Release 5.4.0.20 is available   

Release 5.4.0.20 of FDPR-Pro:

Release 5.4.0.20 introduces a new optimization, --simplify-early-exit (-see), which optimizes prologue of function that commonly perform conditional early exit.

Simply-early-exit optimization

An early-exit condition occurs when a function checks a condition based on the input arguments and based on this condition it decides to exit the function prematurely. By convention the compiler performs various saves and restores that are needed in case the function's body is executed. Under -see a special epilogue is used when that condition is taken which avoids restoring unnecessary registers as well as restoring the return address. In the aggressive form, under -see 1, the prologue is also simplified by performing the branch to the conditional epilogue as early as possible instead of performing first the full frame setup.

Currently -see 0 is implied in -O2 and -see 1 is implied in -O3 and higher. To disable it in any of the -Ox, use -Ox -see -1.

Performance caution when using --killed-regs on Power6

It was found, in particular on Power6, that the --killed-regs (-kr) optimization that eliminates stores of registers that are killed after frequently called functions, may regress performance when combined with aggressive inlining (eg., with -O3 and -O4). To remove -kr from -Ox, add -nokr. Compare performance of -O4 and -O4 -nokr to see if the latter is better.