[llvm-bugs] [Bug 28012] New: Over-aggressive overflow elimination check with call to exit()

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=28012

            Bug ID: 28012
           Summary: Over-aggressive overflow elimination check with call
                    to exit()
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: Loop Optimizer
          Assignee: unassignedbugs at nondot.org
          Reporter: eli.friedman at gmail.com
                CC: atrick at apple.com, llvm-bugs at lists.llvm.org,
                    sanjoy at playingwithpointers.com
    Classification: Unclassified

Testcase:

#include <stdlib.h>
#include <stdio.h>
#include <limits.h>
static int will_add_overflow(int a, int x) {
  return a >= INT_MIN - x;
}
void f(int a, long last_value) {
  if (will_add_overflow(a, 3)) {
    // Leave, and don't actually do the increment, so no UB.
    printf("last_value = %ld\n", last_value);
    exit(0);
  }
}
void (*ff)(int, long) = f;
int main() {
  int a = 0;
  unsigned a_u = 0;
  volatile long last_value;
  do {
    a_u += 3;
    last_value = (long) ((int) a_u);
    ff(a, last_value);
    a += 3;
  } while (a != 46);
  return 0;
}

With clang -O0, prints "last_value = -2147483647". With clang -O2, prints
nothing.  (Tested on x86-64 Linux.)

Basically the same testcase as bug 27315, except that I hid the call to exit().

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