[RFC] Add vec::ordered_remove_if

[Tom de Vries <Tom_deVries at mentor dot com>]

[ was: Re: [libgomp, openacc, openmp, PR83046] Prune removed funcs from 
offload table ]

On 12/28/2017 05:06 PM, Jakub Jelinek wrote:
> On Thu, Dec 28, 2017 at 04:53:29PM +0100, Tom de Vries wrote:
> > --- a/gcc/lto-cgraph.c
> > +++ b/gcc/lto-cgraph.c
> > @@ -1111,6 +1111,16 @@ output_offload_tables (void)
> >     struct lto_simple_output_block *ob
> >       = lto_create_simple_output_block (LTO_section_offload_table);
> >   
> > +  for (unsigned i = 0; i < vec_safe_length (offload_funcs);)
> > +    {
> > +      if (!cgraph_node::get ((*offload_funcs)[i]))
> > +	{
> > +	  offload_funcs->ordered_remove (i);
> > +	  continue;
> > +	}
> > +      i++;
> > +    }

> This has O(n^2) complexity for n == vec_safe_length (offload_funcs).
> Can't you instead just have 2 IVs, one for where we read the vector elt and
> one for where we write it if the 2 are different, then truncate the vector
> if needed at the end?

I wonder if it makes sense to add this function to the vec interface.

Any comments?

Thanks,
- Tom

Add vec::ordered_remove_if

---
 gcc/vec.c | 21 +++++++++++++++++++++
 gcc/vec.h | 39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+)

diff --git a/gcc/vec.c b/gcc/vec.c
index 9a80f34..91e2464 100644
--- a/gcc/vec.c
+++ b/gcc/vec.c
@@ -403,6 +403,26 @@ test_ordered_remove ()
   ASSERT_EQ (9, v.length ());
 }
 
+static bool
+remove_5_7_p (const int &a)
+{
+  return a == 5 || a == 7;
+}
+
+/* Verify that vec::ordered_remove_if works correctly.  */
+
+static void
+test_ordered_remove_if (void)
+{
+  auto_vec <int> v;
+  safe_push_range (v, 0, 10);
+  v.ordered_remove_if (remove_5_7_p);
+  ASSERT_EQ (4, v[4]);
+  ASSERT_EQ (6, v[5]);
+  ASSERT_EQ (8, v[6]);
+  ASSERT_EQ (8, v.length ());
+}
+
 /* Verify that vec::unordered_remove works correctly.  */
 
 static void
@@ -464,6 +484,7 @@ vec_c_tests ()
   test_pop ();
   test_safe_insert ();
   test_ordered_remove ();
+  test_ordered_remove_if ();
   test_unordered_remove ();
   test_block_remove ();
   test_qsort ();
diff --git a/gcc/vec.h b/gcc/vec.h
index f55a41f..857e4f4 100644
--- a/gcc/vec.h
+++ b/gcc/vec.h
@@ -571,6 +571,7 @@ public:
   void truncate (unsigned);
   void quick_insert (unsigned, const T &);
   void ordered_remove (unsigned);
+  void ordered_remove_if (bool (*) (const T &));
   void unordered_remove (unsigned);
   void block_remove (unsigned, unsigned);
   void qsort (int (*) (const void *, const void *));
@@ -1013,6 +1014,31 @@ vec<T, A, vl_embed>::ordered_remove (unsigned ix)
 }
 
 
+/* Remove all elements from this vector for which REMOVE_ELEM_P (elem) holds.
+   Ordering of remaining elements is preserved.  This is an an O(N)
+   operation.  */
+
+template<typename T, typename A>
+inline void
+vec<T, A, vl_embed>::ordered_remove_if (bool (*remove_elem_p) (const T &))
+{
+  unsigned int n = length ();
+  unsigned int write_index = 0;
+  for (unsigned int read_index = 0; read_index < n; ++read_index)
+    {
+      bool remove_p = remove_elem_p (read_index);
+      if (remove_p)
+	continue;
+
+      if (read_index != write_index)
+	m_vecdata[write_index] = m_vecdata[read_index];
+
+      write_index++;
+    }
+  truncate (write_index);
+}
+
+
 /* Remove an element from the IXth position of this vector.  Ordering of
    remaining elements is destroyed.  This is an O(1) operation.  */
 
@@ -1334,6 +1360,7 @@ public:
   void quick_insert (unsigned, const T &);
   void safe_insert (unsigned, const T & CXX_MEM_STAT_INFO);
   void ordered_remove (unsigned);
+  void ordered_remove_if (bool (*) (const T &));
   void unordered_remove (unsigned);
   void block_remove (unsigned, unsigned);
   void qsort (int (*) (const void *, const void *));
@@ -1779,6 +1806,18 @@ vec<T, va_heap, vl_ptr>::ordered_remove (unsigned ix)
 }
 
 
+/* Remove all elements from this vector for which REMOVE_ELEM_P (elem) holds.
+   Ordering of remaining elements is preserved.  This is an an O(N)
+   operation.  */
+
+template<typename T>
+inline void
+vec<T, va_heap, vl_ptr>::ordered_remove_if (bool (*remove_elem_p) (const T &))
+{
+  m_vec->ordered_remove_if (remove_elem_p);
+}
+
+
 /* Remove an element from the IXth position of this vector.  Ordering
    of remaining elements is destroyed.  This is an O(1) operation.  */