Time/space tradeoff [LWN.net]

Time/space tradeoff

Posted May 6, 2004 6:41 UTC (Thu) by joib (guest, #8541)
In reply to: Time/space tradeoff by jzbiciak
Parent article: The cost of inline functions

gcc 3.4 has some optimizations in this area. From http://gcc.gnu.org/gcc-3.4/changes.html:

# A new unit-at-a-time compilation scheme for C, Objective-C, C++ and Java which is enabled via -funit-at-a-time (and implied by -O2). In this scheme a whole file is parsed first and optimized later. The following basic inter-procedural optimizations are implemented:

* Removal of unreachable functions and variables
* Discovery of local functions (functions with static linkage whose address is never taken)
* On i386, these local functions use register parameter passing conventions.
* Reordering of functions in topological order of the call graph to enable better propagation of optimizing hints (such as the stack alignments needed by functions) in the back end.
* Call graph based out-of-order inlining heuristics which allows to limit overall compilation unit growth (--param inline-unit-growth).

Overall, the unit-at-a-time scheme produces a 1.3% improvement for the SPECint2000 benchmark on the i386 architecture (AMD Athlon CPU).
# More realistic code size estimates used by inlining for C, Objective-C, C++ and Java. The growth of large functions can now be limited via --param large-function-insns and --param large-function-growth.

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