1 //===- CodeExtractor.cpp - Pull code region into a new function -----------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the interface to tear out a code region, such as an
11 // individual loop or a parallel section, into a new function, replacing it with
12 // a call to the new function.
14 //===----------------------------------------------------------------------===//
16 #include "llvm/Transforms/Utils/FunctionUtils.h"
17 #include "llvm/Constants.h"
18 #include "llvm/DerivedTypes.h"
19 #include "llvm/Instructions.h"
20 #include "llvm/Module.h"
21 #include "llvm/Pass.h"
22 #include "llvm/Analysis/Dominators.h"
23 #include "llvm/Analysis/LoopInfo.h"
24 #include "llvm/Analysis/Verifier.h"
25 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
26 #include "Support/Debug.h"
27 #include "Support/StringExtras.h"
34 typedef std::vector<Value*> Values;
35 std::set<BasicBlock*> BlocksToExtract;
38 CodeExtractor(DominatorSet *ds = 0) : DS(ds) {}
40 Function *ExtractCodeRegion(const std::vector<BasicBlock*> &code);
43 void findInputsOutputs(Values &inputs, Values &outputs,
44 BasicBlock *newHeader,
45 BasicBlock *newRootNode);
47 Function *constructFunction(const Values &inputs,
48 const Values &outputs,
50 BasicBlock *newRootNode, BasicBlock *newHeader,
51 Function *oldFunction, Module *M);
53 void moveCodeToFunction(Function *newFunction);
55 void emitCallAndSwitchStatement(Function *newFunction,
56 BasicBlock *newHeader,
63 void CodeExtractor::findInputsOutputs(Values &inputs, Values &outputs,
64 BasicBlock *newHeader,
65 BasicBlock *newRootNode) {
66 for (std::set<BasicBlock*>::const_iterator ci = BlocksToExtract.begin(),
67 ce = BlocksToExtract.end(); ci != ce; ++ci) {
69 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
70 // If a used value is defined outside the region, it's an input. If an
71 // instruction is used outside the region, it's an output.
72 if (PHINode *PN = dyn_cast<PHINode>(I)) {
73 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
74 Value *V = PN->getIncomingValue(i);
75 if (!BlocksToExtract.count(PN->getIncomingBlock(i)) &&
76 (isa<Instruction>(V) || isa<Argument>(V)))
80 // All other instructions go through the generic input finder
81 // Loop over the operands of each instruction (inputs)
82 for (User::op_iterator op = I->op_begin(), opE = I->op_end();
84 if (Instruction *opI = dyn_cast<Instruction>(*op)) {
85 // Check if definition of this operand is within the loop
86 if (!BlocksToExtract.count(opI->getParent()))
87 inputs.push_back(opI);
88 } else if (isa<Argument>(*op)) {
89 inputs.push_back(*op);
93 // Consider uses of this instruction (outputs)
94 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
96 if (!BlocksToExtract.count(cast<Instruction>(*UI)->getParent())) {
101 } // for: basic blocks
104 /// constructFunction - make a function based on inputs and outputs, as follows:
105 /// f(in0, ..., inN, out0, ..., outN)
107 Function *CodeExtractor::constructFunction(const Values &inputs,
108 const Values &outputs,
110 BasicBlock *newRootNode,
111 BasicBlock *newHeader,
112 Function *oldFunction,
114 DEBUG(std::cerr << "inputs: " << inputs.size() << "\n");
115 DEBUG(std::cerr << "outputs: " << outputs.size() << "\n");
117 // This function returns unsigned, outputs will go back by reference.
118 Type *retTy = Type::UShortTy;
119 std::vector<const Type*> paramTy;
121 // Add the types of the input values to the function's argument list
122 for (Values::const_iterator i = inputs.begin(),
123 e = inputs.end(); i != e; ++i) {
124 const Value *value = *i;
125 DEBUG(std::cerr << "value used in func: " << value << "\n");
126 paramTy.push_back(value->getType());
129 // Add the types of the output values to the function's argument list.
130 for (Values::const_iterator I = outputs.begin(), E = outputs.end();
132 DEBUG(std::cerr << "instr used in func: " << *I << "\n");
133 paramTy.push_back(PointerType::get((*I)->getType()));
136 DEBUG(std::cerr << "Function type: " << retTy << " f(");
137 for (std::vector<const Type*>::iterator i = paramTy.begin(),
138 e = paramTy.end(); i != e; ++i)
139 DEBUG(std::cerr << *i << ", ");
140 DEBUG(std::cerr << ")\n");
142 const FunctionType *funcType = FunctionType::get(retTy, paramTy, false);
144 // Create the new function
145 Function *newFunction = new Function(funcType,
146 GlobalValue::InternalLinkage,
147 oldFunction->getName() + "_code", M);
148 newFunction->getBasicBlockList().push_back(newRootNode);
150 // Create an iterator to name all of the arguments we inserted.
151 Function::aiterator AI = newFunction->abegin();
153 // Rewrite all users of the inputs in the extracted region to use the
154 // arguments instead.
