[Bug tree-optimization/108487] [10/11/12/13 Regression] ~20-30x slowdown in populating std::vector from std::ranges::iota_view

["Mark_B53 at yahoo dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108487

--- Comment #2 from MARK BOURGEAULT <Mark_B53 at yahoo dot com> ---
>> For fn1, assembly of the inner loop should be identical, so I think the 20% you were seeing may result from different loop alignment with respect to 32b fetch boundary
Yes, it does appear that this is the explanation for the difference.  Here are
the full results:

original code
 * gcc 10.3 -std=c++20 -O3 => fn1 = ~2000ms, fn2 = ~1000ms
 * gcc 10.3 -std=c++20 -O3 -falign-loops=32 => fn1 = ~2000ms, fn2 = ~1000ms
 * gcc 12.2 -std=c++20 -O3 => fn1 = ~2500ms, fn2 = ~32000ms
 * gcc 12.2 -std=c++20 -O3 -falign-loops=32 => fn1 = ~2000ms, fn2 = ~32000ms

fn1 only
 * gcc 10.3 -std=c++20 -O3 => fn1 = ~2500ms
 * gcc 10.3 -std=c++20 -O3 -falign-loops=32 => fn1 = ~2000ms
 * gcc 12.2 -std=c++20 -O3 => fn1 = ~2000ms
 * gcc 12.2 -std=c++20 -O3 -falign-loops=32 => fn1 = ~2000ms

>> Also please note that cloud instances backing godbolt.org have different CPUs, so timing results from different runs are not directly comparable.
Yes, I know.  I really only used godbolt to reach the conclusion that the issue
still exists on trunk.