Fix Emission Bugs (#42)

* Fix unintentional fallthrough cases

* Remove bad alignment

README.md

@@ -7,7 +7,7 @@
 ![CI Status](https://github.com/ethanuppal/cs3110_compiler/actions/workflows/ci.yaml/badge.svg)
 
 > "x86 is simple trust me bro"  
-> Last updated: 2024-05-15 00:23:21.691740
+> Last updated: 2024-05-15 08:53:26.702436
 
 ```
 $ ./main -h

lib/backend/asm_emit.ml

@@ -114,16 +114,16 @@ let emit_preamble ~text =
        (Asm.Label.make ~is_global:false ~is_external:true debug_print_symbol))
 
 let emit_cfg ~text cfg regalloc =
+  let entry = Cfg.entry_to cfg in
   Asm.Section.add text
     (Label
        (Asm.Label.make ~is_global:true ~is_external:false
           (mangle (Cfg.name_of cfg))));
+  (* no need to align here, we can assume as a callee that 8 bytes for the
+     return address was already pushed to the stack. *)
   Asm.Section.add_all text
-    [
-      Push (Register RBP);
-      Mov (Register RBP, Register RSP);
-      Sub (Register RSP, Intermediate (align_offset var_size));
-    ];
+    [ Push (Register RBP); Mov (Register RBP, Register RSP) ];
   (* restore is done at returns *)
   emit_save_registers text Asm.Register.callee_saved_data_registers;
+  Asm.Section.add text (Jmp (Label (Basic_block.label_for entry)));
   Cfg.blocks_of cfg |> List.iter (emit_bb text cfg regalloc)