llvm-mirror/include/llvm/MC/MCSchedule.h
2013-01-10 00:45:19 +00:00

255 lines
10 KiB
C++

//===-- llvm/MC/MCSchedule.h - Scheduling -----------------------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the classes used to describe a subtarget's machine model
// for scheduling and other instruction cost heuristics.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_MC_MCSCHEDULE_H
#define LLVM_MC_MCSCHEDULE_H
#include "llvm/Support/DataTypes.h"
#include <cassert>
namespace llvm {
struct InstrItinerary;
/// Define a kind of processor resource that will be modeled by the scheduler.
struct MCProcResourceDesc {
#ifndef NDEBUG
const char *Name;
#endif
unsigned NumUnits; // Number of resource of this kind
unsigned SuperIdx; // Index of the resources kind that contains this kind.
// Buffered resources may be consumed at some indeterminate cycle after
// dispatch (e.g. for instructions that may issue out-of-order). Unbuffered
// resources always consume their resource some fixed number of cycles after
// dispatch (e.g. for instruction interlocking that may stall the pipeline).
bool IsBuffered;
bool operator==(const MCProcResourceDesc &Other) const {
return NumUnits == Other.NumUnits && SuperIdx == Other.SuperIdx
&& IsBuffered == Other.IsBuffered;
}
};
/// Identify one of the processor resource kinds consumed by a particular
/// scheduling class for the specified number of cycles.
struct MCWriteProcResEntry {
unsigned ProcResourceIdx;
unsigned Cycles;
bool operator==(const MCWriteProcResEntry &Other) const {
return ProcResourceIdx == Other.ProcResourceIdx && Cycles == Other.Cycles;
}
};
/// Specify the latency in cpu cycles for a particular scheduling class and def
/// index. -1 indicates an invalid latency. Heuristics would typically consider
/// an instruction with invalid latency to have infinite latency. Also identify
/// the WriteResources of this def. When the operand expands to a sequence of
/// writes, this ID is the last write in the sequence.
struct MCWriteLatencyEntry {
int Cycles;
unsigned WriteResourceID;
bool operator==(const MCWriteLatencyEntry &Other) const {
return Cycles == Other.Cycles && WriteResourceID == Other.WriteResourceID;
}
};
/// Specify the number of cycles allowed after instruction issue before a
/// particular use operand reads its registers. This effectively reduces the
/// write's latency. Here we allow negative cycles for corner cases where
/// latency increases. This rule only applies when the entry's WriteResource
/// matches the write's WriteResource.
///
/// MCReadAdvanceEntries are sorted first by operand index (UseIdx), then by
/// WriteResourceIdx.
struct MCReadAdvanceEntry {
unsigned UseIdx;
unsigned WriteResourceID;
int Cycles;
bool operator==(const MCReadAdvanceEntry &Other) const {
return UseIdx == Other.UseIdx && WriteResourceID == Other.WriteResourceID
&& Cycles == Other.Cycles;
}
};
/// Summarize the scheduling resources required for an instruction of a
/// particular scheduling class.
///
/// Defined as an aggregate struct for creating tables with initializer lists.
struct MCSchedClassDesc {
static const unsigned short InvalidNumMicroOps = UINT16_MAX;
static const unsigned short VariantNumMicroOps = UINT16_MAX - 1;
#ifndef NDEBUG
const char* Name;
#endif
unsigned short NumMicroOps;
bool BeginGroup;
bool EndGroup;
unsigned WriteProcResIdx; // First index into WriteProcResTable.
unsigned NumWriteProcResEntries;
unsigned WriteLatencyIdx; // First index into WriteLatencyTable.
unsigned NumWriteLatencyEntries;
unsigned ReadAdvanceIdx; // First index into ReadAdvanceTable.
unsigned NumReadAdvanceEntries;
bool isValid() const {
return NumMicroOps != InvalidNumMicroOps;
}
bool isVariant() const {
return NumMicroOps == VariantNumMicroOps;
}
};
/// Machine model for scheduling, bundling, and heuristics.
///
/// The machine model directly provides basic information about the
/// microarchitecture to the scheduler in the form of properties. It also
/// optionally refers to scheduler resource tables and itinerary
/// tables. Scheduler resource tables model the latency and cost for each
/// instruction type. Itinerary tables are an independant mechanism that
/// provides a detailed reservation table describing each cycle of instruction
/// execution. Subtargets may define any or all of the above categories of data
/// depending on the type of CPU and selected scheduler.
class MCSchedModel {
public:
static MCSchedModel DefaultSchedModel; // For unknown processors.
// IssueWidth is the maximum number of instructions that may be scheduled in
// the same per-cycle group.
unsigned IssueWidth;
static const unsigned DefaultIssueWidth = 1;
// MinLatency is the minimum latency between a register write
// followed by a data dependent read. This determines which
// instructions may be scheduled in the same per-cycle group. This
// is distinct from *expected* latency, which determines the likely
// critical path but does not guarantee a pipeline
// hazard. MinLatency can always be overridden by the number of
// InstrStage cycles.
