My vote is for MOZ_ASSERT_UNREACHABLE and MOZ_OPTIMIZE_FOR_UNREACHABLE.
It's really handy to have something like MOZ_ASSERT_UNREACHABLE, instead of
having a bunch of MOZ_ASSERT(false, "Unreachable.") lines.
Consider MOZ_ASSERT_UNREACHABLE being the same as MOZ_OPTIMIZE_FOR_UNREACHABLE
in non-DEBUG builds.
-Jeff
----- Original Message -----
From: "Steve Fink" <sf...@mozilla.com>
To: "Benoit Jacob" <jacob.benoi...@gmail.com>
Cc: "Chris Peterson" <cpeter...@mozilla.com>, "dev-platform"
<dev-platform@lists.mozilla.org>
Sent: Friday, March 28, 2014 1:20:39 PM
Subject: Re: MOZ_ASSUME_UNREACHABLE is being misused
On Fri 28 Mar 2014 01:05:34 PM PDT, Benoit Jacob wrote:
> 2014-03-28 13:23 GMT-04:00 Chris Peterson <cpeter...@mozilla.com>:
>
>> On 3/28/14, 12:25 PM, Benoit Jacob wrote:
>>
>>> Should we give typical code a macro that does what they want and sounds
>>> like what they want? Really, what typical code wants is a no-operation
>>> instead of undefined-behavior; now, that is exactly the same as
>>> MOZ_ASSERT(false, "error"). Maybe this syntax is unnecessarily annoying,
>>> and it would be worth adding a macro for that, i.e. similar to MOZ_CRASH
>>> but only affecting DEBUG builds? What would be a good name for it? Is it
>>> worth keeping a close analogy with the unreachable-marker macro to steer
>>> people away from it --- e.g. maybe MOZ_UNREACHABLE_NO_OPERATION or even
>>> just MOZ_UNREACHABLE? So that people couldn't miss it when they look for
>>> "UNREACHABLE" macros?
>>>
>>
>> How about replacing MOZ_ASSUME_UNREACHABLE with two new macros like:
>>
>> #define MOZ_ASSERT_UNREACHABLE() \
>> MOZ_ASSERT(false, "MOZ_ASSERT_UNREACHABLE")
>>
>> #define MOZ_CRASH_UNREACHABLE() \
>> do { \
>> MOZ_ASSUME_UNREACHABLE_MARKER(); \
>> MOZ_CRASH("MOZ_CRASH_UNREACHABLE"); \
>> } while (0)
>>
>
> MOZ_ASSUME_UNREACHABLE_MARKER tells the compiler "feel free to arbitrarily
> miscompile this, and anything from that point on in this branch, as you may
> assume that this code is unreachable". So it doesn't really serve any
> purpose to add a MOZ_CRASH after a MOZ_ASSUME_UNREACHABLE_MARKER.
MOZ_OPTIMIZE_FOR_UNREACHABLE?
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