feat: add basic block reordering pass and improve codegen naming

- Implement `reorder_blocks` (BBR) pass using DFS to maximize
fallthroughs.
- Update x86_64 backend to use actual function names in call
instructions instead of generic IDs.
- Replace the GCD test case in main with an iterative factorial test
module.
- Remove redundant validation check at the end of the optimization
pipeline.

harness.c

@@ -1,46 +0,0 @@
-#include <stdio.h>
-#include <stdint.h>
-#include <inttypes.h>
-
-// Declare the external assembly function generated by the Rust backend
-extern uint64_t gcd(uint64_t a, uint64_t b);
-
-int main() {
-    // Define an array of test cases: {a, b, expected_result}
-    uint64_t test_cases[][3] = {
-        {48, 18, 6},
-        {54, 24, 6},
-        {7, 13, 1},             // Prime numbers
-        {100, 10, 10},          // One is a multiple of the other
-        {2740, 1760, 20},       // Larger random numbers
-        {1234567890, 90, 90},   // Testing 64-bit bounds
-        {5, 0, 5}               // Edge case: b is 0 (Your IR handles this perfectly!)
-    };
-
-    int num_cases = sizeof(test_cases) / sizeof(test_cases[0]);
-    int passed = 0;
-
-    printf("Running GCD Assembly Tests...\n");
-    printf("-----------------------------\n");
-
-    for (int i = 0; i < num_cases; i++) {
-        uint64_t a = test_cases[i][0];
-        uint64_t b = test_cases[i][1];
-        uint64_t expected = test_cases[i][2];
-
-        // Call out into your compiled assembly!
-        uint64_t result = gcd(a, b);
-
-        if (result == expected) {
-            printf("[PASS] gcd(%" PRIu64 ", %" PRIu64 ") = %" PRIu64 "\n", a, b, result);
-            passed++;
-        } else {
-            printf("[FAIL] gcd(%" PRIu64 ", %" PRIu64 ") = %" PRIu64 " (Expected: %" PRIu64 ")\n", a, b, result, expected);
-        }
-    }
-
-    printf("-----------------------------\n");
-    printf("Results: %d/%d passed.\n", passed, num_cases);
-
-    return (passed == num_cases) ? 0 : 1;
-}

src/backend/x86_64.rs

@@ -540,10 +540,7 @@ impl<'a> X86Backend<'a> {
                 }
             }
             Instruction::Call {
-                dest,
+                dest, func, args, ..
-                func: target_id,
-                args,
-                ..
             } => {
                 let arg_regs = ["rdi", "rsi", "rdx", "rcx", "r8", "r9"];
                 for (i, (_, arg_op)) in args.iter().enumerate() {
@@ -559,7 +556,15 @@ impl<'a> X86Backend<'a> {
                         }
                     }
                 }
-                writeln!(&mut self.assembly, "    call function_{}", target_id.0).unwrap();
+
+                let function_name = self
+                    .module
+                    .functions
+                    .iter()
+                    .find_map(|f| (f.id == *func).then(|| f.name.clone()))
+                    .unwrap();
+
+                writeln!(&mut self.assembly, "    call {}", function_name).unwrap();
                 if args.len() > 6 {
                     let cleanup_size = (args.len() - 6) * 8;
                     writeln!(&mut self.assembly, "    addq ${}, %rsp", cleanup_size).unwrap();

src/main.rs

@@ -1,60 +1,108 @@
 use scarlett::{
-    backend::x86_64::X86Backend,
+    backend::x86_64::X86Backend, builder::IrModuleBuilder, ir::*, passes, validate::validate_module,
-    builder::IrModuleBuilder,
-    ir::{ICmpOp, Operand, Type},
-    passes,
-    validate::validate_module,
 };
 
-fn main() {
+fn build_test_module() -> Module {
     let mut module_builder = IrModuleBuilder::new();
 
-    // 1. Build `gcd(a: i64, b: i64) -> i64`
+    let i32_ty = Type::I32;
+
+    // 1. Define the Factorial Function
+    // factorial(n: i32) -> i32
+    let fact_id = module_builder.new_function_id();
     {
-        let gcd_id = module_builder.new_function_id();
+        let f_builder = module_builder.new_function(
-        let builder =
+            fact_id,
-            module_builder.new_function(gcd_id, "gcd", &[Type::I64, Type::I64], Type::I64);
+            "factorial_iterative",
+            vec![&i32_ty],
+            i32_ty.clone(),
+        );
 
