[llvm] [TableGen] Use bitwise operations to access HwMode ID. (PR #88377)

[Jason Eckhardt via llvm-commits]

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@@ -240,7 +240,23 @@ class MCSubtargetInfo {
     return ProcFeatures;
   }
 
-  virtual unsigned getHwMode() const { return 0; }
+  /// HwMode ID will be stored as bits, allowing users to pull the specific
+  /// HwMode ID (like RegInfo HwMode ID) from the bits as needed. This enables
+  /// users to control multiple features with one hwmode (as previously) or use
+  /// different hwmodes to control different features.
+  enum HwModeType {
+    HwMode_Default,   // Return the smallest HwMode ID of current subtarget.
+    HwMode_ValueType, // Return the HwMode ID that controls the ValueType.
+    HwMode_RegInfo,   // Return the HwMode ID that controls the RegSizeInfo and
+                      // SubRegRange.
+    HwMode_EncodingInfo // Return the HwMode ID that controls the EncodingInfo.
+  };
+
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nvjle wrote:

Since there are now two APIs, please document each one specifically and clearly. Minimally, something along the lines of "Returns a bit vector/set of all hardware modes." for the first, and "Returns a single hardware mode of the requested type."

https://github.com/llvm/llvm-project/pull/88377