Incremental Compilation

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Incremental Compilation

• Jonathan Bachrach
• MIT AI Lab

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Problem

• Do less work than full recompile
• Produce same result as full recompile

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Solution

• Change something in source
• Change all output that would be different
• Leave others alone
• Track dependencies between output and source

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Fun-O-Dylan Approach

• Source broken up into source records
• Compiler takes source records in and produces
  bits out

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Source Records

• Source is broken up into sequence of source
  records
• Each source record contains some contiguous
  source text
• File
• Top-level-form

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Compilation Phases

• Parsing gt forms bindings
• Modeling gt compile-time models
• Conversion gt IR
• Optimization gt IR (method dispatch )
• Code Gen gt bits
• Linking gt bits

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Compilation Records

• Contain compilation products
• One compilation record per source record

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Top Level Forms

• Object-oriented and syntactic representation of
  programmatic forms occurring at top level
• init-world() -- top level call
• define method end -- method definition
• define class end -- class definition
• Registered in compilation records in order
• Contains all information for each form
• Signatures
• Superclasses
• Defined bindings
• Definitions are binding defining top-level-forms

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Bindings

• Objects representing global variables
• Contain
• Name
• Home module
• Defining definitions
• Dependencies

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Dependencies

• Record bindings for given stage depended on

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Incremental Recompilation

• Remembers last source records
• Computes source record diff to say which source
  records have changed or been added
• When source record diffs
• Compile it and
• Rerun any phases of records dependent on it
• by examining deps on all bindings defined by it
• Can increase precision by decreasing size of
  record
• From say file to top-level-form size

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Other Systems

• SmallEiffel
• Eiffel to C compiler
• Most time is spent in C compilation
• Recompute all C each time
• Only recompile C that diffs

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Interactive Compilation

• Live incremental compilation
• Must patch running system
• Difficult in the face of optimization