[X86][SSE] Pull out BUILD_VECTOR operand equivalence tests. NFC.

Pull out element equivalence code from isShuffleEquivalent/isTargetShuffleEquivalent, I've also removed many of the index modulos where possible.

First step toward simply adding some additional equivalence tests.

Author: RKSimon

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -10754,6 +10754,27 @@ static bool isRepeatedTargetShuffleMask(unsigned LaneSizeInBits, MVT VT,
   return true;
 }
 
+/// Checks whether the vector elements referenced by two shuffle masks are
+/// equivalent.
+static bool IsElementEquivalent(int MaskSize, SDValue Op, SDValue ExpectedOp,
+                                int Idx, int ExpectedIdx) {
+  assert(0 <= Idx && Idx < MaskSize && 0 <= ExpectedIdx &&
+         ExpectedIdx < MaskSize && "Out of range element index");
+  if (!Op || !ExpectedOp || Op.getOpcode() != ExpectedOp.getOpcode())
+    return false;
+
+  if (Op.getOpcode() == ISD::BUILD_VECTOR) {
+    // If the values are build vectors, we can look through them to find
+    // equivalent inputs that make the shuffles equivalent.
+    // TODO: Handle MaskSize != Op.getNumOperands()?
+    if (MaskSize == Op.getNumOperands() &&
+        MaskSize == ExpectedOp.getNumOperands())
+      return Op.getOperand(Idx) == ExpectedOp.getOperand(ExpectedIdx);
+  }
+
+  return false;
+}
+
 /// Checks whether a shuffle mask is equivalent to an explicit list of
 /// arguments.
 ///
@@ -10766,28 +10787,23 @@ static bool isRepeatedTargetShuffleMask(unsigned LaneSizeInBits, MVT VT,
 /// in the argument.
 static bool isShuffleEquivalent(SDValue V1, SDValue V2, ArrayRef<int> Mask,
                                 ArrayRef<int> ExpectedMask) {
-  if (Mask.size() != ExpectedMask.size())
-    return false;
-
   int Size = Mask.size();
-
-  // If the values are build vectors, we can look through them to find
-  // equivalent inputs that make the shuffles equivalent.
-  auto *BV1 = dyn_cast<BuildVectorSDNode>(V1);
-  auto *BV2 = dyn_cast<BuildVectorSDNode>(V2);
+  if (Mask.size() != (int)ExpectedMask.size())
+    return false;
 
   for (int i = 0; i < Size; ++i) {
     assert(Mask[i] >= -1 && "Out of bound mask element!");
-    if (Mask[i] >= 0 && Mask[i] != ExpectedMask[i]) {
-      auto *MaskBV = Mask[i] < Size ? BV1 : BV2;
-      auto *ExpectedBV = ExpectedMask[i] < Size ? BV1 : BV2;
-      if (!MaskBV || !ExpectedBV ||
-          MaskBV->getOperand(Mask[i] % Size) !=
-              ExpectedBV->getOperand(ExpectedMask[i] % Size))
+    int MaskIdx = Mask[i];
+    int ExpectedIdx = ExpectedMask[i];
+    if (0 <= MaskIdx && MaskIdx != ExpectedIdx) {
+      SDValue MaskV = MaskIdx < Size ? V1 : V2;
+      SDValue ExpectedV = ExpectedIdx < Size ? V1 : V2;
+      MaskIdx = MaskIdx < Size ? MaskIdx : (MaskIdx - Size);
+      ExpectedIdx = ExpectedIdx < Size ? ExpectedIdx : (ExpectedIdx - Size);
+      if (!IsElementEquivalent(Size, MaskV, ExpectedV, MaskIdx, ExpectedIdx))
         return false;
     }
   }
-
   return true;
 }
 
@@ -10814,22 +10830,17 @@ static bool isTargetShuffleEquivalent(ArrayRef<int> Mask,
   if (!isUndefOrZeroOrInRange(Mask, 0, 2 * Size))
     return false;
 
-  // If the values are build vectors, we can look through them to find
-  // equivalent inputs that make the shuffles equivalent.
-  auto *BV1 = dyn_cast_or_null<BuildVectorSDNode>(V1);
-  auto *BV2 = dyn_cast_or_null<BuildVectorSDNode>(V2);
-  BV1 = ((BV1 && Size != (int)BV1->getNumOperands()) ? nullptr : BV1);
-  BV2 = ((BV2 && Size != (int)BV2->getNumOperands()) ? nullptr : BV2);
-
   for (int i = 0; i < Size; ++i) {
-    if (Mask[i] == SM_SentinelUndef || Mask[i] == ExpectedMask[i])
+    int MaskIdx = Mask[i];
+    int ExpectedIdx = ExpectedMask[i];
+    if (MaskIdx == SM_SentinelUndef || MaskIdx == ExpectedIdx)
       continue;
     if (0 <= Mask[i] && 0 <= ExpectedMask[i]) {
-      auto *MaskBV = Mask[i] < Size ? BV1 : BV2;
-      auto *ExpectedBV = ExpectedMask[i] < Size ? BV1 : BV2;
-      if (MaskBV && ExpectedBV &&
-          MaskBV->getOperand(Mask[i] % Size) ==
-              ExpectedBV->getOperand(ExpectedMask[i] % Size))
+      SDValue MaskV = MaskIdx < Size ? V1 : V2;
+      SDValue ExpectedV = ExpectedIdx < Size ? V1 : V2;
+      MaskIdx = MaskIdx < Size ? MaskIdx : (MaskIdx - Size);
+      ExpectedIdx = ExpectedIdx < Size ? ExpectedIdx : (ExpectedIdx - Size);
+      if (IsElementEquivalent(Size, MaskV, ExpectedV, MaskIdx, ExpectedIdx))
         continue;
     }
     // TODO - handle SM_Sentinel equivalences.