Clear upper bits of 64-bit indexing register when using types smaller than 64 bits.
Clear upper bits of 64-bit indexing register when using types smaller than 64 bits.

APPROVED=ken
OCL=27811
CL=27823

mhennings/marcohennings-go,sanjosh/sanjos100-tipc,rflanagan/reginaldflanagan-project1,Triskite/willstone-goclone,bryanxu/go-zh,d0f/go-zh,sanjosh/sanjos100-tipc,mhennings/marcohennings-go,bryanxu/go-zh,rflanagan/reginaldflanagan-project1,webfd/go-zh,sanjosh/sanjos100-tipc,npe9/noahevans-go9,sanjosh/sanjos100-tipc,rflanagan/reginaldflanagan-project1,rdp/rogerpack2005-golang,rdp/rogerpack2005-golang,webfd/go-zh,Triskite/willstone-goclone,webfd/go-zh,sanjosh/sanjos100-tipc,scirelli/scirelli-go,glycerine/jeaten-go-arrayof-structof,bryanxu/go-zh,rdp/rogerpack2005-golang,rdp/rogerpack2005-golang,scirelli/scirelli-go,glycerine/jeaten-go-arrayof-structof,Triskite/willstone-goclone,webfd/go-zh,webfd/go-zh,mhennings/marcohennings-go,glycerine/jeaten-go-arrayof-structof,scirelli/scirelli-go,npe9/noahevans-go9,npe9/noahevans-go9,glycerine/jeaten-go-arrayof-structof,mhennings/marcohennings-go,scirelli/scirelli-go,bryanxu/go-zh,glycerine/jeaten-go-arrayof-structof,scirelli/scirelli-go,sanjosh/sanjos100-tipc,rflanagan/reginaldflanagan-project1,Triskite/willstone-goclone,sanjosh/sanjos100-tipc,webfd/go-zh,mhennings/marcohennings-go,rdp/rogerpack2005-golang,d0f/go-zh,rflanagan/reginaldflanagan-project1,Triskite/willstone-goclone,Triskite/willstone-goclone,npe9/noahevans-go9,rflanagan/reginaldflanagan-project1,scirelli/scirelli-go,bryanxu/go-zh,mhennings/marcohennings-go,mhennings/marcohennings-go,sanjosh/sanjos100-tipc,Triskite/willstone-goclone,webfd/go-zh,bryanxu/go-zh,Triskite/willstone-goclone,d0f/go-zh,bryanxu/go-zh,bryanxu/go-zh,glycerine/jeaten-go-arrayof-structof,rdp/rogerpack2005-golang,webfd/go-zh,npe9/noahevans-go9,d0f/go-zh,d0f/go-zh,scirelli/scirelli-go,d0f/go-zh,glycerine/jeaten-go-arrayof-structof,d0f/go-zh,npe9/noahevans-go9,npe9/noahevans-go9,d0f/go-zh,scirelli/scirelli-go,rdp/rogerpack2005-golang,rflanagan/reginaldflanagan-project1,rdp/rogerpack2005-golang,npe9/noahevans-go9,rflanagan/reginaldflanagan-project1,mhennings/marcohennings-go,glycerine/jeaten-go-arrayof-structof