//
// (-1) Standard in-order processor.
// Use InstrItinerary OperandCycles as MinLatency.
// If no OperandCycles exist, then use the cycle of the last InstrStage.
//
// (0) Out-of-order processor, or in-order with bundled dependencies.
// RAW dependencies may be dispatched in the same cycle.
// Optional InstrItinerary OperandCycles provides expected latency.
//
// (>0) In-order processor with variable latencies.
// Use the greater of this value or the cycle of the last InstrStage.
// Optional InstrItinerary OperandCycles provides expected latency.
// TODO: can't yet specify both min and expected latency per operand.
int MinLatency;
static const int DefaultMinLatency = -1;
// LoadLatency is the expected latency of load instructions.
//
// If MinLatency >= 0, this may be overriden for individual load opcodes by
// InstrItinerary OperandCycles.
unsigned LoadLatency;
static const unsigned DefaultLoadLatency = 4;
// HighLatency is the expected latency of "very high latency" operations.
// See TargetInstrInfo::isHighLatencyDef().
// By default, this is set to an arbitrarily high number of cycles
// likely to have some impact on scheduling heuristics.
// If MinLatency >= 0, this may be overriden by InstrItinData OperandCycles.
unsigned HighLatency;
static const unsigned DefaultHighLatency = 10;
// ILPWindow is the number of cycles that the scheduler effectively ignores
// before attempting to hide latency. This should be zero for in-order cpus to
// always hide expected latency. For out-of-order cpus, it may be tweaked as
// desired to roughly approximate instruction buffers. The actual threshold is
// not very important for an OOO processor, as long as it isn't too high. A
// nonzero value helps avoid rescheduling to hide latency when its is fairly
// obviously useless and makes register pressure heuristics more effective.
unsigned ILPWindow;
static const unsigned DefaultILPWindow = 0;
// MispredictPenalty is the typical number of extra cycles the processor
// takes to recover from a branch misprediction.
unsigned MispredictPenalty;
static const unsigned DefaultMispredictPenalty = 10;
private:
unsigned ProcID;
const MCProcResourceDesc *ProcResourceTable;
const MCSchedClassDesc *SchedClassTable;
unsigned NumProcResourceKinds;
unsigned NumSchedClasses;
// Instruction itinerary tables used by InstrItineraryData.
friend class InstrItineraryData;
const InstrItinerary *InstrItineraries;
public:
// Default's must be specified as static const literals so that tablegenerated
// target code can use it in static initializers. The defaults need to be
// initialized in this default ctor because some clients directly instantiate
// MCSchedModel instead of using a generated itinerary.
MCSchedModel(): IssueWidth(DefaultIssueWidth),
MinLatency(DefaultMinLatency),
LoadLatency(DefaultLoadLatency),
HighLatency(DefaultHighLatency),
ILPWindow(DefaultILPWindow),
MispredictPenalty(DefaultMispredictPenalty),
ProcID(0), ProcResourceTable(0), SchedClassTable(0),
NumProcResourceKinds(0), NumSchedClasses(0),
InstrItineraries(0) {
(void)NumProcResourceKinds;
(void)NumSchedClasses;
}
// Table-gen driven ctor.
MCSchedModel(unsigned iw, int ml, unsigned ll, unsigned hl, unsigned ilp,
unsigned mp, unsigned pi, const MCProcResourceDesc *pr,
const MCSchedClassDesc *sc, unsigned npr, unsigned nsc,
const InstrItinerary *ii):
IssueWidth(iw), MinLatency(ml), LoadLatency(ll), HighLatency(hl),
ILPWindow(ilp), MispredictPenalty(mp), ProcID(pi), ProcResourceTable(pr),
SchedClassTable(sc), NumProcResourceKinds(npr), NumSchedClasses(nsc),
InstrItineraries(ii) {}
unsigned getProcessorID() const { return ProcID; }
/// Does this machine model include instruction-level scheduling.
bool hasInstrSchedModel() const { return SchedClassTable; }
unsigned getNumProcResourceKinds() const {
return NumProcResourceKinds;
}
const MCProcResourceDesc *getProcResource(unsigned ProcResourceIdx) const {
assert(hasInstrSchedModel() && "No scheduling machine model");
assert(ProcResourceIdx < NumProcResourceKinds && "bad proc resource idx");
return &ProcResourceTable[ProcResourceIdx];
}
const MCSchedClassDesc *getSchedClassDesc(unsigned SchedClassIdx) const {
assert(hasInstrSchedModel() && "No scheduling machine model");
assert(SchedClassIdx < NumSchedClasses && "bad scheduling class idx");
return &SchedClassTable[SchedClassIdx];
}
};
} // End llvm namespace
#endif