Add some details to the llvm-cov documentation. <rdar://problem/15819496>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208098 91177308-0d34-0410-b5e6-96231b3b80d8
Have the SubtargetFeature help routine just not return a number and
fall back to the normal path without a cpu. While doing this fix
llc to just exit when we don't have a module to process instead of
asserting.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208102 91177308-0d34-0410-b5e6-96231b3b80d8
Special case aliases in GlobalValue::getAlignment.

An alias has the address of what it points to, so it also has the same
alignment.

This allows a few optimizations to see past aliases for free.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208103 91177308-0d34-0410-b5e6-96231b3b80d8
Implememting named register intrinsics

This patch implements the infrastructure to use named register constructs in
programs that need access to specific registers (bare metal, kernels, etc).

So far, only the stack pointer is supported as a technology preview, but as it
is, the intrinsic can already support all non-allocatable registers from any
architecture.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208104 91177308-0d34-0410-b5e6-96231b3b80d8