Typical Advice

 advice #30006: Loop at line 22 cannot be scheduled efficiently, as it
contains a function call ("function_name"). Try making "function_name" an
inline function.

Why is the Compiler giving this Advice ?

There is a function call within a loop, which prevents the software-pipelining loop optimization. Software-pipelining is a key optimization for achieving good performance. You may see reduced performance without software pipelining.

What it means:

For improved performance, at optimization levels --opt_level=2 (-O2) and --opt_level=3 (-O3), the compiler attempts to software pipeline your loops. Sometimes the compiler may not be able to inline a function call that is in a loop. Because the compiler could not inline the function call, the loop could not be software pipelined, and the loop could not efficiently scheduled.

Typical testcase: In the code below, call to function "func2" prevents software pipelining.

 void func1(int *p, int *q, int n)
{
unsigned int i;

for (i = 0; i < n; i++)
{
int t = func2(i);

 ; other operations
}
}
int function func2() { . . . }

However if the function func2 is inlined, it:

• Saves the overhead of a function call
• The compiler is free to optimize the function in context with surrounding code

Automatic inlining is controlled by the "inline" keyword; use it to allow inlining of specific functions :

 inline int function func2() { . . . }

Risks, Severity

The function call "func2" in the loop, prevents software pipelining and better performance. While inlining improves performance, expanding functions inline may increase code size, especially inlining a function that is called in a number of places. Function inlining is optimal for functions that are called only from a small number of places and for small functions.

Suggested Action

Inline function call to "func2".

More Resources

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Go to the TI Compiler's e2e online forum! 

For technical support please post your questions at http://e2e.ti.com.