[llvm] Merge sourcelocation in CSEMIRBuilder::getDominatingInstrForID. (PR #90922)

[Adrian Prantl via llvm-commits]

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@@ -243,6 +243,10 @@ class MachineIRBuilder {
   }
 
 public:
+  /// This is the merged location of an instruction which is a result of a fold
+  /// in the legalizer.
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adrian-prantl wrote:

I feel like MachineIRBuilder shouldn't need to know about the legalizer?

https://github.com/llvm/llvm-project/pull/90922