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[Bug tree-optimization/18880] DSE is not doing its job for global variables
- From: "law at redhat dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 19 Jan 2005 06:46:09 -0000
- Subject: [Bug tree-optimization/18880] DSE is not doing its job for global variables
- References: <20041208022054.18880.pinskia@gcc.gnu.org>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Additional Comments From law at redhat dot com 2005-01-19 06:46 -------
Subject: Re: DSE is not doing its job for
global variables
On Wed, 2005-01-19 at 02:44 +0000, dje at gcc dot gnu dot org wrote:
> ------- Additional Comments From dje at gcc dot gnu dot org 2005-01-19 02:44 -------
> Steven's experiments seem to demonstrate that the current DSE implementation is
> not very effective. GCC 4.0 includes RTL optimizations that will catch most if
> not all of these cases, so it is not as if this will cause GCC to miss some
> optimizations.
Err, umm, wrong. I checked when I wrote the original code and I just
double checked tonight. The tree DSE implementation as is stands right
now, today, without any improvements, will catch things which the RTL
optimizers will miss. And there are some pretty simple things that can
be done to make it more effective, though to be really effective we need
better alias analysis. The stuff we have now sucks badly.
Jeff
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18880