Timeline for When I test out the difference in time between shifting and multiplying in C, there is no difference. Why?

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May 2, 2018 at 14:48	comment	added	derobert		@AkshayLAradhya I can't say what your compiler is doing, but I confirmed again that `gcc -O3` (now with 7.3) still removes the loop entirely. (Make sure to switch to a long instead of int if required, otherwise it optimizes it into an infinite loop due to overflow).
May 2, 2018 at 14:37	comment	added	DollarAkshay		I get what you are saying, but I don't think the compiler is removing the entire loop. You can easily test out this theory by simply increasing the number of iterations. You will see that increasing the iterations does make the program take longer. If the loop was entirely removed this wouldn't be the case.
Jul 22, 2014 at 22:08	comment	added	derobert		@MichaelT Yep. That's what I meant by "Note that a sufficiently determined optimizer could still optimize away the loop (it relies entirely on constants known at compile time)."
Jul 22, 2014 at 22:07	review	First posts
Jul 23, 2014 at 0:45
Jul 22, 2014 at 22:07	comment	added	user40980		Note also that the optimizer can (and will) optimize out operations on constants (even in a loop) as shown in sqrt c# vs sqrt c++ where the optimizer was able to replace a loop summing a value with the actual sum. To defeat that optimization you need to use something determined at runtime (such as a command line argument).
Jul 22, 2014 at 21:58	history	answered	derobert	CC BY-SA 3.0