Hi Byoungyoung Lee, > Is there anyway in gcc to log the information about which compiler > options were actually used to optimize each function? > For example, if I compile a program with option -O3, how could I > figure out which specific options (such as -funroll-loops or something > like that) were used to optimize function X ? I use this technique: echo '' | gcc -O3 -fverbose-asm -S -xc - -o O3.s cat O3.s In the created O3.s assembly source comment, it mentions which flags were enabled by the -O3 switch. If you want a detailed assembly line-by-line diagnostic of which particular optimization was used for a given algorithm, you'll have to do some more sleuthing. Such as using -fno-<flag> to disable all the flags, and enable them one-by-one. Or perhaps by dumping the compiler state after each optimization pass (which I think is usually only used as a diagnostic aid for making changes to GCC itself). Also, the majority of optimizations do not have a toggle-able flag to enable/disable them. As I understand it... -O1 enables a whole lot of optimizations that do not have toggle-able flags. -O2 enables a few more. -O3 enables one-or-two more. HTH, --Eljay
