1 //===- ProfileEstimatorPass.cpp - LLVM Pass to estimate profile info ------===//
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 implements a concrete implementation of profiling information that
11 // estimates the profiling information in a very crude and unimaginative way.
13 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "profile-estimator"
15 #include "llvm/Pass.h"
16 #include "llvm/Analysis/Passes.h"
17 #include "llvm/Analysis/ProfileInfo.h"
18 #include "llvm/Analysis/LoopInfo.h"
19 #include "llvm/Support/CommandLine.h"
20 #include "llvm/Support/Debug.h"
21 #include "llvm/Support/raw_ostream.h"
22 #include "llvm/Support/Format.h"
25 static cl::opt<double>
27 "profile-estimator-loop-weight", cl::init(10),
28 cl::value_desc("loop-weight"),
29 cl::desc("Number of loop executions used for profile-estimator")
33 class ProfileEstimatorPass : public FunctionPass, public ProfileInfo {
36 std::set<BasicBlock*> BBToVisit;
37 std::map<Loop*,double> LoopExitWeights;
38 std::map<Edge,double> MinimalWeight;
40 static char ID; // Class identification, replacement for typeinfo
41 explicit ProfileEstimatorPass(const double execcount = 0)
42 : FunctionPass(&ID), ExecCount(execcount) {
43 if (execcount == 0) ExecCount = LoopWeight;
46 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
48 AU.addRequired<LoopInfo>();
51 virtual const char *getPassName() const {
52 return "Profiling information estimator";
55 /// run - Estimate the profile information from the specified file.
56 virtual bool runOnFunction(Function &F);
58 virtual void recurseBasicBlock(BasicBlock *BB);
60 void inline printEdgeWeight(Edge);
62 } // End of anonymous namespace
64 char ProfileEstimatorPass::ID = 0;
65 static RegisterPass<ProfileEstimatorPass>
66 X("profile-estimator", "Estimate profiling information", false, true);
68 static RegisterAnalysisGroup<ProfileInfo> Y(X);
71 const PassInfo *ProfileEstimatorPassID = &X;
73 FunctionPass *createProfileEstimatorPass() {
74 return new ProfileEstimatorPass();
77 /// createProfileEstimatorPass - This function returns a Pass that estimates
78 /// profiling information using the given loop execution count.
79 Pass *createProfileEstimatorPass(const unsigned execcount) {
80 return new ProfileEstimatorPass(execcount);
84 static double ignoreMissing(double w) {
85 if (w == ProfileInfo::MissingValue) return 0;
89 static void inline printEdgeError(ProfileInfo::Edge e, const char *M) {
90 DEBUG(errs() << "-- Edge " << e << " is not calculated, " << M << "\n");
93 void inline ProfileEstimatorPass::printEdgeWeight(Edge E) {
94 DEBUG(errs() << "-- Weight of Edge " << E << ":"
95 << format("%20.20g", getEdgeWeight(E)) << "\n");
98 // recurseBasicBlock() - This calculates the ProfileInfo estimation for a
99 // single block and then recurses into the successors.
100 // The algorithm preserves the flow condition, meaning that the sum of the
101 // weight of the incoming edges must be equal the block weight which must in
102 // turn be equal to the sume of the weights of the outgoing edges.
103 // Since the flow of an block is deterimined from the current state of the
104 // flow, once an edge has a flow assigned this flow is never changed again,
105 // otherwise it would be possible to violate the flow condition in another
107 void ProfileEstimatorPass::recurseBasicBlock(BasicBlock *BB) {
109 // Break the recursion if this BasicBlock was already visited.
110 if (BBToVisit.find(BB) == BBToVisit.end()) return;
112 // Read the LoopInfo for this block.
113 bool BBisHeader = LI->isLoopHeader(BB);
114 Loop* BBLoop = LI->getLoopFor(BB);
116 // To get the block weight, read all incoming edges.
118 std::set<BasicBlock*> ProcessedPreds;
119 for ( pred_iterator bbi = pred_begin(BB), bbe = pred_end(BB);
120 bbi != bbe; ++bbi ) {
121 // If this block was not considered already, add weight.
122 Edge edge = getEdge(*bbi,BB);
123 double w = getEdgeWeight(edge);
124 if (ProcessedPreds.insert(*bbi).second) {
125 BBWeight += ignoreMissing(w);
127 // If this block is a loop header and the predecessor is contained in this
128 // loop, thus the edge is a backedge, continue and do not check if the
130 if (BBisHeader && BBLoop->contains(*bbi)) {
131 printEdgeError(edge, "but is backedge, continueing");
134 // If the edges value is missing (and this is no loop header, and this is
135 // no backedge) return, this block is currently non estimatable.
136 if (w == MissingValue) {
137 printEdgeError(edge, "returning");
141 if (getExecutionCount(BB) != MissingValue) {
142 BBWeight = getExecutionCount(BB);
145 // Fetch all necessary information for current block.
