[llvm] r175293 - add SCEVParameterRewriter

[Chandler Carruth]

On Fri, Feb 15, 2013 at 12:55 PM, Sebastian Pop <spop at codeaurora.org> wrote:

> +
> +  /// The ScevRewriter takes a scalar evolution expression and copies
> all its
> +  /// components. The result after a rewrite is an identical SCEV.
> +  struct ScevRewriter
> +    : public SCEVVisitor<ScevRewriter, const SCEV*> {
>

This class seems to have a pretty weird design to me... So the base class
is a CRTP visitor, and this class is then derived again, and many of the
visit methods are now virtual.

It seems like the better design would be to use consistent CRTP explicit
delegation for the entire type hierarchy instead of using a mixture of CRTP
and virtual dispatch.

In particular, virtual dispatch is remarkably inefficient for visitor
patterns where you really want the inliner to be able to form a
jump-table-loop.
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