Fix VectorLegalizer::ExpandUINT_TO_FLOAT -- wrong results for v*f64

[Rutt]

Summary

This code inadvertently does a 32 bit calculation whose result must be 64 bits, resulting in incorrect floating point conversions.

When the underlying components of the vector are f64, BW is 64 and the shift:

1 << (BW/2) results in an undefined result when BW >= 31.

We need to write as lL << (BW/2) in order to do the shift in 64 bits with a 64 bit result

llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp

   SDValue HalfWordMask = DAG.getConstant(HWMask, DL, VT);
 
   // Two to the power of half-word-size.
-  SDValue TWOHW = DAG.getConstantFP(1 << (BW / 2), DL, Op.getValueType());
+  SDValue TWOHW = DAG.getConstantFP(1L << (BW / 2), DL, Op.getValueType());
 
   // Clear upper part of LO, lower HI
   SDValue HI = DAG.getNode(ISD::SRL, DL, VT, Op.getOperand(0), HalfWord);