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)))
78 else if (Instruction *opI = dyn_cast<Instruction>(V)) {
79 if (!BlocksToExtract.count(opI->getParent()))
80 inputs.push_back(opI);
81 } else if (isa<Argument>(V))
85 // All other instructions go through the generic input finder
86 // Loop over the operands of each instruction (inputs)
87 for (User::op_iterator op = I->op_begin(), opE = I->op_end();
89 if (Instruction *opI = dyn_cast<Instruction>(*op)) {
90 // Check if definition of this operand is within the loop
91 if (!BlocksToExtract.count(opI->getParent()))
92 inputs.push_back(opI);
93 } else if (isa<Argument>(*op)) {
94 inputs.push_back(*op);
98 // Consider uses of this instruction (outputs)
99 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
101 if (!BlocksToExtract.count(cast<Instruction>(*UI)->getParent())) {
102 outputs.push_back(I);
106 } // for: basic blocks
109 /// constructFunction - make a function based on inputs and outputs, as follows:
110 /// f(in0, ..., inN, out0, ..., outN)
112 Function *CodeExtractor::constructFunction(const Values &inputs,
113 const Values &outputs,
115 BasicBlock *newRootNode,
116 BasicBlock *newHeader,
117 Function *oldFunction,
119 DEBUG(std::cerr << "inputs: " << inputs.size() << "\n");
120 DEBUG(std::cerr << "outputs: " << outputs.size() << "\n");
122 // This function returns unsigned, outputs will go back by reference.
123 Type *retTy = Type::UShortTy;
124 std::vector<const Type*> paramTy;
126 // Add the types of the input values to the function's argument list
127 for (Values::const_iterator i = inputs.begin(),
128 e = inputs.end(); i != e; ++i) {
129 const Value *value = *i;
130 DEBUG(std::cerr << "value used in func: " << value << "\n");
131 paramTy.push_back(value->getType());
134 // Add the types of the output values to the function's argument list.
135 for (Values::const_iterator I = outputs.begin(), E = outputs.end();
137 DEBUG(std::cerr << "instr used in func: " << *I << "\n");
138 paramTy.push_back(PointerType::get((*I)->getType()));
141 DEBUG(std::cerr << "Function type: " << retTy << " f(");
142 for (std::vector<const Type*>::iterator i = paramTy.begin(),
143 e = paramTy.end(); i != e; ++i)
144 DEBUG(std::cerr << *i << ", ");
145 DEBUG(std::cerr << ")\n");
147 const FunctionType *funcType = FunctionType::get(retTy, paramTy, false);
149 // Create the new function
150 Function *newFunction = new Function(funcType,
151 GlobalValue::InternalLinkage,
152 oldFunction->getName() + "_code", M);
153 newFunction->getBasicBlockList().push_back(newRootNode);
155 // Create an iterator to name all of the arguments we inserted.
156 Function::aiterator AI = newFunction->abegin();
158 // Rewrite all users of the inputs in the extracted region to use the
159 // arguments instead.
160 for (unsigned i = 0, e = inputs.size(); i != e; ++i, ++AI) {
161 AI->setName(inputs[i]->getName());
162 std::vector<User*> Users(inputs[i]->use_begin(), inputs[i]->use_end());
163 for (std::vector<User*>::iterator use = Users.begin(), useE = Users.end();
165 if (Instruction* inst = dyn_cast<Instruction>(*use))
166 if (BlocksToExtract.count(inst->getParent()))
167 inst->replaceUsesOfWith(inputs[i], AI);
170 // Set names for all of the output arguments.
171 for (unsigned i = 0, e = outputs.size(); i != e; ++i, ++AI)
172 AI->setName(outputs[i]->getName()+".out");
175 // Rewrite branches to basic blocks outside of the loop to new dummy blocks
176 // within the new function. This must be done before we lose track of which
177 // blocks were originally in the code region.
