[PowerPC] Set the innermost hot loop to align 32 bytes
If the nested loop is an innermost loop, prefer to a 32-byte alignment, so that
we can decrease cache misses and branch-prediction misses. Actual alignment of
the loop will depend on the hotness check and other logic in alignBlocks.
The old code will only align hot loop to 32 bytes when the LoopSize larger than
16 bytes and smaller than 32 bytes, this patch will align the innermost hot loop
to 32 bytes not only for the hot loop whose size is 16~32 bytes.
Reviewed By: steven.zhang, jsji
Differential Revision: https://reviews.llvm.org/D61228