1. Copyright Joey Paquet, 20001 Lecture 9 Table-Driven Syntax-Directed Translation (Top-Down and Bottom-Up)

2. Copyright Joey Paquet, 20002 Part I Top-Down Table-Driven Syntax-Directed Translation

3. Copyright Joey Paquet, 20003 Top-Down Table-Driven SDT Augment the parser algorithm to implement attribute migration Problem: the attributes have to be pushed and popped at a different pace compared to symbols on the stack Solution: use an additional stack (the semantic stack) to store the attributes

4. Copyright Joey Paquet, 20004 Top-Down Table-Driven SDT Insert example slides here

5. Copyright Joey Paquet, 20005 Part II Bottom-Up Table-Driven Syntax-Directed Translation

6. Copyright Joey Paquet, 20006 Bottom-Up SDT Syntax-directed translation is much easier to implement bottom-up than top-down. Synthetized attributes are propagated from the bottom-up, so we have this propagation mechanism for free in a bottom-up parse The presence of inherited attributes generally comes from the elimination of left-recursions and ambiguities. As these are not a problem in bottom-up parsing, we seldom need to process inherited attributes in bottom-up translation In bottom-up translation, the parse and semantic stacks move in synchronism. Semantic rules are triggered as handles are popped from the stack

7. Copyright Joey Paquet, 20007 Bottom-Up SDT The tree is built by grafting subtrees (handles) to the nodes The semantic actions build the subtrees and for the grafts generally through simple pointer manipulations Generally, all nodes (internal or leaves) are of the same type. Differences can be managed by using a variant record structure: nodeKind = (internal,leaf) treeNode = record token : tokenType case kind : nodeKind of internal : (left,right : *treeNode) leaf : (location : integer) end

8. Copyright Joey Paquet, 20008 Bottom-Up SDT Tree nodes may also contain a pointer to a linked list of instruction (e.g. 3AC or ASM) that will be filled later in the code generation (translation) phase. Such a representation enables high-level code optimization To manage the creating of the tree, the frames on the stack need to incorporate tree structures: symbolType = (nonTerm,term) frame = record case symbolType of nonTerm : (root : *nodePtr) term : (loc : integer) end

9. Copyright Joey Paquet, 20009 Bottom-Up SDT We need a makeTree function that will be used to create subtrees and a makeLeaf function that will be used to create tree leaves: nodePtr makeTree(op tokenType, rightSon,leftSon nodePtr{ nodePtr = new(nodePtr) rootPtr.kind = internal rootPtr.token = op rootPtr.left = leftSon rootPtr.right = rightSon return rootPtr}

10. Copyright Joey Paquet, 200010 Bottom-Up SDT nodePtr makeLeaf(tok tokenType, location integer{ rootPtr = new(nodePtr) leafPtr.kind = leaf leafPtr.token = tok leafPtr.location = location return leafPtr}

11. Copyright Joey Paquet, 200011 Bottom-Up SDT: Example Insert example slides here

12. Copyright Joey Paquet, 200012 Bottom-Up SDT We can use a similar process to build other kinds of intermediate representations A similar process can also be used to generate target code directly, but that diminishes the possibilities of high-level code optimization