YASAQ Yet another silly academic question - how does "code optimization" really works?
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Run into a coder who for whatever and unknown reason posted in this "style": .... return A+B; return A+B; } and duplicated few other lines of code also. Obviously the second "return" won't ever be executed ( unless used after "if" for example ). My question is - does the "optimizer" do anything with subsequent and identical lines of code assuming the first line does not modify anything? Just asking, and yes , I did ask the originator, but he was too busy "fixing" his illogical code elsewhere and did not seems interested in such trivial matters. Cheers Vaclav
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Any half decent compiler would optimize out the second statement as it serves no purpose.
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Run into a coder who for whatever and unknown reason posted in this "style": .... return A+B; return A+B; } and duplicated few other lines of code also. Obviously the second "return" won't ever be executed ( unless used after "if" for example ). My question is - does the "optimizer" do anything with subsequent and identical lines of code assuming the first line does not modify anything? Just asking, and yes , I did ask the originator, but he was too busy "fixing" his illogical code elsewhere and did not seems interested in such trivial matters. Cheers Vaclav
Vaclav_Sal wrote:
does the "optimizer" do anything with subsequent and identical lines of code
Why does it matter? Code itself requires very little space in pretty much all modern applications perhaps only excluding very small (device itself is small) embedded processing apps. And since the line can never execute, regardless of anything like a normal language, that means the space that the code actually takes up is the only part that is relevant in any normal 'optimization' discussion.
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Vaclav_Sal wrote:
does the "optimizer" do anything with subsequent and identical lines of code
Why does it matter? Code itself requires very little space in pretty much all modern applications perhaps only excluding very small (device itself is small) embedded processing apps. And since the line can never execute, regardless of anything like a normal language, that means the space that the code actually takes up is the only part that is relevant in any normal 'optimization' discussion.
"Why does it matter?" Why do you bother to reply if you cannot stay on subject and really answer the question? To everybody else: Observed on C++ code written for Arduino "toy" controller. "They" use some version of cpp compiler, sorry do not know exactly which one. It changes ( version ) often. I agree that such code should not compile on limited resources "embedded" hardware, as pointed out. But the compiler does not know that, right? There may be an option in compiler setup,but I have not search for it. Maybe when I get my messy code fixed I'll check it. Thanks Cheers Vaclav
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"Why does it matter?" Why do you bother to reply if you cannot stay on subject and really answer the question? To everybody else: Observed on C++ code written for Arduino "toy" controller. "They" use some version of cpp compiler, sorry do not know exactly which one. It changes ( version ) often. I agree that such code should not compile on limited resources "embedded" hardware, as pointed out. But the compiler does not know that, right? There may be an option in compiler setup,but I have not search for it. Maybe when I get my messy code fixed I'll check it. Thanks Cheers Vaclav
Vaclav_Sal wrote:
I agree that such code should not compile on limited resources "embedded" hardware, as pointed out. But the compiler does not know that, right?
Well it should; 'general' compilers have an option to tell them the target hardware. Without such an option how can they know what code to generate? I am still not sure what this question is really about, do you have an actual problem that needs resolving?
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"Why does it matter?" Why do you bother to reply if you cannot stay on subject and really answer the question? To everybody else: Observed on C++ code written for Arduino "toy" controller. "They" use some version of cpp compiler, sorry do not know exactly which one. It changes ( version ) often. I agree that such code should not compile on limited resources "embedded" hardware, as pointed out. But the compiler does not know that, right? There may be an option in compiler setup,but I have not search for it. Maybe when I get my messy code fixed I'll check it. Thanks Cheers Vaclav
Vaclav_Sal wrote:
"Why does it matter?"
Why do you bother to reply if you cannot stay on subject and really answer the questionYou said "optimization". Focusing on 'micro' optimization is meaningless. Focusing on business optimization is very relevant and thus the context of my response. So yes it is on subject in less you meant something else when you said "optimization".
Vaclav_Sal wrote:
But the compiler does not know that, right?
When one is targeting specific 'small' embedded spaces the following is probably always relevant (I only say probably because I am not familiar with every possible small device.) - The entire application must take into account the embedded space. - I doubt seriously that the cross compiler would not be specific to the device and perhaps even specific to the version of the device (certainly true is all of the limited cases I have worked with.) - Cross compilers can often have language limitations. For example (quite a bit in the past) a C cross compiler that I used did not support floating point numbers in any form.
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VC6-VC10 produce unreachable code warnings (C4702) /W4, but much to my surprise not at /W3.
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"Why does it matter?" Why do you bother to reply if you cannot stay on subject and really answer the question? To everybody else: Observed on C++ code written for Arduino "toy" controller. "They" use some version of cpp compiler, sorry do not know exactly which one. It changes ( version ) often. I agree that such code should not compile on limited resources "embedded" hardware, as pointed out. But the compiler does not know that, right? There may be an option in compiler setup,but I have not search for it. Maybe when I get my messy code fixed I'll check it. Thanks Cheers Vaclav
"They" use some version of cpp compiler, sorry do not know exactly which one. Seems likely it'd be a GCC, or nowadays maybe even LLVM. Have a look at command line options -W4 or -Wall. One of the two options (or very similar) would probably tell you "Silly user, now you gone and made a mess out of stuff again!". :-)
