[clang] Patch series to reapply #118734 and substantially improve it (PR #120534)

[Chandler Carruth via cfe-commits]

================
@@ -482,17 +488,42 @@ void clang::EmitClangBuiltins(const RecordKeeper &Records, raw_ostream &OS) {
   for (const auto *BuiltinRecord :
        Records.getAllDerivedDefinitions("AtomicBuiltin"))
     collectBuiltins(BuiltinRecord, Builtins);
-
   unsigned NumAtomicBuiltins = Builtins.size();
 
   for (const auto *BuiltinRecord :
        Records.getAllDerivedDefinitions("Builtin")) {
     if (BuiltinRecord->isSubClassOf("AtomicBuiltin"))
       continue;
+    // Prefixed builtins are also special and we emit them last so they can have
+    // their own representation that skips the prefix.
+    if (BuiltinRecord->getValueAsOptionalDef("RequiredNamePrefix"))
+      continue;
+
     collectBuiltins(BuiltinRecord, Builtins);
   }
 
+  // Now collect (and count) the prefixed builtins.
+  unsigned NumPrefixedBuiltins = Builtins.size();
+  const Record *first_prefix = nullptr;
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chandlerc wrote:

Doh, just an accident, sorry. Out of the habits of LLVM style, fixed.

https://github.com/llvm/llvm-project/pull/120534