X86: Refactor type-splitting to target-legal size vector to a helper function

[zvi]

Summary

This is a preparatory step for D41811: refactoring code for breaking vector operands of binary operation to legal-types.

[RKSimon]

LGTM with a couple of minors

lib/Target/X86/X86ISelLowering.cpp

33987

operations

34001

As this is now a general function, please add an assertion (same for 256/128 cases):

assert((VT.getSizeInBits() % 512) == 0 && "Illegal vector size");

34006

As this is now a general function, please add for the else clause:

assert(Subtarget.hasSSE2() && "SSE2 required");

[zvi]

Add asserions for type sizes and fix typo in comment

lib/Target/X86/X86ISelLowering.cpp

   if (!TLI.isTypeLegal(In.getValueType()) || !TLI.isTypeLegal(VT))
     return SDValue();
   if (auto USatVal = detectUSatPattern(In, VT))
     if (isSATValidOnAVX512Subtarget(In.getValueType(), VT, Subtarget))
       return DAG.getNode(X86ISD::VTRUNCUS, DL, VT, USatVal);
   return SDValue();
 }
 
+// Helper for splitting operands of a binary operation to legal target size and
+// apply a function on each part.
+// Useful for operationa that are available on SSE2 in 128-bit, on AVX2 in
+// 256-bit and on AVX512BW in 512-bit.
+// The argument VT is the type used for deciding if/how to split the operands
+// Op0 and Op1. Op0 and Op1 do *not* have to be of type VT.
+// The argument Builder is a function that will be applied on each split psrt:
+// SDValue Builder(SelectionDAG&G, SDLoc, SDValue, SDValue)
+template <typename F>
+SDValue SplitBinaryOpsAndApply(SelectionDAG &DAG, const X86Subtarget &Subtarget,
+                               SDLoc DL, EVT VT, SDValue Op0, SDValue Op1,
+                               F Builder) {
+  assert(Subtarget.hasSSE2() && "Target assumed to support at least SSE2");
+  unsigned NumSubs = 1;
+  if (Subtarget.hasBWI()) {
+    if (VT.getSizeInBits() > 512)
+      NumSubs = VT.getSizeInBits() / 512;
+  } else if (Subtarget.hasAVX2()) {
+    if (VT.getSizeInBits() > 256)
+      NumSubs = VT.getSizeInBits() / 256;
+  } else {
+    if (VT.getSizeInBits() > 128)
+      NumSubs = VT.getSizeInBits() / 128;
+  }
+
+  if (NumSubs == 1)
+    return Builder(DAG, DL, Op0, Op1);
+
+  SmallVector<SDValue, 4> Subs;
+  EVT InVT = Op0.getValueType();
+  EVT SubVT = EVT::getVectorVT(*DAG.getContext(), InVT.getScalarType(),
+                               InVT.getVectorNumElements() / NumSubs);
+  for (unsigned i = 0; i != NumSubs; ++i) {
+    unsigned Idx = i * SubVT.getVectorNumElements();
+    SDValue LHS = extractSubVector(Op0, Idx, DAG, DL, SubVT.getSizeInBits());
+    SDValue RHS = extractSubVector(Op1, Idx, DAG, DL, SubVT.getSizeInBits());
+    Subs.push_back(Builder(DAG, DL, LHS, RHS));
+  }
+  return DAG.getNode(ISD::CONCAT_VECTORS, DL, VT, Subs);
+}
+
 /// This function detects the AVG pattern between vectors of unsigned i8/i16,
 /// which is c = (a + b + 1) / 2, and replace this operation with the efficient
 /// X86ISD::AVG instruction.
 static SDValue detectAVGPattern(SDValue In, EVT VT, SelectionDAG &DAG,
                                 const X86Subtarget &Subtarget,
                                 const SDLoc &DL) {
   if (!VT.isVector() || !VT.isSimple())
     return SDValue();

         return false;
       uint64_t Val = C->getZExtValue();
       if (Val < Min || Val > Max)
         return false;
     }
     return true;
   };
 
