[llvm] CodeGen: Add RegisterClass by HwMode (PR #158269)

[Matt Arsenault via llvm-commits]

================
@@ -43,22 +43,48 @@ class MCInstrInfo {
   const ComplexDeprecationPredicate *ComplexDeprecationInfos;
   unsigned NumOpcodes;              // Number of entries in the desc array
 
+protected:
+  // Pointer to 2d array [NumHwModes][NumRegClassByHwModes]
+  const int16_t *RegClassByHwModeTables;
+  int16_t NumRegClassByHwModes;
+
 public:
   /// Initialize MCInstrInfo, called by TableGen auto-generated routines.
   /// *DO NOT USE*.
   void InitMCInstrInfo(const MCInstrDesc *D, const unsigned *NI, const char *ND,
                        const uint8_t *DF,
-                       const ComplexDeprecationPredicate *CDI, unsigned NO) {
+                       const ComplexDeprecationPredicate *CDI, unsigned NO,
+                       const int16_t *RCHWTables = nullptr,
+                       int16_t NumRegClassByHwMode = 0) {
     LastDesc = D + NO - 1;
     InstrNameIndices = NI;
     InstrNameData = ND;
     DeprecatedFeatures = DF;
     ComplexDeprecationInfos = CDI;
     NumOpcodes = NO;
+    RegClassByHwModeTables = RCHWTables;
+    NumRegClassByHwModes = NumRegClassByHwMode;
   }
 
   unsigned getNumOpcodes() const { return NumOpcodes; }
 
+  const int16_t *getRegClassByHwModeTable(unsigned ModeId) const {
+    assert(RegClassByHwModeTables && NumRegClassByHwModes != 0 &&
+        "MCInstrInfo not properly initialized");
----------------
arsenm wrote:

```suggestion
    assert(RegClassByHwModeTables && NumRegClassByHwModes != 0 &&
          "MCInstrInfo not properly initialized");
```

https://github.com/llvm/llvm-project/pull/158269