[Bug middle-end/84309] New: [8 Regression] Wrong-code with -ffast-math

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84309

            Bug ID: 84309
           Summary: [8 Regression] Wrong-code with -ffast-math
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mpolacek at gcc dot gnu.org
  Target Milestone: ---

Target: x86_64-pc-linux-gnu

typedef __SIZE_TYPE__ size_t;
double pow (double x, double y);
double log2 (double x);

int
main ()
{
  size_t a = 1024;
  size_t b = 16 * 1024;
  size_t c = pow (2, (log2 (a) + log2 (b)) / 2);
  if (c != 4 * 1024)
    __builtin_abort ();
  return 0;
}

$ xgcc x.c -lm; ./a.out
$ xgcc x.c -lm -ffast-math; ./a.out
Aborted (core dumped)