[Bug rtl-optimization/15248] [4.0 Regression] Reload may generate stores to read-only memory

["law at redhat dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From law at redhat dot com  2005-05-17 17:03 -------
Subject: Re:  [4.0 Regression] Reload may
	generate stores to read-only memory

On Sat, 2005-05-07 at 16:52 +0000, ebotcazou at gcc dot gnu dot org
wrote:
> ------- Additional Comments From ebotcazou at gcc dot gnu dot org  2005-05-07 16:52 -------
> > I don't know that I'm in a position to make a good decision here, but I 
> > do agree with Jeff -- it would be a lot more compelling to make the 
> > change if there was actually a demonstrable problem -- especially coming 
> > from non-synthetic code.
> 
> I presume you'd like to have a testcase that fails with 4.0.x?  Because I can
> hardly think of a more demonstrable problem than this one: Jeff's analysis for
> 4.1.x was exactly the same as mine for 3.3.x and nothing has changed in the code.
It's still a relatively difficult bug to tickle.  It only appeared in
the mainline as a side effect of improvements to the jump threading code

Block duplication followed by redundancy elimination resulted in having
a pseudo-pseudo copy where the source pseudo was equivalent to a 
readonly mem and the RTL optimizers did not eliminate the pseudo-pseudo
copy.

Bernd has done some additional work on this problem and we may be
converging on a better solution than simply ignoring these problematical
equivalences.

Jeff



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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15248