1 files changed, 59 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 92706e1f116..9633a8c873a 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -565,15 +565,72 @@ bool TargetLowering::SimplifyDemandedBits(SDValue Op, const APInt &DemandedBits,
 }
 
 // TODO: Can we merge SelectionDAG::GetDemandedBits into this?
-// TODO: Under what circumstances can we create nodes? BITCAST? Constant?
+// TODO: Under what circumstances can we create nodes? Constant folding?
 SDValue TargetLowering::SimplifyMultipleUseDemandedBits(
     SDValue Op, const APInt &DemandedBits, const APInt &DemandedElts,
     SelectionDAG &DAG, unsigned Depth) const {
   if (Depth >= 6) // Limit search depth.
     return SDValue();
 
+  unsigned NumElts = DemandedElts.getBitWidth();
   KnownBits LHSKnown, RHSKnown;
   switch (Op.getOpcode()) {
+  case ISD::BITCAST: {
+    SDValue Src = peekThroughBitcasts(Op.getOperand(0));
+    EVT SrcVT = Src.getValueType();
+    EVT DstVT = Op.getValueType();
+    unsigned NumSrcEltBits = SrcVT.getScalarSizeInBits();
+    unsigned NumDstEltBits = DstVT.getScalarSizeInBits();
+
+    if (NumSrcEltBits == NumDstEltBits)
+      if (SDValue V = SimplifyMultipleUseDemandedBits(
+              Src, DemandedBits, DemandedElts, DAG, Depth + 1))
+        return DAG.getBitcast(DstVT, V);
+
+    // TODO - bigendian once we have test coverage.
+    if (SrcVT.isVector() && (NumDstEltBits % NumSrcEltBits) == 0 &&
+        DAG.getDataLayout().isLittleEndian()) {
+      unsigned Scale = NumDstEltBits / NumSrcEltBits;
+      unsigned NumSrcElts = SrcVT.getVectorNumElements();
+      APInt DemandedSrcBits = APInt::getNullValue(NumSrcEltBits);
+      APInt DemandedSrcElts = APInt::getNullValue(NumSrcElts);
+      for (unsigned i = 0; i != Scale; ++i) {
+        unsigned Offset = i * NumSrcEltBits;
+        APInt Sub = DemandedBits.extractBits(NumSrcEltBits, Offset);
+        if (!Sub.isNullValue()) {
+          DemandedSrcBits |= Sub;
+          for (unsigned j = 0; j != NumElts; ++j)
+            if (DemandedElts[j])
+              DemandedSrcElts.setBit((j * Scale) + i);
+        }
+      }
+
+      if (SDValue V = SimplifyMultipleUseDemandedBits(
+              Src, DemandedSrcBits, DemandedSrcElts, DAG, Depth + 1))
+        return DAG.getBitcast(DstVT, V);
+    }
+
+    // TODO - bigendian once we have test coverage.
+    if ((NumSrcEltBits % NumDstEltBits) == 0 &&
+        DAG.getDataLayout().isLittleEndian()) {
+      unsigned Scale = NumSrcEltBits / NumDstEltBits;
+      unsigned NumSrcElts = SrcVT.isVector() ? SrcVT.getVectorNumElements() : 1;
+      APInt DemandedSrcBits = APInt::getNullValue(NumSrcEltBits);
+      APInt DemandedSrcElts = APInt::getNullValue(NumSrcElts);
+      for (unsigned i = 0; i != NumElts; ++i)
+        if (DemandedElts[i]) {
+          unsigned Offset = (i % Scale) * NumDstEltBits;
+          DemandedSrcBits.insertBits(DemandedBits, Offset);
+          DemandedSrcElts.setBit(i / Scale);
+        }
+
+      if (SDValue V = SimplifyMultipleUseDemandedBits(
+              Src, DemandedSrcBits, DemandedSrcElts, DAG, Depth + 1))
+        return DAG.getBitcast(DstVT, V);
+    }
+
+    break;
+  }
   case ISD::AND: {
     LHSKnown = DAG.computeKnownBits(Op.getOperand(0), DemandedElts, Depth + 1);
     RHSKnown = DAG.computeKnownBits(Op.getOperand(1), DemandedElts, Depth + 1);
@@ -625,7 +682,7 @@ SDValue TargetLowering::SimplifyMultipleUseDemandedBits(
     // If all the demanded elts are from one operand and are inline,
     // then we can use the operand directly.
     bool AllUndef = true, IdentityLHS = true, IdentityRHS = true;
-    for (unsigned i = 0, NumElts = ShuffleMask.size(); i != NumElts; ++i) {
+    for (unsigned i = 0; i != NumElts; ++i) {
       int M = ShuffleMask[i];
       if (M < 0 || !DemandedElts[i])
         continue;