[PATCH] Decimal floats can never be an frange::singleton_p.

[Aldy Hernandez <aldyh@redhat.com>]

As Jakub mentioned in the PR, because many numbers have multiple
possible representations, we can't reliably return true here.

I'll commit this if tests pass.

I wonder if its worth even handling decimal floats in frange, since
there's a lot of things we can't represent.  I suppose even though we
could never propagate an actual value with VRP, we could fold
conditionals (symbolic and stuff outside ranges, etc) ??.  

Thoughts?

	PR middle-end/106831

gcc/ChangeLog:

	* value-range.cc (frange::singleton_p): Return false for
	DECIMAL_FLOAT_TYPE_P.
---
 gcc/value-range.cc | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/gcc/value-range.cc b/gcc/value-range.cc
index c3f668a811a..12a3750d078 100644
--- a/gcc/value-range.cc
+++ b/gcc/value-range.cc
@@ -647,6 +647,14 @@ frange::singleton_p (tree *result) const
       if (HONOR_NANS (m_type) && !get_nan ().no_p ())
 	return false;
 
+      // Because the significand is not normalized (there is no
+      // implicit leading "1").  Most values with less than 7
+      // significant digits have multiple possible representations.
+      // Zero has 192 possible representations (or twice that for
+      // signed zeros).
+      if (DECIMAL_FLOAT_TYPE_P (m_type))
+	return false;
+
       // Return the appropriate zero if known.
       if (HONOR_SIGNED_ZEROS (m_type) && zero_p ())
 	{
-- 
2.37.1