gas: Optimize variable reference on assembly

We were moving the stack data for variable reference to another stack
position ending up with two pointer to the same value.

    // a: i32 = 1;
    mov $1, -8(%rbp)
    // b: i32 = a;
    mov -8(%rbp), %rax
    mov %rax, -24(%rbp)
    mov -24(%rbp), %rax
    mov %rax, -16(%rbp)

After this changes, we wont create a new temp space on stack if we don't
need it. See bellow the example after the optimization:

    // a: i32 = 1;
    mov $1, -8(%rbp)
    // b: i32 = a;
    mov -8(%rbp), %rax
    mov %rax, -16(%rbp)

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

1 files changed, 2 insertions, 0 deletions

diff --git a/src/gas_assembly_generator.h b/src/gas_assembly_generator.h
index 8501a67..92972f9 100644
--- a/src/gas_assembly_generator.h
+++ b/src/gas_assembly_generator.h
@@ -25,12 +25,14 @@ typedef enum evaluation_result_kind_t
 {
   EVALUATION_RESULT_VOID,
   EVALUATION_RESULT_ON_RAX,
+  EVALUATION_RESULT_ON_STACK,
   EVALUATION_RESULT_AS_LITERAL_INTEGER
 } evaluation_result_kind_t;
 
 typedef union evaluation_result_data_t
 {
   int64_t literal_int;
+  int stack_offset;
 } evaluation_result_data_t;
 
 typedef struct evaluation_result_t