[llvm] [NFC][TableGen] Add accessors for various instruction subclasses (PR #146615)

[Min-Yih Hsu via llvm-commits]

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@@ -211,10 +211,9 @@ void CodeGenTarget::ReadInstructions() const {
 
   // Parse the instructions defined in the .td file.
   for (const Record *R : Insts) {
-    auto &Inst = Instructions[R];
+    auto &Inst = InstructionMap[R];
     Inst = std::make_unique<CodeGenInstruction>(R);
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mshockwave wrote:

nit: since we're changing this part of the code, should we just use a normal `insert` or `try_emplace` instead?

https://github.com/llvm/llvm-project/pull/146615