-        let ptr_x = builder.build_alloc(Type::I64);
+        // 1. Block Definitions
-        let ptr_y = builder.build_alloc(Type::I64);
+        let loop_cond_block = f_builder.create_block();
+        let loop_body_block = f_builder.create_block();
+        let exit_block = f_builder.create_block();
 
-        let param_0 = builder.get_param(0).unwrap();
+        // Allocate space for 'res' (accumulator) and 'i' (counter)
-        builder.build_store(Type::I64, ptr_x, param_0);
+        let res_ptr = f_builder.build_alloc(i32_ty.clone());
+        let i_ptr = f_builder.build_alloc(i32_ty.clone());
 
-        let param_1 = builder.get_param(1).unwrap();
+        let n = f_builder.get_param(0).expect("Param 0 missing");
-        builder.build_store(Type::I64, ptr_y, param_1);
+        let const_1 = Operand::Integer(1);
 
-        let loop_cond = builder.create_block();
+        // res = 1; i = n;
-        let loop_body = builder.create_block();
+        f_builder.build_store(i32_ty.clone(), res_ptr.clone(), const_1.clone());
-        let loop_merge = builder.create_block();
+        f_builder.build_store(i32_ty.clone(), i_ptr.clone(), n);
 
-        builder.build_jump(loop_cond);
+        f_builder.build_jump(loop_cond_block);
-        builder.switch_to_block(loop_cond);
 
-        let val_y = builder.build_load(Type::I64, ptr_y);
+        // 2. Loop Condition Block: i > 1
-        let cond = builder.build_icmp(ICmpOp::Ne, val_y, Operand::Integer(0));
+        f_builder.switch_to_block(loop_cond_block);
+        let current_i = f_builder.build_load(i32_ty.clone(), i_ptr.clone());
+        let is_gt_1 = f_builder.build_icmp(ICmpOp::Ugt, current_i, const_1.clone());
 
-        builder.build_branch(cond, loop_body, loop_merge);
+        // If i > 1 goto body, else goto exit
-        builder.switch_to_block(loop_body);
+        f_builder.build_branch(is_gt_1, loop_body_block, exit_block);
 
-        let val_x = builder.build_load(Type::I64, ptr_x);
+        // 3. Loop Body Block: res = res * i; i = i - 1;
-        let val_y = builder.build_load(Type::I64, ptr_y);
+        f_builder.switch_to_block(loop_body_block);
-        let rem = builder.build_urem(Type::I64, val_x, val_y);
 
-        builder.build_store(Type::I64, ptr_x, val_y);
+        let val_res = f_builder.build_load(i32_ty.clone(), res_ptr.clone());
-        builder.build_store(Type::I64, ptr_y, rem);
+        let val_i = f_builder.build_load(i32_ty.clone(), i_ptr.clone());
 
-        builder.build_jump(loop_cond);
+        // res = res * i
-        builder.switch_to_block(loop_merge);
+        let updated_res = f_builder.build_mul(i32_ty.clone(), val_res, val_i.clone());
+        f_builder.build_store(i32_ty.clone(), res_ptr.clone(), updated_res);
 
-        let val_x = builder.build_load(Type::I64, ptr_x);
+        // i = i - 1
-        builder.build_return(Type::I64, val_x);
+        let updated_i = f_builder.build_sub(i32_ty.clone(), val_i, const_1);
+        f_builder.build_store(i32_ty.clone(), i_ptr.clone(), updated_i);
 
-        module_builder.complete_function();
+        // Jump back to condition
+        f_builder.build_jump(loop_cond_block);
+
+        // 4. Exit Block: return res
+        f_builder.switch_to_block(exit_block);
+        let final_res = f_builder.build_load(i32_ty.clone(), res_ptr);
+        f_builder.build_return(i32_ty.clone(), final_res);
     }
+    module_builder.complete_function();
 
