-OiLib: Optimize Library Functions

OPTIMIZATIONS

Function

-OiLib[=<arguments>] 

<arguments> are one or multiple of following suboptions:

b: inline calls to the strlen() function

d: inline calls to the fabs() or fabsf() functions

e: inline calls to the memset() function

f: inline calls to the memcpy() function

g: replace shifts left of 1 by array lookup

None

None

None

This option enables the compiler to optimize specific known library functions to reduce execution time. The Compiler frequently uses small functions such as strcpy(), strcmp(), and so forth. The following functions are optimized:

• strcpy() (only available for ICG-based backends)
• strlen() (e.g., strlen("abc"))
• abs() or fabs() (e.g., `f = fabs(f);')
• memset() is optimized only if:
  • the result is not used
  • memset() is used to zero out
  • the size for the zero out is in the range 1 - 0xff
  • the ANSI library header file <string.h> is included

    An example for this is:

    (void)memset(&buf, 0, 50);

    In this case, the call to memset() is replaced with a call to _memset_clear_8bitCount present in the ANSI library (string.c).

• memcpy() is optimized only if:
  • the result is not used,
  • the size for the copy out is in the range 0 to 0xff,
  • the ANSI library header file <string.h> is included.

    An example for this is:

    (void)memcpy(&buf, &buf2, 30);

    In this case the call to memcpy() is replaced with a call to _memcpy_8bitCount present in the ANSI library (string.c).

• (char)1 << val is replaced by _PowOfTwo_8[val] if _PowOfTwo_8 is known at compile time. Similarly, for 16-bit and 32-bit shifts, the arrays _PowOfTwo_16 and _PowOfTwo_32 are used. These constant arrays contain the values 1, 2, 4, 8, etc. They are declared in hidef.h. This optimization is performed only when optimizing for time.
• -Oilib without arguments: optimize calls to all supported library functions.

Compiling the f() function with the -Oilib=a compiler option (only available for ICG-based backends):

void f(void) { 

  char *s = strcpy(s, ct); 

} 

This translates in a similar fashion to the following function:

void g(void) { 

  s2 = s; 

  while(*s2++ = *ct++); 

} 

-Oi: Inlining