InstructionSimplify: Refactor foldIdentityShuffles. NFC.

[zvi]

Summary

Minor refactoring of foldIdentityShuffles() which allows the removal of a
ConstantDataVector::get() in SimplifyShuffleVectorInstruction.

[spatel]

LGTM - thanks!

lib/Analysis/InstructionSimplify.cpp

Value *llvm::SimplifyCastInst(unsigned CastOpc, Value *Op, Type *Ty,
                               const SimplifyQuery &Q) {
   return ::SimplifyCastInst(CastOpc, Op, Ty, Q, RecursionLimit);
 }
 
 /// For the given destination element of a shuffle, peek through shuffles to
 /// match a root vector source operand that contains that element in the same
 /// vector lane (ie, the same mask index), so we can eliminate the shuffle(s).
 static Value *foldIdentityShuffles(int DestElt, Value *Op0, Value *Op1,
-                                   Constant *Mask, Value *RootVec, int RootElt,
+                                   int MaskVal, Value *RootVec,
                                    unsigned MaxRecurse) {
   if (!MaxRecurse--)
     return nullptr;
 
   // Bail out if any mask value is undefined. That kind of shuffle may be
   // simplified further based on demanded bits or other folds.
-  int MaskVal = ShuffleVectorInst::getMaskValue(Mask, RootElt);
   if (MaskVal == -1)
     return nullptr;
 
   // The mask value chooses which source operand we need to look at next.
-  Value *SourceOp;
   int InVecNumElts = Op0->getType()->getVectorNumElements();
-  if (MaskVal < InVecNumElts) {
-    RootElt = MaskVal;
-    SourceOp = Op0;
-  } else {
+  int RootElt = MaskVal;
+  Value *SourceOp = Op0;
+  if (MaskVal >= InVecNumElts) {
     RootElt = MaskVal - InVecNumElts;
     SourceOp = Op1;
   }
 
   // If the source operand is a shuffle itself, look through it to find the
   // matching root vector.
   if (auto *SourceShuf = dyn_cast<ShuffleVectorInst>(SourceOp)) {
     return foldIdentityShuffles(
         DestElt, SourceShuf->getOperand(0), SourceShuf->getOperand(1),
-        SourceShuf->getMask(), RootVec, RootElt, MaxRecurse);
+        SourceShuf->getMaskValue(RootElt), RootVec, MaxRecurse);
   }
 
   // TODO: Look through bitcasts? What if the bitcast changes the vector element
   // size?
 
   // The source operand is not a shuffle. Initialize the root vector value for
   // this shuffle if that has not been done yet.
   if (!RootVec)
if (Op0Const && !Op1Const) {
     std::swap(Op0, Op1);
     for (int &Idx : Indices) {
       if (Idx == -1)
         continue;
       Idx = Idx < (int)InVecNumElts ? Idx + InVecNumElts : Idx - InVecNumElts;
       assert(Idx >= 0 && Idx < (int)InVecNumElts * 2 &&
              "shufflevector mask index out of range");
     }
-    Mask = ConstantDataVector::get(
-        Mask->getContext(),
-        makeArrayRef(reinterpret_cast<uint32_t *>(Indices.data()),
-                     MaskNumElts));
   }
 
   // A shuffle of a splat is always the splat itself. Legal if the shuffle's
   // value type is same as the input vectors' type.
   if (auto *OpShuf = dyn_cast<ShuffleVectorInst>(Op0))
     if (isa<UndefValue>(Op1) && RetTy == InVecTy &&
         OpShuf->getMask()->getSplatValue())
       return Op0;
 
   // 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?
   if (find(Indices, -1) != Indices.end())
     return nullptr;
 
   // 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
     // exceeds the limit, this will fail to simplify.
-    RootVec = foldIdentityShuffles(i, Op0, Op1, Mask, RootVec, i, MaxRecurse);
+    RootVec =
+        foldIdentityShuffles(i, Op0, Op1, Indices[i], RootVec, MaxRecurse);
 
     // We can't replace a widening/narrowing shuffle with one of its operands.
     if (!RootVec || RootVec->getType() != RetTy)
       return nullptr;
   }
   return RootVec;
 }