How many GCC optimization levels are there?
I tried gcc -O1, gcc -O2, gcc -O3, and gcc -O4
If I use a really large number, it won't work.
However, I have tried
gcc -O100
and it compiled.
How many optimization levels are there?
To be pedantic, there are 8 different valid -O options you can give to gcc, though there are some that mean the same thing.
The original version of this answer stated there were 7 options. GCC has since added -Og to bring the total to 8.
From the man page:
-O (Same as -O1)-O0 (do no optimize, the default if no optimization level is specified)-O1 (optimize minimally, favoring compilation time)-O2 (optimize more, without speed/size tradeoff)-O3 (optimize even more, favoring speed)-Ofast (optimize very aggressively to the point of breaking standard compliance, favoring speed. May change program behavior)-Og (Optimize debugging experience. -Og enables optimizations that do not interfere with debugging. It should be the
optimization level of choice for the standard edit-compile-debug cycle, offering a reasonable level of optimization
while maintaining fast compilation and a good debugging experience.)-Os (Optimize for size. -Os enables all -O2 optimizations that do not typically increase code size. It also performs further optimizations
designed to reduce code size.
-Os disables the following optimization flags: -falign-functions -falign-jumps -falign-loops -falign-labels -freorder-blocks -freorder-blocks-and-partition -fprefetch-loop-arrays -ftree-vect-loop-version)There may also be platform specific optimizations, as @pauldoo notes, OS X has -Oz.