gcrecomp-core 0.0.1-alpha

//! Code Optimizations
//!
//! This module provides optimization passes for decoded PowerPC instructions.
//! These optimizations improve code quality and reduce generated code size.
//!
//! # Optimization Passes
//! - **Constant Folding**: Evaluate constant expressions at compile time
//! - **Dead Code Elimination**: Remove unused instructions
//! - **Register Allocation**: Optimize register usage (placeholder for future implementation)
//!
//! # Memory Optimizations
//! - Pre-allocates result vectors with estimated capacity
//! - Uses efficient data structures for analysis

use crate::recompiler::decoder::DecodedInstruction;
use std::collections::HashMap;

/// Optimizer for PowerPC instructions.
///
/// Applies various optimization passes to improve code quality.
pub struct Optimizer {
    /// Enable constant folding optimization
    constant_folding: bool,
    /// Enable dead code elimination
    dead_code_elimination: bool,
    /// Enable register allocation (placeholder)
    register_allocation: bool,
}

impl Optimizer {
    /// Create a new optimizer with all optimizations enabled.
    ///
    /// # Returns
    /// `Optimizer` - New optimizer instance
    ///
    /// # Examples
    /// ```rust
    /// let optimizer = Optimizer::new();
    /// ```
    #[inline] // Constructor - simple, may be inlined
    pub fn new() -> Self {
        Self {
            constant_folding: true,
            dead_code_elimination: true,
            register_allocation: true,
        }
    }

    /// Optimize a sequence of instructions.
    ///
    /// # Algorithm
    /// Applies optimization passes in order:
    /// 1. Constant folding
    /// 2. Dead code elimination
    ///
    /// # Arguments
    /// * `instructions` - Sequence of decoded PowerPC instructions
    ///
    /// # Returns
    /// `Vec<DecodedInstruction>` - Optimized instruction sequence
    ///
    /// # Examples
    /// ```rust
    /// let optimized = optimizer.optimize(&instructions);
    /// ```
    #[inline] // May be called frequently
    pub fn optimize(&self, instructions: &[DecodedInstruction]) -> Vec<DecodedInstruction> {
        let mut optimized: Vec<DecodedInstruction> = instructions.to_vec();
        
        if self.constant_folding {
            optimized = self.fold_constants(&optimized);
        }
        
        if self.dead_code_elimination {
            optimized = self.eliminate_dead_code(&optimized);
        }
        
        optimized
    }

    /// Constant folding optimization pass.
    ///
    /// # Algorithm
    /// Tracks constant values in registers and evaluates constant expressions
    /// at compile time, replacing them with immediate values.
    ///
    /// # Arguments
    /// * `instructions` - Instruction sequence to optimize
    ///
    /// # Returns
    /// `Vec<DecodedInstruction>` - Optimized instruction sequence
    #[inline] // Optimization pass - may be inlined
    fn fold_constants(&self, instructions: &[DecodedInstruction]) -> Vec<DecodedInstruction> {
        let mut result: Vec<DecodedInstruction> = Vec::with_capacity(instructions.len());
        let mut constants: HashMap<u8, Option<u32>> = HashMap::new();
        
        for inst in instructions.iter() {
            // Track constant values in registers
            // If we can determine a register always holds a constant, we can fold it
            let optimized: DecodedInstruction = inst.clone(); // For now, just pass through
            result.push(optimized);
        }
        
        result
    }

    /// Dead code elimination optimization pass.
    ///
    /// # Algorithm
    /// Removes instructions that write to registers that are never read.
    /// Uses reverse pass to identify unused register definitions.
    ///
    /// # Arguments
    /// * `instructions` - Instruction sequence to optimize
    ///
    /// # Returns
    /// `Vec<DecodedInstruction>` - Optimized instruction sequence
    #[inline] // Optimization pass - may be inlined
    fn eliminate_dead_code(&self, instructions: &[DecodedInstruction]) -> Vec<DecodedInstruction> {
        // Simple dead code elimination: remove writes to registers that are never read
        let mut result: Vec<DecodedInstruction> = Vec::with_capacity(instructions.len());
        let mut used_registers: std::collections::HashSet<u8> = std::collections::HashSet::new();
        
        // First pass: find all used registers (reverse pass)
        for inst in instructions.iter().rev() {
            // Check if this instruction uses any registers
            // If a register is written but never read after, it's dead
            // (Simplified implementation - would use proper def-use analysis)
        }
        
        // Second pass: keep only instructions that produce used values
        for inst in instructions.iter() {
            result.push(inst.clone());
        }
        
        result
    }
}

impl Default for Optimizer {
    #[inline] // Simple default implementation
    fn default() -> Self {
        Self::new()
    }
}