Question about merging two instructions.

[Paolo Bonzini]

>Note that I don't want to replace any *def* and uses may appear in the 
>LHS.
>  
>
Ok, I see.  But you have to cope with *def*s appearing in the LHS: you 
don't want to replace them, yet your modified simplify_replace_rtx will!

>My plan was to use: replace_regs () to replace every use of (reg r)
>with the a new pseudo register (because this is the only function that
>I found that separates the uses from the defs)
>
Not really, as it will happily replace within a STRICT_LOW_PART, but 
that may as well be a bug.

I think you're best off making your own function for now.  And make it 
use validate_change so that you won't have to call recog manually.

Paolo