gas: Optimize the stack utilization

Until now, every computation was pushed onto stack witch creates
unnecessary stack manipulation and makes the generated code hard to read
and understand.

Now, the latest computation is stored and could be either a literal or a
value on a register.

When it is a register we may need to push the value to stack to avoid
data loss. Now if it is a literal, hence, we can just set the value onto
a register.

  example/main.pipa before this commit:

    .global _start
    .text
    _start:
      push %rbp
      mov %rsp, %rbp
      mov $69, %rax    ; <- There is no reason to store data in rax
      mov %rax, %rdi
      mov $60, %rax
      syscall
      pop %rbp

  example/main.pipa after this commit:

    .global _start
    .text
    _start:
      push %rbp
      mov %rsp, %rbp
      mov $69, %rdi   ; <- Fixed!
      mov $60, %rax
      syscall
      pop %rbp

  example/variables.pipa before this commit:

    .global _start
    .text
    _start:
      push %rbp
      mov %rsp, %rbp
      mov $12, %rax
      mov %rax, -8(%rbp)
      mov $32, %rax
      mov %rax, -16(%rbp)
      mov -8(%rbp), %rax
      mov %rax, -32(%rbp)
      mov -16(%rbp), %rax
      mov -32(%rbp), %rcx
      add %rcx, %rax
      mov %rax, -32(%rbp)
      mov $2, %rax
      mov -32(%rbp), %rcx
      mul %rcx
      mov %rax, -24(%rbp)
      mov $1, %rax
      mov %rax, -40(%rbp)
      mov $33, %rax
      mov %rax, -48(%rbp)
      mov -24(%rbp), %rax
      mov -48(%rbp), %rcx
      sub %rcx, %rax
      mov -40(%rbp), %rcx
      add %rcx, %rax
      mov %rax, -32(%rbp)
      mov $2, %rax
      mov %rax, -40(%rbp)
      mov -32(%rbp), %rax
      mov -40(%rbp), %rcx
      xor %rdx, %rdx
      div %rcx
      mov %rax, %rdi
      mov $60, %rax
      syscall
      pop %rbp

  example/variables.pipa after this commit:

    .global _start
    .text
    _start:
      push %rbp
      mov %rsp, %rbp
      mov $12, -8(%rbp)
      mov $32, -16(%rbp)
      mov -8(%rbp), %rax
      mov %rax, -32(%rbp)
      mov -16(%rbp), %rax
      mov -32(%rbp), %rcx
      add %rcx, %rax
      mov %rax, -32(%rbp)
      mov -32(%rbp), %rcx
      mov $2, %rax
      mul %rcx
      mov %rax, -24(%rbp)
      mov -24(%rbp), %rax
      mov $33, %rcx
      sub %rcx, %rax
      mov $1, %rcx
      add %rcx, %rax
      mov %rax, -32(%rbp)
      mov -32(%rbp), %rax
      mov $2, %rcx
      xor %rdx, %rdx
      div %rcx
      mov %rax, %rdi
      mov $60, %rax
      syscall
      pop %rbp

Less 8 instructions!

Signed-off-by: Carlos Maniero <carlosmaniero@gmail.com>
Reviewed-by: Johnny Richard <johnny@johnnyrichard.com>

0 files changed, 0 insertions, 0 deletions