Sharing Between Translation Units in C++ Program Databases
Samuel C. Kendall Glenn Allin
Sun Microsystems Laboratories, Inc. CenterLine Software, Inc.
2 Elizabeth Drive 10 Fawcett Street
Chelmsford, MA\x1301824 Cambridge, MA\x1302138
A C++ program database represents information about C++ code,
typically to enable program browsing or debugging. Such databases can
grow very large. The growth is fundamentally due to the translation
unit (TU) program structure C++ inherited from C: a naively designed
database will consist largely of representations of redundant or
unused code from header files.
This paper measures the effect of some techniques for shrinking this
naively designed database: the elision of unused entities from a TU,
and the sharing or linking (generically, the combination) of redundant
entities across TUs. We also measure the overhead imposed by the
segregation of class types with external linkage from those with
We define and measure these techniques for our own database, which was
designed with very specific requirements. We also discuss techniques
and organizations used in other program databases to save space:
sharing at header file granularity; ruthless simplification of the
database; and lazy loading of data into the database. Finally, we note
the potential problems associated with independently implemented
translators feeding into the same database.
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