Revert "[SelectionDAG] Use logic right shift to avoid loop hang"

This reverts commit b73229e.

It caused LIT failure on non-X86 targets.

Author: KanRobert

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -5459,6 +5459,9 @@ static SDValue ExpandPowI(const SDLoc &DL, SDValue LHS, SDValue RHS,
 
     if (DAG.getTargetLoweringInfo().isBeneficialToExpandPowI(
             Val, DAG.shouldOptForSize())) {
+      // Get the exponent as a positive value.
+      if (Val < 0)
+        Val = -Val;
       // We use the simple binary decomposition method to generate the multiply
       // sequence.  There are more optimal ways to do this (for example,
       // powi(x,15) generates one more multiply than it should), but this has
@@ -5478,8 +5481,7 @@ static SDValue ExpandPowI(const SDLoc &DL, SDValue LHS, SDValue RHS,
 
         CurSquare = DAG.getNode(ISD::FMUL, DL, CurSquare.getValueType(),
                                 CurSquare, CurSquare);
-        // Use logic right shift
-        Val = int(unsigned(Val) >> 1);
+        Val >>= 1;
       }
 
       // If the original was negative, invert the result, producing 1/(x*x*x).