1 //===- lib/CodeGen/MachineTraceMetrics.h - Super-scalar metrics -*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines the interface for the MachineTraceMetrics analysis pass
11 // that estimates CPU resource usage and critical data dependency paths through
12 // preferred traces. This is useful for super-scalar CPUs where execution speed
13 // can be limited both by data dependencies and by limited execution resources.
15 // Out-of-order CPUs will often be executing instructions from multiple basic
16 // blocks at the same time. This makes it difficult to estimate the resource
17 // usage accurately in a single basic block. Resources can be estimated better
18 // by looking at a trace through the current basic block.
20 // For every block, the MachineTraceMetrics pass will pick a preferred trace
21 // that passes through the block. The trace is chosen based on loop structure,
22 // branch probabilities, and resource usage. The intention is to pick likely
23 // traces that would be the most affected by code transformations.
25 // It is expensive to compute a full arbitrary trace for every block, so to
26 // save some computations, traces are chosen to be convergent. This means that
27 // if the traces through basic blocks A and B ever cross when moving away from
28 // A and B, they never diverge again. This applies in both directions - If the
29 // traces meet above A and B, they won't diverge when going further back.
31 // Traces tend to align with loops. The trace through a block in an inner loop
32 // will begin at the loop entry block and end at a back edge. If there are
33 // nested loops, the trace may begin and end at those instead.
35 // For each trace, we compute the critical path length, which is the number of
36 // cycles required to execute the trace when execution is limited by data
37 // dependencies only. We also compute the resource height, which is the number
38 // of cycles required to execute all instructions in the trace when ignoring
41 // Every instruction in the current block has a slack - the number of cycles
42 // execution of the instruction can be delayed without extending the critical
45 //===----------------------------------------------------------------------===//
47 #ifndef LLVM_CODEGEN_MACHINE_TRACE_METRICS_H
48 #define LLVM_CODEGEN_MACHINE_TRACE_METRICS_H
50 #include "llvm/ADT/ArrayRef.h"
51 #include "llvm/ADT/DenseMap.h"
52 #include "llvm/CodeGen/MachineFunctionPass.h"
53 #include "llvm/CodeGen/TargetSchedule.h"
57 class InstrItineraryData;
58 class MachineBasicBlock;
61 class MachineLoopInfo;
62 class MachineRegisterInfo;
63 class TargetInstrInfo;
64 class TargetRegisterInfo;
67 class MachineTraceMetrics : public MachineFunctionPass {
68 const MachineFunction *MF;
69 const TargetInstrInfo *TII;
70 const TargetRegisterInfo *TRI;
71 const MachineRegisterInfo *MRI;
72 const MachineLoopInfo *Loops;
73 TargetSchedModel SchedModel;
79 MachineTraceMetrics();
80 void getAnalysisUsage(AnalysisUsage&) const;
81 bool runOnMachineFunction(MachineFunction&);
83 void verifyAnalysis() const;
85 friend class Ensemble;
88 /// Per-basic block information that doesn't depend on the trace through the
90 struct FixedBlockInfo {
91 /// The number of non-trivial instructions in the block.
92 /// Doesn't count PHI and COPY instructions that are likely to be removed.
95 /// True when the block contains calls.
98 FixedBlockInfo() : InstrCount(~0u), HasCalls(false) {}
100 /// Returns true when resource information for this block has been computed.
101 bool hasResources() const { return InstrCount != ~0u; }
103 /// Invalidate resource information.
104 void invalidate() { InstrCount = ~0u; }
107 /// Get the fixed resource information about MBB. Compute it on demand.
108 const FixedBlockInfo *getResources(const MachineBasicBlock*);
110 /// Get the scaled number of cycles used per processor resource in MBB.
111 /// This is an array with SchedModel.getNumProcResourceKinds() entries.
112 /// The getResources() function above must have been called first.
114 /// These numbers have already been scaled by SchedModel.getResourceFactor().
115 ArrayRef<unsigned> getProcResourceCycles(unsigned MBBNum) const;
117 /// A virtual register or regunit required by a basic block or its trace
120 /// The virtual register required, or a register unit.
123 /// For virtual registers: Minimum height of the defining instruction.
124 /// For regunits: Height of the highest user in the trace.
127 LiveInReg(unsigned Reg, unsigned Height = 0) : Reg(Reg), Height(Height) {}
130 /// Per-basic block information that relates to a specific trace through the
131 /// block. Convergent traces means that only one of these is required per
132 /// block in a trace ensemble.
133 struct TraceBlockInfo {
134 /// Trace predecessor, or NULL for the first block in the trace.
135 /// Valid when hasValidDepth().
136 const MachineBasicBlock *Pred;
138 /// Trace successor, or NULL for the last block in the trace.
139 /// Valid when hasValidHeight().
