[llvm] [SelectionDAG] Add function for `peekThroughFreeze` (PR #195324)

[Matt Arsenault via llvm-commits]

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@@ -1977,6 +1977,14 @@ LLVM_ABI SDValue peekThroughInsertVectorElt(SDValue V,
 /// If \p V is not a truncation, it is returned as-is.
 LLVM_ABI SDValue peekThroughTruncates(SDValue V);
 
+/// Return the non-frozen source operand of \p V if it exists.
+/// If \p V is not a freeze, it is returned as-is.
+LLVM_ABI SDValue peekThroughFreeze(SDValue V);
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arsenm wrote:

Implement inline? 

https://github.com/llvm/llvm-project/pull/195324