[Bug middle-end/59990] New: [4.7/4.8/4.9 regression] incorrect memcpy optimization

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59990

            Bug ID: 59990
           Summary: [4.7/4.8/4.9 regression] incorrect memcpy optimization
           Product: gcc
           Version: 4.7.3
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ebotcazou at gcc dot gnu.org
            Target: i?86-*-*

This is a regression introduced in the 4.7.x series of compilers, visible on
x86 but probably reproducible on other platforms.  If you compile:

extern void abort (void);

unsigned char value[4] = { 66, 9, 160, 255 };

int main (void)
{
  volatile float f;
  unsigned char a[4];

  __builtin_memcpy ((void *)&f, value, 4);
  __builtin_memcpy (a, (void *)&f, 4);
  if (a[2] != 160)
    abort ();

  return 0;
}

with optimization enabled, it aborts at run time because FP instructions are
incorrectly used to implement the memcpy operations.