[LSR] Don't force bases of foldable formulae to the final type.

Summary:
Before emitting code for scaled registers, we prevent
SCEVExpander from hoisting any scaled addressing mode
by emitting all the bases first. However, these bases
are being forced to the final type, resulting in some
odd code.

For example, if the type of the base is an integer and
the final type is a pointer, we will emit an inttoptr
for the base, a ptrtoint for the scale, and then a
'reverse' GEP where the GEP pointer is actually the base
integer and the index is the pointer. It's more intuitive
to use the pointer as a pointer and the integer as index.

Patch by: Bevin Hansson

Reviewers: atrick, qcolombet, sanjoy

Reviewed By: qcolombet

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D42103

llvm-svn: 323946