Re: Avoid generating useless range info

[Jakub Jelinek <jakub@redhat.com>]

On Tue, Jun 27, 2017 at 06:26:46AM -0400, Aldy Hernandez wrote:
> How about this?

@@ -360,6 +363,22 @@ set_range_info (tree name, enum value_range_type range_type,
     }
 }
 
+/* Store range information RANGE_TYPE, MIN, and MAX to tree ssa_name
+   NAME while making sure we don't store useless range info.  */
+
+void
+set_range_info (tree name, enum value_range_type range_type,
+		const wide_int_ref &min, const wide_int_ref &max)
+{
+  /* A range of the entire domain is really no range at all.  */
+  tree type = TREE_TYPE (name);
+  if (min == wi::min_value (TYPE_PRECISION (type), TYPE_SIGN (type))
+      && max == wi::max_value (TYPE_PRECISION (type), TYPE_SIGN (type)))
+    return;
+
+  set_range_info_raw (name, range_type, min, max);
+}
+

Won't this misbehave if we have a narrower range on some SSA_NAME and
call set_range_info to make it VARYING?
In that case (i.e. SSA_NAME_RANGE_INFO (name) != NULL), we should either
set_range_info_raw too (if nonzero_bits is not all ones) or clear
SSA_NAME_RANGE_INFO (otherwise).
 
 /* Gets range information MIN, MAX and returns enum value_range_type
    corresponding to tree ssa_name NAME.  enum value_range_type returned
@@ -419,9 +438,13 @@ set_nonzero_bits (tree name, const wide_int_ref &mask)
 {
   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
   if (SSA_NAME_RANGE_INFO (name) == NULL)
-    set_range_info (name, VR_RANGE,
-		    TYPE_MIN_VALUE (TREE_TYPE (name)),
-		    TYPE_MAX_VALUE (TREE_TYPE (name)));
+    {
+      if (mask == -1)
+	return;
+      set_range_info_raw (name, VR_RANGE,
+			  TYPE_MIN_VALUE (TREE_TYPE (name)),
+			  TYPE_MAX_VALUE (TREE_TYPE (name)));
+    }
   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
   ri->set_nonzero_bits (mask);

Similarly, if SSA_NAME_RANGE_INFO is previously non-NULL, but min/max
are VARYING and the new mask is -1, shouldn't we free it rather than
set it to the default?

If we consider the cases rare enough to worry about, at least your
above
  if (min == wi::min_value (TYPE_PRECISION (type), TYPE_SIGN (type))
      && max == wi::max_value (TYPE_PRECISION (type), TYPE_SIGN (type)))
should be
  gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
  if (SSA_NAME_RANGE_INFO (name) == NULL
      && min == wi::min_value (TYPE_PRECISION (type), TYPE_SIGN (type))
      && max == wi::max_value (TYPE_PRECISION (type), TYPE_SIGN (type)))
We'd then not misbehave, just might in some rare cases keep
SSA_NAME_RANGE_INFO non-NULL even if it contains the default stuff.

	Jakub