Do modern compilers optimize multiplication by 1 and -1

Question

If I write

template<int sign>
inline int add_sign(int x) {
    return sign * x;
}

template int add_sign<-1>(int x);
template int add_sign<1>(int x);

Are most C++ compilers smart enough to optimize the multiplication by 1 or -1 into some faster operation (no-op or negation)?

Answer 1

Yes. This is part of a class of simple optimizations known as arithmetic local optimizations. For example 1 * x can be simplified statically to x, likewise -1 * x can be simplified to -x. Production compilers all do this and far more complex optimizations as well.

Answer 2

For g++, use g++ -S Foo.cc to view the assembler and determine whether the template has been optimized or not. For clang, take a look at this question. For Visual Studio, take a look at this question.