https://github.com/python/cpython
Profile Guided Optimization
PGO takes advantage of recent versions of the GCC or Clang compilers. If used, either via configure --enable-optimizations or by manually running make profile-opt regardless of configure flags, the optimized build process will perform the following steps:
The entire Python directory is cleaned of temporary files that may have resulted from a previous compilation.
An instrumented version of the interpreter is built, using suitable compiler flags for each flavour. Note that this is just an intermediary step. The binary resulting from this step is not good for real life workloads as it has profiling instructions embedded inside.
After the instrumented interpreter is built, the Makefile will run a training workload. This is necessary in order to profile the interpreter execution. Note also that any output, both stdout and stderr, that may appear at this step is suppressed.
The final step is to build the actual interpreter, using the information collected from the instrumented one. The end result will be a Python binary that is optimized; suitable for distribution or production installation.
Link Time Optimization
Enabled via configure's --with-lto flag. LTO takes advantage of the ability of recent compiler toolchains to optimize across the otherwise arbitrary .o file boundary when building final executables or shared libraries for additional performance gains.