[clang] [CIR][NFC] Use tablegen to create CIRAttrToValue visitor declarations (PR #187607)

[Erich Keane via cfe-commits]

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@@ -29,6 +29,11 @@ include "clang/CIR/Interfaces/ASTAttrInterfaces.td"
 class CIR_Attr<string name, string attrMnemonic, list<Trait> traits = []>
     : AttrDef<CIR_Dialect, name, traits> {
   let mnemonic = attrMnemonic;
+
+  // When set, clang-tblgen includes this attribute in the DirectToLLVM
+  // `CIRAttrToValue` TypeSwitch and emits a `visitCirAttr` declaration;
+  // a matching definition must exist in LowerToLLVM.cpp.
+  bit hasAttrToValueLowering = 0;
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erichkeane wrote:

Can we have a FIXME on this to explore some of the suggested Heuristics you mentioned (TypeInterface/etc?).  Would be nice if someone could check that out someday

https://github.com/llvm/llvm-project/pull/187607