AMDGPU: Use inbounds when calculating workitem offset

When promoting allocas to LDS, we know we are indexing
into a specific area just created, and the calculation
will also never overflow.

Also emit some of the muls as nsw nuw, because instcombine
infers this already from the range metadata. I think
putting this on the other adds and muls might be OK too,
but I'm not 100% sure.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@259545 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed