[Bug c/114554] New: In O2-3 optimization, this code runs in an infinite loop.

[nmodnation at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114554

            Bug ID: 114554
           Summary: In O2-3 optimization, this code runs in an infinite
                    loop.
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nmodnation at gmail dot com
  Target Milestone: ---

#include <stdio.h>
#include <stdint.h>

static void wymum(uint64_t* p1, uint64_t* p2) {
  int64_t v1;
  int64_t v2;
  int64_t v3;
  int64_t v4;
  int64_t v5;
  int64_t v6;
  int64_t v7;
  int64_t v8;
  int64_t v9;
  int64_t v10;
  int64_t v11;
  int64_t t1;
  int32_t t2;
  int64_t t3;
  int64_t t4;
  t1 = *p1;
  t1 = (uint64_t)t1 >> (uint64_t)32;
  v1 = t1;
  t1 = *p2;
  t1 = (uint64_t)t1 >> (uint64_t)32;
  v2 = t1;
  t2 = (uint32_t)*p1;
  v3 = (uint64_t)(uint32_t)t2;
  t2 = (uint32_t)*p2;
  v4 = (uint64_t)(uint32_t)t2;
  t1 = v1;
  t1 *= v2;
  v5 = t1;
  t1 = v1;
  t1 *= v4;
  v6 = t1;
  t1 = v2;
  t1 *= v3;
  v7 = t1;
  t1 = v3;
  t1 *= v4;
  v8 = t1;
  t1 = v6;
  t1 = (uint64_t)t1 << (uint64_t)32;
  t3 = v8;
  t3 += t1;
  v9 = t3;
  t2 = (uint64_t)v9 < (uint64_t)v8 ? 1 : 0;
  v10 = (int64_t)t2;
  t1 = v7;
  t1 = (uint64_t)t1 << (uint64_t)32;
  t3 = v9;
  t3 += t1;
  v11 = t3;
  t2 = (uint64_t)v11 < (uint64_t)v9 ? 1 : 0;
  t1 = (int64_t)t2;
  v10 += t1;
  t1 = v6;
  t1 = (uint64_t)t1 >> (uint64_t)32;
  t3 = v7;
  t3 = (uint64_t)t3 >> (uint64_t)32;
  t4 = v5;
  t4 += t1;
  t4 += t3;
  t4 += v10;
  *p1 = v11;
  *p2 = t4;
  return;
}

static uint64_t wymix(uint64_t p1, uint64_t p2) {
  wymum(&p1, &p2);
  return p1 ^ p2;
}

static uint64_t wyrand(int64_t* p1) {
  *p1 += 3257665815644502181;
  return wymix(*p1, *p1 ^ -8378864009470890807);
}

int main(int argc, char **argv) {
  int64_t seed = 1;
  int i = 0;
  for (; i < 10; i++) {
    printf("%llx\n", wyrand(&seed));
  }
  return 0;
}

// gcc -O2 -o bug bug.c

It is not a solution, but it can be resolved by modifying it as shown below.

1. static uint64_t wyrand(int64_t* p1) => static uint64_t wyrand(uint64_t* p1)
2. int64_t seed = 1; => uint64_t seed = 1;