155 for (unsigned i = 0, e = inputs.size(); i != e; ++i, ++AI) {
156 AI->setName(inputs[i]->getName());
157 std::vector<User*> Users(inputs[i]->use_begin(), inputs[i]->use_end());
158 for (std::vector<User*>::iterator use = Users.begin(), useE = Users.end();
160 if (Instruction* inst = dyn_cast<Instruction>(*use))
161 if (BlocksToExtract.count(inst->getParent()))
162 inst->replaceUsesOfWith(inputs[i], AI);
165 // Set names for all of the output arguments.
166 for (unsigned i = 0, e = outputs.size(); i != e; ++i, ++AI)
167 AI->setName(outputs[i]->getName()+".out");
170 // Rewrite branches to basic blocks outside of the loop to new dummy blocks
171 // within the new function. This must be done before we lose track of which
172 // blocks were originally in the code region.
173 std::vector<User*> Users(header->use_begin(), header->use_end());
174 for (unsigned i = 0, e = Users.size(); i != e; ++i)
175 // The BasicBlock which contains the branch is not in the region
176 // modify the branch target to a new block
177 if (TerminatorInst *TI = dyn_cast<TerminatorInst>(Users[i]))
178 if (!BlocksToExtract.count(TI->getParent()) &&
179 TI->getParent()->getParent() == oldFunction)
180 TI->replaceUsesOfWith(header, newHeader);
185 void CodeExtractor::moveCodeToFunction(Function *newFunction) {
186 Function *oldFunc = (*BlocksToExtract.begin())->getParent();
187 Function::BasicBlockListType &oldBlocks = oldFunc->getBasicBlockList();
188 Function::BasicBlockListType &newBlocks = newFunction->getBasicBlockList();
190 for (std::set<BasicBlock*>::const_iterator i = BlocksToExtract.begin(),
191 e = BlocksToExtract.end(); i != e; ++i) {
192 // Delete the basic block from the old function, and the list of blocks
193 oldBlocks.remove(*i);
195 // Insert this basic block into the new function
196 newBlocks.push_back(*i);
201 CodeExtractor::emitCallAndSwitchStatement(Function *newFunction,
202 BasicBlock *codeReplacer,
205 // Emit a call to the new function, passing allocated memory for outputs and
206 // just plain inputs for non-scalars
207 std::vector<Value*> params(inputs);
209 // Get an iterator to the first output argument.
210 Function::aiterator OutputArgBegin = newFunction->abegin();
211 std::advance(OutputArgBegin, inputs.size());
213 for (unsigned i = 0, e = outputs.size(); i != e; ++i) {
214 Value *Output = outputs[i];
215 // Create allocas for scalar outputs
217 new AllocaInst(outputs[i]->getType(), 0, Output->getName()+".loc",
218 codeReplacer->getParent()->begin()->begin());
219 params.push_back(alloca);
221 LoadInst *load = new LoadInst(alloca, Output->getName()+".reload");
222 codeReplacer->getInstList().push_back(load);
223 std::vector<User*> Users(outputs[i]->use_begin(), outputs[i]->use_end());
224 for (unsigned u = 0, e = Users.size(); u != e; ++u) {
225 Instruction *inst = cast<Instruction>(Users[u]);
226 if (!BlocksToExtract.count(inst->getParent()))
227 inst->replaceUsesOfWith(outputs[i], load);
231 CallInst *call = new CallInst(newFunction, params, "targetBlock");
232 codeReplacer->getInstList().push_front(call);
234 // Now we can emit a switch statement using the call as a value.
235 SwitchInst *TheSwitch = new SwitchInst(call, codeReplacer, codeReplacer);
237 // Since there may be multiple exits from the original region, make the new
238 // function return an unsigned, switch on that number. This loop iterates
239 // over all of the blocks in the extracted region, updating any terminator
240 // instructions in the to-be-extracted region that branch to blocks that are
241 // not in the region to be extracted.
242 std::map<BasicBlock*, BasicBlock*> ExitBlockMap;
244 unsigned switchVal = 0;
245 for (std::set<BasicBlock*>::const_iterator i = BlocksToExtract.begin(),
246 e = BlocksToExtract.end(); i != e; ++i) {
247 TerminatorInst *TI = (*i)->getTerminator();
248 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
249 if (!BlocksToExtract.count(TI->getSuccessor(i))) {
250 BasicBlock *OldTarget = TI->getSuccessor(i);
251 // add a new basic block which returns the appropriate value
252 BasicBlock *&NewTarget = ExitBlockMap[OldTarget];
254 // If we don't already have an exit stub for this non-extracted
255 // destination, create one now!
256 NewTarget = new BasicBlock(OldTarget->getName() + ".exitStub",
259 ConstantUInt *brVal = ConstantUInt::get(Type::UShortTy, switchVal++);
260 ReturnInst *NTRet = new ReturnInst(brVal, NewTarget);
262 // Update the switch instruction.
