[e-lang] Killing the MatchBindExpr

[Kevin Reid]

On May 3, 2006, at 2:31, Mark S. Miller wrote:

> Many languages (such as C and Java) have constant-time switch  
> constructs (at least when the case values are dense). Currently, if  
> the E programmer writes a simple switch which should be compiled to  
> a constant time dispatch, this is first expanded to an 'else if'  
> chain. Although Dan reports that gcc will actually optimize some  
> 'else if' chains to constant time dispatches, that's a lot to ask  
> of an optimizer. But if the switch is passed through directly to  
> Kernel-E, then it should be easier for reasonable E implementations  
> to recognize some of the simple cases they can turn into constant  
> time dispatches.

Why would it be a lot to ask?

It is trivial (and only O(n) instead of O(1)) to pattern-match the  
else-if chain rather than a single 'SwitchExpr', and the optimizer is  
then able to recognize structures which are similar to a switch  
expression but not specifically written that way.

There are cases where a high-level construct is easier to optimize  
but I don't think this is one of them.

-- 
Kevin Reid                            <http://homepage.mac.com/kpreid/>