[llvm] [SLP] Extract isIdentityOrder to common routine [probably NFC] (PR #106582)

[Alexey Bataev via llvm-commits]

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@@ -1364,6 +1364,19 @@ class BoUpSLP {
   /// Perform LICM and CSE on the newly generated gather sequences.
   void optimizeGatherSequence();
 
+  /// Does this non-empty order represent an identity order?  Identity
+  /// should be represented as an empty order, so this is used to
+  /// decide if we can canonicalize a computed order.  Undef elements
+  /// (represented as size) are ignored.
+  bool IsIdentityOrder(ArrayRef<unsigned> Order) const {
+    assert(!Order.empty());
+    const unsigned Sz = Order.size();
+    for (unsigned Idx : seq<unsigned>(0, Sz))
+      if (Idx != Order[Idx] && Order[Idx] != Sz)
+        return false;
+    return true;
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alexey-bataev wrote:

`return all_of(enumerate(Order), [&](const auto &P) { return P.value() == P.index() || P.value() == Sz; });`

https://github.com/llvm/llvm-project/pull/106582