Reading-in the input IL ASTs - <Step 0>

  • Files:

FlowGraphBuilder FGThreads FlowGraphNormalizer LabelHeap

       Tapenade.loadGeneralLibraries()
       CallGraph.readILstream()
       --> FlowGraphBuilder.build()
           --> FlowGraphBuilder.treeStream2FlowGraph()
           --> unit.makeFlowGraph()

At the very beginning of this step, Tapenade reads special (user-modifiable) files that provide information about standard procedures (Intrinsics, Externals...) Done by Tapenade.loadGeneralLibraries(), calling class GeneralLibReader. Information is about number and data-types of arguments (params, side-effect, or globals), and about the effect of the procedure on its arguments (InOut, differentiable dependencies...) Information can also provide expressions for the partial derivatives of the procedure. Information can also provide code to expand each procedure call in-line (see below)

Then the AST’s of the actual source code are read (CallGraph.readILstream()\rightarrowFlowGraphBuilder.build()) The input AST’s arrive through a BufferedReader stream. Tree operators are seen before tree children trees. Atomic tree operators are seen before the atomic tree’s value. Just after the tree of the last child of a List-arity tree, the Stream spits an endOfList “operator”. Progressively, as the AST’s are read from the Streams, actions are done that build the IR. This is not done through a callback nor a visitor mechanism: instead, a driver routine explicitly pops data from the current Stream, and accordingly progressively builds the IR. This driver handles its context, i.e.

  • The current nesting of files/classes/methods/functions around the current point in the AST Stream.

  • The current nesting of namespaces

  • The SymbolTable corresponding to the current point

When the driver reaches the body of a procedure definition, the IR building is subcontracted to FlowGraphBuilder.treeStream2FlowGraph(), that manages an additional context about the threads of control that reach the current point in the AST stream. Holds in particular:

  • When in a procedure, the current nest of control operators controlling the current point.

  • When in a procedure, the current list of Control-Flow arriving to this point (argument FGThreads threads)

Each time the driver has completed eating a complete procedure, it runs a normalization step (unit.makeFlowGraph()) that solves computed GOTOs, removes empty Block’s, groups successive Block’s, groups redundant Flow Arrows, etc.