Previously, the regalloc required all liveins to be defined by a
pseudoinstruction at the start of the function body. The regalloc.rs
compatibility shim did this, but it's slightly inconvenient when using
the API directly. This change allows pinned vregs to be implicit liveins
to the function body instead.
Simplify pinned-vreg API: don't require slice of all pinned vregs.
Previously, we kept a bool flag `is_pinned` in the `VRegData`, and we
required a `&[VReg]` of all pinned vregs to be provided by
`Function::pinned_vregs()`. This was (I think) done for convenience, but
it turns out not to really be necessary, as we can just query
`is_pinned_vreg` where needed (and in the likely implementation, e.g. in
Cranelift, this will be a `< NUM_PINNED_VREGS` check that can be
inlined). This adds convenience for the embedder (the main benefit), and
also reduces complexity, removes some state, and avoids some work
initializing the regalloc state for a run.
Support for debug-labels.
If the client adds labels to vregs across ranges of instructions in the
input program, the regalloc will provide metadata in the `Output` that
describes the `Allocation`s in which each such vreg is stored for those
ranges. This allows the client to emit debug metadata telling a debugger
where to find program values at each point in the program.
Even if the trace log level is disabled, the presence of the trace!
macro still has a significant impact on performance because it is
present in the inner loops of the allocator.
Removing the trace! calls at compile-time reduces instruction count by
~7%.
The documentation says that this is only used for heuristics, but it
is never actually called. This should be removed for now and perhaps
added back later if we find an actual use for it.
This feature needs more thought; for now we will of course continue to
support pinned vregs, but perhaps we can do better for
"pass-through-and-forget" operands that are given non-allocatable
registers.
This reverts commit 736f636c36.
Still has a fuzzbug in interaction between R->R and V->R moves. Will
likely rework to make pinned-vreg handling more general but want to save
a checkpoint here; idea for rework:
- set allocs immediately if an Operand is a pinned vreg;
- reserve preg ranges;
- then, in rest of liveness computation / LR construction, convert
pinned-vregs to operands with constraints, but otherwise do not
special-case as we do in this commit.
Also requires some metadata in edit output to properly hook up the
checker in regalloc.rs to track user-moves without seeing the original
insts with operands.
