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Performs transformations (optimizations) on a control flow graph.
There are several optimizations performed by classes in this package.
Older Java compilers produced poor code for initializing arrays.
BLOAT can replace this poor code with more efficient code by loading
the array from the constant pool. Dead code elimination removes code
from a method that does not contribute to the final output of the
program.
Value numbering associates a number with each expression such that
if two expressions have the same number, they have the same value. A
value folder is then used to eliminate redundent nodes from and to
propagate constants through the control flow graph.
Constant propagation removes unnecessary assignments by replacing
variables that are assigned constant values with those values. Copy
propagation removes unnecessary assignments to varibles to other
variables.
BLOAT was designed to optimize classes that were to be run inside a
persistent system that required special opcodes to perform operation
such as checking an object cache for a certain resident object. The
analysis that BLOAT does can eliminate some of these checks.
SSA-based partial redundency elimination (PRE) of expressions and
access paths can also be performed on a control flow graph. If a
calculation is redundent along one control flow path leading to a
merge point, PRE computes it once along all paths, assigns the
result to a variable, and replaces further occurrences of the
calculation with that variable. This way, the expression is only
computed once along any given control flow path.
Finally, peephole optimizations are performed on Java bytecode.
For instance, a push instruction followed by a pop instruction is
useless and can be removed. Additionally, unreachable code is removed
from the method.
This package also contains several auxiliary classes that perform
operations like determining whether or not an expression has side
effects and comparing two nodes.
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