dead code elimination

**Dead code elimination** is the **compiler pass that removes graph operations whose results are never used** - it prunes unused computation paths and reduces runtime cost, memory usage, and graph complexity. **What Is Dead code elimination?** - **Definition**: Delete nodes and subgraphs with no impact on final observable outputs. - **Common Sources**: Disabled debug branches, obsolete intermediate values, and unused auxiliary outputs. - **Optimization Effect**: Lowers operation count and can expose new fusion or scheduling opportunities. - **Correctness Requirement**: Must preserve behavior of all outputs and side-effectful operations. **Why Dead code elimination Matters** - **Runtime Savings**: Unused work is removed entirely from execution path. - **Memory Reduction**: No allocation for intermediates that are not consumed. - **Graph Clarity**: Smaller graphs simplify analysis, debugging, and downstream compilation. - **Deployment Efficiency**: Pruned models are easier to run on constrained inference environments. - **Optimization Cascade**: Cleaner graphs improve effectiveness of later compiler transformations. **How It Is Used in Practice** - **Liveness Analysis**: Trace output dependencies backward to identify unreachable nodes. - **Side-Effect Guard**: Exclude operations that must execute for state or logging semantics. - **Regression Tests**: Validate output equivalence and performance improvement after elimination. Dead code elimination is **a foundational cleanup pass for efficient execution graphs** - removing unused operations improves speed, memory footprint, and maintainability.