erichkeane wrote:
> > If you really want to work around MSVC's bug, you could change tablegen to
> > emit the string literals as constant globals / StringLiteral
>
> I spent a bit thinking about this, and this function is incredibly wasteful.
> It ends up re-doing a ton of work that is ALREADY done. It was convenient at
> the time to write it that way, but with a little intelligence at tablegen, we
> can simplify this function a million-times.
>
> Some things we can do (and should do all): 1- We can calculate the scope, so
> we don't actually compare those. We're checking against "clang" and ""
> constantly, lets pre-calculate that into some sort of enum. There are only so
> many valid values here (and, IIRC, this has already been checked to be
> valid), so we can switch on those easily. PERHAPS another tablegen file to
> make sure we get all the normalized ones, but pretty trivial.
>
> 2- we could reduce the number of comparisons against the name: At that point,
> it ends up being:
>
> ```
> if (Name == "aarch64_sve_pcs") {
> if (getSyntax() == AttributeCommonInfo::AS_GNU && calculatedScope ==
> Scope::None)
> return 0;
> if (getSyntax() == AttributeCommonInfo::AS_CXX11 && calculatedScope ==
> Scope::Clang)
> return 1;
> if (getSyntax() == AttributeCommonInfo::AS_C23 && calculatedScope == Clang)
> return 2;
> ```
>
> 3- STOP being dummies and re-doing all the work that the `trie` in
> getAttrKind already did! We already know that the spelling is one-of-a-couple
> for each of the variants, so the actual 'does this string match this other
> one' is useless, we just need to know which it is in a list. MOST (including
> the one in the example above), all are the same, so those comparisons are
> dumb/wasted. Lets see if we can remove those.
>
> For cases where there are multiple spellings, we can compare length! For
> example: 1st I found where spelling matters, is `AT_ArgumentWithTypeTag:`,
> which is either `argument_with_type_tag` or `pointer_with_type_tag`. At THAT
> point, we could just do `Name.length() == 22` and `Name.length() == 21`.
>
> We already know it is ONE of those two, and just need to figure out which.
>
> IN SUMMARY: I am convinced somewhat we can just teach tablegen to be
> 'smarter' about this file and save ourselves ~100% of those string compares
> and replace them with numeric comparisons, or enum comparisons.
>
> The result is something that is: A- acceptable to the community/maintainers
> B- sidesteps/never has this problem again for MSVC C- Improves performance.
BTW, @chinmaydd : Please let me know if this is something you're able to do. I
might be able to free up some cycles later this week/next week to put effort
into this if not.
https://github.com/llvm/llvm-project/pull/114285
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