[llvm] [RISCV] Initial codegen support for the XRivosVizip extension (PR #131933)

[Craig Topper via llvm-commits]

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@@ -4611,6 +4613,43 @@ static bool isElementRotate(std::array<std::pair<int, int>, 2> &SrcInfo,
          SrcInfo[1].second - SrcInfo[0].second == (int)NumElts;
 }
 
+static bool isAlternating(std::array<std::pair<int, int>, 2> &SrcInfo,
+                          ArrayRef<int> Mask, bool &Polarity) {
+  int NumElts = Mask.size();
+  bool NonUndefFound = false;
+  for (unsigned i = 0; i != Mask.size(); ++i) {
+    int M = Mask[i];
+    if (M < 0)
+      continue;
+    int Src = M >= (int)NumElts;
+    int Diff = (int)i - (M % NumElts);
+    bool C = Src == SrcInfo[1].first && Diff == SrcInfo[1].second;
+    if (!NonUndefFound) {
+      NonUndefFound = true;
+      Polarity = (C == i % 2);
+      continue;
+    }
+    if ((Polarity && C != i % 2) || (!Polarity && C == i % 2))
+      return false;
+  }
+  return true;
+}
+
+static bool isZipEven(std::array<std::pair<int, int>, 2> &SrcInfo,
+                      ArrayRef<int> Mask) {
+  bool Polarity;
+  return SrcInfo[0].second == 0 && SrcInfo[1].second == 1 &&
+         isAlternating(SrcInfo, Mask, Polarity) && Polarity;
+  ;
+}
+
+static bool isZipOdd(std::array<std::pair<int, int>, 2> &SrcInfo,
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topperc wrote:

`const std::array`?

https://github.com/llvm/llvm-project/pull/131933