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4. The Transforms

4.1 Transform Order

   gd_reduce gd_builtin namespace aggregate gd_filter gd_alias funct_type
   gd_derived gd_enum gd_objects gd_func gd_literals gd_operators gd_actuals
   gd_break gd_goto gd_return gd_labels gd_for gd_while gd_if gd_switch gd_block
   gd_statements gd_nameref classes gd_typedecls ordinals gd_filter merge_builtin
   zap_builtin zap_other gd_filter

4.4 General Transform Approach

    for each node in the graph
       if the node type is the one I want
         -- do something.

This leads to very fast transforms. However, it also means that the garbage collector needs to be invoked on a more frequent basis, because nodes cut off from the main graph retain thier node type and may influence part of a transform unless specifically collected by the gd_filter.

4.3 Transforms

• gd_reduce - this transform is applied at the very beginning. It removes the unused built in types and predefined functions from the GD graph. These include built in types for fortran and java.
• gd_filter - a general garbage collector. This filter walks the graph marking reachable nodes and marks all other nodes as deleted. This filter is applied more than once during the transforms
• namespace - changes the representation of namespace
• gd_builtin - changes gcc declarations for the builtin types to datrix built_in type nodes.
• aggregate - converts the type nodes for classes, struct and unions
• gd_derived - converts derived types (pointers, arrays, etc)
• funct_type - converts function types in GCC. This does not include function definitions, on the types.  For function definitions, these nodes will be deleted, but retained for external function declarations
• gd_enum - handle enumerated types
• gd_alias - handles typedef
• gd_objects - fields of structures, untions and classes, definitions of local variables, parameters
• gd_func - handles function declarations
• gd_literals - conversion of nodes representing literals
• gd_operators - handles expressions
• gd_acutals - arguments in procedure and function calls
• gd_statements - handles most simple statements
• gd_break - converts the break statement
• gd_label - converts label statements
• gd_for - the for statement, handles conversion of internal blocks
• gd_while - the while statement, converts internal blocks
• gd_if - the if statement, converts internal blocks
• gd_switch - the switch statement, case labels and linkage of internal statements
• gd_block - handles statement blocks (delimited by '{ and "})
• gd_classes - follows class inheritance
• gd_nameref - inserts namerefs into object references. GCC refers directly to the definition of the field, Datrix requires a nameref node as a place holder
• gd_typedecls - GCC uses two nodes for each type declaration. We conver the second node, This node traverses the graph and removes the extra nodes
• ordinals - the gd representation implicitly represents the position of nodes within the graph. This pass adds the ordinal attribute for output.
• zap_builtin - zaps any unused builtin nodes. These are nodes not removed by gd_reduce because they were used by parts of the graph that have since been removed.
• zap_other - the other_ptr in the base node structure is used for some house keeping. By the end any housekeeping used by that pointer is finished. null the pointer so the final garbage collect removes all but relevant nodes.

4.3 Auxilary Files

• gd_utils.c - This file provides several simple utility routines and a definition of some static data. The most usefull routine is the newNode routine which allocates a new node in the data structure.
• gd_walkers.c - This file provides a walking algorithm that calls a callback routine for each node_ptr in the graph structure. It permits general moving of pointers.
• gd_next.c - finds (or sets) the 'next' node using some general criteria. Used for walking statement lists, etc. Not all of the transforms use this file, some have thier own copies (and should be fixed to use the single central copy).  The other_node pointer in the common block is used to chain Datrix statments in GCC node sequences before the block containing the current statement has been fixed.