From: Jim Wilson <wilson@cygnus.com>
To: linux-ia64@vger.kernel.org
Subject: Re: [Linux-ia64] gcc bug (2.9-ia64-000216-final)
Date: Tue, 03 Oct 2000 01:02:02 +0000 [thread overview]
Message-ID: <marc-linux-ia64-105590678205540@msgid-missing> (raw)
In-Reply-To: <marc-linux-ia64-105590678205537@msgid-missing>
This is a memory aliasing bug that causes the instruction scheduler to perform
invalid code movement. It only occurs when both const and volatile are
present on a function argument.
When you use volatile, the compiler forces the argument to the stack. When
you use const, the compiler marks the stack read as a const read, but does not
also similarly mark the stack write. Thus the scheduler thinks the write and
read do not alias and can be re-ordered. If I use -O2 -fno-schedule-insns I
get correct code. For a more complicated example, you might also need to use
-fno-schedule-insns2. Or you can just use -O to avoid the problem.
The new toolchain does not have this bug.
Jim
prev parent reply other threads:[~2000-10-03 1:02 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2000-10-02 22:43 [Linux-ia64] gcc bug (2.9-ia64-000216-final) Steve Tynor
2000-10-03 1:02 ` Jim Wilson [this message]
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