From: Paul Floyd <paulf@free.fr>
To: "gcc@gcc.gnu.org" <gcc@gcc.gnu.org>
Subject: Re: Safe transposition of logical and operands
Date: Mon, 18 Sep 2023 09:03:20 +0200 [thread overview]
Message-ID: <c1887f72-d532-1cc1-f71c-9fdd4f4ed056@free.fr> (raw)
In-Reply-To: <CAH6eHdQvHsqFsanMiSzO90_u-PC1eBZCWkJS0SUy71wQ=sUoLQ@mail.gmail.com>
On 17-09-23 22:51, Jonathan Wakely wrote:
>
> Why would it be trapping? It's loading an int64_t, which might be
> uninitialised but it can't trap.
In this context I think that Valgrind is considering that any memory
load could trap.
> *f on a std::optional is not like dereferencing a pointer, the int64_t
> memory location is always present as part of the object.
For this
movq 40(%rbx), %rax
unless you know that what RBX+40 is pointing to is safe to dereference
it's not different to dereferencing a pointer.
So I think that the problem is that Valgrind is being cautious and not
allowing any loads but GCC is accepting what it considers safe loads
from the stack.
A+
Paul
next prev parent reply other threads:[~2023-09-18 7:03 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-17 19:33 Paul Floyd
2023-09-17 20:51 ` Jonathan Wakely
2023-09-18 7:03 ` Paul Floyd [this message]
2023-09-18 7:23 ` Jonathan Wakely
2023-09-18 8:00 ` Richard Biener
2023-09-18 14:46 ` Floyd, Paul
2023-09-18 14:55 ` Richard Biener
2023-09-18 17:56 ` Paul Floyd
2023-09-18 19:09 ` Martin Uecker
2023-09-18 20:15 ` Paul Floyd
2023-09-18 20:52 ` Martin Uecker
2023-09-19 5:03 ` Paul Floyd
2023-09-18 9:36 ` Jonathan Wakely
2023-09-18 10:30 ` Andreas Schwab
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