what is compiler feedback based optimization? is it available with arm gcc compiler?

Question

what is compiler feedback(not linker feedback) based optimization? How to get this feedback file for arm gcc compiler?

Answer 1

Read the chapter of the GCC documentation dedicated to optimizations (and also the section about ARM in GCC: ARM options)

You can use:

• link-time optimization (LTO) by compiling and linking with -flto in addition of other optimization flags (so make CC='gcc -flto -O2'): the linking phase also do optimizations (so the compiler is linking files containing not only object code, but also intermediate GIMPLE internal compiler representation)
• profile-guided optimization (PGO, with -fprofile-generate, -fprofile-use, -fauto-profile etc...): you first generate code with profiling instructions, you run some representative benchmarks to get profiling information, and you compile a second time using these profiling information.

^{You could mix both approaches and give a lot of other optimization flags. Be sure to be consistent with them.}

On x86 & x86-64 (and ARM natively) you might also use -mtune=native and there are lots of other -mtune possibilities.

Some people call profile-based optimization compiler feedback optimization (because dynamic runtime profile information is given back into the compiler). I prefer the "profile-guided optimization" term. See also this old question.