[X86] Pass the parent SDNode to X86DAGToDAGISel::selectScalarSSELoad to...

[X86] Pass the parent SDNode to X86DAGToDAGISel::selectScalarSSELoad to simplify the hasSingleUseFromRoot handling.

Some of the calls to hasSingleUseFromRoot were passing the load itself. If the load's chain result has a user this would count against that. By getting the true parent of the match and ensuring any intermediate between the match and the load have a single use we can avoid this case. isLegalToFold will take care of checking users of the load's data output.

This fixed at least fma-scalar-memfold.ll to succed without the peephole pass.

llvm-svn: 334908