Why exceptions for error handling is so important

[via Digitalmars-d]

On Tuesday, 13 January 2015 at 03:05:57 UTC, Walter Bright wrote:
> On 1/12/2015 4:40 PM, deadalnix wrote:
>> These are trash register. Meaning the callee can put whatever 
>> in them. The
>> caller must consider them trashed after the call.
>>
>> So no, it do NOT increase register pressure.
>
> 1. the register must be assigned a value - that has a cost

xor on Haswell has a reciprocal throughput of 0.25, meaning 
execution of 4 instructions per cycle per core.

> 3. it prevents EDX from being used by the return value, when 
> the return value is larger than a single register size

Store the error in TLS memory using a write-through (no load from 
memory) instruction and use the carry-flag instead then (assuming 
the return instruction does not clear carry). CLC has reciprocal 
throughput of 0.25 too.

> 4. static functions may not need to follow the C ABI register 
> convention, and can be so optimized

D calls D, no problem.

D calls C, no problem, C can't return D errors...

C calls D, a problem no matter what solution you pick.