rust_compiler/libs/optimizer/src/dead_store_elimination.rs

@@ -1,5 +1,5 @@
 use crate::helpers::get_destination_reg;
-use il::{Instruction, InstructionNode, Operand};
+use il::{Instruction, InstructionNode};
 use std::collections::HashMap;
 
 /// Pass: Dead Store Elimination
@@ -93,114 +93,6 @@ fn eliminate_overwritten_stores<'a>(
     }
 }
 
-/// Backward pass: Remove stores that are never read before function return
-fn eliminate_unread_stores<'a>(
-    input: Vec<InstructionNode<'a>>,
-) -> (Vec<InstructionNode<'a>>, bool) {
-    use std::collections::HashSet;
-    let mut changed = false;
-    let mut to_remove = Vec::new();
-    
-    // Find function boundaries by matching push/pop pairs of sp (register 17)
-    let mut function_ranges = Vec::new();
-    let mut stack = Vec::new();
-    
-    for (i, node) in input.iter().enumerate() {
-        match &node.instruction {
-            Instruction::Push(Operand::Register(17)) => {
-                stack.push(i);
-            }
-            Instruction::Pop(Operand::Register(17)) => {
-                if let Some(start) = stack.pop() {
-                    // Find the j ra after the pop sp
-                    let mut end = i;
-                    for j in (i + 1)..input.len() {
-                        if matches!(input[j].instruction, Instruction::Jump(Operand::Register(16))) {
-                            end = j;
-                            break;
-                        }
-                    }
-                    function_ranges.push((start, end));
-                }
-            }
-            _ => {}
-        }
-    }
-
-    // Process each function independently
-    for (func_start, func_end) in function_ranges {
-        // Process this function backward
-        let mut live_registers: HashSet<u8> = HashSet::new();
-        
-        // First pass: find which registers are actually read in the function
-        for i in func_start..=func_end {
-            let node = &input[i];
-            for reg in 0..16 {
-                if crate::helpers::reg_is_read(&node.instruction, reg) {
-                    live_registers.insert(reg);
-                }
-            }
-        }
-        
-        // Clear live registers - we'll rebuild it as we go backward
-        live_registers.clear();
-        
-        // Start from the end of the function, working backward
-        for i in (func_start..=func_end).rev() {
-            let node = &input[i];
-            
-            // Skip stack management instructions
-            if matches!(node.instruction, Instruction::Push(_) | Instruction::Pop(_)) {
-                continue;
-            }
-
-            // If instruction writes to a register (assignment/computation)
-            if let Some(dest_reg) = get_destination_reg(&node.instruction) {
-                // If the register isn't live (not read after this write), this write is dead
-                if !live_registers.contains(&dest_reg) {
-                    to_remove.push(i);
-                    changed = true;
-                    // Don't process the reads of this dead instruction
-                    continue;
-                } else {
-                    // This instruction is live. Check what it reads and marks as live.
-                    for reg in 0..16 {
-                        if crate::helpers::reg_is_read(&node.instruction, reg) {
-                            live_registers.insert(reg);
-                        }
-                    }
-                    // This instruction defines the register, so remove it from live set
-                    live_registers.remove(&dest_reg);
-                }
-            } else {
-                // Instruction doesn't write - just track reads
-                for reg in 0..16 {
-                    if crate::helpers::reg_is_read(&node.instruction, reg) {
-                        live_registers.insert(reg);
-                    }
-                }
-            }
-        }
-    }
-
-    if !to_remove.is_empty() {
-        let output = input
-            .into_iter()
-            .enumerate()
-            .filter_map(|(i, node)| {
-                if to_remove.contains(&i) {
-                    None
-                } else {
-                    Some(node)
-                }
-            })
-            .collect();
-        (output, true)
-    } else {
-        (input, changed)
-    }
-}
-
 /// Simplified check: Does this instruction read the register?
 fn reg_is_read_or_affects_control(instr: &Instruction, reg: u8) -> bool {
     use crate::helpers::reg_is_read;
@@ -231,31 +123,4 @@ mod tests {
         assert!(changed);
         assert_eq!(output.len(), 1);
     }
-
-    #[test]
-    fn test_dead_store_in_function() {
-        // Test that dead stores inside functions are removed
-        // Function structure: push sp, push ra, code, pop ra, pop sp, j ra
-        let input = vec![
-            InstructionNode::new(Instruction::Push(Operand::Register(17)), None),
-            InstructionNode::new(Instruction::Push(Operand::Register(16)), None),
-            InstructionNode::new(
-                Instruction::Move(Operand::Register(1), Operand::Number(5.into())),
-                None,
-            ),
-            // r1 is never read, so the move above should be dead
-            InstructionNode::new(
-                Instruction::Move(Operand::Register(15), Operand::Number(42.into())),
-                None,
-            ),
-            InstructionNode::new(Instruction::Pop(Operand::Register(16)), None),
-            InstructionNode::new(Instruction::Pop(Operand::Register(17)), None),
-            InstructionNode::new(Instruction::Jump(Operand::Register(16)), None),
-        ];
-
-        let (output, changed) = dead_store_elimination(input);
-        assert!(changed, "Dead store should be detected");
-        // Should remove the move r1 5 (index 2) and move r15 42 (index 3) since neither is read
-        assert_eq!(output.len(), 5);
-    }
 }