178 std::vector<User*> Users(header->use_begin(), header->use_end());
179 for (unsigned i = 0, e = Users.size(); i != e; ++i)
180 // The BasicBlock which contains the branch is not in the region
181 // modify the branch target to a new block
182 if (TerminatorInst *TI = dyn_cast<TerminatorInst>(Users[i]))
183 if (!BlocksToExtract.count(TI->getParent()) &&
184 TI->getParent()->getParent() == oldFunction)
185 TI->replaceUsesOfWith(header, newHeader);
190 void CodeExtractor::moveCodeToFunction(Function *newFunction) {
191 Function *oldFunc = (*BlocksToExtract.begin())->getParent();
192 Function::BasicBlockListType &oldBlocks = oldFunc->getBasicBlockList();
193 Function::BasicBlockListType &newBlocks = newFunction->getBasicBlockList();
195 for (std::set<BasicBlock*>::const_iterator i = BlocksToExtract.begin(),
196 e = BlocksToExtract.end(); i != e; ++i) {
197 // Delete the basic block from the old function, and the list of blocks
198 oldBlocks.remove(*i);
200 // Insert this basic block into the new function
201 newBlocks.push_back(*i);
206 CodeExtractor::emitCallAndSwitchStatement(Function *newFunction,
207 BasicBlock *codeReplacer,
210 // Emit a call to the new function, passing allocated memory for outputs and
211 // just plain inputs for non-scalars
212 std::vector<Value*> params(inputs);
214 // Get an iterator to the first output argument.
215 Function::aiterator OutputArgBegin = newFunction->abegin();
216 std::advance(OutputArgBegin, inputs.size());
218 for (unsigned i = 0, e = outputs.size(); i != e; ++i) {
219 Value *Output = outputs[i];
220 // Create allocas for scalar outputs
222 new AllocaInst(outputs[i]->getType(), 0, Output->getName()+".loc",
223 codeReplacer->getParent()->begin()->begin());
224 params.push_back(alloca);
226 LoadInst *load = new LoadInst(alloca, Output->getName()+".reload");
227 codeReplacer->getInstList().push_back(load);
228 std::vector<User*> Users(outputs[i]->use_begin(), outputs[i]->use_end());
229 for (unsigned u = 0, e = Users.size(); u != e; ++u) {
230 Instruction *inst = cast<Instruction>(Users[u]);
231 if (!BlocksToExtract.count(inst->getParent()))
232 inst->replaceUsesOfWith(outputs[i], load);
236 CallInst *call = new CallInst(newFunction, params, "targetBlock");
237 codeReplacer->getInstList().push_front(call);
239 // Now we can emit a switch statement using the call as a value.
240 SwitchInst *TheSwitch = new SwitchInst(call, codeReplacer, codeReplacer);
242 // Since there may be multiple exits from the original region, make the new
243 // function return an unsigned, switch on that number. This loop iterates
244 // over all of the blocks in the extracted region, updating any terminator
245 // instructions in the to-be-extracted region that branch to blocks that are
246 // not in the region to be extracted.
247 std::map<BasicBlock*, BasicBlock*> ExitBlockMap;
249 unsigned switchVal = 0;
250 for (std::set<BasicBlock*>::const_iterator i = BlocksToExtract.begin(),
251 e = BlocksToExtract.end(); i != e; ++i) {
252 TerminatorInst *TI = (*i)->getTerminator();
253 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
254 if (!BlocksToExtract.count(TI->getSuccessor(i))) {
255 BasicBlock *OldTarget = TI->getSuccessor(i);
256 // add a new basic block which returns the appropriate value
257 BasicBlock *&NewTarget = ExitBlockMap[OldTarget];
259 // If we don't already have an exit stub for this non-extracted
260 // destination, create one now!
261 NewTarget = new BasicBlock(OldTarget->getName() + ".exitStub",
264 ConstantUInt *brVal = ConstantUInt::get(Type::UShortTy, switchVal++);
265 ReturnInst *NTRet = new ReturnInst(brVal, NewTarget);
267 // Update the switch instruction.
268 TheSwitch->addCase(brVal, OldTarget);
270 // Restore values just before we exit
271 // FIXME: Use a GetElementPtr to bunch the outputs in a struct
272 Function::aiterator OAI = OutputArgBegin;
273 for (unsigned out = 0, e = outputs.size(); out != e; ++out, ++OAI)
275 DS->dominates(cast<Instruction>(outputs[out])->getParent(),
277 new StoreInst(outputs[out], OAI, NTRet);
280 // rewrite the original branch instruction with this new target
281 TI->setSuccessor(i, NewTarget);
285 // Now that we've done the deed, make the default destination of the switch
286 // instruction be one of the exit blocks of the region.
287 if (TheSwitch->getNumSuccessors() > 1) {
288 // FIXME: this is broken w.r.t. PHI nodes, but the old code was more broken.
289 // This edge is not traversable.
290 TheSwitch->setSuccessor(0, TheSwitch->getSuccessor(1));
295 /// ExtractRegion - Removes a loop from a function, replaces it with a call to
296 /// new function. Returns pointer to the new function.
