Function Definition Syntax Tree

Function Definition Syntax Tree Lecture 34 Section 6.9 Robb T. Koether Hampden-Sydney College Wed, Apr 15, 2015 Robb T. Koether (Hampden-Sydney College) Function Definition Syntax Tree Wed, Apr 15, 2015 1 / 21

1 Function Definition Syntax Trees Function Return Function End 2 The Symbol Table 3 Assignment Robb T. Koether (Hampden-Sydney College) Function Definition Syntax Tree Wed, Apr 15, 2015 2 / 21

Outline 1 Function Definition Syntax Trees Function Return Function End 2 The Symbol Table 3 Assignment Robb T. Koether (Hampden-Sydney College) Function Definition Syntax Tree Wed, Apr 15, 2015 3 / 21

Building the Function Definition Syntax Tree The function definition syntax tree is rather simple. Recall that it is the responsibility of the calling function (the caller ) to push the actual parameters onto the stack. Therefore, in the syntax tree for the function definition, we do not need to deal with the actual parameters, but only the formal parameters and the local variables. The formal parameters and local variables are not part of the syntax tree. Robb T. Koether (Hampden-Sydney College) Function Definition Syntax Tree Wed, Apr 15, 2015 4 / 21

Building the Function Definition Syntax Tree To write the assembly code for the beginning of a function definition, we must know The name of the function. The size of the local variable block. The relevant production is fbeg fname fargs } dcls Therefore, the information is available. This information will be stored in the left and right subtrees of a FUNC tree. Robb T. Koether (Hampden-Sydney College) Function Definition Syntax Tree Wed, Apr 15, 2015 5 / 21

Building the Function Definition Syntax Tree From the production fbeg fname fargs } dcls we see that the function name, parameters, and declarations have already been processed. Also, the function name should be global, while the parameters and declarations should be local. Therefore, we must call on enter_block() after installing the function name, but before installing the parameters or local variables. Robb T. Koether (Hampden-Sydney College) Function Definition Syntax Tree Wed, Apr 15, 2015 6 / 21

A Function Definition Syntax Tree FUNC f.mode ID f.id.name f.mode NUM n.num Robb T. Koether (Hampden-Sydney College) Function Definition Syntax Tree Wed, Apr 15, 2015 7 / 21

A Function Definition Syntax Tree Name of the function FUNC f.mode ID f.id.name f.mode NUM n.num Robb T. Koether (Hampden-Sydney College) Function Definition Syntax Tree Wed, Apr 15, 2015 7 / 21

A Function Definition Syntax Tree FUNC f.mode ID f.id.name f.mode NUM n.num Return type Robb T. Koether (Hampden-Sydney College) Function Definition Syntax Tree Wed, Apr 15, 2015 7 / 21

A Function Definition Syntax Tree ID f.id.name f.mode FUNC f.mode NUM n.num Size of the local variable block Robb T. Koether (Hampden-Sydney College) Function Definition Syntax Tree Wed, Apr 15, 2015 7 / 21

Building the Function Return Syntax Tree To write the assembly code to return from a function, we must know The return type. The object to be returned. The return type will be stored in the SymbolTable class variable ret_type. (It is also stored in the mode member of the function s IdEntry.) Robb T. Koether (Hampden-Sydney College) Function Definition Syntax Tree Wed, Apr 15, 2015 9 / 21

Function Return Syntax Trees RET rettype RET rettype RET rettype e e.mode CAST rettype e e.mode Robb T. Koether (Hampden-Sydney College) Function Definition Syntax Tree Wed, Apr 15, 2015 10 / 21

Building the Function End Syntax Tree To write the assembly code for the end of a function definition, we do not need any special information, although we will know the name of the function. This marks the physical end of the function. A return statement marks a logical end. Robb T. Koether (Hampden-Sydney College) Function Definition Syntax Tree Wed, Apr 15, 2015 12 / 21

Building the Function End Syntax Tree Since this marks the physical end of the function, the block level should be decreased. Be sure to call on leave_block() to do this, so that it can delete the hash table of local variables. Robb T. Koether (Hampden-Sydney College) Function Definition Syntax Tree Wed, Apr 15, 2015 13 / 21

Return at End of Function At the end of the function, there needs to be an automatic return, even if the programmer did not write a return statement. But then, what about the return value? Similarly, what if the programmer writes return; without specifying a return value when there should be one? Robb T. Koether (Hampden-Sydney College) Function Definition Syntax Tree Wed, Apr 15, 2015 14 / 21

A Function End Syntax Tree FEND f.mode ID f.mode Robb T. Koether (Hampden-Sydney College) Function Definition Syntax Tree Wed, Apr 15, 2015 15 / 21

The Symbol Table The background work of processing the function definition is to install in the symbol table The function identifier at the GLOBAL level. Each formal parameter at the PARAM level. Each local variable at the LOCAL level. Robb T. Koether (Hampden-Sydney College) Function Definition Syntax Tree Wed, Apr 15, 2015 17 / 21

The Symbol Table The semantic action of the productions fargs ( args ) ( ) args args, arg arg arg type ID will install each parameter in the symbol table. Each will be given a positive offset equal to the current value of f_arg_size. Then f_arg_size is increased by the size of the parameter. Robb T. Koether (Hampden-Sydney College) Function Definition Syntax Tree Wed, Apr 15, 2015 18 / 21

The Symbol Table The semantic action of the productions fbeg fname fargs { dcls dcls dcls dcl ε dcl type ID ; will install each local variable in the symbol table. For each local variable, f_dcl_size is increased by the size of the local variable. Then it is given a negative offset equal to the current value of f_dcl_size. Robb T. Koether (Hampden-Sydney College) Function Definition Syntax Tree Wed, Apr 15, 2015 19 / 21

Assignment Assignment Read Section 6.9. Robb T. Koether (Hampden-Sydney College) Function Definition Syntax Tree Wed, Apr 15, 2015 21 / 21