Revert r180189.

This should bring the ppc bots back. I will try to write a test that would
have found the problem on a little endian system too.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180194 91177308-0d34-0410-b5e6-96231b3b80d8
LoopVectorizer: Bail out if we don't have datalayout we need it

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180195 91177308-0d34-0410-b5e6-96231b3b80d8
LoopVectorize: Scalarize padded types

This patch disables memory-instruction vectorization for types that need padding
bytes, e.g., x86_fp80 has 10 bytes store size with 6 bytes padding in darwin on
x86_64. Because the load/store vectorization is performed by the bit casting to
a packed vector, which has incompatible memory layout due to the lack of padding
bytes, the present vectorizer produces inconsistent result for memory
instructions of those types.
This patch checks an equality of the AllocSize of a scalar type and allocated
size for each vector element, to ensure that there is no padding bytes and the
array can be read/written using vector operations.

Patch by Daisuke Takahashi!

Fixes PR15758.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180196 91177308-0d34-0410-b5e6-96231b3b80d8
LoopVectorizer: Change variable name Stride to ConsecutiveStride

This makes it easier to read the code.

No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180197 91177308-0d34-0410-b5e6-96231b3b80d8