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

[via llvm-commits]

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@@ -382,6 +385,10 @@ class MCRegisterInfo {
     return RegStrings + get(RegNo).Name;
   }
 
+  bool isConstant(MCRegister RegNo) const {
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rin-arm wrote:

Oh yeah, absolutely.

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