[COMMITTED] Irange::intersect with nonzero bits can indicate change incorrectly.

[COMMITTED] Irange::intersect with nonzero bits can indicate change incorrectly.

[Andrew MacLeod]

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irange::intersect returns true if the intersection operation changes the 
value. If both ranges had nonzero bits set, intersect_nonzero_bits was 
not checking to see if the operation actually changes the bits or not, 
it changed the mask and returned true.

Bootstrapped on x86_64-pc-linux-gnu with no regressions.  Pushed.

Andrew

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From 7cc2824e39440dd71a9d2832c51ef260bb36d8ca Mon Sep 17 00:00:00 2001
From: Andrew MacLeod <amacleod@redhat.com>
Date: Mon, 31 Oct 2022 09:53:01 -0400
Subject: [PATCH 1/3] Intersect with nonzero bits can indicate change
 incorrectly.

	* value-range.cc (irange::intersect_nonzero_bits): If new
	non-zero mask is the same as original, flag no change.
---
 gcc/value-range.cc | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/gcc/value-range.cc b/gcc/value-range.cc
index 03b3c4b4a65..3743ec714b3 100644
--- a/gcc/value-range.cc
+++ b/gcc/value-range.cc
@@ -3017,6 +3017,10 @@ irange::intersect_nonzero_bits (const irange &r)
   if (mask_to_wi (m_nonzero_mask, t) != mask_to_wi (r.m_nonzero_mask, t))
     {
       wide_int nz = get_nonzero_bits () & r.get_nonzero_bits ();
+      // If the nonzero bits did not change, return false.
+      if (nz == get_nonzero_bits ())
+	return false;
+
       m_nonzero_mask = wide_int_to_tree (t, nz);
       if (set_range_from_nonzero_bits ())
 	return true;
-- 
2.37.3