[llvm] [NFC][AsmPrinter] Refactor FrameIndexExprs as a std::set (PR #66433)

[David Blaikie via llvm-commits]

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@@ -158,7 +153,7 @@ class Multi {
 };
 /// Single location defined by (potentially multiple) MMI entries.
 struct MMI {
-  mutable SmallVector<FrameIndexExpr, 1> FrameIndexExprs;
+  std::set<FrameIndexExpr> FrameIndexExprs;
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dwblaikie wrote:

Another possibilty would be a `SetVector`? (though then it's insertion ordered, rather than `<` ordered - not sure if that's sufficiently stable for the needs? perhaps not)

https://github.com/llvm/llvm-project/pull/66433