gcc Compiler Optimization Options [From the man gcc page.]

• -O Optimize. Optimizing compilation takes somewhat more time, and a lot more memory for a large function.

  Without `-O', the compiler's goal is to reduce the cost of compilation and to make debugging produce the expected results. Statements are independent: if you stop the program with a breakpoint between statements, you can then assign a new value to any variable or change the program counter to any other statement in the function and get exactly the results you would expect from the source code.

  Without `-O', only variables declared register are allocated in registers.

  With `-O', the compiler tries to reduce code size and execution time.

• -fforce-mem Force memory operands to be copied into registers before doing arithmetic on them. This may produce better code by making all memory references potential common subexpressions. When they are not common subexpressions, instruction combination should eliminate the separate register-load.

• -fforce-addr Force memory address constants to be copied into registers before doing arithmetic on them. This may produce better code just as `-fforce-mem' may.

• -finline Pay attention the inline keyword. Normally the negation of this option `-fno-inline' is used to keep the compiler from expanding any functions inline.

• -finline-functions Integrate all simple functions into their callers. The compiler heuristically decides which functions are simple enough to be worth integrating in this way.

• -fcaller-saves Enable values to be allocated in registers that will be clobbered by function calls, by emitting extra instructions to save and restore the registers around such calls. Such allocation is done only when it seems to result in better code than would otherwise be produced.