Performance difference
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@JonB The default optimization level for MSVC in Release build is
/O2and it gives me the same result forfunc1andfunc2: https://godbolt.org/z/rjL--B. Are you sure you checked it right?@Chris-Kawa
Yes, because I wasn't comparing against release build, or whatever defaults that might or might not use. (The OP never mentioned release build or what optimization level, which is why I wrote behaviour would depend on that, plus compiler.) For simplicity I was comparing plain-Oagainst-O.... They both differ with no-Oat all.gccwent identical at-Oonward, formsvcthey still differ at plain-O, I had to go to-O1to make them the same. Just saying. -
@JonB Yeah, but no sane project uses that. MSVC has an established set of defaults for Release and Debug builds and most if not every build system uses that. Unless you care much for debug build performance (which is the case in some, admittedly small, set of cases) there's little worth in analyzing anything but Release configuration.
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@JonB Yeah, but no sane project uses that. MSVC has an established set of defaults for Release and Debug builds and most if not every build system uses that. Unless you care much for debug build performance (which is the case in some, admittedly small, set of cases) there's little worth in analyzing anything but Release configuration.
@Chris-Kawa
The following is perhaps a conversation for another time/thread. We (originally) produced cross-platform tools (started a long time ago, not Qt). I gave up compiling with any optimization flags (any compiler, any platform) allowed back in the last millennium, as I could not deal with the bugged code (oh yes!) they generated which would show up under circumstances at customer sites. Ever since then I have never trusted any compiler's optimization flags, because the potential bug penalty outweighed any benefit I might gain in quicker code. We release our code stripped of debug but not compiler optimized. Do you (really) believe I should rethink now after all these years?! -
@Chris-Kawa
The following is perhaps a conversation for another time/thread. We (originally) produced cross-platform tools (started a long time ago, not Qt). I gave up compiling with any optimization flags (any compiler, any platform) allowed back in the last millennium, as I could not deal with the bugged code (oh yes!) they generated which would show up under circumstances at customer sites. Ever since then I have never trusted any compiler's optimization flags, because the potential bug penalty outweighed any benefit I might gain in quicker code. We release our code stripped of debug but not compiler optimized. Do you (really) believe I should rethink now after all these years?!I gave up compiling with any optimization flags
That's truly horrible!
Ever since then I have never trusted any compiler's optimization flags
As I said - each compiler has an established set of options for their Release and Debug builds. Those are by far the most tested configs on the planet. If you're afraid of bugs that's where there's least of them.
We release our code stripped of debug but not compiler optimized.
That's unbelievably awful. I wish you hadn't told me that and I could go on not knowing that there's software released this way.
Do you (really) believe I should rethink now after all these years?!
Absolutely! Do that right this moment! :D No, seriously, the overhead you're imposing on your runtime if you don't enable optimizations is absurd - For example unoptimized STL in MSVC has often something like 20x overhead. Just look at that absolutely basic example above - you're using walls of code and function calls, thrashing cache and draining energy where you could do 2 very fast instructions!
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I gave up compiling with any optimization flags
That's truly horrible!
Ever since then I have never trusted any compiler's optimization flags
As I said - each compiler has an established set of options for their Release and Debug builds. Those are by far the most tested configs on the planet. If you're afraid of bugs that's where there's least of them.
We release our code stripped of debug but not compiler optimized.
That's unbelievably awful. I wish you hadn't told me that and I could go on not knowing that there's software released this way.
Do you (really) believe I should rethink now after all these years?!
Absolutely! Do that right this moment! :D No, seriously, the overhead you're imposing on your runtime if you don't enable optimizations is absurd - For example unoptimized STL in MSVC has often something like 20x overhead. Just look at that absolutely basic example above - you're using walls of code and function calls, thrashing cache and draining energy where you could do 2 very fast instructions!
@Chris-Kawa
You are going over the top IMHO! Not optimizing is not that bad, despite what you say. I cannot comment on, say, STL in MSVC. Our apps are I/O bound in system code, file handling, database access etc., so local optimization (of our own code) is not going to be that significant over the whole experience.Your points are valid, but they do not address the reality of what we found: your code can be as optimized as you feel like, but that's useless if we/the user cannot trust the code because of empirical observation of bugged code generation under compiler optimization. Being burnt all those years ago has left a fear that perhaps you have never experienced.
If I ever rethought the situation (you are inspiring me now!) I guess I would give optimization a go now. You are saying that you can guarantee that e.g. MSVC will not have a single bug in optimized code generated? Serious question.
