revert r301766: InstructionSimplify: Canonicalize shuffle operands. NFC-ish

Turns out this wasn't NFC-ish at all because there's a bug processing shuffles
that change the size of their input vectors (that case always seems to trip us
up). 

This should fix PR32872 while we investigate how it failed and reduce a testcase:
https://bugs.llvm.org/show_bug.cgi?id=32872
 

llvm-svn: 301977

1 files changed, 20 insertions, 29 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 2f25a118366..7aa6abf8fa4 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4056,13 +4056,20 @@ static Value *SimplifyShuffleVectorInst(Value *Op0, Value *Op1, Constant *Mask,
   unsigned MaskNumElts = Mask->getType()->getVectorNumElements();
   unsigned InVecNumElts = InVecTy->getVectorNumElements();
 
+  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);
   assert(MaskNumElts == Indices.size() &&
          "Size of Indices not same as number of mask elements?");
 
-  // Canonicalization: If mask does not select elements from an input vector,
-  // replace that input vector with undef.
+  // 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) {
     if (Indices[i] == -1)
@@ -4072,39 +4079,23 @@ static Value *SimplifyShuffleVectorInst(Value *Op0, Value *Op1, Constant *Mask,
     else
       MaskSelects1 = true;
   }
-  if (!MaskSelects0)
-    Op0 = UndefValue::get(InVecTy);
-  if (!MaskSelects1)
-    Op1 = UndefValue::get(InVecTy);
-
-  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);
-
-  // Canonicalization: if only one input vector is constant, it shall be the
-  // second one.
-  if (Op0Const && !Op1Const) {
-    std::swap(Op0, Op1);
-    for (auto &Idx : Indices) {
-      if (Idx == -1)
-        continue;
-      Idx = Idx < (int)MaskNumElts ? Idx + MaskNumElts : Idx - MaskNumElts;
-    }
-    Mask = ConstantDataVector::get(
-        Mask->getContext(),
-        makeArrayRef(reinterpret_cast<uint32_t *>(Indices.data()),
-                     MaskNumElts));
-  }
+  if (!MaskSelects0 && Op1Const)
+    return ConstantFoldShuffleVectorInstruction(UndefValue::get(InVecTy),
+                                                Op1Const, Mask);
+  if (!MaskSelects1 && Op0Const)
+    return ConstantFoldShuffleVectorInstruction(Op0Const,
+                                                UndefValue::get(InVecTy), Mask);
 
   // 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 &&
+    if (!MaskSelects1 && RetTy == InVecTy &&
         OpShuf->getMask()->getSplatValue())
       return Op0;
+  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.