This method was important back when result values couldn't be moved
between instructions. Now that results can be moved, value aliases do
everything we need.
Copy instructions are still used to break interferences in the register
allocator's coalescing phase, but there isn't really any reason to use a
copy instruction over a value alias anywhere else.
After and during register allocation, copy instructions are significant,
so we never want to "see through" them like the resolve_copies()
function did.
This is related to #166, but probably doesn't fix the underlying
problem.
This is a verification pass that can be run after register allocation.
It verifies that value locations are consistent with constraints on
their uses, and that the register diversions are consistent.
Make it clear that register diversions are local to an EBB only. This
affects what branch relaxation is allowed to do.
The verify_locations() takes an optional Liveness parameter which is
used to check that no diverted values are live across CFG edges.
When "binemit" tests encode instructions, keep track of the current set
of register diversions, and use the diverted locations to check operand
constraints.
This matches how constraints are applied during a real binemit phase.
These are parallels to the existing regmove instruction, but the divert
the value to and from a stack slot.
Like regmove diversions, this is a temporary diversion that must be
local to the EBB.
The register constraint solver schedules a set of move instructions to
execute before the instruction getting colored. In extreme cases, this
is not possible because there are no available registers to break cycles
in the register assignments that must be scheduled.
When that happens, we spill one register to an emergency slot so it
becomes available for implementing the assignment cycle. Then the
original register is restored.
The coloring pass can't yet understand the spill and fill move types.
This will be implemented next.
This makes it possible to materialize new RegClass references without
requiring a RegInfo reference to be passed around.
- Move the RegInfo::toprc() method to RegClassData.
- Rename RegClassData::intersect() to intersect_index() and provide a
new intersect() which returns a register class.
- Remove some &RegInfo parameters that are no longer needed.
Fixes#165.
The constraint solver's schedule_move() function sometimes need to use
an extra available register when the moves to be scheduled contains
cycles.
The pending moves have associated register classes that come from the
constraint programming. Since the moves have hard-coded to and from
registers, these register classes are only meant to indicate the
register sizes. In particular, we can use the whole top-level register
class when scavenging for a spare register to break a cycle.
The controlling type variable passed to the format constructor in the
InstBuilder trait is not just used to generate the result values. In an
EncCursor, it is also used to encode the instruction, so VOID doesn't
work.
When we detect interference between the values that have already been
merged into the candidate virtual register and an EBB argument, we first
try to resolve the conflict by splitting. We also check if the existing
interfering value is fundamentally incompatible with the branch
instruction so it needs to be removed from the virtual register,
restarting the merge operation.
However, this existing interfering value is not necessarily the only
interference, so the split is not guaranteed to resolve the conflict. If
it turns out that splitting didn't resolve the conflict, restart the
merge after removing this second conflicting value.
A value passed as an argument to a function call may live in an incoming
stack slot initially. Fix the call legalizer so it copies such an
argument into the expected outgoing stack slot for the call.
This removes the `optimize` option, as one can do that with
`--set`, eg. `--set opt_level=best`. And it adds an option to
print the compilation output.
And, it enables simple_gvn and licm for opt_level=best.
This removes the `optimize` option, as one can do that with
`--set`, eg. `--set opt_level=best`. And it adds an option to
print the compilation output.
