Compiler design pdf
COMPILER DESIGN PDF CODE
However, in practice it is also common for code sections to represent dead or unreachable code only under certain conditions, which may not be known at the time of compilation or assembly. Therefore, it is reasonable attempting to remove dead code through dead code elimination at compile time.
Dynamic dead code elimination ĭead code is normally considered dead unconditionally. Robert Shillingsburg (aka Shillner) improved on the algorithm and developed a companion algorithm for removing useless control-flow operations. An algorithm based on static single assignment form (SSA) appears in the original journal article on SSA form by Ron Cytron et al. Historically, dead code elimination was performed using information derived from data-flow analysis. Subsequent dead code elimination removes those calculations and completes the effect (without complicating the strength-reduction algorithm). For example, the classic techniques for operator strength reduction insert new computations into the code and render the older, more expensive computations dead. In practice, much of the dead code that an optimizer finds is created by other transformations in the optimizer.
This technique is common in debugging to optionally activate blocks of code using an optimizer with dead code elimination eliminates the need for using a preprocessor to perform the same task. Int foo ( void ) īecause the expression 0 will always evaluate to false, the code inside the if statement can never be executed, and dead code elimination would remove it entirely from the optimized program.