[Mesa-dev] Let's talk about -DDEBUG

[Ian Romanick]

On 12/12/18 4:13 PM, Dylan Baker wrote:
> Quoting Rob Clark (2018-12-12 15:52:47)
>> On Wed, Dec 12, 2018 at 6:25 PM Dylan Baker <dylan at pnwbakers.com> wrote:
>>>
>>> In the autotools discussion I've come to realize that we also need to talk about
>>> the -DDEBUG guard. It seems that there are two different uses, and thus two
>>> different asks about it:
>>>
>>> - Nine (and RadeonSI?) use -DDEBUG to hide generic debugging
>>> - NIR and Intel (at least) use -DDEBUG to hide really expensive checks that are
>>>   useful, but necessarily tank performance.
>>>
>>> The first group would like -DDEBUG in debugoptimized builds, the second
>>> obviously doesn't.
>>>
>>> Is the right solution to move the first group being !NDEBUG, or would it be
>>> better to split DEBUG into two different defines such as DEBUG_MESSAGES and
>>> EXPENSIVE_VALIDATION (paint the bikeshed whatever color you like), with the
>>> first for both debug and debugoptimized and the second only in debug builds?
>>
>> I guess my use cases for !=release builds are:
>>
>> + I want all the expensive checking because I'm not in it to win the
>>   deqp/piglit fps race
>> + I want debug syms for profiling and/or valgrind, but otherwise
>>   want something close to a release build but with debug syms
>>
>>
>> That said, I can get behind replacing DEBUG with !NDEBUG or
>> EXPENSIVE_DEBUG or whatever permutation of that color folks prefer
>>
>>
>> BR,
>> -R
> 
> I guess I should have covered that:
> 
> autotools had effectively two build types "debug" and "not debug", "debug" set
> "-DDEBUG -g -O2", "not debug" set -DNDEBUG
> 
> Meson has 4 build types, and a separate toggle for NDEBUG:
> debug: -O0 -DDEBUG (we add -DDEBUG)
> debugoptimzed: -O2 -g
> release: -O2
> plain: (nothing)

About 5 minutes into using meson, I started using plain builds with my
own flags set.  I can configure it *exactly* the way I want without
bothering or being bothered by anyone.  I haven't looked back since.

> Meson doesn't define NDEBUG by default, so if you want to turn off asserts you
> need to add -Db_ndebug=true
> 
> autotools debug is roughly between meson's debugoptimized and debug, while
> autotools non-debug corresponds to meson's plain buildtype.
> 
> Dylan
> 
> 
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