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@Chris-Kawa
You are going over the top IMHO! Not optimizing is not that bad, despite what you say. I cannot comment on, say, STL in MSVC. Our apps are I/O bound in system code, file handling, database access etc., so local optimization (of our own code) is not going to be that significant over the whole experience.Your points are valid, but they do not address the reality of what we found: your code can be as optimized as you feel like, but that's useless if we/the user cannot trust the code because of empirical observation of bugged code generation under compiler optimization. Being burnt all those years ago has left a fear that perhaps you have never experienced.
If I ever rethought the situation (you are inspiring me now!) I guess I would give optimization a go now. You are saying that you can guarantee that e.g. MSVC will not have a single bug in optimized code generated? Serious question.
You are going over the top! Not optimizing is not that bad
Yes, yes it is. The user visible impact might not be that severe in some types of apps but the underlying waste is unquestionable. In particular cases, like gaming, it can drop a game from 120 frames per second to the lower 20s.
Being burnt all those years ago has left a fear that perhaps you have never experienced.
A horse looked at me the wrong way 20 years ago so i don't use cars and walk everywhere.
You are saying that you can guarantee that e.g. MSVC will not have a single bug in optimized code generated?
No, I can't guarantee that for any existing software. I can guarantee that config used by millions of apps will be better tested than config used by dozens.
Serious question.
Serious answer then - I'd bet that if you turned on optimization after years of not using them your software would crash a lot, finding bugs you didn't even knew were there. Debug builds for example zero out memory before use so you can be sure you have garbage pointers lurking if you don't do release builds. Threading and synchronization is another area where unoptimized builds tend to mask a lot of problems, because they just run slower and you don't see races that often.
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You are going over the top! Not optimizing is not that bad
Yes, yes it is. The user visible impact might not be that severe in some types of apps but the underlying waste is unquestionable. In particular cases, like gaming, it can drop a game from 120 frames per second to the lower 20s.
Being burnt all those years ago has left a fear that perhaps you have never experienced.
A horse looked at me the wrong way 20 years ago so i don't use cars and walk everywhere.
You are saying that you can guarantee that e.g. MSVC will not have a single bug in optimized code generated?
No, I can't guarantee that for any existing software. I can guarantee that config used by millions of apps will be better tested than config used by dozens.
Serious question.
Serious answer then - I'd bet that if you turned on optimization after years of not using them your software would crash a lot, finding bugs you didn't even knew were there. Debug builds for example zero out memory before use so you can be sure you have garbage pointers lurking if you don't do release builds. Threading and synchronization is another area where unoptimized builds tend to mask a lot of problems, because they just run slower and you don't see races that often.
@Chris-Kawa
I respect what you suggest, and am grateful for food for thought/your experiences. (And, yes, if I were releasing a game/frame-rate-critical app the situation would be different.) Just to be clear, I did not say we release "debug" builds, I said we release compiling/linking not for debug (e.g. so no memory zeroing, nor memory debug functions, nor debug libraries) but equally not with any optimization (-O...) compilation.A horse looked at me the wrong way 20 years ago so i don't use cars and walk everywhere.
Yep, I don't use horses ;-)
Purely, purely OOI: is whatever software you develop used in-house, or is it sold to external customers where you cannot replicate their environment?
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@Chris-Kawa
I respect what you suggest, and am grateful for food for thought/your experiences. (And, yes, if I were releasing a game/frame-rate-critical app the situation would be different.) Just to be clear, I did not say we release "debug" builds, I said we release compiling/linking not for debug (e.g. so no memory zeroing, nor memory debug functions, nor debug libraries) but equally not with any optimization (-O...) compilation.A horse looked at me the wrong way 20 years ago so i don't use cars and walk everywhere.
Yep, I don't use horses ;-)
Purely, purely OOI: is whatever software you develop used in-house, or is it sold to external customers where you cannot replicate their environment?
is whatever software you develop used in-house, or is it sold to external customers where you cannot replicate their environment?
I'm a game developer so both. We do in-house tools, big and small, think from Notepad to Photoshop size, used by few hundreds of people locally at their stations and on a set of servers, and then the game itself goes to all sorts of PCs and consoles across millions of players around the world so a very diverse set of hardware and software configurations.
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is whatever software you develop used in-house, or is it sold to external customers where you cannot replicate their environment?
