On Thu, 2011-10-06 at 11:35 -0600, Jeff Law wrote:
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> On 10/06/11 04:13, Richard Guenther wrote:
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> >
> > People have already commented on pieces, so I'm looking only at the
> > tree-ssa-reassoc.c pieces (did you consider piggy-backing on IVOPTs
> > instead? The idea is to expose additional CSE opportunities,
> > right? So it's sort-of a strength-reduction optimization on scalar
> > code (classically strength reduction in loops transforms for (i) {
> > z = i*x; } to z = 0; for (i) { z += x }). That might be worth in
> > general, even for non-address cases. So - if you rename that thing
> > to tree-ssa-strength-reduce.c you can get away without
> > piggy-backing on anything ;) If you structure it to detect a
> > strength reduction opportunity (thus, you'd need to match
> > two/multiple of the patterns at the same time) that would be a
> > bonus ... generalizing it a little bit would be another.
> There's a variety of literature that uses PRE to detect and optimize
> straightline code strength reduction. I poked at it at one time (RTL
> gcse framework) and it looked reasonably promising. Never pushed it
> all the way through.
>
> jeff
I ran across http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22586 and
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35308 that show this
question has come up before. The former also suggested a PRE-based
approach.
