问JIT热编译

EN

-fbranch-probabilities
   After running a program compiled with -fprofile-arcs
   (see Options for Debugging Your Program or gcc), you can compile it a second
   time using -fbranch-probabilities, to improve optimizations based on the number
   of times each branch was taken. When a program compiled with -fprofile-arcs
   exits, it saves arc execution counts to a file called sourcename.gcda for each
   source file. The information in this data file is very dependent on the
   structure of the generated code, so you must use the same source code and the
   same optimization options for both compilations. 

   With -fbranch-probabilities, GCC puts a ‘REG_BR_PROB’ note on each ‘JUMP_INSN’
   and ‘CALL_INSN’. These can be used to improve optimization. Currently, they are
   only used in one place: in reorg.c, instead of guessing which path a branch is
   most likely to take, the ‘REG_BR_PROB’ values are used to exactly determine
   which path is taken more often.