[gcc r13-2445] Disable decimal floating point in frange.

[Aldy Hernandez <aldyh@gcc.gnu.org>]

https://gcc.gnu.org/g:b4d8a56a4c62ba8bca55469ae2b841fb4e1334a4

commit r13-2445-gb4d8a56a4c62ba8bca55469ae2b841fb4e1334a4
Author: Aldy Hernandez <aldyh@redhat.com>
Date:   Mon Sep 5 15:41:39 2022 +0200

    Disable decimal floating point in frange.
    
    As Jakub mentioned in the PR, because many numbers have multiple
    possible representations, we can't reliably return true for singleton_p.
    For that matter, we may not be capable of modeling them just yet.
    Disabling them until someone with DFP knowledge can opine or extend
    frange.
    
            PR middle-end/106831
    
    gcc/ChangeLog:
    
            * value-range.h (frange::supports_p): Disable decimal floats.
            * range-op-float.cc (frange_drop_inf): Remove DECIMAL_FLOAT_MODE_P
            check.
            (frange_drop_ninf): Same.

Diff:
---
 gcc/range-op-float.cc | 10 ----------
 gcc/value-range.h     |  5 ++++-
 2 files changed, 4 insertions(+), 11 deletions(-)

diff --git a/gcc/range-op-float.cc b/gcc/range-op-float.cc
index 7301e5a060b..050f07a9867 100644
--- a/gcc/range-op-float.cc
+++ b/gcc/range-op-float.cc
@@ -204,11 +204,6 @@ frelop_early_resolve (irange &r, tree type,
 static inline void
 frange_drop_inf (frange &r, tree type)
 {
-  // FIXME: build_real() bails on decimal float modes when called with
-  // a max representable endpoint.
-  if (DECIMAL_FLOAT_MODE_P (TYPE_MODE (type)))
-    return;
-
   REAL_VALUE_TYPE max;
   real_max_representable (&max, type);
   frange tmp (type, r.lower_bound (), max);
@@ -221,11 +216,6 @@ frange_drop_inf (frange &r, tree type)
 static inline void
 frange_drop_ninf (frange &r, tree type)
 {
-  // FIXME: build_real() bails on decimal float modes when called with
-  // a max representable endpoint.
-  if (DECIMAL_FLOAT_MODE_P (TYPE_MODE (type)))
-    return;
-
   REAL_VALUE_TYPE min;
   real_min_representable (&min, type);
   frange tmp (type, min, r.upper_bound ());
diff --git a/gcc/value-range.h b/gcc/value-range.h
index bc00f3d5b08..645dc76c33a 100644
--- a/gcc/value-range.h
+++ b/gcc/value-range.h
@@ -338,7 +338,10 @@ public:
 	  value_range_kind = VR_RANGE);
   static bool supports_p (const_tree type)
   {
-    return SCALAR_FLOAT_TYPE_P (type);
+    // ?? Decimal floats can have multiple representations for the
+    // same number.  Supporting them may be as simple as just
+    // disabling them in singleton_p.  No clue.
+    return SCALAR_FLOAT_TYPE_P (type) && !DECIMAL_FLOAT_TYPE_P (type);
   }
   virtual tree type () const override;
   virtual void set (tree, tree, value_range_kind = VR_RANGE) override;