linux-kernel - Re: [PATCH] usbhid: Fix lockdep unannotated irqs-off warning

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Message-ID: <CA+55aFzR8VjVS1XpkJT33-8Mq97QeUAg=YzuQVr8t-7ikJkUjA@mail.gmail.com>
Date:	Mon, 27 Jun 2016 13:36:40 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Sedat Dilek <sedat.dilek@...il.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	David Laight <David.Laight@...lab.com>,
	Jiri Kosina <jikos@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Tejun Heo <tj@...nel.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Benjamin Tissoires <benjamin.tissoires@...hat.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Andy Lutomirski <luto@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	USB list <linux-usb@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] usbhid: Fix lockdep unannotated irqs-off warning

On Mon, Jun 27, 2016 at 1:27 PM, Sedat Dilek <sedat.dilek@...il.com> wrote:
>
> I just grepped for some "buzzwords" people gave me in this
> email-thread and I was looking at (llvm.git HEAD - upcoming v3.9
> release) and found these comments in [1]
>
>
> [1] https://github.com/llvm-mirror/llvm/blob/master/lib/Target/X86/X86InstrInfo.cpp#L4516

Christ. That's still pretty bad. Using LAHF/SAHF is just wrong.

But at least it's not semantically buggy any more, it's just stupid and slow.

Apparently the problem is that LLVM doesn't actually track flags as
different conditions, but as a single register, and doesn't know which
bits of it matter.

I guess the SETO + LAHF/SAHF is the best llvm can do then. But it
doesn't speak well of the code generation quality.

                Linus