4.6.6 Options for Controlling Optimization

The options shown in the table below control compiler optimizations and are described in the sections that follow. The table also indicates whether a compiler license is required to select the optimization level. See Optimizations for a description of the sorts of optimizations possible.

Many of these controls specify a set of optimizations and that some sets disable certain optimizations, thus a ‘select all options’ approach will not produce the most compact output.

Table 4-24. General Optimization Options
Option (links to explanatory section)	License	Builds with
`-O0`	No	Minimal optimizations (default).
`-O` `-O1`	No	Optimization level 1.
`-O2`	No	Optimization level 2.
`-O3`	Yes	Optimization level 3.
`-Og`	No	Less optimizations for better debugging.
`-Os`	Yes	Size-orientated optimizations.
`-fasmfile`	No	Optimizations applied to assembly source files.
`-fcacheconst`	Yes	Objects qualified `const` potentially in RAM.
`-flocal`	No	Local optimization set only.
`--nofallback`	No	Only the selected optimization level and with no license-imposed fall back to a lesser level.