[PATCH] [compiler-rt] fix and simplify GetMaxVirtualAddress for ppc64*

[Will Schmidt]

>>! In D6044#5, @kcc wrote:
> I wonder if you can add a powerpc-specific test for this. 

Maybe. :-)   
Is there an existing test that checks for something similar for other platforms?  I'm not very familiar with the existing set of tests, so not sure what the options are, or what is practical.

http://reviews.llvm.org/D6044