Is a shift instruction faster than an IMUL instruction?

Question

Which one is faster -

val = val*10;

or

val = (val<<3) + (val<<2);

How many clock cycles does imul take when compared to shift instruction?

Answer 1

This is the 21st century. Modern hardware and compilers know how to produce highly optimised code. Writing multiplication using shifts won't help performance but it will help you to produce code with bugs in.

You have demonstrated this yourself with code that multiplies by 12 rather than 10.

Answer 2

I'd say, just write val = val * 10; or val *= 10;, and let the compiler worry about such questions.