263 TheSwitch->addCase(brVal, OldTarget);
265 // Restore values just before we exit
266 // FIXME: Use a GetElementPtr to bunch the outputs in a struct
267 Function::aiterator OAI = OutputArgBegin;
268 for (unsigned out = 0, e = outputs.size(); out != e; ++out, ++OAI)
270 DS->dominates(cast<Instruction>(outputs[out])->getParent(),
272 new StoreInst(outputs[out], OAI, NTRet);
275 // rewrite the original branch instruction with this new target
276 TI->setSuccessor(i, NewTarget);
280 // Now that we've done the deed, make the default destination of the switch
281 // instruction be one of the exit blocks of the region.
282 if (TheSwitch->getNumSuccessors() > 1) {
283 // FIXME: this is broken w.r.t. PHI nodes, but the old code was more broken.
284 // This edge is not traversable.
285 TheSwitch->setSuccessor(0, TheSwitch->getSuccessor(1));
290 /// ExtractRegion - Removes a loop from a function, replaces it with a call to
291 /// new function. Returns pointer to the new function.
295 /// find inputs and outputs for the region
297 /// for inputs: add to function as args, map input instr* to arg#
298 /// for outputs: add allocas for scalars,
299 /// add to func as args, map output instr* to arg#
301 /// rewrite func to use argument #s instead of instr*
303 /// for each scalar output in the function: at every exit, store intermediate
304 /// computed result back into memory.
306 Function *CodeExtractor::ExtractCodeRegion(const std::vector<BasicBlock*> &code)
308 // 1) Find inputs, outputs
309 // 2) Construct new function
310 // * Add allocas for defs, pass as args by reference
311 // * Pass in uses as args
312 // 3) Move code region, add call instr to func
314 BlocksToExtract.insert(code.begin(), code.end());
316 Values inputs, outputs;
318 // Assumption: this is a single-entry code region, and the header is the first
319 // block in the region.
320 BasicBlock *header = code[0];
321 for (unsigned i = 1, e = code.size(); i != e; ++i)
322 for (pred_iterator PI = pred_begin(code[i]), E = pred_end(code[i]);
324 assert(BlocksToExtract.count(*PI) &&
325 "No blocks in this region may have entries from outside the region"
326 " except for the first block!");
328 Function *oldFunction = header->getParent();
330 // This takes place of the original loop
331 BasicBlock *codeReplacer = new BasicBlock("codeRepl", oldFunction);
333 // The new function needs a root node because other nodes can branch to the
334 // head of the loop, and the root cannot have predecessors
335 BasicBlock *newFuncRoot = new BasicBlock("newFuncRoot");
336 newFuncRoot->getInstList().push_back(new BranchInst(header));
338 // Find inputs to, outputs from the code region
340 // If one of the inputs is coming from a different basic block and it's in a
341 // phi node, we need to rewrite the phi node:
343 // * All the inputs which involve basic blocks OUTSIDE of this region go into
344 // a NEW phi node that takes care of finding which value really came in.
345 // The result of this phi is passed to the function as an argument.
347 // * All the other phi values stay.
349 // FIXME: PHI nodes' incoming blocks aren't being rewritten to accomodate for
350 // blocks moving to a new function.
351 // SOLUTION: move Phi nodes out of the loop header into the codeReplacer, pass
352 // the values as parameters to the function
353 findInputsOutputs(inputs, outputs, codeReplacer, newFuncRoot);
355 // Step 2: Construct new function based on inputs/outputs,
356 // Add allocas for all defs
357 Function *newFunction = constructFunction(inputs, outputs, code[0],
359 codeReplacer, oldFunction,
360 oldFunction->getParent());
362 emitCallAndSwitchStatement(newFunction, codeReplacer, inputs, outputs);
364 moveCodeToFunction(newFunction);
366 // Loop over all of the PHI nodes in the entry block (code[0]), and change any
367 // references to the old incoming edge to be the new incoming edge.
368 for (BasicBlock::iterator I = code[0]->begin();
369 PHINode *PN = dyn_cast<PHINode>(I); ++I)
370 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
371 if (!BlocksToExtract.count(PN->getIncomingBlock(i)))
372 PN->setIncomingBlock(i, newFuncRoot);
374 DEBUG(if (verifyFunction(*newFunction)) abort());
378 /// ExtractCodeRegion - slurp a sequence of basic blocks into a brand new
381 Function* llvm::ExtractCodeRegion(DominatorSet &DS,
382 const std::vector<BasicBlock*> &code) {
383 return CodeExtractor(&DS).ExtractCodeRegion(code);
386 /// ExtractBasicBlock - slurp a natural loop into a brand new function
388 Function* llvm::ExtractLoop(DominatorSet &DS, Loop *L) {
389 return CodeExtractor(&DS).ExtractCodeRegion(L->getBlocks());
392 /// ExtractBasicBlock - slurp a basic block into a brand new function
394 Function* llvm::ExtractBasicBlock(BasicBlock *BB) {
395 std::vector<BasicBlock*> Blocks;
396 Blocks.push_back(BB);
397 return CodeExtractor().ExtractCodeRegion(Blocks);