Teach SCCP to create notconstant lattice values from inequality
assumes and nonnull metadata, and update getConstant() to make
use of them. Additionally isOverdefined() needs to be changed to
consider notconstant an overdefined value.
Handling inequality branches is delayed until our branch on undef
story in other passes has been improved.
Differential Revision: https://reviews.llvm.org/D83643
When all else fails, use range metadata to constrain the result
of loads and calls. It should also be possible to use !nonnull,
but that would require some general support for inequalities in
SCCP first.
Differential Revision: https://reviews.llvm.org/D83179
Nikita Popov