[PATCH] Add HLE target feature

[Michael Liao]

Hi Krzysztof,

On Wed, 2013-02-27 at 18:55 -0600, Krzysztof Parzyszek wrote:
> On 2/27/2013 6:01 PM, Jeffrey Yasskin wrote:
> >
> > This is why we need the langref patch before looking into the
> > implementation. These annotations are something like the !nontemporal
> > metadata on loads, in that they hint to the implementation that
> > certain properties will hold on a particular use of the existing
> > atomic instructions, and certain targets can take advantage of that to
> > emit better code. On uses where those properties don't hold, the
> > existing code is better.
> 
> Ok, so help me understand this---is the proposed metatada providing 
> information that cannot be obtained by analysis of the code, or is this 
> only meant to be a way for the programmer to provide an explicit hint to 
> the compiler?

so far, it's the only way for developer to specify them explicitly.
Trying to optimize critical section into speculative transaction region
selectively based on it's profitable or not sounds to me a good topic
for research.

Yours
- Michael

> 
> I can understand the need for platform-specific options (like pragmas), 
> but I am not aware of any precedents for this in LLVM, and how that 
> would be handled.  I guess metadata would be the way after all...
> 
> -Krzysztof
>