AMDGPU: More bits of frame index are known to be zero

The maximum private allocation for the whole GPU is 4G,
so the maximum possible index for a single workitem is the
maximum size divided by the smallest granularity for a dispatch.

This increases the number of known zero high bits, which
enables more offset folding. The maximum private size per
workitem with this is 128M but may be smaller still.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@262153 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed