This has been observed for the AVR target, but could perhaps also apply to other targets.
Recent versions of GCC (4.1.1 and 4.3.0 trunk are confirmed) tend to inline static functions with -Os even when they are being called more than once, thus resulting in larger code than necessary. This violates the objective of -Os to only apply those additional optimizations from level 2 that will not increase the code size. GCC 3.x versions did not do this, so it's an optimization regression. Compiling the attached simple code snippet (which is completely independent of the AVR target) with -Os, and either with or without -DNOINLINE yields: ... /* function main size 17 (13) */ ... /* function main size 31 (27) */ ... -- Summary: -Os inlines functions that are called more than once (optimization regression) Product: gcc Version: 4.3.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: j at uriah dot heep dot sax dot de GCC target triplet: avr-*-* http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30908