive of the
mailing list for the GCC project.
Re: [PATCH] Fix PR optimization/13653
- From: Joern Rennecke <joern dot rennecke at superh dot com>
- To: ebotcazou at libertysurf dot fr (Eric Botcazou)
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Tue, 25 May 2004 15:49:26 +0100 (BST)
- Subject: Re: [PATCH] Fix PR optimization/13653
> The problem is in the loop optimizer: if a giv happens to carry the /u flag,
> is reduced but not replaceable, moves from the new register to the original
> one with the /u flag are generated, thus breaking the semantics of
> RTX_UNCHANGING_P. This is further exacerbated here because the loop is
> unrolled twice, so an unchanging read from the first loop can be intertwined
> with an unchanging write from the second loop.
> The proposed fix is to prevent givs that carry the /u flag and are not
> replaceable from being reduced by the loop optimizer. Bootstrapped/regtested
> on i586-redhat-linux-gnu (3.3 branch). OK for all branches?
Whouldn't it be more straightforward to clear the /u flag for the giv
when strength reduction goes ahead?