More optimizations and snapshot integration tests

rust_compiler/libs/optimizer/src/strength_reduction.rs

@@ -0,0 +1,63 @@
+use il::{Instruction, InstructionNode, Operand};
+use rust_decimal::Decimal;
+
+/// Pass: Strength Reduction
+/// Replaces expensive operations with cheaper equivalents.
+/// Example: x * 2 -> add x x x (addition is typically faster than multiplication)
+pub fn strength_reduction<'a>(
+    input: Vec<InstructionNode<'a>>,
+) -> (Vec<InstructionNode<'a>>, bool) {
+    let mut output = Vec::with_capacity(input.len());
+    let mut changed = false;
+
+    for mut node in input {
+        let reduced = match &node.instruction {
+            // x * 2 = x + x
+            Instruction::Mul(dst, a, Operand::Number(n)) if *n == Decimal::from(2) => {
+                Some(Instruction::Add(dst.clone(), a.clone(), a.clone()))
+            }
+            Instruction::Mul(dst, Operand::Number(n), b) if *n == Decimal::from(2) => {
+                Some(Instruction::Add(dst.clone(), b.clone(), b.clone()))
+            }
+
+            // Future: Could add power-of-2 optimizations using bit shifts if IC10 supports them
+            // x * 4 = (x + x) + (x + x) or x << 2
+            // x / 2 = x >> 1
+
+            _ => None,
+        };
+
+        if let Some(new) = reduced {
+            node.instruction = new;
+            changed = true;
+        }
+
+        output.push(node);
+    }
+
+    (output, changed)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_mul_two_to_add() {
+        let input = vec![InstructionNode::new(
+            Instruction::Mul(
+                Operand::Register(1),
+                Operand::Register(2),
+                Operand::Number(Decimal::from(2)),
+            ),
+            None,
+        )];
+
+        let (output, changed) = strength_reduction(input);
+        assert!(changed);
+        assert!(matches!(
+            output[0].instruction,
+            Instruction::Add(Operand::Register(1), Operand::Register(2), Operand::Register(2))
+        ));
+    }
+}