profile-count: Avoid overflows into uninitialized [PR112303]

The testcase in the patch ICEs with
--- gcc/tree-scalar-evolution.cc
+++ gcc/tree-scalar-evolution.cc
@@ -3881,7 +3881,7 @@ final_value_replacement_loop (class loop *loop)

       /* Propagate constants immediately, but leave an unused initialization
         around to avoid invalidating the SCEV cache.  */
-      if (CONSTANT_CLASS_P (def) && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rslt))
+      if (0 && CONSTANT_CLASS_P (def) && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rslt))
        replace_uses_by (rslt, def);

       /* Create the replacement statements.  */
(the addition of the above made the ICE latent), because profile_count
addition doesn't check for overflows and if unlucky, we can even overflow
into the uninitialized value.
Getting really huge profile counts is very easy even when not using
recursive inlining in loops, e.g.
__attribute__((noipa)) void
bar (void)
{
  __builtin_exit (0);
}

__attribute__((noipa)) void
foo (void)
{
  for (int i = 0; i < 1000; ++i)
  for (int j = 0; j < 1000; ++j)
  for (int k = 0; k < 1000; ++k)
  for (int l = 0; l < 1000; ++l)
  for (int m = 0; m < 1000; ++m)
  for (int n = 0; n < 1000; ++n)
  for (int o = 0; o < 1000; ++o)
  for (int p = 0; p < 1000; ++p)
  for (int q = 0; q < 1000; ++q)
  for (int r = 0; r < 1000; ++r)
  for (int s = 0; s < 1000; ++s)
  for (int t = 0; t < 1000; ++t)
  for (int u = 0; u < 1000; ++u)
  for (int v = 0; v < 1000; ++v)
  for (int w = 0; w < 1000; ++w)
  for (int x = 0; x < 1000; ++x)
  for (int y = 0; y < 1000; ++y)
  for (int z = 0; z < 1000; ++z)
  for (int a = 0; a < 1000; ++a)
  for (int b = 0; b < 1000; ++b)
    bar ();
}

int
main ()
{
  foo ();
}
reaches the maximum count already on the 11th loop.

Some other methods of profile_count like apply_scale already
do use MIN (val, max_count) before assignment to m_val, this patch
just extends that to operator{+,+=} methods.
Furthermore, one overload of apply_probability wasn't using
safe_scale_64bit and so could very easily overflow as well
- prob is required to be [0, 10000] and if m_val is near the max_count,
it can overflow even with multiplications by 8.

2024-03-28  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/112303
	* profile-count.h (profile_count::operator+): Perform
	addition in uint64_t variable and set m_val to MIN of that
	val and max_count.
	(profile_count::operator+=): Likewise.
	(profile_count::operator-=): Formatting fix.
	(profile_count::apply_probability): Use safe_scale_64bit
	even in the int overload.

	* gcc.c-torture/compile/pr112303.c: New test.

diff --git a/gcc/profile-count.h b/gcc/profile-count.h
index b3d776475e2ca1376e61fe08e4eed364d2c0b2db..6bbd476cb7fef6745ce8570e68dba328525e5ed9 100644 (file)
--- a/gcc/profile-count.h
+++ b/gcc/profile-count.h
@@ -910,7 +910,8 @@ public:
 
       profile_count ret;
       gcc_checking_assert (compatible_p (other));
-      ret.m_val = m_val + other.m_val;
+      uint64_t ret_val = m_val + other.m_val;
+      ret.m_val = MIN (ret_val, max_count);
       ret.m_quality = MIN (m_quality, other.m_quality);
       return ret;
     }
@@ -929,7 +930,8 @@ public:
       else
        {
           gcc_checking_assert (compatible_p (other));
-         m_val += other.m_val;
+         uint64_t ret_val = m_val + other.m_val;
+         m_val = MIN (ret_val, max_count);
          m_quality = MIN (m_quality, other.m_quality);
        }
       return *this;
@@ -957,7 +959,7 @@ public:
       else
        {
           gcc_checking_assert (compatible_p (other));
-         m_val = m_val >= other.m_val ? m_val - other.m_val: 0;
+         m_val = m_val >= other.m_val ? m_val - other.m_val : 0;
          m_quality = MIN (m_quality, other.m_quality);
        }
       return *this;
@@ -1127,7 +1129,9 @@ public:
       if (!initialized_p ())
        return uninitialized ();
       profile_count ret;
-      ret.m_val = RDIV (m_val * prob, REG_BR_PROB_BASE);
+      uint64_t tmp;
+      safe_scale_64bit (m_val, prob, REG_BR_PROB_BASE, &tmp);
+      ret.m_val = tmp;
       ret.m_quality = MIN (m_quality, ADJUSTED);
       return ret;
     }

diff --git a/gcc/testsuite/gcc.c-torture/compile/pr112303.c b/gcc/testsuite/gcc.c-torture/compile/pr112303.c
new file mode 100644 (file)
index 0000000..01937da
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/compile/pr112303.c
@@ -0,0 +1,25 @@
+/* PR tree-optimization/112303 */
+
+int a, b, d, e, f, **g, h;
+char c;
+
+int *
+foo (void)
+{
+  for (int i = 0; i < 3; i++)
+    {
+      for (h = 0; h < 2; h++)
+       ;
+      if (!b)
+       break;
+    }
+  while (f)
+    while (e)
+      {
+       c = 0;
+       while (d)
+         while (a)
+           *g = foo ();
+      }
+  return 0;
+}