140 const MachineBasicBlock *Succ;
142 /// The block number of the head of the trace. (When hasValidDepth()).
145 /// The block number of the tail of the trace. (When hasValidHeight()).
148 /// Accumulated number of instructions in the trace above this block.
149 /// Does not include instructions in this block.
152 /// Accumulated number of instructions in the trace below this block.
153 /// Includes instructions in this block.
154 unsigned InstrHeight;
158 InstrDepth(~0u), InstrHeight(~0u),
159 HasValidInstrDepths(false), HasValidInstrHeights(false) {}
161 /// Returns true if the depth resources have been computed from the trace
162 /// above this block.
163 bool hasValidDepth() const { return InstrDepth != ~0u; }
165 /// Returns true if the height resources have been computed from the trace
166 /// below this block.
167 bool hasValidHeight() const { return InstrHeight != ~0u; }
169 /// Invalidate depth resources when some block above this one has changed.
170 void invalidateDepth() { InstrDepth = ~0u; HasValidInstrDepths = false; }
172 /// Invalidate height resources when a block below this one has changed.
173 void invalidateHeight() { InstrHeight = ~0u; HasValidInstrHeights = false; }
175 /// Assuming that this is a dominator of TBI, determine if it contains
176 /// useful instruction depths. A dominating block can be above the current
177 /// trace head, and any dependencies from such a far away dominator are not
178 /// expected to affect the critical path.
180 /// Also returns true when TBI == this.
181 bool isUsefulDominator(const TraceBlockInfo &TBI) const {
182 // The trace for TBI may not even be calculated yet.
183 if (!hasValidDepth() || !TBI.hasValidDepth())
185 // Instruction depths are only comparable if the traces share a head.
186 if (Head != TBI.Head)
188 // It is almost always the case that TBI belongs to the same trace as
189 // this block, but rare convoluted cases involving irreducible control
190 // flow, a dominator may share a trace head without actually being on the
191 // same trace as TBI. This is not a big problem as long as it doesn't
192 // increase the instruction depth.
193 return HasValidInstrDepths && InstrDepth <= TBI.InstrDepth;
196 // Data-dependency-related information. Per-instruction depth and height
197 // are computed from data dependencies in the current trace, using
200 /// Instruction depths have been computed. This implies hasValidDepth().
201 bool HasValidInstrDepths;
203 /// Instruction heights have been computed. This implies hasValidHeight().
204 bool HasValidInstrHeights;
206 /// Critical path length. This is the number of cycles in the longest data
207 /// dependency chain through the trace. This is only valid when both
208 /// HasValidInstrDepths and HasValidInstrHeights are set.
209 unsigned CriticalPath;
211 /// Live-in registers. These registers are defined above the current block
212 /// and used by this block or a block below it.
213 /// This does not include PHI uses in the current block, but it does
214 /// include PHI uses in deeper blocks.
215 SmallVector<LiveInReg, 4> LiveIns;
217 void print(raw_ostream&) const;
220 /// InstrCycles represents the cycle height and depth of an instruction in a
223 /// Earliest issue cycle as determined by data dependencies and instruction
224 /// latencies from the beginning of the trace. Data dependencies from
225 /// before the trace are not included.
228 /// Minimum number of cycles from this instruction is issued to the of the
229 /// trace, as determined by data dependencies and instruction latencies.
233 /// A trace represents a plausible sequence of executed basic blocks that
234 /// passes through the current basic block one. The Trace class serves as a
235 /// handle to internal cached data structures.
240 unsigned getBlockNum() const { return &TBI - &TE.BlockInfo[0]; }
243 explicit Trace(Ensemble &te, TraceBlockInfo &tbi) : TE(te), TBI(tbi) {}
244 void print(raw_ostream&) const;
246 /// Compute the total number of instructions in the trace.
247 unsigned getInstrCount() const {
248 return TBI.InstrDepth + TBI.InstrHeight;
251 /// Return the resource depth of the top/bottom of the trace center block.
252 /// This is the number of cycles required to execute all instructions from
253 /// the trace head to the trace center block. The resource depth only
254 /// considers execution resources, it ignores data dependencies.
255 /// When Bottom is set, instructions in the trace center block are included.
256 unsigned getResourceDepth(bool Bottom) const;
258 /// Return the resource length of the trace. This is the number of cycles
259 /// required to execute the instructions in the trace if they were all
260 /// independent, exposing the maximum instruction-level parallelism.
262 /// Any blocks in Extrablocks are included as if they were part of the
263 /// trace. Likewise, extra resources required by the specified scheduling
264 /// classes are included. For the caller to account for extra machine
265 /// instructions, it must first resolve each instruction's scheduling class.
