<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/63644>63644</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Long compile time at -O3 on x86_64-linux_gnu (a long latent issue)
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          shao-hua-li
      </td>
    </tr>
</table>

<pre>
    For the following code, clang at -O3 would need more than 25 seconds to compile on my machine. `opt-bisect-limit` shows that `Loop Strength Reduction` takes most of the time.

```console
% cat a.c
int a, b;
long d;
int e(int f) {
  int c;
  for (; c; c++)
    if (f << c)
      return c;
  return 0;
}
void g() {
  a = 0;
  for (; a > -22; a--) {
    d = b + d + d;
    b = e(d);
  }
}

int main(){}
%
% time clang-tk a.c -O2

real    0m0.061s
user    0m0.031s
sys     0m0.026s
%
% time clang-tk a.c -O3

real    0m26.647s
user    0m25.463s
sys     0m1.163s
%
```
</pre>
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