R600/SI: Fix unreachable with a sext_in_reg to an illegal type.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204945 91177308-0d34-0410-b5e6-96231b3b80d8
R600: Implement isZExtFree.

This allows 64-bit operations that are truncated to be reduced
to 32-bit ones.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204946 91177308-0d34-0410-b5e6-96231b3b80d8
InstCombine: Don't combine constants on unsigned icmps

Fixes a miscompile introduced in r204912.  It would miscompile code like
(unsigned)(a + -49) <= 5U.  The transform would turn this into
(unsigned)a < 55U, which would return true for values in [0, 49], when
it should not.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204948 91177308-0d34-0410-b5e6-96231b3b80d8