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. See Optimizations for a description of the sorts of optimizations possible.

Many of these controls specify a set of optimizations and some optimization 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)	Builds with
`-O0`	Minimal optimizations (default).
`-O` `-O1`	Optimization level 1.
`-O2`	Optimization level 2.
`-O3`	Optimization level 3.
`-Og`	Less optimizations for better debugging.
`-Os`	Size-orientated optimizations.
`-fasmfile`	Optimizations applied to assembly source files.
`-fcacheconst`	Objects qualified `const` potentially in RAM.
`-f[no-]interrupt-context-loops`	Loops being considered when preserving working registers in interrupt context switch code
`-flocal`	Local optimization set only.
`--nofallback`	No longer has any effect and is ignored by the compiler.
`-fzeroallram=off\|on\|auto`	All RAM zeroed at startup