[DAGCombiner] Bugfix in isAlias().

Since i1 is a legal type, this:

  NumBytes = Op1->getMemoryVT().getSizeInBits() >> 3;

is wrong and should be instead

  NumBytes = Op0->getMemoryVT().getStoreSize();

There seems to be more places where this should be fixed outside DAGCombiner.

Review: Hal Finkel
https://bugs.llvm.org/show_bug.cgi?id=35366

llvm-svn: 318824