[vector] Infrastructure for calling math routines in .s files

[Vladimir Ivanov]

> So I am sending out the initial patch which adds infrastructure (plus one implementation - exp) in order to be able to call these assembly routines from JIT compiled code. In a subsequent patches, we will contribute the other implementations in form of assembly files.
> http://cr.openjdk.java.net/~rlupusoru/panama/webrev_callsvml_09/index.html

Wow, vector calls! Nice! :-)

My main concern is amount of changes in shared code needed. I'd like to 
see the logic somehow confined just to those vector stub calls.

Some suggestions:

   (1) introduce new node for calling vector stubs - CallLeafVector?
        - no need in CallLeafNode::has_vector_arguments_or_return()

   (2) Implement custom calling convention instead of extending 
c_calling_convention. It seems there is a need for a limited set of 
shapes (unary, binary, ?) and even having those cases hard-coded should 
be fine. It can simplify the patch in the following way:
        - have the logic factored out into platform-specific 
vector_calling_convention() / vector_return_value();
        - get rid of T_VECTOR* basic types
        - no need to extend return_value in x86_64.ad for vector types

> Please take a look at the patch and let me know if you have any questions. I would like to point out that among changes there are also a few which make sure that compiler does not tag with "NO_FP" any calls that may end up calling methods that are using FP/vector code. This is quite important for Vector API since unlike auto-vectorizer, there may be live vector registers at any point in the code.

Doesn't it cause problems for floats/doubles in xmm registers then? I 
have some doubts all those cases are problematic, but, anyway, I suggest 
to handle it separately and focus on vector stub calls alone here.

Best regards,
Vladimir Ivanov