-    // 2. Finish, Validate, Optimize, and Compile
+    // 2. Define the Main Function
-    let mut module = module_builder.finish();
+    let main_id = module_builder.new_function_id();
+    {
+        let f_builder = module_builder.new_function(
+            main_id,
+            "main",
+            vec![], // no params
+            i32_ty.clone(),
+        );
+
+        // 1. Allocate space for an integer on the stack
+        let ptr = f_builder.build_alloc(i32_ty.clone());
+
+        // 2. Store the value '5' into that pointer
+        let input_val = Operand::Integer(5);
+        f_builder.build_store(i32_ty.clone(), ptr.clone(), input_val);
+
+        // 3. Load the value back from the pointer
+        let loaded_val = f_builder.build_load(i32_ty.clone(), ptr);
+
+        // 4. Call factorial(loaded_val)
+        let args = [(i32_ty.clone(), loaded_val)];
+        let final_result = f_builder.build_call(i32_ty.clone(), fact_id, args.iter());
+
+        // 5. Return the result of the factorial call
+        f_builder.build_return(i32_ty.clone(), final_result);
+    }
+    module_builder.complete_function();
+
+    // Finalize the module
+    module_builder.finish()
+}
+
+fn main() {
+    let mut module = build_test_module();
 
     validate_module(&module).expect("failed to validate module");
     passes::optimize(&mut module);

src/passes/bbr.rs

@@ -0,0 +1,76 @@
+use std::collections::{HashMap, HashSet};
+
+use crate::ir::*;
+
+/// Runs the Block Reordering pass to maximize fallthroughs and minimize jumps.
+pub fn reorder_blocks(module: &mut Module) {
+    for func in &mut module.functions {
+        reorder_blocks_in_func(func);
+    }
+}
+
+fn reorder_blocks_in_func(func: &mut Function) {
+    if func.blocks.is_empty() {
+        return;
+    }
+
+    let mut order = Vec::new();
+    let mut visited = HashSet::new();
+
+    // 1. Recursive Depth-First Search to build the optimal chain of blocks
+    fn dfs(
+        id: BlockId,
+        blocks: &[BasicBlock],
+        visited: &mut HashSet<BlockId>,
+        order: &mut Vec<BlockId>,
+    ) {
+        if !visited.insert(id) {
+            return; // Stop if we hit a loop backedge or already visited block
+        }
+        order.push(id);
+
+        let block = blocks.iter().find(|b| b.id == id).unwrap();
+
+        match block.terminator {
+            Terminator::Jump(target) => {
+                // Instantly follow unconditional jumps to chain them together
+                dfs(target, blocks, visited, order);
+            }
+            Terminator::Branch {
+                then_block,
+                else_block,
+                ..
+            } => {
+                // HEURISTIC: Visit the `else_block` immediately.
+                // This places it directly next to the current block in memory,
+                // allowing our x86-64 backend to omit the branch and fall through.
+                dfs(else_block, blocks, visited, order);
+
+                // Then, recursively process the `then_block` path.
+                dfs(then_block, blocks, visited, order);
+            }
+            Terminator::Return { .. } | Terminator::Unknown => {}
+        }
+    }
+
+    // Start traversing from the function's official entry point
+    dfs(func.entry_block_id, &func.blocks, &mut visited, &mut order);
+
+    // 2. Rebuild the function's block vector in the newly computed order
+    let mut block_map: HashMap<BlockId, BasicBlock> =
+        func.blocks.drain(..).map(|b| (b.id, b)).collect();
+
+    // Push the blocks back into the function in our optimized DFS order
+    for id in order {
+        if let Some(block) = block_map.remove(&id) {
+            func.blocks.push(block);
+        }
+    }
+
+    // 3. Append any unreachable blocks that the DFS missed.
+    // Note: If you run your Dead Code Elimination pass before this,
+    // `block_map` will already be completely empty by this point.
+    for (_, block) in block_map {
+        func.blocks.push(block);
+    }
+}

src/passes/mod.rs

@@ -1,5 +1,6 @@
-use crate::{ir::Module, validate::validate_module};
+use crate::ir::Module;
 
+pub mod bbr;
 pub mod cfp;
 pub mod cpp;
 pub mod dce;
@@ -12,6 +13,6 @@ pub fn optimize(module: &mut Module) {
     cfp::fold_constants(module);
     dce::eliminate_dead_code(module);
     cpp::propagate_copies(module);
+    bbr::reorder_blocks(module);
     des::destroy_ssa(module);
-    validate_module(module).expect("failed to validate module after optimization passes");
 }