More optimizations and snapshot integration tests

rust_compiler/libs/optimizer/src/dead_code.rs

@@ -0,0 +1,82 @@
+use il::{Instruction, InstructionNode};
+
+/// Pass: Redundant Move Elimination  
+/// Removes moves where source and destination are the same: `move rx rx`
+pub fn remove_redundant_moves<'a>(
+    input: Vec<InstructionNode<'a>>,
+) -> (Vec<InstructionNode<'a>>, bool) {
+    let mut output = Vec::with_capacity(input.len());
+    let mut changed = false;
+    for node in input {
+        if let Instruction::Move(dst, src) = &node.instruction
+            && dst == src
+        {
+            changed = true;
+            continue;
+        }
+        output.push(node);
+    }
+    (output, changed)
+}
+
+/// Pass: Dead Code Elimination
+/// Removes unreachable code after unconditional jumps.
+pub fn remove_unreachable_code<'a>(
+    input: Vec<InstructionNode<'a>>,
+) -> (Vec<InstructionNode<'a>>, bool) {
+    let mut output = Vec::with_capacity(input.len());
+    let mut changed = false;
+    let mut dead = false;
+    for node in input {
+        if let Instruction::LabelDef(_) = node.instruction {
+            dead = false;
+        }
+        if dead {
+            changed = true;
+            continue;
+        }
+        if let Instruction::Jump(_) = node.instruction {
+            dead = true
+        }
+        output.push(node);
+    }
+    (output, changed)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use il::{Instruction, InstructionNode, Operand};
+
+    #[test]
+    fn test_remove_redundant_move() {
+        let input = vec![InstructionNode::new(
+            Instruction::Move(Operand::Register(1), Operand::Register(1)),
+            None,
+        )];
+
+        let (output, changed) = remove_redundant_moves(input);
+        assert!(changed);
+        assert_eq!(output.len(), 0);
+    }
+
+    #[test]
+    fn test_remove_unreachable() {
+        let input = vec![
+            InstructionNode::new(Instruction::Jump(Operand::Label("main".into())), None),
+            InstructionNode::new(
+                Instruction::Add(
+                    Operand::Register(1),
+                    Operand::Number(1.into()),
+                    Operand::Number(2.into()),
+                ),
+                None,
+            ),
+            InstructionNode::new(Instruction::LabelDef("main".into()), None),
+        ];
+
+        let (output, changed) = remove_unreachable_code(input);
+        assert!(changed);
+        assert_eq!(output.len(), 2);
+    }
+}