[Bug tree-optimization/117100] New: [13 regression] ImageMagick miscompiled with -O1 -funswitch-loops

[sjames at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117100

            Bug ID: 117100
           Summary: [13 regression] ImageMagick miscompiled with -O1
                    -funswitch-loops
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sjames at gcc dot gnu.org
  Target Milestone: ---

Hopefully this reduction is right. Originally reported downstream in Gentoo at
https://bugs.gentoo.org/941208 where IM would give a black PNG when built with
-O3 with GCC 13.

```
#include <stdbool.h>
#include <stdlib.h>

static int count = 0;

double PerceptibleReciprocal(const double x) {
  double sign;

  sign = x < 0.0 ? -1.0 : 1.0;
  return (sign / 1.0e-12);
}

bool CompositeImage(int compose) {
  double Sa = count;
  double pixel = 65535;
  double gamma = 1.0;

  for (int i = 0; i < 3; i++) {
    switch (compose) {
      case 1:
      case 61: {
        pixel = 65535 * gamma * Sa;
        break;
      }
      case 39: {
        gamma = PerceptibleReciprocal(0);
        break;
      }
      case 17: {
        /* When things are OK, we reach here. */
        exit(0);
        break;
      }
      default: {
        break;
      }
    }

    /* This must be a switch to break. */
    switch (compose) {
      case 20:
      case 30:
      case 50: {
        gamma = PerceptibleReciprocal(0);
        break;
      }
      default: {
        break;
      }
    }

    if (pixel < 0 || pixel >= 65535) {
      __builtin_abort();
    }
  }

  count++;
  return true;
}

int main() {
  CompositeImage(1);
  CompositeImage(17);
}
```