Any x86 instruction that reads from an invariant location is invariant.

Any x86 instruction that reads from an invariant location is invariant.
This allows us to sink things like:
	cvtsi2sd	32(%esp), %xmm1
when reading from the argument area, for example.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45895 91177308-0d34-0410-b5e6-96231b3b80d8