Example: GCC compiler optimization report for benchmark stream

• stream source code snippet

  /* ---
   Tuned vector scale:  b[] = scalar * c[]
  
   In:  STREAM_ARRAY_SIZE_thread, scalar, c[]
   Out: b[]
  --- */
  void static inline tuned_STREAM_Scale(const STREAM_TYPE scalar) {
      #pragma omp parallel default(none) shared(scalar, STREAM_ARRAY_SIZE_thread)
      {
          #ifdef __INTEL_COMPILER
              // Instructs the compiler to use non-temporal (that is, streaming) stores
              #pragma vector nontemporal
          #endif
          #pragma omp simd aligned(b, c : alignment_bytes)
          for (long int j = 0; j < STREAM_ARRAY_SIZE_thread; j++) {
              b[j] = scalar * c[j]; // Line: 337
          }
      }
  }
  
  /* ---
  Tuned vector add: c[] = a[] + b[]
  
  In:  STREAM_ARRAY_SIZE_thread, a[], b[]
  Out: c[]
  --- */
  void static inline tuned_STREAM_Add() {
      #pragma omp parallel default(none) shared(STREAM_ARRAY_SIZE_thread)
      {
          #ifdef __INTEL_COMPILER
              // Instructs the compiler to use non-temporal (that is, streaming) stores
              #pragma vector nontemporal
          #endif
          #pragma omp simd aligned(a, b, c : alignment_bytes)
          for (long int j = 0; j < STREAM_ARRAY_SIZE_thread; j++) {
              c[j] = a[j] + b[j];  // Line: 357
          }
      }
  }

• Compile benchmark with vectorization report enabled

  module add compiler/gnu
  gcc -std=c11 -Ofast -march=native -flto -fopenmp \
      -fopt-info-vec \
      stream.c

• Output

  ...
  stream.OpenMP.c:337:30: optimized: loop vectorized using 32 byte vectors
  stream.OpenMP.c:337:30: optimized: loop vectorized using 16 byte vectors
  stream.OpenMP.c:357:21: optimized: loop vectorized using 32 byte vectors
  stream.OpenMP.c:357:21: optimized: loop vectorized using 16 byte vectors
  ...