I will attempt one myself. I will gladly accept a better answer from Travis Brown or Miles Sabin. Nat can currently not be used to represent large numbers In the current implementation of Nat, the value corresponds to the number of nested shapeless.Succ[] types: scala> Nat(3) res10: shapeless.Succ[shapeless.Succ[shapeless.Succ[shapeless._0]]] = Succ() So to represent the number … Read more
Yes, it is possible. For example, for gcc you can use __builtin_unreachable to tell the compiler about impossible conditions, like so: if (value < 0 || value > 36) __builtin_unreachable(); We can wrap the condition above in a macro: #define assume(cond) do { if (!(cond)) __builtin_unreachable(); } while (0) And use it like so: assume(x … Read more
The reason is that lambdas are function objects so passing them to a function template will instantiate a new function specifically for that object. The compiler can thus trivially inline the lambda call. For functions, on the other hand, the old caveat applies: a function pointer gets passed to the function template, and compilers traditionally … Read more
You can use the -Q –help=target options: gcc -march=native -Q –help=target … The -v option may also be of use. You can see the documentation on the –help option here.
It’s c = i && (&i);, with the second part being redundant, since &i will never evaluate to false. For a user-defined type, where you can actually overload unary operator &, it might be different, but it’s still a very bad idea. If you turn on warnings, you’ll get something like: warning: the address of … Read more
Rust originally did enable LLVM’s noalias attribute, but this caused miscompiled code. When all supported LLVM versions no longer miscompile the code, it will be re-enabled. If you add -Zmutable-noalias=yes to the compiler options, you get the expected assembly: adds: mov eax, dword ptr [rsi] add eax, eax add dword ptr [rdi], eax ret Simply … Read more
Consider this code, int some_int = 100; while(some_int == 100) { //your code } When this program gets compiled, the compiler may optimize this code, if it finds that the program never ever makes any attempt to change the value of some_int, so it may be tempted to optimize the while loop by changing it … Read more