146 SmallVector<Edge, 8> ExitEdges;
147 SmallVector<Edge, 8> Edges;
149 BBLoop->getExitEdges(ExitEdges);
152 // If this is a loop header, consider the following:
153 // Exactly the flow that is entering this block, must exit this block too. So
155 // *) get all the exit edges, read the flow that is already leaving this
156 // loop, remember the edges that do not have any flow on them right now.
157 // (The edges that have already flow on them are most likely exiting edges of
158 // other loops, do not touch those flows because the previously caclulated
159 // loopheaders would not be exact anymore.)
160 // *) In case there is not a single exiting edge left, create one at the loop
161 // latch to prevent the flow from building up in the loop.
162 // *) Take the flow that is not leaving the loop already and distribute it on
163 // the remaining exiting edges.
164 // (This ensures that all flow that enters the loop also leaves it.)
165 // *) Increase the flow into the loop by increasing the weight of this block.
166 // There is at least one incoming backedge that will bring us this flow later
167 // on. (So that the flow condition in this node is valid again.)
169 double incoming = BBWeight;
170 // Subtract the flow leaving the loop.
171 std::set<Edge> ProcessedExits;
172 for (SmallVector<Edge, 8>::iterator ei = ExitEdges.begin(),
173 ee = ExitEdges.end(); ei != ee; ++ei) {
174 if (ProcessedExits.insert(*ei).second) {
175 double w = getEdgeWeight(*ei);
176 if (w == MissingValue) {
177 Edges.push_back(*ei);
178 // Check if there is a necessary minimal weight, if yes, subtract it
180 if (MinimalWeight.find(*ei) != MinimalWeight.end()) {
181 incoming -= MinimalWeight[*ei];
182 DEBUG(errs() << "Reserving " << format("%.20g",MinimalWeight[*ei]) << " at " << (*ei) << "\n");
189 // If no exit edges, create one:
190 if (Edges.size() == 0) {
191 BasicBlock *Latch = BBLoop->getLoopLatch();
193 Edge edge = getEdge(Latch,0);
194 EdgeInformation[BB->getParent()][edge] = BBWeight;
195 printEdgeWeight(edge);
196 edge = getEdge(Latch, BB);
197 EdgeInformation[BB->getParent()][edge] = BBWeight * ExecCount;
198 printEdgeWeight(edge);
202 // Distribute remaining weight to the exting edges. To prevent fractions
203 // from building up and provoking precision problems the weight which is to
204 // be distributed is split and the rounded, the last edge gets a somewhat
205 // bigger value, but we are close enough for an estimation.
206 double fraction = floor(incoming/Edges.size());
207 for (SmallVector<Edge, 8>::iterator ei = Edges.begin(), ee = Edges.end();
212 incoming -= fraction;
216 EdgeInformation[BB->getParent()][*ei] += w;
217 // Read necessary minimal weight.
218 if (MinimalWeight.find(*ei) != MinimalWeight.end()) {
219 EdgeInformation[BB->getParent()][*ei] += MinimalWeight[*ei];
220 DEBUG(errs() << "Additionally " << format("%.20g",MinimalWeight[*ei]) << " at " << (*ei) << "\n");
222 printEdgeWeight(*ei);
224 // Add minimal weight to paths to all exit edges, this is used to ensure
225 // that enough flow is reaching this edges.
227 const BasicBlock *Dest = GetPath(BB, (*ei).first, p, GetPathToDest);
229 const BasicBlock *Parent = p.find(Dest)->second;
230 Edge e = getEdge(Parent, Dest);
231 if (MinimalWeight.find(e) == MinimalWeight.end()) {
232 MinimalWeight[e] = 0;
234 MinimalWeight[e] += w;
235 DEBUG(errs() << "Minimal Weight for " << e << ": " << format("%.20g",MinimalWeight[e]) << "\n");
239 // Increase flow into the loop.
240 BBWeight *= (ExecCount+1);
243 BlockInformation[BB->getParent()][BB] = BBWeight;
244 // Up until now we considered only the loop exiting edges, now we have a
245 // definite block weight and must distribute this onto the outgoing edges.
246 // Since there may be already flow attached to some of the edges, read this
247 // flow first and remember the edges that have still now flow attached.
249 std::set<BasicBlock*> ProcessedSuccs;
251 succ_iterator bbi = succ_begin(BB), bbe = succ_end(BB);
252 // Also check for (BB,0) edges that may already contain some flow. (But only
253 // in case there are no successors.)
255 Edge edge = getEdge(BB,0);
256 EdgeInformation[BB->getParent()][edge] = BBWeight;
257 printEdgeWeight(edge);
259 for ( ; bbi != bbe; ++bbi ) {
260 if (ProcessedSuccs.insert(*bbi).second) {
261 Edge edge = getEdge(BB,*bbi);
262 double w = getEdgeWeight(edge);
263 if (w != MissingValue) {
264 BBWeight -= getEdgeWeight(edge);
266 Edges.push_back(edge);
267 // If minimal weight is necessary, reserve weight by subtracting weight
268 // from block weight, this is readded later on.
