[MCSchedule] Add the ability to compute the latency and throughput information for MCInst.
This patch extends the MCSchedModel API with new methods that can be used to
obtain the latency and reciprocal througput information for an MCInst.
Scheduling models have recently gained the ability to resolve variant scheduling
classes associated with MCInst objects. Before, models were only able to resolve
a variant scheduling class from a MachineInstr object.
This patch is mainly required by D47374 to avoid regressing a pair of x86
specific -print-schedule tests for btver2. Patch D47374 introduces a new variant
class to teach the btver scheduling model (x86 target) how to correctly compute
the latency profile for some zero-idioms using the new scheduling predicates.
The new methods added by this patch would be mainly used by llc when flag
-print-schedule is specified. In particular, tests that contain inline assembly
require that code is parsed at code emission stage into a sequence of MCInst.
That forces the print-schedule functionality to query the latency/rthroughput
information for MCInst instructions too. If we don't expose this new API, then
we lose "-print-schedule" test coverage as soon as variant scheduling classes
are added to the x86 models.
The tablegen SubtargetEmitter changes teaches how to query latency profile
information using a object that derives from TargetSubtargetInfo. Note that this
should really have been part of r333286. To avoid code duplication, the logic
that "resolves" variant scheduling classes for MCInst, has been moved to a
common place in MC. That logic is used by the "resolveVariantSchedClass" methods
redefined in override by the tablegen'd GenSubtargetInfo classes.
Differential Revision: https://reviews.llvm.org/D47536