[llvm] [WIP][RFC] Teach MCA constant registers do not create dependencies (PR #89387)

[Min-Yih Hsu via llvm-commits]

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@@ -126,6 +126,9 @@ struct MCRegisterDesc {
   /// Index into list with lane mask sequences. The sequence contains a lanemask
   /// for every register unit.
   uint16_t RegUnitLaneMasks;
+
+  // Returns true for constant registers
+  bool Constant;
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mshockwave wrote:

nit: I would prefer `IsConstant`.

https://github.com/llvm/llvm-project/pull/89387