From: Peter Zijlstra <peterz@infradead.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@kernel.org>,
"H. Peter Anvin" <hpa@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andy Lutomirski <luto@amacapital.net>,
Borislav Petkov <bp@alien8.de>,
Linus Torvalds <torvalds@linux-foundation.org>,
Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH 02/10] x86, asm: use bool for bitops and other assembly outputs
Date: Wed, 8 Jun 2016 11:39:47 +0200 [thread overview]
Message-ID: <20160608093947.GQ30154@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <9ce48c59-4b9c-bd48-ce07-b230376fba0f@zytor.com>
On Wed, Jun 08, 2016 at 02:31:31AM -0700, H. Peter Anvin wrote:
> On 06/08/16 02:20, Ingo Molnar wrote:
> >
> > Yeah, absolutely. I hate 'bool' with a vengence but if 'int' generates worse code
> > with modern compilers then I'm not going to argue for worse code. Would a 'char'
> > return type be very weird?
> >
>
> Yes. I have to admit I don't share your hatred for "bool" -- it gives
> the compiler a fairly crucial bit of information about what the possible
> values are for a certain piece of data.
>
> Upcasting to char loses that, and may case gcc to manifest the value as
> an integer instead of retaining it in the flags. It is, however, less
> likely to cause gcc to then try to widen the value to word size (which
> is an extra instruction on x86), but moving the value out of and back
> into the flags register is the big cost.
So I think using bool as return type or argument is fine, using it in
structures is 'insane'.
next prev parent reply other threads:[~2016-06-08 9:40 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-07 23:30 [PATCH 00/10] x86: use gcc 6+ asm flag output feature H. Peter Anvin
2016-06-07 23:31 ` [PATCH 01/10] x86, bitops: remove use of "sbb" to return CF H. Peter Anvin
2016-06-07 23:39 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-07 23:31 ` [PATCH 02/10] x86, asm: use bool for bitops and other assembly outputs H. Peter Anvin
2016-06-07 23:40 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-08 7:49 ` [PATCH 02/10] " Peter Zijlstra
2016-06-08 8:28 ` Ingo Molnar
2016-06-08 8:33 ` Ingo Molnar
2016-06-08 8:55 ` H. Peter Anvin
2016-06-08 9:01 ` Ingo Molnar
2016-06-08 9:12 ` H. Peter Anvin
2016-06-08 9:20 ` Ingo Molnar
2016-06-08 9:31 ` H. Peter Anvin
2016-06-08 9:39 ` Peter Zijlstra [this message]
2016-06-08 9:43 ` H. Peter Anvin
2016-06-08 9:40 ` H. Peter Anvin
2016-06-08 8:58 ` H. Peter Anvin
2016-06-08 9:06 ` Ingo Molnar
2016-06-07 23:31 ` [PATCH 03/10] x86, asm: change the GEN_*_RMWcc() macros to not quote the condition H. Peter Anvin
2016-06-07 23:40 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-07 23:31 ` [PATCH 04/10] x86, asm: define CC_SET() and CC_OUT() macros H. Peter Anvin
2016-06-07 23:40 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-08 5:09 ` [PATCH 04/10] " Andy Lutomirski
2016-06-08 19:29 ` H. Peter Anvin
2016-06-08 19:34 ` H. Peter Anvin
2016-06-08 19:35 ` Borislav Petkov
2016-06-07 23:31 ` [PATCH 05/10] x86, asm: change GEN_*_RMWcc() to use CC_SET()/CC_OUT() H. Peter Anvin
2016-06-07 23:41 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-07 23:31 ` [PATCH 06/10] x86, asm: Use CC_SET()/CC_OUT() in <asm/bitops.h> H. Peter Anvin
2016-06-07 23:41 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-07 23:31 ` [PATCH 07/10] x86, asm: Use CC_SET()/CC_OUT() in <asm/percpu.h> H. Peter Anvin
2016-06-07 23:42 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-07 23:31 ` [PATCH 08/10] x86, asm: Use CC_SET()/CC_OUT() in <asm/rwsem.h> H. Peter Anvin
2016-06-07 23:42 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-07 23:31 ` [PATCH 09/10] x86, asm: Use CC_SET()/CC_OUT() and static_cpu_has() in archrandom.h H. Peter Anvin
2016-06-07 23:42 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-08 5:12 ` [PATCH 09/10] " Andy Lutomirski
2016-06-07 23:31 ` [PATCH 10/10] x86, asm, boot: Use CC_SET()/CC_OUT() in arch/x86/boot/boot.h H. Peter Anvin
2016-06-07 23:43 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-08 8:00 ` [PATCH 00/10] x86: use gcc 6+ asm flag output feature Peter Zijlstra
2016-06-08 8:56 ` H. Peter Anvin
2016-06-08 8:26 ` Ingo Molnar
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