I'm a game developer so both. We do in-house tools, big and small, think from Notepad to Photoshop size, used by few hundreds of people locally at their stations and on a set of servers, and then the game itself goes to all sorts of PCs and consoles across millions of players around the world so a very diverse set of hardware and software configurations.
@Chris-Kawa
Yeah, a rather different situation from us, "mission critical".Final question: now that you know I am not saying we release with any debug compilation/libraries/anything (which I agree would be terrible), only that we do not compile our own code with
-O..., [plus it's not a game] are you willing to relax your condemnation a little, or am I still going to Hell in a handbasket? :) -
@Chris-Kawa
Yeah, a rather different situation from us, "mission critical".Final question: now that you know I am not saying we release with any debug compilation/libraries/anything (which I agree would be terrible), only that we do not compile our own code with
-O..., [plus it's not a game] are you willing to relax your condemnation a little, or am I still going to Hell in a handbasket? :)a rather different situation from us, "mission critical".
We "release" tools almost daily so If I cause a crash a large group of people can't do their work and that costs, so it's pretty mission critical too, although not life threatening. Well, maybe just mine when those angry people come to me :)
If you're under some regulations then it's not on you. I know there are industries where changing a configuration can mean a year of retesting, reapproving and certification. A lot of aviation for example still uses languages and compilers from the 70s because of that fact. If your software can kill a patient because you flipped a flag then it definitely should not be an ad hoc decision.
are you willing to relax your condemnation a little, or am I still going to Hell?
I'm not saying you're going to hell. I'm just saying you're gonna have a lot of regrets lying on your death bed ;) White bears drowning, bees vanishing, Australia burning, all that life people wasted waiting for your software to finish...
It's just a waste, that's all. A thing that can be done in microsecond you do in three. Nothing more, nothing less. It's the same as throwing out garbage on the pavement - it's not a world ending event, but how you feel about it is up to you.
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For me the question is most OOI.
While writing code I try to always choose the best solution,
while this is not always possible, stuff like this is rarely documented and
consistent so I appreciate everyone responding. You learn new stuff every day! -
a rather different situation from us, "mission critical".
We "release" tools almost daily so If I cause a crash a large group of people can't do their work and that costs, so it's pretty mission critical too, although not life threatening. Well, maybe just mine when those angry people come to me :)
If you're under some regulations then it's not on you. I know there are industries where changing a configuration can mean a year of retesting, reapproving and certification. A lot of aviation for example still uses languages and compilers from the 70s because of that fact. If your software can kill a patient because you flipped a flag then it definitely should not be an ad hoc decision.
are you willing to relax your condemnation a little, or am I still going to Hell?
I'm not saying you're going to hell. I'm just saying you're gonna have a lot of regrets lying on your death bed ;) White bears drowning, bees vanishing, Australia burning, all that life people wasted waiting for your software to finish...
It's just a waste, that's all. A thing that can be done in microsecond you do in three. Nothing more, nothing less. It's the same as throwing out garbage on the pavement - it's not a world ending event, but how you feel about it is up to you.
@Chris-Kawa said in Performance difference:
I'm just saying you're gonna have a lot of regrets lying on your death bed ;)
Believe me, one thing I will not be thinking about/regretting on my deathbed is whether I did or did not switch on a compiler optimization flag ;-)
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@Chris-Kawa said in Performance difference:
I'm just saying you're gonna have a lot of regrets lying on your death bed ;)
Believe me, one thing I will not be thinking about/regretting on my deathbed is whether I did or did not switch on a compiler optimization flag ;-)
@JonB It doesn't happen often but one switch can sometimes change the world. Anyways, I'm happy to see you confident in your future predicting abilities. Fingers crossed you're right.
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@JonB It doesn't happen often but one switch can sometimes change the world. Anyways, I'm happy to see you confident in your future predicting abilities. Fingers crossed you're right.
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@Chris-Kawa
With your surname, are you from down-under?@JonB Not sure what you mean. My last name is Polish and translates to coffee, which reminds me I'm up for a break :) Have a nice day.
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@JonB Not sure what you mean. My last name is Polish and translates to coffee, which reminds me I'm up for a break :) Have a nice day.
@Chris-Kawa
It looked a bit like "Kiwi" to me, I was way off. "("Down-under" means Australia or New Zealand.) It may be wasted on you, but the one thing I was thinking I might regret on my deathbed is that Kylie never chose to marry me. I do not believe that is because she is disappointed that I did not use compiler optimizations ;-) All the best :)
