[TargetLowering] SimplifyDemandedBits - call SimplifyDemandedBits in bitcast handling

When bitcasting from a source op to a larger bitwidth op, split the demanded bits and OR them on top of one another and demand those merged bits in the SimplifyDemandedBits call on the source op.

llvm-svn: 357992

1 files changed, 16 insertions, 6 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 89d9a55c3f7..114bb1c11f6 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -1395,36 +1395,46 @@ bool TargetLowering::SimplifyDemandedBits(
       }
     }
 
-    // If bitcast from a vector, see if we can use SimplifyDemandedVectorElts by
-    // demanding the element if any bits from it are demanded.
+    // Bitcast from a vector using SimplifyDemanded Bits/VectorElts.
+    // Demand the elt/bit if any of the original elts/bits are demanded.
     // TODO - bigendian once we have test coverage.
     // TODO - bool vectors once SimplifyDemandedVectorElts has SETCC support.
     if (SrcVT.isVector() && NumSrcEltBits > 1 &&
         (BitWidth % NumSrcEltBits) == 0 &&
         TLO.DAG.getDataLayout().isLittleEndian()) {
-      auto GetDemandedSrcMask = [&](APInt &DemandedSrcElts) -> bool {
+      auto GetDemandedSrcMask = [&](APInt &DemandedSrcBits,
+                                    APInt &DemandedSrcElts) -> bool {
         unsigned Scale = BitWidth / NumSrcEltBits;
         unsigned NumSrcElts = SrcVT.getVectorNumElements();
+        DemandedSrcBits = APInt::getNullValue(NumSrcEltBits);
         DemandedSrcElts = APInt::getNullValue(NumSrcElts);
         for (unsigned i = 0; i != Scale; ++i) {
           unsigned Offset = i * NumSrcEltBits;
           APInt Sub = DemandedBits.extractBits(NumSrcEltBits, Offset);
-          if (!Sub.isNullValue())
+          if (!Sub.isNullValue()) {
+            DemandedSrcBits |= Sub;
             for (unsigned j = 0; j != NumElts; ++j)
               if (DemandedElts[j])
                 DemandedSrcElts.setBit((j * Scale) + i);
+          }
         }
         return true;
       };
 
-      APInt DemandedSrcElts;
-      if (GetDemandedSrcMask(DemandedSrcElts)) {
+      APInt DemandedSrcBits, DemandedSrcElts;
+      if (GetDemandedSrcMask(DemandedSrcBits, DemandedSrcElts)) {
         APInt KnownSrcUndef, KnownSrcZero;
         if (SimplifyDemandedVectorElts(Src, DemandedSrcElts, KnownSrcUndef,
                                        KnownSrcZero, TLO, Depth + 1))
           return true;
+
+        KnownBits KnownSrcBits;
+        if (SimplifyDemandedBits(Src, DemandedSrcBits, DemandedSrcElts,
+                                 KnownSrcBits, TLO, Depth + 1))
+          return true;
       }
     }
+
     // If this is a bitcast, let computeKnownBits handle it.  Only do this on a
     // recursive call where Known may be useful to the caller.
     if (Depth > 0) {