Re: Avoid generating useless range info

[Aldy Hernandez <aldyh@redhat.com>]

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On 06/27/2017 06:38 AM, Jakub Jelinek wrote:
> 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).

Good point.  Fixed.

>   
>   /* 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?

Here, if SSA_NAME_RANGE_INFO is previously non-NULL then we proceed as 
always-- just set the nonzero bits to whatever was specified (without 
clearning SSA_NAME_RANGE_INFO).  A mask of -1 and an SSA_NAME_RANGE_INFO 
of non-NULL can coexist just fine.

How about this?

Aldy

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gcc/

	* tree-ssanames.c (set_range_info_raw): Abstract from ...
	(set_range_info): ...here.  Only call set_range_info_raw if domain
	is useful.
	(set_nonzero_bits): Call set_range_info_raw.
	* tree-ssanames.h (set_range_info_raw): New.

gcc/testsuite/

	* gcc.dg/Walloca-14.c: Adapt test to recognize new complaint of
	unbounded use.

diff --git a/gcc/testsuite/gcc.dg/Walloca-14.c b/gcc/testsuite/gcc.dg/Walloca-14.c
index 723dbe5..f3e3f57 100644
--- a/gcc/testsuite/gcc.dg/Walloca-14.c
+++ b/gcc/testsuite/gcc.dg/Walloca-14.c
@@ -9,5 +9,6 @@ g (int *p)
   extern void f (void *);
 
   void *q = __builtin_alloca (p); /* { dg-warning "passing argument 1" } */
+  /* { dg-warning "unbounded use of 'alloca'" "unbounded" { target *-*-* } 11 } */
   f (q);
 }
diff --git a/gcc/tree-ssanames.c b/gcc/tree-ssanames.c
index 353c7b1..0053b01 100644
--- a/gcc/tree-ssanames.c
+++ b/gcc/tree-ssanames.c
@@ -320,11 +320,14 @@ make_ssa_name_fn (struct function *fn, tree var, gimple *stmt,
   return t;
 }
 
-/* Store range information RANGE_TYPE, MIN, and MAX to tree ssa_name NAME.  */
+/* Helper function for set_range_info.
+
+   Store range information RANGE_TYPE, MIN, and MAX to tree ssa_name
+   NAME.  */
 
 void
-set_range_info (tree name, enum value_range_type range_type,
-		const wide_int_ref &min, const wide_int_ref &max)
+set_range_info_raw (tree name, enum value_range_type range_type,
+		    const wide_int_ref &min, const wide_int_ref &max)
 {
   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
   gcc_assert (range_type == VR_RANGE || range_type == VR_ANTI_RANGE);
@@ -360,6 +363,34 @@ 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)
+{
+  gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
+
+  /* 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)))
+    {
+      range_info_def *ri = SSA_NAME_RANGE_INFO (name);
+      if (ri == NULL)
+	return;
+      if (ri->get_nonzero_bits () == -1)
+	{
+	  ggc_free (ri);
+	  SSA_NAME_RANGE_INFO (name) = NULL;
+	  return;
+	}
+    }
+
+  set_range_info_raw (name, range_type, min, max);
+}
+
 
 /* Gets range information MIN, MAX and returns enum value_range_type
    corresponding to tree ssa_name NAME.  enum value_range_type returned
@@ -419,9 +450,13 @@ 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);
 }
diff --git a/gcc/tree-ssanames.h b/gcc/tree-ssanames.h
index 9a18394..f7e032f 100644
--- a/gcc/tree-ssanames.h
+++ b/gcc/tree-ssanames.h
@@ -69,6 +69,9 @@ struct GTY ((variable_size)) range_info_def {
 /* Sets the value range to SSA.  */
 extern void set_range_info (tree, enum value_range_type, const wide_int_ref &,
 			    const wide_int_ref &);
+extern void set_range_info_raw (tree, enum value_range_type,
+				const wide_int_ref &,
+				const wide_int_ref &);
 /* Gets the value range from SSA.  */
 extern enum value_range_type get_range_info (const_tree, wide_int *,
 					     wide_int *);