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Diagnostic 15542: xxxx was not vectorized: inner loop was already vectorized

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Cause:

This vectorization diagnostic is emitted starting from Intel(R) C++ Compiler 15.0. This diagnostic message is emitted when we have a nested "for" loop and the inner loop is vectorized. When the inner "for" loop is vectorized, this diagnostic is emitted for the outer loop.

Examples:

#define N 1000
float A[N][N];
void foo(int n){
  int i,j;
  for (i=0;i<n;i++){
    for (j=0;j<n;j++){
      A[i][j]++;
    }
  }
}

$ icpc test52.cc -c -qopt-report2 -qopt-report-phase=vec -qopt-report-file=stderr

Begin optimization report for: foo(int)

    Report from: Vector optimizations [vec]


LOOP BEGIN at test52.cc(5,3)
   remark #15542: loop was not vectorized: inner loop was already vectorized

   LOOP BEGIN at test52.cc(6,5)
      remark #15399: vectorization support: unroll factor set to 4
      remark #15300: LOOP WAS VECTORIZED
   LOOP END

   LOOP BEGIN at test52.cc(6,5)
   <Remainder>
      remark #15301: REMAINDER LOOP WAS VECTORIZED
   LOOP END

   LOOP BEGIN at test52.cc(6,5)
   <Remainder>
   LOOP END
LOOP END


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