Inlining substitutes selected function calls with copies of
the function’s object code. Only functions that meet the
optimizer’s criteria are inlined. Inlining may result in
slightly larger executable files. However, this increase in size
is offset by the elimination of time-consuming procedure calls and
procedure returns.
At +O3, inlining is performed within a file; at +O4, it is performed across files. Inlining is affected
by the +O[no]inline[=namelist] and +Oinline_budget=n command-line options. See Chapter 7 “Controlling
optimization” for more information.
Example 5-2 Inlining
within single source file
The following is an example of inlining at the source code
level. Before inlining, the C source file looks like this:
/* Return the greatest common divisor of two positive integers,*/
/* int1 and int2, computed using Euclid's algorithm. (Return 0 */
/* if either is not positive.) */
int gcd(int int1,int int2)
{
int inttemp;
if ( (int1 <= 0) || (int2 <= 0) ) {
return(0);
}
do {
if (int1 < int2) {
inttemp = int1;
int1 = int2;
int2 = inttemp;
}
int1 = int1 - int2;
} while (int1 > 0);
return(int2);
}main()
{
int xval,yval,gcdxy;
.
. /* statements before call to gcd */
.
gcdxy = gcd(xval,yval);
.
. /* statements after call to gcd */
.
} |
After inlining, main looks like this:
main()
{
int xval,yval,gcdxy;
.
. /* statements before inlined version of gcd */
.
{
int int1;
int int2; int1 = xval;
int2 = yval;
{
int inttemp; if ( (int1 <= 0) || (int2 <= 0) ){
gcdxy = (0);
goto AA003;
}
do {
if (int1 < int2){
inttemp = int1;
int1 = int2;
int2 = inttemp;
}
int1 = int1 - int2;
} while (int1 > 0);
gcdxy = (int2);
}
}
AA003 : ;
.
. /* statements after inlined version of gcd */
.
} |
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