266 unsigned getResourceLength(
267 ArrayRef<const MachineBasicBlock*> Extrablocks = None,
268 ArrayRef<const MCSchedClassDesc*> ExtraInstrs = None) const;
270 /// Return the length of the (data dependency) critical path through the
272 unsigned getCriticalPath() const { return TBI.CriticalPath; }
274 /// Return the depth and height of MI. The depth is only valid for
275 /// instructions in or above the trace center block. The height is only
276 /// valid for instructions in or below the trace center block.
277 InstrCycles getInstrCycles(const MachineInstr *MI) const {
278 return TE.Cycles.lookup(MI);
281 /// Return the slack of MI. This is the number of cycles MI can be delayed
282 /// before the critical path becomes longer.
283 /// MI must be an instruction in the trace center block.
284 unsigned getInstrSlack(const MachineInstr *MI) const;
286 /// Return the Depth of a PHI instruction in a trace center block successor.
287 /// The PHI does not have to be part of the trace.
288 unsigned getPHIDepth(const MachineInstr *PHI) const;
291 /// A trace ensemble is a collection of traces selected using the same
292 /// strategy, for example 'minimum resource height'. There is one trace for
293 /// every block in the function.
295 SmallVector<TraceBlockInfo, 4> BlockInfo;
296 DenseMap<const MachineInstr*, InstrCycles> Cycles;
297 SmallVector<unsigned, 0> ProcResourceDepths;
298 SmallVector<unsigned, 0> ProcResourceHeights;
301 void computeTrace(const MachineBasicBlock*);
302 void computeDepthResources(const MachineBasicBlock*);
303 void computeHeightResources(const MachineBasicBlock*);
304 unsigned computeCrossBlockCriticalPath(const TraceBlockInfo&);
305 void computeInstrDepths(const MachineBasicBlock*);
306 void computeInstrHeights(const MachineBasicBlock*);
307 void addLiveIns(const MachineInstr *DefMI, unsigned DefOp,
308 ArrayRef<const MachineBasicBlock*> Trace);
311 MachineTraceMetrics &MTM;
312 virtual const MachineBasicBlock *pickTracePred(const MachineBasicBlock*) =0;
313 virtual const MachineBasicBlock *pickTraceSucc(const MachineBasicBlock*) =0;
314 explicit Ensemble(MachineTraceMetrics*);
315 const MachineLoop *getLoopFor(const MachineBasicBlock*) const;
316 const TraceBlockInfo *getDepthResources(const MachineBasicBlock*) const;
317 const TraceBlockInfo *getHeightResources(const MachineBasicBlock*) const;
318 ArrayRef<unsigned> getProcResourceDepths(unsigned MBBNum) const;
319 ArrayRef<unsigned> getProcResourceHeights(unsigned MBBNum) const;
323 virtual const char *getName() const =0;
324 void print(raw_ostream&) const;
325 void invalidate(const MachineBasicBlock *MBB);
328 /// Get the trace that passes through MBB.
329 /// The trace is computed on demand.
330 Trace getTrace(const MachineBasicBlock *MBB);
333 /// Strategies for selecting traces.
335 /// Select the trace through a block that has the fewest instructions.
341 /// Get the trace ensemble representing the given trace selection strategy.
342 /// The returned Ensemble object is owned by the MachineTraceMetrics analysis,
343 /// and valid for the lifetime of the analysis pass.
344 Ensemble *getEnsemble(Strategy);
346 /// Invalidate cached information about MBB. This must be called *before* MBB
347 /// is erased, or the CFG is otherwise changed.
349 /// This invalidates per-block information about resource usage for MBB only,
350 /// and it invalidates per-trace information for any trace that passes
353 /// Call Ensemble::getTrace() again to update any trace handles.
354 void invalidate(const MachineBasicBlock *MBB);
357 // One entry per basic block, indexed by block number.
358 SmallVector<FixedBlockInfo, 4> BlockInfo;
360 // Cycles consumed on each processor resource per block.
361 // The number of processor resource kinds is constant for a given subtarget,
362 // but it is not known at compile time. The number of cycles consumed by
363 // block B on processor resource R is at ProcResourceCycles[B*Kinds + R]
364 // where Kinds = SchedModel.getNumProcResourceKinds().
365 SmallVector<unsigned, 0> ProcResourceCycles;
367 // One ensemble per strategy.
368 Ensemble* Ensembles[TS_NumStrategies];
370 // Convert scaled resource usage to a cycle count that can be compared with
372 unsigned getCycles(unsigned Scaled) {
373 unsigned Factor = SchedModel.getLatencyFactor();
374 return (Scaled + Factor - 1) / Factor;
378 inline raw_ostream &operator<<(raw_ostream &OS,
379 const MachineTraceMetrics::Trace &Tr) {
384 inline raw_ostream &operator<<(raw_ostream &OS,
385 const MachineTraceMetrics::Ensemble &En) {
389 } // end namespace llvm