Cc

[jgarzik]

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[Copilot]

Pull request overview

This PR adds compiler optimization infrastructure to the pcc C99 compiler, introducing the -O flag to enable optimizations. The changes include two core optimization passes (InstCombine for algebraic simplifications and constant folding, DCE for dead code elimination), comprehensive test coverage, significant refactoring of linearize.rs to improve maintainability, and cleanup of dead code warnings.

• InstCombine pass performs constant folding (2+3→5) and algebraic simplifications (x+0→x, x*1→x, etc.)
• DCE pass removes unused instructions using mark-sweep algorithm
• Optimization passes run iteratively until fixed point (max 10 iterations)

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
cc/opt.rs	New optimization pass runner infrastructure with fixed-point iteration
cc/instcombine.rs	New instruction combining pass with 1400+ lines of simplification rules
cc/dce.rs	New dead code elimination pass with mark-sweep algorithm
cc/tests/features/optimization.rs	Comprehensive correctness tests for optimization passes
cc/tests/common/mod.rs	Added helpers for running tests with optimization flags
cc/linearize.rs	Large refactoring extracting helper methods for better code organization
cc/ir.rs	Added helper methods for pseudo management (next_pseudo_id, create_const_pseudo)
cc/main.rs	Added -O CLI flag and optimization integration point
cc/target.rs	Removed unnecessary dead_code allow attributes
cc/arch/x86_64/lir.rs	Cleanup: removed unused helper methods, added targeted allow(dead_code)
cc/arch/aarch64/lir.rs	Cleanup: removed unused helper methods, added targeted allow(dead_code)
cc/TODO.md	Added detailed documentation for future optimization passes
cc/README.md	Updated feature list noting constant expression evaluation not yet implemented

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