[CIR][CodeGen] Introduce CIR CXXSpecialMember attribute

[bruteforceboy]

I think this one is self-explanatory, so I will not write much 🙂‍

Adding this attribute helps in optimizations like #1653, and using the attribute it's easy to create operations like cir.std.vector.ctor/cir.std.vector.dtor by just modifying IdiomRecognizer a bit. I believe it will also be useful for future optimizations. Finally, I updated quite a number of tests so they now reflect this attribute.

Please, let me know if you see any issues.

[bcardosolopes]

Thanks for adding more of the building blocks here. In the future it'd be nice to have a representation for struct/class more closer to C++ and it will probably be easier to extract this type of information, but to prevent over engineering early, it feels right to incrementally add pieces that can enable us to better analyze C++ code and make transformations easier to write.

Can you look into changing LifetimeChecker.cpp to use this attribute instead of the current AST approach?

[bcardosolopes]

(@andykaylor @erichkeane @dkolsen-pgi in case you have any extra thoughts here)

[andykaylor]

Do we also want to set this attribute on cir.func definitions/declarations?

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[bruteforceboy]

A few updates:

1. The attribute is now attached to the FuncOp (like ctor<type>) instead of the call
2. The attribute now stores Type instead of a string
3. I updated LifetimeChecker.cpp to make use of this attribute instead of the AST approach
4. I added a couple of traits for the ctor attribute, and I think we can extend as necessary in the future
5. CIR_CXXCtorDtor is now CIR_CXXSpecialMember
6. Updated a couple of tests to reflect the ctor/dtor attribute.

cc: @bcardosolopes, @erichkeane, @andykaylor

[erichkeane]

1 comment, else seems reasonable, I'm happy when the others are.

[bcardosolopes]

Thanks for the update, one more round of suggestions

[bcardosolopes]

Thanks for the updates, one more round!

[bcardosolopes]

Thanks for your patience, more comments!

[xlauko]

Suggested change

	if (auto oa = parser.parseOptionalAttribute(ctorAttr); oa.has_value())
	state.addAttribute(cxxSpecialMemberAttr, ctorAttr);
	if (auto oa = parser.parseOptionalAttribute(dtorAttr); oa.has_value())
	state.addAttribute(cxxSpecialMemberAttr, dtorAttr);
	if (auto oa = parser.parseOptionalAttribute(ctorAttr))
	state.addAttribute(cxxSpecialMemberAttr, ctorAttr);
	if (auto oa = parser.parseOptionalAttribute(dtorAttr))
	state.addAttribute(cxxSpecialMemberAttr, dtorAttr);

[bruteforceboy]

parser.parseOptionalAttribute returns mlir::OptionalParseResult, so the oa.has_value() part is necessary to make the condition boolean.

[bcardosolopes]

You are not using oa, so might as well do if (parser.parseOptionalAttribute(dtorAttr).has_value())?

[bruteforceboy]

You are not using oa, so might as well do if (parser.parseOptionalAttribute(dtorAttr).has_value())?

right, updated!

[bcardosolopes]

LGTM pending last discussion item