GHC.JS.Opt.Simple

Simple optimizer for the JavaScript IR

This is a simple optimizer for the JavaScript IR. It is intended to be the first optimization pass after generating the JavaScript IR.

Design

The optimizer is invoked on the top-level JStat. It leaves the top-level scope alone, but traverses into each function body and optimizes it. Nested functions are mostly left alone, since they are uncommon in generated code.

The optimizations are:

• rename local variables to shorter names

• remove unused variables

• remove trivial assignments: x = x

• "float" expressions without side effects:

• var x = 1; var y = x + 1; -> var y = 1 + 1;

Limitations

The simple optimization pass is intended to be fast and applicable to almost all generated JavaScript code. Limitations are:

• optimization is disabled if an eval statement is encountered

• variables declared in nested scopes are not renamed