local data flow

[Joern RENNECKE]

Kenneth Zadeck wrote:

>Updating the LR dataflow when splitting a basic block is generally
>pretty easy. 
>You start from the end of the block and just interpret the uses and defs
>for each insn.
>  
>
This means duplicating this aspect of the propagate_block functionality.
If we really have to do this in multiple places, we should have a function
to do that.

>The code in the new version of if-cvt actually does this where it
>replaces the old code that used to call propagate block.
>  
>
Even propagate_block clouldn't handle stack regs properly.  The problem is
that arithmetic operations of implicit pushses / pops, which effectively 
renames
your registers
You won't see this problem for passes that run before reg-stack.