Editing Loop splitting (section)

==Loop peeling==
Loop peeling is a special case of loop splitting which splits any problematic first (or last) few iterations from the loop and performs them outside of the loop body.

Suppose a loop was written like this:
<syntaxhighlight lang="c">
 int p = 10;
 for (int i=0; i<10; ++i)
 {
   y[i] = x[i] + x[p];
   p = i;
 }
</syntaxhighlight>
Notice that <code>p = 10</code> only for the first iteration, and for all other iterations, <code>p = i - 1</code>. A compiler can take advantage of this by [[loop unwinding|unwinding]] (or "peeling") the first iteration from the loop.

After peeling the first iteration, the code would look like this:
<syntaxhighlight lang="c">
 y[0] = x[0] + x[10];
 for (int i=1; i<10; ++i)
 {
   y[i] = x[i] + x[i-1];
 }
</syntaxhighlight>
This equivalent form eliminates the need for the variable <code>p</code> inside the loop body.

Loop peeling was introduced in [[GNU Compiler Collection|gcc]] in version 3.4. More generalised loop splitting was added in GCC 7.<ref name="R1"/>