Add test case and merge usecases fo SHL

Author: Rohit Aggarwal

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -56523,6 +56523,14 @@ static SDValue combineGatherScatter(SDNode *N, SelectionDAG &DAG,
     // Attempt to move shifted index into the address scale, allows further
     // index truncation below.
     if (Index.getOpcode() == ISD::SHL && isa<ConstantSDNode>(Scale)) {
+      unsigned BitWidth = Index.getScalarValueSizeInBits();
+      unsigned MaskBits = BitWidth - Log2_32(Scale->getAsZExtVal());
+      APInt DemandedBits = APInt::getLowBitsSet(BitWidth, MaskBits);
+      if (TLI.SimplifyDemandedBits(Index, DemandedBits, DCI)) {
+        if (N->getOpcode() != ISD::DELETED_NODE)
+          DCI.AddToWorklist(N);
+        return SDValue(N, 0);
+      }
       uint64_t ScaleAmt = Scale->getAsZExtVal();
       if (auto MinShAmt = DAG.getValidMinimumShiftAmount(Index)) {
         if (*MinShAmt >= 1 && (*MinShAmt + Log2_64(ScaleAmt)) < 4 &&
@@ -56588,14 +56596,14 @@ static SDValue combineGatherScatter(SDNode *N, SelectionDAG &DAG,
 
   EVT PtrVT = TLI.getPointerTy(DAG.getDataLayout());
 
-  if (Index.getOpcode() == ISD::SHL) {
-    unsigned BitWidth = Index.getScalarValueSizeInBits();
-    unsigned MaskBits = BitWidth - Log2_32(Scale->getAsZExtVal());
-    APInt DemandedBits = APInt::getLowBitsSet(BitWidth, MaskBits);
-    if (TLI.SimplifyDemandedBits(Index, DemandedBits, DCI)) {
-      return SDValue(N, 0);
-    }
-  }
+  // if (Index.getOpcode() == ISD::SHL) {
+  //   unsigned BitWidth = Index.getScalarValueSizeInBits();
+  //   unsigned MaskBits = BitWidth - Log2_32(Scale->getAsZExtVal());
+  //   APInt DemandedBits = APInt::getLowBitsSet(BitWidth, MaskBits);
+  //   if (TLI.SimplifyDemandedBits(Index, DemandedBits, DCI)) {
+  //     return SDValue(N, 0);
+  //   }
+  // }
   // Try to move splat adders from the index operand to the base
   // pointer operand. Taking care to multiply by the scale. We can only do
   // this when index element type is the same as the pointer type.