Optimization is off by default

[Voileexperiments]

Apparently compiler flag for C++ runner does not have optimization turned on, as well as other languages.

This is arguably wrong because it's non-standard: standard optimization parameter used across most languages (if available) in OJ ecosystem (e.g IOI [1], ACM [2], Codeforces[3][4]) is -O2, so CW should use -O2 by default too.

Now there is #699, but OPTIONS_GHC pragma overrides command-line options anyway so it shouldn't be a problem:

NOTE: The contents of OPTIONS_GHC are appended to the command-line options, so options given in the source file override those given on the command-line.

[kazk]

C/C++ needs an update in general. I'm going to turn on the warnings as well which was turned off because Codewars used to treat stderr as error.

[Voileexperiments]

For C++, I used this OB snippet for testing optimization:

#include <iostream>

typedef int (*Function)();

static Function Do;

static int EraseAll() {
  std::cout << "Safe!\n";
  return 1;
}

void NeverCalled() {
  Do = EraseAll;
}

int test() {
  return Do();
}

Calling test in -O1 or above will not crash because Do = EraseAll is completely optimized in these cases (check with Compiler Explorer).

A kumite is available here.

[Voileexperiments]

C/C++ needs an update in general

I suppose the update includes using the newest version of clang/gcc?

Also compiler optimization flag applies to many other languages besides C/C++, so they have to be checked against as well.

[Voileexperiments]

Also, ref: #706

[kazk]

-O2 was added to newer versions of C/C++.

[Voileexperiments]

What about other languages that has similar optimization settings?