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Description of variable eliminator.

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libjulia/optimiser/README.md
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@ -54,8 +54,27 @@ As an example, neither ``mload`` nor ``mstore`` would be allowed.
## Full Function Inliner
## Variable Eliminator
## Rematerialisation
The rematerialisation stage tries to replace variable references by the expression that
was last assigned to the variable. This is of course only beneficial if this expression
is comparatively cheap to evaluate. Furthermore, it is only semantically equivalent if
the value of the expression did not change between the point of assignment and the
point of use. The main benefit of this stage is that it can save stack slots if it
leads to a variable being eliminated completely (see below), but it can also
save a DUP opcode on the EVM if the expression is very cheap.
The algorithm only allows movable expressions (see above for a definition) in this case.
Expressions that contain other variables are also disallowed if one of those variables
have been assigned to in the meantime. This is also not applied to variables where
assignment and use span across loops and conditionals.
## Unused Definition Pruner
If a variable or function is not referenced, it is removed from the code.
If there are two assignments to a variable where the first one is a movable expression
and the variable is not used between the two assignments (and the second is not inside
a loop or conditional, the first one is not inside), the first assignment is removed.
## Unused Declaration Pruner
## Function Unifier