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Diffstat (limited to 'contrib/llvm/lib/CodeGen/MachineTraceMetrics.h')
| -rw-r--r-- | contrib/llvm/lib/CodeGen/MachineTraceMetrics.h | 341 |
1 files changed, 341 insertions, 0 deletions
diff --git a/contrib/llvm/lib/CodeGen/MachineTraceMetrics.h b/contrib/llvm/lib/CodeGen/MachineTraceMetrics.h new file mode 100644 index 000000000000..c5b86f31dba8 --- /dev/null +++ b/contrib/llvm/lib/CodeGen/MachineTraceMetrics.h @@ -0,0 +1,341 @@ +//===- lib/CodeGen/MachineTraceMetrics.h - Super-scalar metrics -*- 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 interface for the MachineTraceMetrics analysis pass +// that estimates CPU resource usage and critical data dependency paths through +// preferred traces. This is useful for super-scalar CPUs where execution speed +// can be limited both by data dependencies and by limited execution resources. +// +// Out-of-order CPUs will often be executing instructions from multiple basic +// blocks at the same time. This makes it difficult to estimate the resource +// usage accurately in a single basic block. Resources can be estimated better +// by looking at a trace through the current basic block. +// +// For every block, the MachineTraceMetrics pass will pick a preferred trace +// that passes through the block. The trace is chosen based on loop structure, +// branch probabilities, and resource usage. The intention is to pick likely +// traces that would be the most affected by code transformations. +// +// It is expensive to compute a full arbitrary trace for every block, so to +// save some computations, traces are chosen to be convergent. This means that +// if the traces through basic blocks A and B ever cross when moving away from +// A and B, they never diverge again. This applies in both directions - If the +// traces meet above A and B, they won't diverge when going further back. +// +// Traces tend to align with loops. The trace through a block in an inner loop +// will begin at the loop entry block and end at a back edge. If there are +// nested loops, the trace may begin and end at those instead. +// +// For each trace, we compute the critical path length, which is the number of +// cycles required to execute the trace when execution is limited by data +// dependencies only. We also compute the resource height, which is the number +// of cycles required to execute all instructions in the trace when ignoring +// data dependencies. +// +// Every instruction in the current block has a slack - the number of cycles +// execution of the instruction can be delayed without extending the critical +// path. +// +//===----------------------------------------------------------------------===// + +#ifndef LLVM_CODEGEN_MACHINE_TRACE_METRICS_H +#define LLVM_CODEGEN_MACHINE_TRACE_METRICS_H + +#include "llvm/ADT/ArrayRef.h" +#include "llvm/ADT/DenseMap.h" +#include "llvm/CodeGen/MachineFunctionPass.h" + +namespace llvm { + +class InstrItineraryData; +class MachineBasicBlock; +class MachineInstr; +class MachineLoop; +class MachineLoopInfo; +class MachineRegisterInfo; +class TargetInstrInfo; +class TargetRegisterInfo; +class raw_ostream; + +class MachineTraceMetrics : public MachineFunctionPass { + const MachineFunction *MF; + const TargetInstrInfo *TII; + const TargetRegisterInfo *TRI; + const InstrItineraryData *ItinData; + const MachineRegisterInfo *MRI; + const MachineLoopInfo *Loops; + +public: + class Ensemble; + class Trace; + static char ID; + MachineTraceMetrics(); + void getAnalysisUsage(AnalysisUsage&) const; + bool runOnMachineFunction(MachineFunction&); + void releaseMemory(); + void verifyAnalysis() const; + + friend class Ensemble; + friend class Trace; + + /// Per-basic block information that doesn't depend on the trace through the + /// block. + struct FixedBlockInfo { + /// The number of non-trivial instructions in the block. + /// Doesn't count PHI and COPY instructions that are likely to be removed. + unsigned InstrCount; + + /// True when the block contains calls. + bool HasCalls; + + FixedBlockInfo() : InstrCount(~0u), HasCalls(false) {} + + /// Returns true when resource information for this block has been computed. + bool hasResources() const { return InstrCount != ~0u; } + + /// Invalidate resource information. + void invalidate() { InstrCount = ~0u; } + }; + + /// Get the fixed resource information about MBB. Compute it on demand. + const FixedBlockInfo *getResources(const MachineBasicBlock*); + + /// A virtual register or regunit required by a basic block or its trace + /// successors. + struct LiveInReg { + /// The virtual register required, or a register unit. + unsigned Reg; + + /// For virtual registers: Minimum height of the defining instruction. + /// For regunits: Height of the highest user in the trace. + unsigned Height; + + LiveInReg(unsigned Reg, unsigned Height = 0) : Reg(Reg), Height(Height) {} + }; + + /// Per-basic block information that relates to a specific trace through the + /// block. Convergent traces means that only one of these is required per + /// block in a trace ensemble. + struct TraceBlockInfo { + /// Trace predecessor, or NULL for the first block in the trace. + /// Valid when hasValidDepth(). + const MachineBasicBlock *Pred; + + /// Trace successor, or NULL for the last block in the trace. + /// Valid when hasValidHeight(). + const MachineBasicBlock *Succ; + + /// The block number of the head of the trace. (When hasValidDepth()). + unsigned Head; + + /// The block number of the tail of the trace. (When hasValidHeight()). + unsigned Tail; + + /// Accumulated number of instructions in the trace above this block. + /// Does not include instructions in this block. + unsigned InstrDepth; + + /// Accumulated number of instructions in the trace below this block. + /// Includes instructions in this block. + unsigned InstrHeight; + + TraceBlockInfo() : + Pred(0), Succ(0), + InstrDepth(~0u), InstrHeight(~0u), + HasValidInstrDepths(false), HasValidInstrHeights(false) {} + + /// Returns true if the depth resources have been computed from the trace + /// above this block. + bool hasValidDepth() const { return InstrDepth != ~0u; } + + /// Returns true if the height resources have been computed from the trace + /// below this block. + bool hasValidHeight() const { return InstrHeight != ~0u; } + + /// Invalidate depth resources when some block above this one has changed. + void invalidateDepth() { InstrDepth = ~0u; HasValidInstrDepths = false; } + + /// Invalidate height resources when a block below this one has changed. + void invalidateHeight() { InstrHeight = ~0u; HasValidInstrHeights = false; } + + // Data-dependency-related information. Per-instruction depth and height + // are computed from data dependencies in the current trace, using + // itinerary data. + + /// Instruction depths have been computed. This implies hasValidDepth(). + bool HasValidInstrDepths; + + /// Instruction heights have been computed. This implies hasValidHeight(). + bool HasValidInstrHeights; + + /// Critical path length. This is the number of cycles in the longest data + /// dependency chain through the trace. This is only valid when both + /// HasValidInstrDepths and HasValidInstrHeights are set. + unsigned CriticalPath; + + /// Live-in registers. These registers are defined above the current block + /// and used by this block or a block below it. + /// This does not include PHI uses in the current block, but it does + /// include PHI uses in deeper blocks. + SmallVector<LiveInReg, 4> LiveIns; + + void print(raw_ostream&) const; + }; + + /// InstrCycles represents the cycle height and depth of an instruction in a + /// trace. + struct InstrCycles { + /// Earliest issue cycle as determined by data dependencies and instruction + /// latencies from the beginning of the trace. Data dependencies from + /// before the trace are not included. + unsigned Depth; + + /// Minimum number of cycles from this instruction is issued to the of the + /// trace, as determined by data dependencies and instruction latencies. + unsigned Height; + }; + + /// A trace represents a plausible sequence of executed basic blocks that + /// passes through the current basic block one. The Trace class serves as a + /// handle to internal cached data structures. + class Trace { + Ensemble &TE; + TraceBlockInfo &TBI; + + unsigned getBlockNum() const { return &TBI - &TE.BlockInfo[0]; } + + public: + explicit Trace(Ensemble &te, TraceBlockInfo &tbi) : TE(te), TBI(tbi) {} + void print(raw_ostream&) const; + + /// Compute the total number of instructions in the trace. + unsigned getInstrCount() const { + return TBI.InstrDepth + TBI.InstrHeight; + } + + /// Return the resource depth of the top/bottom of the trace center block. + /// This is the number of cycles required to execute all instructions from + /// the trace head to the trace center