Request for reviews (M): 7059037: Use BIS for zeroing on T4

[Vladimir Kozlov]

http://cr.openjdk.java.net/~kvn/7059037/webrev

7059037: Use BIS for zeroing on T4

On T4 BIS to the beginning of cache line always zeros it. Use it for zeroing new
allocated java objects. The main code is in MacroAssembler::bis_zeroing() and is
used by C2 generated code (ClearArray), runtime (Copy::fill_to_aligned_words())
and template interpreter (TemplateTable::_new()). New stub zero_aligned_words
was added to use in runtime.

BIS is used only for objects bigger than BlkZeroingLowLimit (2Kbyte) since it
requires membar. 2Hb was selected based on microbenchmark results.

I also added wrasi(Reg, immI) instruction which I used during development.
VM_Version::has_mru_blk_init() is replaced with has_blk_zeroing() since original
was not used.
Zap new object in CollectedHeap::allocate_from_tlab_slow() instead of zeroing it
since it will be cleaned later in init_obj().
Fixed call sites of check_for_bad_heap_word_value() where klass is not
initialized to avoid the verification failure.