InstructionSimplify: One getShuffleMask() replacing multiple getMaskValue(). NFC.

[zvi]

Summary

This is a preparatory step for D32338.

[RKSimon]

LGTM with one minor

lib/Analysis/InstructionSimplify.cpp

4155

Might be overkill but maybe add assert for MaskNumElts == Indices.size() ?

[spatel]

lib/Analysis/InstructionSimplify.cpp

4189

I think you can use the LLVM version of find() here to reduce C++ ugliness:

if (find(Indices, -1) != Indices.end())

[zvi]

Address Simon and Sanjay's comments.

[spatel]

LGTM.

lib/Analysis/InstructionSimplify.cpp

static Value *SimplifyShuffleVectorInst(Value *Op0, Value *Op1, Constant *Mask,
 
   auto *Op0Const = dyn_cast<Constant>(Op0);
   auto *Op1Const = dyn_cast<Constant>(Op1);
 
   // If all operands are constant, constant fold the shuffle.
   if (Op0Const && Op1Const)
     return ConstantFoldShuffleVectorInstruction(Op0Const, Op1Const, Mask);
 
+  SmallVector<int, 32> Indices;
+  ShuffleVectorInst::getShuffleMask(Mask, Indices);
+
   // If only one of the operands is constant, constant fold the shuffle if the
   // mask does not select elements from the variable operand.
   bool MaskSelects0 = false, MaskSelects1 = false;
   for (unsigned i = 0; i != MaskNumElts; ++i) {
-    int Idx = ShuffleVectorInst::getMaskValue(Mask, i);
-    if (Idx == -1)
+    if (Indices[i] == -1)
       continue;
-    if ((unsigned)Idx < InVecNumElts)
+    if ((unsigned)Indices[i] < InVecNumElts)
       MaskSelects0 = true;
     else
       MaskSelects1 = true;
   }
   if (!MaskSelects0 && Op1Const)
     return ConstantFoldShuffleVectorInstruction(UndefValue::get(InVecTy),
                                                 Op1Const, Mask);
   if (!MaskSelects1 && Op0Const)
static Value *SimplifyShuffleVectorInst(Value *Op0, Value *Op1, Constant *Mask,
   if (auto *OpShuf = dyn_cast<ShuffleVectorInst>(Op1))
     if (!MaskSelects0 && RetTy == InVecTy &&
         OpShuf->getMask()->getSplatValue())
       return Op1;
 
   // Don't fold a shuffle with undef mask elements. This may get folded in a
   // better way using demanded bits or other analysis.
   // TODO: Should we allow this?
-  for (unsigned i = 0; i != MaskNumElts; ++i)
-    if (ShuffleVectorInst::getMaskValue(Mask, i) == -1)
-      return nullptr;
+  if (std::find(Indices.begin(), Indices.end(), -1) != Indices.end())
 
   // Check if every element of this shuffle can be mapped back to the
   // corresponding element of a single root vector. If so, we don't need this
   // shuffle. This handles simple identity shuffles as well as chains of
   // shuffles that may widen/narrow and/or move elements across lanes and back.
   Value *RootVec = nullptr;
   for (unsigned i = 0; i != MaskNumElts; ++i) {
     // Note that recursion is limited for each vector element, so if any element