[clang] [Clang] Refactor diagnostics for SME builtins. (PR #78258)

[Matthew Devereau via cfe-commits]

================
@@ -1720,21 +1720,29 @@ void SVEEmitter::createBuiltinZAState(raw_ostream &OS) {
   for (auto *R : RV)
     createIntrinsic(R, Defs);
 
-  std::map<bool, std::set<std::string>> DefsZAState;
-
-  uint64_t IsSharedZAFlag = getEnumValueForFlag("IsSharedZA");
+  std::map<std::string, std::set<std::string>> IntrinsicsPerState;
   for (auto &Def : Defs) {
-    bool HasZAState = Def->isFlagSet(IsSharedZAFlag);
-    DefsZAState[HasZAState].insert(Def->getMangledName());
+    std::string Key;
+    auto AddToKey = [&Key](std::string S) -> void {
+      Key = Key.empty() ? S : (Key + " | " + S);
+    };
+
+    if (Def->isFlagSet(getEnumValueForFlag("IsInZA")))
+      AddToKey("ArmInZA");
+    else if (Def->isFlagSet(getEnumValueForFlag("IsOutZA")))
+      AddToKey("ArmOutZA");
+    else if (Def->isFlagSet(getEnumValueForFlag("IsInOutZA")))
+      AddToKey("ArmInOutZA");
+
+    if (!Key.empty())
+      IntrinsicsPerState[Key].insert(Def->getMangledName());
----------------
MDevereau wrote:

Am I reading this correctly? `std::string Key;` will create an empty string `Key` at the start of each for loop iteration. The only way to add to this string is via 3 `else if`'s which means the `Key.empty()` check in the lambda will always be true and the else case will never fire.

Therefore you can just replace everything in this for loop with
```c++
    if (Def->isFlagSet(getEnumValueForFlag("IsInZA")))
      IntrinsicsPerState["ArmInZA"].insert(Def->getMangledName());
    else if (Def->isFlagSet(getEnumValueForFlag("IsOutZA")))
      IntrinsicsPerState["ArmOutZA"].insert(Def->getMangledName());
    else if (Def->isFlagSet(getEnumValueForFlag("IsInOutZA")))
      IntrinsicsPerState["ArmInOutZA"].insert(Def->getMangledName());
```

I'm assuming this is meant to be used to output or checks in `clang/include/clang/Basic/arm_sme_builtins_za_state.inc` like `return ArmInZA | ArmOutZA`? These aren't being emitted for me when I build this so I don't think this is doing what it was made for correctly.

https://github.com/llvm/llvm-project/pull/78258