[SLPVectorizer] Remove RawInstructionsData/getMainOpcode and merge into getSameOpcode

[RKSimon]

Summary

This is part of the work to cleanup use of 'alternate' ops so we can use the more general SK_Select shuffle type.

Only getSameOpcode calls getMainOpcode and much of the logic is repeated in both functions. This will require some reworking of D28907 but that patch has hit trouble and is unlikely to be completed anytime soon.

[dtemirbulatov]

looks good for me.

[RKSimon]

Thanks @dtemirbulatov

lib/Transforms/Vectorize/SLPVectorizer.cpp

static Value *isOneOf(Value *OpValue, Value *Op) {
   unsigned IOpcode = I->getOpcode();
   if (sameOpcodeOrAlt(OpInstOpcode, getAltOpcode(OpInstOpcode), IOpcode))
     return Op;
   return OpValue;
 }
 
 namespace {
 
-/// Contains data for the instructions going to be vectorized.
-struct RawInstructionsData {
-  /// Main Opcode of the instructions going to be vectorized.
-  unsigned Opcode = 0;
-
-  /// The list of instructions have some instructions with alternate opcodes.
-  bool HasAltOpcodes = false;
-};
-
-} // end anonymous namespace
-
-/// Checks the list of the vectorized instructions \p VL and returns info about
-/// this list.
-static RawInstructionsData getMainOpcode(ArrayRef<Value *> VL) {
-  auto *I0 = dyn_cast<Instruction>(VL[0]);
-  if (!I0)
-    return {};
-  RawInstructionsData Res;
-  unsigned Opcode = I0->getOpcode();
-  // Walk through the list of the vectorized instructions
-  // in order to check its structure described by RawInstructionsData.
-  for (unsigned Cnt = 0, E = VL.size(); Cnt != E; ++Cnt) {
-    auto *I = dyn_cast<Instruction>(VL[Cnt]);
-    if (!I)
-      return {};
-    if (Opcode != I->getOpcode())
-      Res.HasAltOpcodes = true;
-  }
-  Res.Opcode = Opcode;
-  return Res;
-}
-
-namespace {
-
 /// Main data required for vectorization of instructions.
 struct InstructionsState {
   /// The very first instruction in the list with the main opcode.
   Value *OpValue = nullptr;
 
   /// The main opcode for the list of instructions.
   unsigned Opcode = 0;
 
   /// Some of the instructions in the list have alternate opcodes.
   bool IsAltShuffle = false;
 
   InstructionsState() = default;
   InstructionsState(Value *OpValue, unsigned Opcode, bool IsAltShuffle)
       : OpValue(OpValue), Opcode(Opcode), IsAltShuffle(IsAltShuffle) {}
 };
 
 } // end anonymous namespace
 
 /// \returns analysis of the Instructions in \p VL described in
 /// InstructionsState, the Opcode that we suppose the whole list 
 /// could be vectorized even if its structure is diverse.
 static InstructionsState getSameOpcode(ArrayRef<Value *> VL) {
-  auto Res = getMainOpcode(VL);
-  unsigned Opcode = Res.Opcode;
-  if (!Res.HasAltOpcodes)
-    return InstructionsState(VL[0], Opcode, false);
+  // Make sure these are all Instructions.
+  if (llvm::any_of(VL, [](Value *V) { return !isa<Instruction>(V); }))
+    return InstructionsState(VL[0], 0, false);
+
+  unsigned Opcode = cast<Instruction>(VL[0])->getOpcode();
+  bool HasAltOpcodes = llvm::any_of(VL, [Opcode](Value *V) {
+    return Opcode != cast<Instruction>(V)->getOpcode();
+  });
+
+  // Check for an alternate opcode pattern.
+  if (HasAltOpcodes) {
     unsigned AltOpcode = getAltOpcode(Opcode);
-  // Examine each element in the list instructions VL to determine
-  // if some operations there could be considered as an alternative
-  // (for example as subtraction relates to addition operation).
     for (int Cnt = 0, E = VL.size(); Cnt < E; Cnt++) {
-    auto *I = cast<Instruction>(VL[Cnt]);
-    unsigned InstOpcode = I->getOpcode();
+      unsigned InstOpcode = cast<Instruction>(VL[Cnt])->getOpcode();
       if (InstOpcode != (isOdd(Cnt) ? AltOpcode : Opcode))
         return InstructionsState(VL[0], 0, false);
     }
-  return InstructionsState(VL[0], Opcode, Res.HasAltOpcodes);
+  }
+
+  return InstructionsState(VL[0], Opcode, HasAltOpcodes);
 }
 
 /// \returns true if all of the values in \p VL have the same type or false
 /// otherwise.
 static bool allSameType(ArrayRef<Value *> VL) {
   Type *Ty = VL[0]->getType();
   for (int i = 1, e = VL.size(); i < e; i++)
     if (VL[i]->getType() != Ty)