Loop optimizer issues

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On 29 Jul 2003, Diego Novillo wrote:

> I've been thinking about this proposal and I am not convinced that it
> would be a good idea to merge the two branches.
> 
>       * The tree-ssa branch is primarily trying to replace RTL passes. 
>         This may include the loop optimizer.  So far, it is not clear
>         whether we will actually need to have a sophisticated loop
>         optimizer at the RTL level (if at all).  The only thing that
>         comes to mind that may needed from RTL are:
>               * instruction lengths/costs to guide the unroller
>               * prefetching capabilities and memory costs to guide
>                 software pipelining and memory hierarchy optimizations.

We do BIV-to-GIV conversion and some addressing mode selection in the RTL
loop optimizer. This is critical for targets such as the SH.

Toshi