Redundant (Common) Subexpression Elimination

Global Constant Folding and Propagation

Dead Code Elimination

Conditional Pruning

Conditional Reordering

Assignment Elimination Due to Equality

GOTO Chasing

Array Temporary Elimination

10.3.6 Assignment Elimination Due to Equality

If it is known via data flow analysis and perhaps other optimizations that Value(A) = Value(B), then 

     A := B				Null

This presumes that A and B really are the same variable; that is, they are not both needed later.