一元运算符和二进制运算符之间的性能差异

Question

Is there actually a performance difference between -foo and (-1)*foo where foo is a variable of type int ? In theory the unary operator should be faster. But I think the compiler will optimise this out.

Answer 1

Is there actually a performance difference between -foo and (-1)*foo

Theoretically there can be. The C++ standard makes no guarantees either way.

However, assuming type of foo is an integer, then there is absolutely no difference between the observable behaviour of those expressions. The compiler is therefore in that case allowed to generate an identical binary program for either expression. A ideal optimiser should generate the program that that performs better.

Whether your real compiler generates the same output for both programs is another matter - no real compiler is ideal. You can find out by using the compiler for both alternative programs and then comparing the output.