R600: remove unused variable

Patch by: Jan Vesely

Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>
Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
R600: Change UDIV/UREM to UDIVREM when legalizing types

When legalizing ops, with UDIV/UREM set to expand, they automatically
expand to UDIVREM (if legal or custom).
We need to do this manually for legalize types.

v2:
  SI should be set to Expand because the type is legal, and it is
    automatically lowered to UDIVREM if UDIVREM is Legal/Custom
  R600 should set to UDIV/UREM to Custom because it needs to lower them
    during type legalization

Patch by: Jan Vesely

Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>
Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
R600: Implement iterative algorithm for udivrem

Initial implementation, rather slow

Patch by: Jan Vesely

Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>
Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
R600: optimize the UDIVREM 64 algorithm

This is a squash of several optimization commits:
 - calculate DIV_Lo and DIV_Hi separately
 - use BFE_U32 if we are operating on 32bit values
 - use precomputed constants instead of shifting in UDVIREM
 - skip the first 32 iterations of udivrem

v2: Check whether BFE is supported before using it

Patch by: Jan Vesely

Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>
Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
R600/SI: Only select SALU instructions in the entry or exit block

SALU instructions ignore control flow, so it is not always safe to use
them within branches.  This is a partial solution to this problem
until we can come up with something better.
R600/SI: Custom lower SI_IF and SI_ELSE to avoid machine verifier errors

SI_IF and SI_ELSE are terminators which also produce a value.  For
these instructions ISel always inserts a COPY to move their value
to another basic block.  This COPY ends up between SI_(IF|ELSE)
and the S_BRANCH* instruction at the end of the block.

This breaks MachineBasicBlock::getFirstTerminator() and also the
machine verifier which assumes that terminators are grouped together at
the end of blocks.

To solve this we coalesce the copy away right after ISel to make sure
there are no instructions in between terminators at the end of blocks.
R600: Remove duplicate setting of SELECT expansion.

It's already set in AMDGPUISelLowering for all GPUs

Patch By: Jan Vesely

Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>
Reviewed-by: Tom Stellard <thomas.stellard@amd.com>