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

[Craig Topper via llvm-commits]

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@@ -382,6 +385,10 @@ class MCRegisterInfo {
     return RegStrings + get(RegNo).Name;
   }
 
+  bool isConstant(MCRegister RegNo) const {
+    return get(RegNo).Constant && MCRegister::isPhysicalRegister(RegNo.id());
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topperc wrote:

Isn't an MCRegister always a physical register?

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