300 /// find inputs and outputs for the region
302 /// for inputs: add to function as args, map input instr* to arg#
303 /// for outputs: add allocas for scalars,
304 /// add to func as args, map output instr* to arg#
306 /// rewrite func to use argument #s instead of instr*
308 /// for each scalar output in the function: at every exit, store intermediate
309 /// computed result back into memory.
311 Function *CodeExtractor::ExtractCodeRegion(const std::vector<BasicBlock*> &code)
313 // 1) Find inputs, outputs
314 // 2) Construct new function
315 // * Add allocas for defs, pass as args by reference
316 // * Pass in uses as args
317 // 3) Move code region, add call instr to func
319 BlocksToExtract.insert(code.begin(), code.end());
321 Values inputs, outputs;
323 // Assumption: this is a single-entry code region, and the header is the first
324 // block in the region.
325 BasicBlock *header = code[0];
326 for (unsigned i = 1, e = code.size(); i != e; ++i)
327 for (pred_iterator PI = pred_begin(code[i]), E = pred_end(code[i]);
329 assert(BlocksToExtract.count(*PI) &&
330 "No blocks in this region may have entries from outside the region"
331 " except for the first block!");
333 Function *oldFunction = header->getParent();
335 // This takes place of the original loop
336 BasicBlock *codeReplacer = new BasicBlock("codeRepl", oldFunction);
338 // The new function needs a root node because other nodes can branch to the
339 // head of the loop, and the root cannot have predecessors
340 BasicBlock *newFuncRoot = new BasicBlock("newFuncRoot");
341 newFuncRoot->getInstList().push_back(new BranchInst(header));
343 // Find inputs to, outputs from the code region
345 // If one of the inputs is coming from a different basic block and it's in a
346 // phi node, we need to rewrite the phi node:
348 // * All the inputs which involve basic blocks OUTSIDE of this region go into
349 // a NEW phi node that takes care of finding which value really came in.
350 // The result of this phi is passed to the function as an argument.
352 // * All the other phi values stay.
354 // FIXME: PHI nodes' incoming blocks aren't being rewritten to accomodate for
355 // blocks moving to a new function.
356 // SOLUTION: move Phi nodes out of the loop header into the codeReplacer, pass
357 // the values as parameters to the function
358 findInputsOutputs(inputs, outputs, codeReplacer, newFuncRoot);
360 // Step 2: Construct new function based on inputs/outputs,
361 // Add allocas for all defs
362 Function *newFunction = constructFunction(inputs, outputs, code[0],
364 codeReplacer, oldFunction,
365 oldFunction->getParent());
367 emitCallAndSwitchStatement(newFunction, codeReplacer, inputs, outputs);
369 moveCodeToFunction(newFunction);
371 // Loop over all of the PHI nodes in the entry block (code[0]), and change any
372 // references to the old incoming edge to be the new incoming edge.
373 for (BasicBlock::iterator I = code[0]->begin();
374 PHINode *PN = dyn_cast<PHINode>(I); ++I)
375 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
376 if (!BlocksToExtract.count(PN->getIncomingBlock(i)))
377 PN->setIncomingBlock(i, newFuncRoot);
379 // Look at all successors of the codeReplacer block. If any of these blocks
380 // had PHI nodes in them, we need to update the "from" block to be the code
381 // replacer, not the original block in the extracted region.
382 std::vector<BasicBlock*> Succs(succ_begin(codeReplacer),
383 succ_end(codeReplacer));
384 for (unsigned i = 0, e = Succs.size(); i != e; ++i)
385 for (BasicBlock::iterator I = Succs[i]->begin();
386 PHINode *PN = dyn_cast<PHINode>(I); ++I)
387 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
388 if (BlocksToExtract.count(PN->getIncomingBlock(i)))
389 PN->setIncomingBlock(i, codeReplacer);
392 DEBUG(if (verifyFunction(*newFunction)) abort());
396 /// ExtractCodeRegion - slurp a sequence of basic blocks into a brand new
399 Function* llvm::ExtractCodeRegion(DominatorSet &DS,
400 const std::vector<BasicBlock*> &code) {
401 return CodeExtractor(&DS).ExtractCodeRegion(code);
404 /// ExtractBasicBlock - slurp a natural loop into a brand new function
406 Function* llvm::ExtractLoop(DominatorSet &DS, Loop *L) {
407 return CodeExtractor(&DS).ExtractCodeRegion(L->getBlocks());
410 /// ExtractBasicBlock - slurp a basic block into a brand new function
412 Function* llvm::ExtractBasicBlock(BasicBlock *BB) {
413 std::vector<BasicBlock*> Blocks;
414 Blocks.push_back(BB);
415 return CodeExtractor().ExtractCodeRegion(Blocks);