An identity COPY like this:
%AL = COPY %AL, %EAX<imp-def>
has no semantic effect, but encodes liveness information: Further users
of %EAX only depend on this instruction even though it does not define
the full register.
Replace the COPY with a KILL instruction in those cases to maintain this
liveness information. (This reverts a small part of r238588 but this
time adds a comment explaining why a KILL instruction is useful).
llvm-svn: 274952
For cases where we are truncating an integer vector arithmetic result, it may be better to pre-truncate the input operands - no code to support this yet (scalar is done with SimplifyDemandedBits but adding vector support could be a lot of work) but these tests represent the current codegen status.
Example bugs: PR14666, PR22703
llvm-svn: 263384
Matthias Braun