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Some loops contain two or more induction variables that can be combined into one induction variable.
Example:
The code fragment below has three induction variables (i1, i2, and i3) that can be replaced with one induction variable, thus eliminating two induction variables.
int a[SIZE];
int b[SIZE];
void f (void)
{
int i1, i2, i3;
for (i1 = 0, i2 = 0, i3 = 0; i1 < SIZE; i1++)
a[i2++] = b[i3++];
return;
}
The code fragment below shows the loop after induction variable elimination.
int a[SIZE];
int b[SIZE];
void f (void)
{
int i1;
for (i1 = 0; i1 < SIZE; i1++)
a[i1] = b[i1];
return;
}
Notes:
Induction variable elimination can reduce the number of additions (or subtractions) in a loop, and improve both run-time performance and code space.
Some architectures have auto-increment and auto-decrement instructions that can sometimes be used instead of induction variable elimination.
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