gas: implement function calls

For now function calls are following the C's calling convention, which
means they are using the following registers to pass functions'
arguments:

  rdi, rsi, rdx, rcx, r8, r9

If a function has more then 6 parameters, the compilation will fail.
To enable function with more than 6 parameters we will need to save the
extra arguments on stack.

Naming:

  parameters: function parameters are the variables a function receives.

  arguments: Arguments are the values passed to a function when calling
  it.

Calling mechanism:

  When a function is called, all the expressions passed as argument are
  evaluated, after the evaluation, the result is stored on the register
  that represents its argument position, the first argument will be
  stored on rdi, the second on rsi and so on.

Receiving mechanism:

  When a function starts, the first thing it does is store all the
  registers onto the stack. So rdi will be stored on -8(rbp), rsi on
  -16(rbp) and so on. And, a ref_entry is created making the
  relationship parameter-stack_offset.

Signed-off-by: Carlos Maniero <carlos@maniero.me>

1 files changed, 1 insertions, 5 deletions

diff --git a/examples/main.pipa b/examples/main.pipa
index 5ea0077..2da2231 100644
--- a/examples/main.pipa
+++ b/examples/main.pipa
@@ -1,7 +1,3 @@
-fn give_me_the_number(): i32 {
-  return 69;
-}
-
 fn main(): i32 {
-  return give_me_the_number();
+  return 69;
 }