[PATCH] D25810: [SCEV] Memoize visitMulExpr results in SCEVRewriteVisitor. Fix PR18606

[Li Huang via llvm-commits]

lihuang added inline comments.


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Comment at: include/llvm/Analysis/ScalarEvolutionExpressions.h:540
 
   /// Recursively visits a SCEV expression and re-writes it.
   template<typename SC>
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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.


https://reviews.llvm.org/D25810