[LLVMdev] Back end loop invariant opt

[Chris Lattner]

On Sun, 25 Mar 2007, Andrew Lenharth wrote:
> trivially folded into the load, etc).  The current thinking is a LICM
> and CSE type pass needs to operate on machine code (in a target
> independent way) so that the particularities of each architecture are
> exposed (by virtue of having the machine code selected).  There isn't
> also a way to remove duplicate instructions that are introduced as an
> artifact of the architecture in the DAG stage.  DAG nodes are not a
> 1:1 mapping onto selected instructions.

Andrew is right, but after the isel pass runs, there *should* be a 1-1 
mapping between target dag nodes and machine instrs.  I say "should", 
because we don't always have that at this point, but it is a goal going 
forward.

-Chris

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