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
From 7cc2824e39440dd71a9d2832c51ef260bb36d8ca Mon Sep 17 00:00:00 2001
From: Andrew MacLeod <amacl...@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
