[llvm] [RegisterCoalescer] Mark implicit-defs of super-registers as dead in remat (PR #159110)

[Benjamin Maxwell via llvm-commits]

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@@ -1475,7 +1475,8 @@ bool RegisterCoalescer::reMaterializeTrivialDef(const CoalescerPair &CP,
   // The implicit-def of the super register may have been reduced to
   // subregisters depending on the uses.
 
-  bool NewMIDefinesFullReg = false;
+  TinyPtrVector<MachineOperand *> NewMIImpDefDestReg;
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MacDue wrote:

Reworked this in terms of `NewMIImplDefs` with index tracking. 

https://github.com/llvm/llvm-project/pull/159110