bounds checking and optimization

[David Nadlinger]

On 30 Jun 2021, at 12:43, Johan via digitalmars-d-ldc wrote:
> On Wednesday, 30 June 2021 at 01:18:53 UTC, Bruce Carneal wrote:
>> could c.length be extracted and asserted as being leq a.length and 
>> b.length before we drop in to the loop?
>
> That would be observable behavior change, so not possible. Unless the 
> behavior upon out-of-bounds access is defined as UB.

There might be LLVM optimisation passes to recognise the range checks 
and coalesce them into a single one before the loop header, though – I 
vaguely remember seeing something like this in the tree at some point, 
developed with a few towards Java, and not enabled by default in the 
PassManagerBuilder. We might be able to reuse/adapt that logic.

  — David