np: codegen: Implement initial stack based codegen

This commit introduces the groundwork for the AMD64 PIIR backend. We
will not follow through with the plans of using abstract syntax trees as
they'll overly complicate the project. Instead we'll utilize a ring
buffer to store the list of instructions and a stack machine for the IR
code.

Signed-off-by: Ian Moffett <ian@osmora.org>

1 files changed, 14 insertions, 4 deletions

diff --git a/src/sys/np/codegen/gen_piir.c b/src/sys/np/codegen/gen_piir.c
index e139465..e6623ac 100644
--- a/src/sys/np/codegen/gen_piir.c
+++ b/src/sys/np/codegen/gen_piir.c
@@ -66,12 +66,12 @@ piir_push(struct piir_stack *stack, ir_byte_t byte)
         return -EINVAL;
     }
 
-    if (stack->op_i >= PIIR_STACK_SIZE - 1) {
+    if (stack->op_head >= PIIR_STACK_SIZE - 1) {
         return -1;
     }
 
     spinlock_acquire(&stack->lock);
-    stack->opstore[stack->op_i++] = byte;
+    stack->opstore[stack->op_head++] = byte;
     spinlock_release(&stack->lock);
     return 0;
 }
@@ -88,12 +88,22 @@ piir_pop(struct piir_stack *stack)
         return -EINVAL;
     }
 
-    if (stack->op_i == 0) {
+    /* Don't read past what we can */
+    if (stack->op_tail == stack->op_head) {
+        stack->op_tail = 0;
+        stack->op_head = 0;
         return -1;
     }
 
     spinlock_acquire(&stack->lock);
-    byte = stack->opstore[--stack->op_i];
+
+    /* Grab a byte, reset pointers if empty */
+    byte = stack->opstore[stack->op_tail++];
+    if (stack->op_tail == stack->op_head) {
+        stack->op_tail = 0;
+        stack->op_head = 0;
+    }
+
     spinlock_release(&stack->lock);
     return byte;
 }