Restricting Optimizations

The following options restrict or preclude the compiler's ability to optimize your program:

Option Description
-O0 Disables all optimizations.
-mp1 Improve floating-point precision. Speed impact is less than with -mp.
-fp
IA-32 only		 Disable using the EBP register as a general purpose register.
-prec_div
IA-32 only		 Disables the floating point division-to-multiplication optimization.

-fp_port
IA-32 only

 Round fp results at assignments and casts (some speed impact).
-ftz[-]
Itanium-based
systems only		 Enable [disable] flush denormal results to zero. The -ftz option is OFF by default, but turned ON with -O3.
-IPF_fma[-]
Itanium-based
systems only		 Enable [disable] the combining of floating point multiplies and add/subtract operations.
-IPF_fltacc[-]
Itanium-based
systems only		 Enable [disable] optimizations that affect floating point accuracy.
-IPF_flt_eval_method0
Itanium-based
systems only		 Floating-point operands evaluated to the precision indicated by program.
-IPF_fp_speculation<mode>
Itanium-based
systems only		 Enable floating point speculations with the following <mode> conditions:
  • fast - speculate floating point operations
  • safe - speculate only when safe
  • strict - same as off
  • off - disables speculation of floating-point operations

Note

You can turn off all optimizations for specific functions by using #pragma optimize. In the following example, all optimization is turned off for function foo():

#pragma optimize("", off)

foo(){

...

}

Valid second arguments for #pragma optimize are "on" or "off." With the "on" argument, foo() is compiled with the same optimization as the rest of the program. The compiler ignores first argument values.