269 if (MinimalWeight.find(edge) != MinimalWeight.end()) {
270 BBWeight -= MinimalWeight[edge];
271 DEBUG(errs() << "Reserving " << format("%.20g",MinimalWeight[edge]) << " at " << edge << "\n");
277 double fraction = floor(BBWeight/Edges.size());
278 // Finally we know what flow is still not leaving the block, distribute this
279 // flow onto the empty edges.
280 for (SmallVector<Edge, 8>::iterator ei = Edges.begin(), ee = Edges.end();
283 EdgeInformation[BB->getParent()][*ei] += fraction;
284 BBWeight -= fraction;
286 EdgeInformation[BB->getParent()][*ei] += BBWeight;
288 // Readd minial necessary weight.
289 if (MinimalWeight.find(*ei) != MinimalWeight.end()) {
290 EdgeInformation[BB->getParent()][*ei] += MinimalWeight[*ei];
291 DEBUG(errs() << "Additionally " << format("%.20g",MinimalWeight[*ei]) << " at " << (*ei) << "\n");
293 printEdgeWeight(*ei);
296 // This block is visited, mark this before the recursion.
299 // Recurse into successors.
300 for (succ_iterator bbi = succ_begin(BB), bbe = succ_end(BB);
302 recurseBasicBlock(*bbi);
306 bool ProfileEstimatorPass::runOnFunction(Function &F) {
307 if (F.isDeclaration()) return false;
309 // Fetch LoopInfo and clear ProfileInfo for this function.
310 LI = &getAnalysis<LoopInfo>();
311 FunctionInformation.erase(&F);
312 BlockInformation[&F].clear();
313 EdgeInformation[&F].clear();
315 // Mark all blocks as to visit.
316 for (Function::iterator bi = F.begin(), be = F.end(); bi != be; ++bi)
317 BBToVisit.insert(bi);
319 // Clear Minimal Edges.
320 MinimalWeight.clear();
322 DEBUG(errs() << "Working on function " << F.getNameStr() << "\n");
324 // Since the entry block is the first one and has no predecessors, the edge
325 // (0,entry) is inserted with the starting weight of 1.
326 BasicBlock *entry = &F.getEntryBlock();
327 BlockInformation[&F][entry] = pow(2,32);
328 Edge edge = getEdge(0,entry);
329 EdgeInformation[&F][edge] = BlockInformation[&F][entry];
330 printEdgeWeight(edge);
332 // Since recurseBasicBlock() maybe returns with a block which was not fully
333 // estimated, use recurseBasicBlock() until everything is calculated.
334 bool cleanup = false;
335 recurseBasicBlock(entry);
336 while (BBToVisit.size() > 0 && !cleanup) {
337 // Remember number of open blocks, this is later used to check if progress
339 unsigned size = BBToVisit.size();
341 // Try to calculate all blocks in turn.
342 for (std::set<BasicBlock*>::iterator bi = BBToVisit.begin(),
343 be = BBToVisit.end(); bi != be; ++bi) {
344 recurseBasicBlock(*bi);
345 // If at least one block was finished, break because iterator may be
347 if (BBToVisit.size() < size) break;
350 // If there was not a single block resolved, make some assumptions.
351 if (BBToVisit.size() == size) {
353 for (std::set<BasicBlock*>::iterator BBI = BBToVisit.begin(), BBE = BBToVisit.end();
354 (BBI != BBE) && (!found); ++BBI) {
355 BasicBlock *BB = *BBI;
356 // Try each predecessor if it can be assumend.
357 for (pred_iterator bbi = pred_begin(BB), bbe = pred_end(BB);
358 (bbi != bbe) && (!found); ++bbi) {
359 Edge e = getEdge(*bbi,BB);
360 double w = getEdgeWeight(e);
361 // Check that edge from predecessor is still free.
362 if (w == MissingValue) {
363 // Check if there is a circle from this block to predecessor.
365 const BasicBlock *Dest = GetPath(BB, *bbi, P, GetPathToDest);
367 // If there is no circle, just set edge weight to 0
368 EdgeInformation[&F][e] = 0;
369 DEBUG(errs() << "Assuming edge weight: ");
378 DEBUG(errs() << "No assumption possible in Fuction "<<F.getName()<<", setting all to zero\n");
382 // In case there was no safe way to assume edges, set as a last measure,
383 // set _everything_ to zero.
385 FunctionInformation[&F] = 0;
386 BlockInformation[&F].clear();
387 EdgeInformation[&F].clear();
388 for (Function::const_iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
389 const BasicBlock *BB = &(*FI);
390 BlockInformation[&F][BB] = 0;
391 pred_const_iterator predi = pred_begin(BB), prede = pred_end(BB);
392 if (predi == prede) {
393 Edge e = getEdge(0,BB);
396 for (;predi != prede; ++predi) {
397 Edge e = getEdge(*predi,BB);
400 succ_const_iterator succi = succ_begin(BB), succe = succ_end(BB);
401 if (succi == succe) {
402 Edge e = getEdge(BB,0);
405 for (;succi != succe; ++succi) {
406 Edge e = getEdge(*succi,BB);