Improve computeOverflowForUnsignedAdd/Sub in ValueTracking by
intersecting the computeConstantRange() result into the ConstantRange
created from computeKnownBits(). This allows us to detect some
additional never/always overflows conditions that can't be determined
from known bits.
This revision also adds basic handling for constants to
computeConstantRange(). Non-splat vectors will be handled in a followup.
The signed case will also be handled in a followup, as it needs some
more groundwork.
Differential Revision: https://reviews.llvm.org/D59386
llvm-svn: 356489
208381953b