[PATCH] D25810: [SCEV] Memoize visitMulExpr results in SCEVRewriteVisitor. Fix PR18606
Sanjoy Das via llvm-commits
llvm-commits at lists.llvm.org
Fri Oct 21 11:56:58 PDT 2016
sanjoy added inline comments.
Comment at: include/llvm/Analysis/ScalarEvolutionExpressions.h:540
/// Recursively visits a SCEV expression and re-writes it.
> sanjoy wrote:
> > lihuang wrote:
> > > sanjoy wrote:
> > > > Please document the fact that this only implements "pure" transforms.
> > > Sorry, but by "pure" transform do you mean identity transform? So what about:
> > >
> > > /// Recursively visits a SCEV expression and re-writes an identical SCEV.
> > I meant a transform that maps equal inputs to equal outputs. For instance, I cannot use this framework to implement a transform that maps all `SCEVConstant` s to `getConstant(Counter++)` since then the caching scheme won't work.
> I see, thanks. What about:
> /// This visitor recursively visits a SCEV expression and re-writes it. The result from each visit is cached, so it will return the same SCEV for the same input.
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