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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. struct timeit {
  5.     decltype(chrono::high_resolution_clock::now()) begin;
  6.     const string label;
  7.     timeit(string label = "???") : label(label) { begin = chrono::high_resolution_clock::now(); }
  8.     ~timeit() {
  9.         auto end = chrono::high_resolution_clock::now();
  10.         auto duration = chrono::duration_cast<chrono::milliseconds>(end - begin).count();
  11.         cerr << duration << "ms elapsed [" << label << "]" << endl;
  12.     }
  13. };
  14. const int MAXN = 1e5;
  15. const int NUMITERS = 10000;
  16. int A[MAXN];
  17. int main() {
  18.     {
  19.         timeit x("fused");
  20.         for (int j = 1; j < NUMITERS; j++) {
  21.             for (int i = 0; i < MAXN; i++) {
  22.                 A[i] += j;
  23.                 A[i] *= j;
  24.             }
  25.         }
  26.     }
  27.     {
  28.         timeit x("unfused");
  29.         for (int j = 1; j < NUMITERS; j++) {
  30.             for (int i = 0; i < MAXN; i++)
  31.                 A[i] += j;
  32.             for (int i = 0; i < MAXN; i++)
  33.                 A[i] *= j;
  34.         }
  35.     }
  36.  
  37. }
  38.  
Success #stdin #stdout #stderr 1.51s 4508KB
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stdin
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Standard input is empty
stdout
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Standard output is empty
stderr
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539ms elapsed [fused]
972ms elapsed [unfused]
https://ideone.com/OnbRXU
language:
C++14 (gcc 8.3)
created:
4 years ago
visibility:
public

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