block. The resource depth only + /// considers execution resources, it ignores data dependencies. + /// When Bottom is set, instructions in the trace center block are included. + unsigned getResourceDepth(bool Bottom) const; + + /// Return the resource length of the trace. This is the number of cycles + /// required to execute the instructions in the trace if they were all + /// independent, exposing the maximum instruction-level parallelism. + /// + /// Any blocks in Extrablocks are included as if they were part of the + /// trace. + unsigned getResourceLength(ArrayRef<const MachineBasicBlock*> Extrablocks = + ArrayRef<const MachineBasicBlock*>()) const; + + /// Return the length of the (data dependency) critical path through the + /// trace. + unsigned getCriticalPath() const { return TBI.CriticalPath; } + + /// Return the depth and height of MI. The depth is only valid for + /// instructions in or above the trace center block. The height is only + /// valid for instructions in or below the trace center block. + InstrCycles getInstrCycles(const MachineInstr *MI) const { + return TE.Cycles.lookup(MI); + } + + /// Return the slack of MI. This is the number of cycles MI can be delayed + /// before the critical path becomes longer. + /// MI must be an instruction in the trace center block. + unsigned getInstrSlack(const MachineInstr *MI) const; + + /// Return the Depth of a PHI instruction in a trace center block successor. + /// The PHI does not have to be part of the trace. + unsigned getPHIDepth(const MachineInstr *PHI) const; + }; + + /// A trace ensemble is a collection of traces selected using the same + /// strategy, for example 'minimum resource height'. There is one trace for + /// every block in the function. + class Ensemble { + SmallVector<TraceBlockInfo, 4> BlockInfo; + DenseMap<const MachineInstr*, InstrCycles> Cycles; + friend class Trace; + + void computeTrace(const MachineBasicBlock*); + void computeDepthResources(const MachineBasicBlock*); + void computeHeightResources(const MachineBasicBlock*); + unsigned computeCrossBlockCriticalPath(const TraceBlockInfo&); + void computeInstrDepths(const MachineBasicBlock*); + void computeInstrHeights(const MachineBasicBlock*); + void addLiveIns(const MachineInstr *DefMI, + ArrayRef<const MachineBasicBlock*> Trace); + + protected: + MachineTraceMetrics &MTM; + virtual const MachineBasicBlock *pickTracePred(const MachineBasicBlock*) =0; + virtual const MachineBasicBlock *pickTraceSucc(const MachineBasicBlock*) =0; + explicit Ensemble(MachineTraceMetrics*); + const MachineLoop *getLoopFor(const MachineBasicBlock*) const; + const TraceBlockInfo *getDepthResources(const MachineBasicBlock*) const; + const TraceBlockInfo *getHeightResources(const MachineBasicBlock*) const; + + public: + virtual ~Ensemble(); + virtual const char *getName() const =0; + void print(raw_ostream&) const; + void invalidate(const MachineBasicBlock *MBB); + void verify() const; + + /// Get the trace that passes through MBB. + /// The trace is computed on demand. + Trace getTrace(const MachineBasicBlock *MBB); + }; + + /// Strategies for selecting traces. + enum Strategy { + /// Select the trace through a block that has the fewest instructions. + TS_MinInstrCount, + + TS_NumStrategies + }; + + /// Get the trace ensemble representing the given trace selection strategy. + /// The returned Ensemble object is owned by the MachineTraceMetrics analysis, + /// and valid for the lifetime of the analysis pass. + Ensemble *getEnsemble(Strategy); + + /// Invalidate cached information about MBB. This must be called *before* MBB + /// is erased, or the CFG is otherwise changed. + /// + /// This invalidates per-block information about resource usage for MBB only, + /// and it invalidates per-trace information for any trace that passes + /// through MBB. + /// + /// Call Ensemble::getTrace() again to update any trace handles. + void invalidate(const MachineBasicBlock *MBB); + +private: + // One entry per basic block, indexed by block number. + SmallVector<FixedBlockInfo, 4> BlockInfo; + + // One ensemble per strategy. + Ensemble* Ensembles[TS_NumStrategies]; +}; + +inline raw_ostream &operator<<(raw_ostream &OS, + const MachineTraceMetrics::Trace &Tr) { + Tr.print(OS); + return OS; +} + +inline raw_ostream &operator<<(raw_ostream &OS, + const MachineTraceMetrics::Ensemble &En) { + En.print(OS); + return OS; +} +} // end namespace llvm + +#endif |