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

[Vladimir Panteleev]

On Wednesday, 31 March 2021 at 06:34:04 UTC, Walter Bright wrote:
> On 3/30/2021 10:30 PM, Vladimir Panteleev wrote:
>> On Wednesday, 31 March 2021 at 05:25:48 UTC, Walter Bright 
>> wrote:
>>> It's a win because it uses the address decoder logic which is 
>>> separate from the arithmetic logic unit. This enables it to 
>>> be done in parallel with the ALU.
>> 
>> Is this still true for modern CPUs?
>
> See https://www.agner.org/optimize/optimizing_assembly.pdf page 
> 135.

Thanks!

It also says that LEA may be slower than ADD on some CPUs.

I wrote a small benchmark using the assembler code from a few 
posts ago. It takes the same time on my AMD CPU, but the ADD is 
indeed slower than the LEA on the old Intel CPU on the server. :) 
Unfortunately I don't have access to a modern Intel CPU to test.

>>> Although not relevant for this particular example, it also 
>>> doesn't need another register for the intermediate value.
>> Haven't CPUs used register renaming for a long time now? It's 
>> also pretty rare to see x86_64 code that uses all registers.
>
> If you use a register that needs to be saved on the stack, it's 
> going to cost.

Sure, but why would you do that? If I'm reading the ABI spec 
correctly, almost all registers belong to the callee, and don't 
need to be saved/restored, and there's probably little reason to 
call a function in the middle of such a computation and therefore 
save the interim value on the stack.