Eliding of slice range checking

[welkam]

On Wednesday, 23 October 2019 at 11:20:59 UTC, Per Nordlöw wrote:
> Does DMD/LDC avoid range-checking in slice-expressions such as 
> the one in my array-overload of `startsWith` defined as
>
> bool startsWith(T)(scope const(T)[] haystack,
>                    scope const(T)[] needle)
> {
>     if (haystack.length >= needle.length)
>     {
>         return haystack[0 .. needle.length] == needle; // is 
> slice range checking avoid here?
>     }
>     return false;
> }
>
> ///
> @safe pure nothrow @nogc unittest
> {
>     auto x = "beta version";
>     assert(x.startsWith("beta"));
> }
>
> when building in release mode?
>
> I remember a DMD pull from Ian Buclaw that enabled some eliding 
> but I don't remember if it includes the case above.
>
> How can I investigate the codegen myself here?

I remember in some video Chandler Carruth said that value range 
propagation across function boundary was implemented in llvm but 
later removed because it produced no performance improvement for 
C and C++ code. I wonder how it fare when used on D code.