Time to move std.experimental.checkedint to std.checkedint ?

[Vladimir Panteleev]

On Wednesday, 31 March 2021 at 04:08:02 UTC, Andrei Alexandrescu 
wrote:
> Not much to write home about. The jumps scale linearly with the 
> number of primitive operations:
>
> https://godbolt.org/z/r3sj1T4hc

Right, but as we both know, speed doesn't necessarily scale with 
the number of instructions for many decades now.

Curiosity got the better of me and I played with this for a bit.

Here is my program:

https://dump.cy.md/d7b7ae5c2d15c8c0127fd96dd74909a1/main.zig

Two interesting observations:

1. The compiler (whether it's the Zig frontend or the LLVM 
backend) is smart about adding the checks. If it can prove that 
the values will never overflow, then the overflow checks aren't 
emitted. I had to trick it into thinking that they may overflow, 
when in practice they never will.

1b. The compiler is actually that aware of the checks, that in 
one of my attempts to get it to always emit them, it actually 
generated a version of the function with and without the checks, 
and called the unchecked version in the case where it knew that 
it will never overflow! Amazing!

2. After finally getting it to always generate the checks, and 
benchmarking the results, the difference in run time I'm seeing 
between ReleaseFast and ReleaseSafe is a measly 2.7%. The 
disassembly looks all right too: https://godbolt.org/z/3nY7Ee4ff

Personally, 2.7% is a price I'm willing to pay any day, if it 
helps save me from embarrassments like 
https://github.com/CyberShadow/btdu/issues/1 :)