gcc/testsuite/gcc.dg/pure-2.c

/* { dg-do compile } */
/* { dg-options "-O2 -Wsuggest-attribute=pure -fno-finite-loops" } */
/* { dg-add-options bind_pic_locally } */

extern int extern_const(int a) __attribute__ ((pure));
extern int v;

/* Trivial.  */
int
foo1(int a)  /* { dg-bogus "normally" "detect pure candidate" } */
{ /* { dg-warning "pure" "detect pure candidate" { target *-*-* } "10" } */
  return v;
}

/* Loops known to be normally and extern const calls should be safe.  */
int __attribute__ ((noinline))
foo2(int n)  /* { dg-bogus "normally" "detect pure candidate" } */
{ /* { dg-warning "pure" "detect pure candidate" { target *-*-* } "17" } */
  int ret = 0;
  int i;
  for (i=0; i<n; i++)
    ret+=extern_const (i);
  return ret;
}

/* No warning here; we can work it by ourselves.  */
static int __attribute__ ((noinline))
foo2b(int n)
{
  int ret = 0;
  int i;
  for (i=0; i<n; i++)
    ret+=extern_const (i);
  return ret;
}

/* Unbounded loops are not safe.  */
static int __attribute__ ((noinline))
foo3(unsigned int n) /* { dg-warning "pure\[^\n\]* normally" "detect pure candidate" } */
{
  int ret = 0;
  unsigned int i;
  for (i=0; extern_const (i+n); n++)
    ret+=extern_const (i);
  return ret;
}

int
foo4(int n)  /* { dg-warning "pure\[^\n\]* normally" "detect pure candidate" } */
{
  return foo3(n) + foo2b(n);
}

int
foo5(int n)  /* { dg-bogus "normally" "detect pure candidate" } */
{  /* { dg-warning "pure" "detect pure candidate" { target *-*-* } "55" } */
  return foo2(n);
}