Intel® Advisor Help
Possible register spilling was detected and all vector registers are in use. This may negatively impact performance, because the spilled variable must be loaded to and unloaded from main memory. Improve performance by decreasing vector register pressure.
The current directive unroll factor increases vector register pressure. To fix: Decrease unroll factor using a directive: #pragma nounroll or #pragma unroll.
Example:
void nounroll(int a[], int b[], int c[], int d[])
{
#pragma nounroll
for (int i = 1; i < 100; i++)
{
b[i] = a[i] + 1;
d[i] = c[i] + 1;
}
}
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Possible register spilling along with high vector register pressure is preventing effective vectorization. To fix: Use the directive #pragma distribute_point or rewrite your code to distribute the source loop. This can decrease register pressure as well as enable software pipelining and improve both instruction and data cache use.
Example:
#define NUM 1024
void loop_distribution_pragma2(
double a[NUM], double b[NUM], double c[NUM],
double x[NUM], double y[NUM], double z[NUM] )
{
int i;
// After distribution or splitting the loop.
for (i=0; i< NUM; i++)
{
a[i] = a[i] +i;
b[i] = b[i] +i;
c[i] = c[i] +i;
#pragma distribute_point
x[i] = x[i] +i;
y[i] = y[i] +i;
z[i] = z[i] +i;
}
}
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