[gcc r12-4965] Avoid left shift of negative value in ipa-modref-tree.h

[Jan Hubicka <hubicka@gcc.gnu.org>]

https://gcc.gnu.org/g:9cc8ca8da90426f625481195a2127a5e86689bcd

commit r12-4965-g9cc8ca8da90426f625481195a2127a5e86689bcd
Author: Jan Hubicka <hubicka@ucw.cz>
Date:   Fri Nov 5 23:17:50 2021 +0100

    Avoid left shift of negative value in ipa-modref-tree.h
    
    gcc/ChangeLog:
    
            PR ipa/103082
            * ipa-modref-tree.h (struct modref_access_node): Avoid left shift
            of negative value

Diff:
---
 gcc/ipa-modref-tree.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/gcc/ipa-modref-tree.h b/gcc/ipa-modref-tree.h
index 9976e489697..bc428d193d2 100644
--- a/gcc/ipa-modref-tree.h
+++ b/gcc/ipa-modref-tree.h
@@ -116,8 +116,13 @@ struct GTY(()) modref_access_node
 	       if (!known_le (parm_offset, a.parm_offset)
 		   && !range_info_useful_p ())
 		 return false;
+	       /* We allow negative aoffset_adj here in case
+		  there is an useful range.  This is because adding
+		  a.offset may result in non-ngative offset again.
+		  Ubsan fails on val << LOG_BITS_PER_UNIT where val
+		  is negative.  */
 	       aoffset_adj = (a.parm_offset - parm_offset)
-			     << LOG2_BITS_PER_UNIT;
+			     * BITS_PER_UNIT;
 	    }
 	}
       if (range_info_useful_p ())