linux-kernel - RE: [PATCH v2 01/12] regmap-irq: Convert bool bitfields to unsigned int

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Message-ID: <b9da7e05ce96443cacc1df9b2672eb51@AcuMS.aculab.com>
Date:   Fri, 24 Jun 2022 14:28:55 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Joe Perches' <joe@...ches.com>,
        Aidan MacDonald <aidanmacdonald.0x0@...il.com>
CC:     Mark Brown <broonie@...nel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Matti Vaittinen <mazziesaccount@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 01/12] regmap-irq: Convert bool bitfields to unsigned
 int

From: Joe Perches 
> Sent: 24 June 2022 14:45
...
> I'm trying to show that conversions of bool:1->unsigned int:1
> as being trivial are not so trivial after all.
> 
> It's fairly common to have code like:
> 
> 	[bool] foo.bar = some_value & SETTING;
> 
> where some value is tested for a mask/bit and a non-zero is true.
> 
> So conversions of foo.bar from bool:1 to unsigned int:1 are not
> wise unless all possible side effects are known.

I can never decide whether:
	bool_c = bool_a & bool_b;
can be compiled to a simple 'and' instruction, or requires a
load of instructions in case bool_a and/or bool_b has a non-zero
value without the bottom bit set.

All other C types are cpu register types - so you know what happens.
IMHO bool is an abomination and should not be used :-)

	David

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