RFR: 8203220: Introduce ATTRIBUTE_ALIGNED macro

[Kim Barrett]

> On May 15, 2018, at 9:31 AM, Per Liden <per.liden at oracle.com> wrote:
> 
> This patch introduces a global ATTRIBUTE_ALIGNED(x) macro, which expands to __attribute__((aligned(x)) or the equivalent of that.
> 
> We already use this attribute is some parts of the code, but we haven't had a macro in globalDefinitions.hpp for this.
> 
> In the src/hotspot/cpu/x86/macroAssembler_x86_*.cpp files I chose to keep the ALIGNED_(x) and just define it as ATTRIBUTE_ALIGNED(x), instead of changing all uses of it.
> 
> Also, for GCC I've included a workaround for a known bug (see the comment in the file). I thought it would be nice to include that since it might otherwise affect quite a few systems.
> 
> And finally, we don't really have a uniform naming standard for these types of attributes. E.g. we have NOINLINE/ALWAYSINLINE and we have ATTRIBUTE_PRINTF. I chose to use the ATTRIBUTE_ prefix, instead of just ALIGNED, since ALIGNED is somewhat generic and we already have at least one place where a variable is named ALIGNED, so it would conflict.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8203220
> Webrev: http://cr.openjdk.java.net/~pliden/8203220/webrev.0
> 
> Testing: hs-tier{1,2}
> 
> /Per

Looks good.