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> Why do you expect that? Because I wrote it? > Nobody ever promised you that. I just assumed that compiler writers had empathy for humans, my bad. > It doe

> Why do you expect that? Because I wrote it? > Nobody ever promised you that. I just assumed that compiler writers had empathy for humans, my bad. > It doesn’t! According to the spec we’re both working off. If you think the spec is wrong then change it. But I can’t guess what you want unless you tell me using the spec. How big is the spec and how many working programmers do you think are super intimately familiar? Do you think this article would be on the front page if this information wasn't surprising? Are you building a compiler for humans, or are you just chasing metrics and getting the smug satisfaction of telling users "I told you so" when shit doesn't work in an intuitive way? If you want to beat me over the head with "the spec says", you win, master language lawyer. I build things for a living and I like it when the code I specify is the code that's generated. You can blame users all you want, but maybe after the trillionth zero day exploit because nobody gets these things right you might consider empathy and developer ergonomics.

jmgao 5y ago
> I build things for a living and I like it when the code I specify is the code that's generated. Okay, then specify -O0 and enjoy your dumpster fire performance.
- overgard 5y ago
  To be fair, it's usually like 5% slower. But I also don't usually have control over the flags if I'm writing a library.
  - umanwizard 5y ago
    I’d be curious to know what benchmarks you’re using on which O0 is only 5% slower. I suspect your program must be almost entirely IO-bound, if this is the case. In that case, Python, Ruby, or shell probably wouldn’t be much slower either.
    - overgard 5y ago
      Writing games, I've rarely seen the optimizer do anything of substantial use.
- SAI_Peregrinus 5y ago
  -O0 doesn't necessarily change this. After all, optimizations aren't allowed to violate the spec (if they do, they're buggy). So any code that can be output by an optimizing compiler could (in principle) be output by a non-optimizing compiler.
chrisseaton 5y ago
> I like it when the code I specify is the code that's generated But you aren't specifying it! You're asking me to follow extra constraints that you haven't written down and we haven't agreed. Don't you think it's unreasonable when you say it out loud like that? If you want extra constraints on top of what is already agreed in the spec then we can do that, but you have to ask for it and you have to bring me a workable spec. You want me to 'intuit' but really you want me to read your mind and follow a lot of unwritten rules!
- overgard 5y ago
  I think we have a fundamental difference on what a compiler should do. I want the compiler to take my exact instructions and generate the best machine code it can, that follows those exact instructions. You want to rewrite my program to be more optimal. The tension here is that, even though I'm sure you can do that, I have to debug the result, and the result I have to debug is now stripped of symbols and super hard to relate back to my original source code. So ok, I am only adding one constraint but it's a big one: don't ever change the line-by-line meaning of my source code. If I wrote a line of code I intended for it to be executed, I don't want my memsets removed or my atomics collapsed, not because you can't do it, but because I need to debug it. I don't think taking advantage of undefined behavior to create optimizations is useful because being wrong 10% faster isn't really that useful. And I think optimizations like removing memsets are a really bad idea; not only does it potentially make peoples data insecure but the only people that are ever going to find a bug like that are people looking for vulnerabilities. And frankly, here's the thing: I don't care that much about most of your optimizations. If I'm making my code fast, what I'm fretting about is designing my data structures to fit in cache, or using SIMD instructions, or offloading work to the GPU or other coprocessors. Screwing with the meaning of my code just makes my life harder.
  - josephcsible 5y ago
    I think you're severely underestimating how much slower everything would be if compilers weren't allowed to optimize anymore.

jmgao 5y ago

> I build things for a living and I like it when the code I specify is the code that's generated. Okay, then specify -O0 and enjoy your dumpster fire performance.

overgard 5y ago
To be fair, it's usually like 5% slower. But I also don't usually have control over the flags if I'm writing a library.
- umanwizard 5y ago
  I’d be curious to know what benchmarks you’re using on which O0 is only 5% slower. I suspect your program must be almost entirely IO-bound, if this is the case. In that case, Python, Ruby, or shell probably wouldn’t be much slower either.
  - overgard 5y ago
    Writing games, I've rarely seen the optimizer do anything of substantial use.
SAI_Peregrinus 5y ago
-O0 doesn't necessarily change this. After all, optimizations aren't allowed to violate the spec (if they do, they're buggy). So any code that can be output by an optimizing compiler could (in principle) be output by a non-optimizing compiler.

chrisseaton 5y ago

> I like it when the code I specify is the code that's generated But you aren't specifying it! You're asking me to follow extra constraints that you haven't written down and we haven't agreed. Don't you think it's unreasonable when you say it out loud like that? If you want extra constraints on top of what is already agreed in the spec then we can do that, but you have to ask for it and you have to bring me a workable spec. You want me to 'intuit' but really you want me to read your mind and follow a lot of unwritten rules!

overgard 5y ago
I think we have a fundamental difference on what a compiler should do. I want the compiler to take my exact instructions and generate the best machine code it can, that follows those exact instructions. You want to rewrite my program to be more optimal. The tension here is that, even though I'm sure you can do that, I have to debug the result, and the result I have to debug is now stripped of symbols and super hard to relate back to my original source code. So ok, I am only adding one constraint but it's a big one: don't ever change the line-by-line meaning of my source code. If I wrote a line of code I intended for it to be executed, I don't want my memsets removed or my atomics collapsed, not because you can't do it, but because I need to debug it. I don't think taking advantage of undefined behavior to create optimizations is useful because being wrong 10% faster isn't really that useful. And I think optimizations like removing memsets are a really bad idea; not only does it potentially make peoples data insecure but the only people that are ever going to find a bug like that are people looking for vulnerabilities. And frankly, here's the thing: I don't care that much about most of your optimizations. If I'm making my code fast, what I'm fretting about is designing my data structures to fit in cache, or using SIMD instructions, or offloading work to the GPU or other coprocessors. Screwing with the meaning of my code just makes my life harder.
- josephcsible 5y ago
  I think you're severely underestimating how much slower everything would be if compilers weren't allowed to optimize anymore.