Re: Add a constant_range_value_p function (PR 92033)

[Richard Sandiford <richard.sandiford@arm.com>]

Richard Biener <richard.guenther@gmail.com> writes:
> On October 14, 2019 2:32:43 PM GMT+02:00, Richard Sandiford <richard.sandiford@arm.com> wrote:
>>Richard Biener <richard.guenther@gmail.com> writes:
>>> On Fri, Oct 11, 2019 at 4:42 PM Richard Sandiford
>>> <richard.sandiford@arm.com> wrote:
>>>>
>>>> The range-tracking code has a pretty hard-coded assumption that
>>>> is_gimple_min_invariant is equivalent to "INTEGER_CST or invariant
>>>> ADDR_EXPR".  It seems better to add a predicate specifically for
>>>> that rather than contiually fight cases in which it can't handle
>>>> other invariants.
>>>>
>>>> Tested on aarch64-linux-gnu and x86_64-linux-gnu.  OK to install?
>>>
>>> ICK.  Nobody is going to remember this new restriction and
>>> constant_range_value_p reads like constant_value_range_p ;)
>>>
>>> Btw, is_gimple_invariant_address shouldn't have been exported,
>>> it's only use could have used is_gimple_min_invariant...
>>
>>What do you think we should do instead?
>
> Just handle POLY_INT_CST in a few place to quickly enough drop to varying. 

OK, how about this?  Aldy's suggestion would be fine by me too,
but I thought I'd try this first given Aldy's queasiness about
allowing POLY_INT_CSTs further in.

The main case in which this gives useful ranges is a lower bound
of A + B * X becoming A when B >= 0.  E.g.:

  (1) [32 + 16X, 100] -> [32, 100]
  (2) [32 + 16X, 32 + 16X] -> [32, MAX]

But the same thing can be useful for the upper bound with negative
X coefficients.

We can revisit this later if keeping a singleton range for (2)
would be better.

Tested as before.

Richard


2019-10-15  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	PR middle-end/92033
	* poly-int.h (constant_lower_bound_with_limit): New function.
	(constant_upper_bound_with_limit): Likewise.
	* doc/poly-int.texi: Document them.
	* tree-vrp.c (value_range_base::set): Convert POLY_INT_CST bounds
	into the worst-case INTEGER_CST bounds.

Index: gcc/poly-int.h
===================================================================
--- gcc/poly-int.h	2019-07-10 19:41:26.395898027 +0100
+++ gcc/poly-int.h	2019-10-15 11:30:14.099625553 +0100
@@ -1528,6 +1528,29 @@ constant_lower_bound (const poly_int_pod
   return a.coeffs[0];
 }
 
+/* Return the constant lower bound of A, given that it is no less than B.  */
+
+template<unsigned int N, typename Ca, typename Cb>
+inline POLY_CONST_COEFF (Ca, Cb)
+constant_lower_bound_with_limit (const poly_int_pod<N, Ca> &a, const Cb &b)
+{
+  if (known_ge (a, b))
+    return a.coeffs[0];
+  return b;
+}
+
+/* Return the constant upper bound of A, given that it is no greater
+   than B.  */
+
+template<unsigned int N, typename Ca, typename Cb>
+inline POLY_CONST_COEFF (Ca, Cb)
+constant_upper_bound_with_limit (const poly_int_pod<N, Ca> &a, const Cb &b)
+{
+  if (known_le (a, b))
+    return a.coeffs[0];
+  return b;
+}
+
 /* Return a value that is known to be no greater than A and B.  This
    will be the greatest lower bound for some indeterminate values but
    not necessarily for all.  */
Index: gcc/doc/poly-int.texi
===================================================================
--- gcc/doc/poly-int.texi	2019-03-08 18:14:25.333011645 +0000
+++ gcc/doc/poly-int.texi	2019-10-15 11:30:14.099625553 +0100
@@ -803,6 +803,18 @@ the assertion is known to hold.
 @item constant_lower_bound (@var{a})
 Assert that @var{a} is nonnegative and return the smallest value it can have.
 
+@item constant_lower_bound_with_limit (@var{a}, @var{b})
+Return the least value @var{a} can have, given that the context in
+which @var{a} appears guarantees that the answer is no less than @var{b}.
+In other words, the caller is asserting that @var{a} is greater than or
+equal to @var{b} even if @samp{known_ge (@var{a}, @var{b})} doesn't hold.
+
+@item constant_upper_bound_with_limit (@var{a}, @var{b})
+Return the greatest value @var{a} can have, given that the context in
+which @var{a} appears guarantees that the answer is no greater than @var{b}.
+In other words, the caller is asserting that @var{a} is less than or equal
+to @var{b} even if @samp{known_le (@var{a}, @var{b})} doesn't hold.
+
 @item lower_bound (@var{a}, @var{b})
 Return a value that is always less than or equal to both @var{a} and @var{b}.
 It will be the greatest such value for some indeterminate values
Index: gcc/tree-vrp.c
===================================================================
--- gcc/tree-vrp.c	2019-10-14 09:04:54.515259320 +0100
+++ gcc/tree-vrp.c	2019-10-15 11:30:14.099625553 +0100
@@ -727,6 +727,24 @@ value_range_base::set (enum value_range_
       return;
     }
 
+  /* Convert POLY_INT_CST bounds into worst-case INTEGER_CST bounds.  */
+  if (POLY_INT_CST_P (min))
+    {
+      tree type_min = vrp_val_min (TREE_TYPE (min), true);
+      widest_int lb
+	= constant_lower_bound_with_limit (wi::to_poly_widest (min),
+					   wi::to_widest (type_min));
+      min = wide_int_to_tree (TREE_TYPE (min), lb);
+    }
+  if (POLY_INT_CST_P (max))
+    {
+      tree type_max = vrp_val_max (TREE_TYPE (max), true);
+      widest_int ub
+	= constant_upper_bound_with_limit (wi::to_poly_widest (max),
+					   wi::to_widest (type_max));
+      max = wide_int_to_tree (TREE_TYPE (max), ub);
+    }
+
   /* Nothing to canonicalize for symbolic ranges.  */
   if (TREE_CODE (min) != INTEGER_CST
       || TREE_CODE (max) != INTEGER_CST)