-  // Split vectors to legal target size and apply AVG.
-  auto LowerToAVG = [&](SDValue Op0, SDValue Op1) {
-    unsigned NumSubs = 1;
-    if (Subtarget.hasBWI()) {
-      if (VT.getSizeInBits() > 512)
-        NumSubs = VT.getSizeInBits() / 512;
-    } else if (Subtarget.hasAVX2()) {
-      if (VT.getSizeInBits() > 256)
-        NumSubs = VT.getSizeInBits() / 256;
-    } else {
-      if (VT.getSizeInBits() > 128)
-        NumSubs = VT.getSizeInBits() / 128;
-    }
-
-    if (NumSubs == 1)
-      return DAG.getNode(X86ISD::AVG, DL, VT, Op0, Op1);
-
-    SmallVector<SDValue, 4> Subs;
-    EVT SubVT = EVT::getVectorVT(*DAG.getContext(), VT.getScalarType(),
-                                 VT.getVectorNumElements() / NumSubs);
-    for (unsigned i = 0; i != NumSubs; ++i) {
-      unsigned Idx = i * SubVT.getVectorNumElements();
-      SDValue LHS = extractSubVector(Op0, Idx, DAG, DL, SubVT.getSizeInBits());
-      SDValue RHS = extractSubVector(Op1, Idx, DAG, DL, SubVT.getSizeInBits());
-      Subs.push_back(DAG.getNode(X86ISD::AVG, DL, SubVT, LHS, RHS));
-    }
-    return DAG.getNode(ISD::CONCAT_VECTORS, DL, VT, Subs);
-  };
-
   // Check if each element of the vector is left-shifted by one.
   auto LHS = In.getOperand(0);
   auto RHS = In.getOperand(1);
   if (!IsConstVectorInRange(RHS, 1, 1))
     return SDValue();
   if (LHS.getOpcode() != ISD::ADD)
     return SDValue();
 
   // Detect a pattern of a + b + 1 where the order doesn't matter.
   SDValue Operands[3];
   Operands[0] = LHS.getOperand(0);
   Operands[1] = LHS.getOperand(1);
 
+  auto AVGBuilder = [](SelectionDAG &DAG, SDLoc DL, SDValue Op0, SDValue Op1) {
+    return DAG.getNode(X86ISD::AVG, DL, Op0.getValueType(), Op0, Op1);
+  };
+
   // Take care of the case when one of the operands is a constant vector whose
   // element is in the range [1, 256].
   if (IsConstVectorInRange(Operands[1], 1, ScalarVT == MVT::i8 ? 256 : 65536) &&
       Operands[0].getOpcode() == ISD::ZERO_EXTEND &&
       Operands[0].getOperand(0).getValueType() == VT) {
     // The pattern is detected. Subtract one from the constant vector, then
     // demote it and emit X86ISD::AVG instruction.
     SDValue VecOnes = DAG.getConstant(1, DL, InVT);
     Operands[1] = DAG.getNode(ISD::SUB, DL, InVT, Operands[1], VecOnes);
     Operands[1] = DAG.getNode(ISD::TRUNCATE, DL, VT, Operands[1]);
-    return LowerToAVG(Operands[0].getOperand(0), Operands[1]);
+    return SplitBinaryOpsAndApply(DAG, Subtarget, DL, VT,
+                                  Operands[0].getOperand(0), Operands[1],
+                                  AVGBuilder);
   }
 
   if (Operands[0].getOpcode() == ISD::ADD)
     std::swap(Operands[0], Operands[1]);
   else if (Operands[1].getOpcode() != ISD::ADD)
     return SDValue();
   Operands[2] = Operands[1].getOperand(0);
   Operands[1] = Operands[1].getOperand(1);
 
   // Now we have three operands of two additions. Check that one of them is a
   // constant vector with ones, and the other two are promoted from i8/i16.
   for (int i = 0; i < 3; ++i) {
     if (!IsConstVectorInRange(Operands[i], 1, 1))
       continue;
     std::swap(Operands[i], Operands[2]);
 
     // Check if Operands[0] and Operands[1] are results of type promotion.
     for (int j = 0; j < 2; ++j)
       if (Operands[j].getOpcode() != ISD::ZERO_EXTEND ||
           Operands[j].getOperand(0).getValueType() != VT)
         return SDValue();
 
-    // The pattern is detected, emit X86ISD::AVG instruction.
-    return LowerToAVG(Operands[0].getOperand(0), Operands[1].getOperand(0));
+    // The pattern is detected, emit X86ISD::AVG instruction(s).
+    return SplitBinaryOpsAndApply(DAG, Subtarget, DL, VT,
+                                  Operands[0].getOperand(0),
+                                  Operands[1].getOperand(0), AVGBuilder);
   }
 
   return SDValue();
 }
 
 static SDValue combineLoad(SDNode *N, SelectionDAG &DAG,
                            TargetLowering::DAGCombinerInfo &DCI,
                            const X86Subtarget &Subtarget) {