Optimize binary_op generation to use less stack if possible

04_semantics_and_running/main.py

@@ -487,24 +487,65 @@ def compile_ast(node: ASTnode, compile_data: CompileData) -> None:
             else:
                 assert node.child_rhs.type == 'int'
 
-            # calculate LHS and store it on stack
+
+            old_code = compile_data.code
+
+            # compile LHS
+            compile_data.code = []
             compile_ast(node.child_lhs, compile_data)
+            lhs_code = compile_data.code
+
+            # compile RHS
+            compile_data.code = []
+            compile_ast(node.child_rhs, compile_data)
+            rhs_code = compile_data.code
+
+            compile_data.code = old_code
+
+            # check if we can use temporary registers instead of stack
+            temp_registers = ['%rcx', '%r8', '%r9', '%r10', '%r11']
+            temp_reg = None
+            for reg in temp_registers:
+                valid = True
+                for instruction in lhs_code:
+                    if reg in instruction.operands:
+                        valid = False
+                        break
+                if valid:
+                    temp_reg = reg
+                    break
+
+            # check if lhs uses call, this determines whether we need to align stack
+            lhs_call = False
+            for instruction in lhs_code:
+                if instruction.opcode == 'call':
+                    lhs_call = True
+                    break
+
+            # Add code for RHS calculation
+            compile_data.code += rhs_code
+            if temp_reg is not None:
+                compile_data.code.append(Instruction('movq', ['%rax', temp_reg]))
+            elif not lhs_call:
+                compile_data.code.append(Instruction('pushq', ['%rax']))
+            else:
                 compile_data.code.append(Instruction('subq', ['$16', '%rsp']))
                 compile_data.code.append(Instruction('movq', ['%rax', '0(%rsp)']))
 
-            # calculate RHS and store it in RCX
+            # Add code for LHS calculation
-            compile_ast(node.child_rhs, compile_data)
+            compile_data.code += lhs_code
-            if node.child_lhs.type == 'date' and node.child_rhs.type == 'int':
+            if temp_reg is not None:
-                # multiply RHS by number of seconds in a day so we can perform arithmetic on dates
+                compile_data.code.append(Instruction('movq', [temp_reg, '%rcx']))
-                compile_data.code.append(Instruction('imulq', ['$86400', '%rax', '%rcx']))
+            elif not lhs_call:
+                compile_data.code.append(Instruction('popq', ['%rcx']))
             else:
-                compile_data.code.append(Instruction('movq', ['%rax', '%rcx']))
+                compile_data.code.append(Instruction('movq', ['0(%rsp)', '%rcx']))
-
-            # prepare registers, RAX contains LHS and RCX contains RHS
-            # and restore restore stack
-            compile_data.code.append(Instruction('movq', ['0(%rsp)', '%rax']))
                 compile_data.code.append(Instruction('addq', ['$16', '%rsp']))
 
+            # If we are adding or subtracting dates with integers, multiply the integer by number of seconds in a day
+            if node.child_lhs.type == 'date' and node.child_rhs.type == 'int':
+                compile_data.code.append(Instruction('imulq', ['$86400', '%rcx']))
+
             # perform operation
             if node.value == '+':
                 compile_data.code.append(Instruction('addq', ['%rcx', '%rax']))