[dmd-internals] opApply with alias instead of delegate?

[Brad Roberts]

Personally, I think that the d front end ought to be changed to take the op
apply code and insert it at the call point around the loop body.  Essentially
inlining the loop infrastructure rather than having it called as a function.

Even if left as a function call + a delegate, that's about the easiest case of
inlining a delegate.  I'd really like to see that part of the inliner fixed
since it'd result in a general improvement rather than a specific one.  I took a
crack at it a while back and ran into some roadblocks -- fixable ones, I think.
 Once this 64 bit stuff is mostly put to bed, maybe I can meet with Walter and
we can work out a solution.

I do agree that the performance cost of opApply is unfortunate.

On 1/9/2011 12:03 PM, David Simcha wrote:
> I found this goodie in opover.c of the DMD source, and am wondering if/when it
> will be implemented fully.  I think that opApply with an alias instead of a
> delegate would be a great thing to have, rather than having to rely on a
> "sufficiently smart compiler" to inline delegates for opApply (LDC does this
> sometimes, though not very reliably) or not being able to use opApply in ultra
> performance-critical situations (status quo with DMD).  Is there any fundamental
> reason design reason why this didn't work out, or is it just yet another
> low-priority todo?
> 
> /*******************************************
>  * Infer foreach arg types from a template function opApply which looks like:
>  *    int opApply(alias int func(ref uint))() { ... }
>  */
> 
> #if 0
> void inferApplyArgTypesZ(TemplateDeclaration *tstart, Parameters *arguments)
> {
>     for (TemplateDeclaration *td = tstart; td; td = td->overnext)
>     {
>         if (!td->scope)
>         {
>             error("forward reference to template %s", td->toChars());
>             return;
>         }
>         if (!td->onemember || !td->onemember->toAlias()->isFuncDeclaration())
>         {
>             error("is not a function template");
>             return;
>         }
>         if (!td->parameters || td->parameters->dim != 1)
>             continue;
>         TemplateParameter *tp = (TemplateParameter *)td->parameters->data[0];
>         TemplateAliasParameter *tap = tp->isTemplateAliasParameter();
>         if (!tap || !tap->specType || tap->specType->ty != Tfunction)
>             continue;
>         TypeFunction *tf = (TypeFunction *)tap->specType;
>         if (inferApplyArgTypesY(tf, arguments) == 0)    // found it
>             return;
>     }
> }
> #endif
> 
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