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
This re-applies r268760, reverted in r268794.
Fixes http://llvm.org/PR27670
The original imp-defs assertion was way overzealous: forward all
implicit operands, except imp-defs of the new super-reg def (r268787
for GR64, but also possible for GR16->GR32), or imp-uses of the new
super-reg use.
While there, mark the source use as Undef, and add an imp-use of the
old source reg: that should cover any case of dead super-regs.
At the stage the pass runs, flags are unlikely to matter anyway;
still, let's be as correct as possible.
Also add MIR tests for the various interesting cases.
Original commit message:
Codesize is less (16) or equal (8), and we avoid partial
dependencies.
Differential Revision: http://reviews.llvm.org/D19999
llvm-svn: 268831
In the commentary for D11660, I wasn't sure if it was alright to create new
integer machine instructions without also creating the implicit EFLAGS operand.
From what I can see, the implicit operand is always created by the MachineInstrBuilder
based on the instruction type, so we don't have to do that explicitly. However, in
reviewing the debug output, I noticed that the operand was not marked as 'dead'.
The machine combiner should do that to preserve future optimization opportunities
that may be checking for that dead EFLAGS operand themselves.
Differential Revision: http://reviews.llvm.org/D11696
llvm-svn: 243990
Add i16, i32, i64 imul machine instructions to the list of reassociation
candidates.
A new bit of logic is needed to handle integer instructions: they have an
implicit EFLAGS operand, so we have to make sure it's dead in order to do
any reassociation with integer ops.
Differential Revision: http://reviews.llvm.org/D11660
llvm-svn: 243756
Matthias Braun