From: Mikael Morin <mikael.morin@sfr.fr>
To: gcc-patches <gcc-patches@gcc.gnu.org>
Subject: [Patch] sext_hwi: Avoid left shift of negative value undefined behaviour
Date: Thu, 06 Aug 2015 10:26:00 -0000 [thread overview]
Message-ID: <55C33636.7020907@sfr.fr> (raw)
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Hello,
this avoids an error found with bootstrap-ubsan.
Regression tested on x86_64-unknown-linux-gnu. OK for trunk?
Mikael
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2015-08-05 Mikael Morin <mikael@gcc.gnu.org>
* hwint.h (sext_hwi): Rewrite without undefined behaviour on
negative SRC.
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diff --git a/gcc/hwint.h b/gcc/hwint.h
index 3793986..9c3eda0 100644
--- a/gcc/hwint.h
+++ b/gcc/hwint.h
@@ -246,8 +246,9 @@ sext_hwi (HOST_WIDE_INT src, unsigned int prec)
else
{
gcc_checking_assert (prec < HOST_BITS_PER_WIDE_INT);
- int shift = HOST_BITS_PER_WIDE_INT - prec;
- return (src << shift) >> shift;
+ HOST_WIDE_INT sign_mask = HOST_WIDE_INT_1 << (prec - 1);
+ HOST_WIDE_INT value_mask = (HOST_WIDE_INT_1U << prec) - HOST_WIDE_INT_1U;
+ return (((src & value_mask) ^ sign_mask) - sign_mask);
}
}
next reply other threads:[~2015-08-06 10:26 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-06 10:26 Mikael Morin [this message]
2015-08-11 19:49 ` Jeff Law
2015-08-12 11:01 ` Richard Biener
2015-08-12 11:07 ` Markus Trippelsdorf
2015-08-12 11:09 ` Richard Biener
2015-08-12 13:34 ` Mikael Morin
2015-08-12 17:02 ` Jeff Law
2015-08-12 17:12 ` Richard Biener
2015-08-12 18:07 ` Jeff Law
2015-08-12 18:32 ` Richard Biener
2015-08-12 18:41 ` Jeff Law
2015-08-12 20:07 ` Richard Sandiford
2015-08-12 20:53 ` Mike Stump
2015-08-13 10:11 ` Richard Biener
2015-08-13 18:01 ` Mike Stump
2015-08-14 7:31 ` Richard Biener
2015-08-18 15:35 ` Mikael Morin
2015-08-18 17:51 ` Jeff Law
2015-08-13 11:03 ` Mikael Morin
2015-08-13 11:06 ` Mikael Morin
2015-08-13 11:09 ` Markus Trippelsdorf
2015-08-13 11:20 ` Richard Biener
2015-08-13 13:48 ` Marek Polacek
2015-08-13 13:55 ` Markus Trippelsdorf
2015-08-13 13:57 ` Marek Polacek
2015-08-12 19:20 ` Mike Stump
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