A generic code extractor: given a list of BasicBlocks, it will rip them out into

a new function, taking care of inputs and outputs.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@11935 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 573 insertions, 0 deletions

diff --git a/lib/Transforms/Utils/CodeExtractor.cpp b/lib/Transforms/Utils/CodeExtractor.cpp
new file mode 100644
index 0000000000..38f3c8a4c6
--- /dev/null
+++ b/lib/Transforms/Utils/CodeExtractor.cpp
@@ -0,0 +1,573 @@
+//===- CodeExtractor.cpp - Pull code region into a new function -----------===//
+// 
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+// 
+//===----------------------------------------------------------------------===//
+//
+// This file implements the interface to tear out a code region, such as an
+// individual loop or a parallel section, into a new function, replacing it with
+// a call to the new function.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/BasicBlock.h"
+#include "llvm/Constants.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/Instructions.h"
+#include "llvm/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/FunctionUtils.h"
+#include "Support/Debug.h"
+#include "Support/StringExtras.h"
+#include <algorithm>
+#include <map>
+#include <vector>
+using namespace llvm;
+
+namespace {
+
+  inline bool contains(const std::vector<BasicBlock*> &V, const BasicBlock *BB){
+    return std::find(V.begin(), V.end(), BB) != V.end();
+  }
+
+  /// getFunctionArg - Return a pointer to F's ARGNOth argument.
+  ///
+  Argument *getFunctionArg(Function *F, unsigned argno) {
+    Function::aiterator ai = F->abegin();
+    while (argno) { ++ai; --argno; }
+    return &*ai;
+  }
+
+  struct CodeExtractor {
+    typedef std::vector<Value*> Values;
+    typedef std::vector<std::pair<unsigned, unsigned> > PhiValChangesTy;
+    typedef std::map<PHINode*, PhiValChangesTy> PhiVal2ArgTy;
+    PhiVal2ArgTy PhiVal2Arg;
+
+  public:
+    Function *ExtractCodeRegion(const std::vector<BasicBlock*> &code);
+
+  private:
+    void findInputsOutputs(const std::vector<BasicBlock*> &code,
+                           Values &inputs,
+                           Values &outputs,
+                           BasicBlock *newHeader,
+                           BasicBlock *newRootNode);
+
+    void processPhiNodeInputs(PHINode *Phi,
+                              const std::vector<BasicBlock*> &code,
+                              Values &inputs,
+                              BasicBlock *newHeader,
+                              BasicBlock *newRootNode);
+
+    void rewritePhiNodes(Function *F, BasicBlock *newFuncRoot);
+
+    Function *constructFunction(const Values &inputs,
+                                const Values &outputs,
+                                BasicBlock *newRootNode, BasicBlock *newHeader,
+                                const std::vector<BasicBlock*> &code,
+                                Function *oldFunction, Module *M);
+
+    void moveCodeToFunction(const std::vector<BasicBlock*> &code,
+                            Function *newFunction);
+
+    void emitCallAndSwitchStatement(Function *newFunction,
+                                    BasicBlock *newHeader,
+                                    const std::vector<BasicBlock*> &code,
+                                    Values &inputs,
+                                    Values &outputs);
+
+  };
+}
+
+void CodeExtractor::processPhiNodeInputs(PHINode *Phi,
+                                         const std::vector<BasicBlock*> &code,
+                                         Values &inputs,
+                                         BasicBlock *codeReplacer,
+                                         BasicBlock *newFuncRoot)
+{
+  // Separate incoming values and BasicBlocks as internal/external. We ignore
+  // the case where both the value and BasicBlock are internal, because we don't
+  // need to do a thing.
+  std::vector<unsigned> EValEBB;
+  std::vector<unsigned> EValIBB;
+  std::vector<unsigned> IValEBB;
+
+  for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
+    Value *phiVal = Phi->getIncomingValue(i);
+    if (Instruction *Inst = dyn_cast<Instruction>(phiVal)) {
+      if (contains(code, Inst->getParent())) {
+        if (!contains(code, Phi->getIncomingBlock(i)))
+          IValEBB.push_back(i);
+      } else {
+        if (contains(code, Phi->getIncomingBlock(i)))
+          EValIBB.push_back(i);
+        else
+          EValEBB.push_back(i);
+      }
+    } else if (Constant *Const = dyn_cast<Constant>(phiVal)) {
+      // Constants are internal, but considered `external' if they are coming
+      // from an external block.
+      if (!contains(code, Phi->getIncomingBlock(i)))
+        EValEBB.push_back(i);
+    } else if (Argument *Arg = dyn_cast<Argument>(phiVal)) {
+      // arguments are external
+      if (contains(code, Phi->getIncomingBlock(i)))
+        EValIBB.push_back(i);
+      else
+        EValEBB.push_back(i);
+    } else {
+      phiVal->dump();
+      assert(0 && "Unhandled input in a Phi node");
+    }
+  }
+
+  // Both value and block are external. Need to group all of
+  // these, have an external phi, pass the result as an
+  // argument, and have THIS phi use that result.
+  if (EValEBB.size() > 0) {
+    if (EValEBB.size() == 1) {
+      // Now if it's coming from the newFuncRoot, it's that funky input
+      unsigned phiIdx = EValEBB[0];
+      if (!dyn_cast<Constant>(Phi->getIncomingValue(phiIdx)))
+      {
+        PhiVal2Arg[Phi].push_back(std::make_pair(phiIdx, inputs.size()));
+        // We can just pass this value in as argument
+        inputs.push_back(Phi->getIncomingValue(phiIdx));
+      }
+      Phi->setIncomingBlock(phiIdx, newFuncRoot);
+    } else {
+      PHINode *externalPhi = new PHINode(Phi->getType(), "extPhi");
+      codeReplacer->getInstList().insert(codeReplacer->begin(), externalPhi);
+      for (std::vector<unsigned>::iterator i = EValEBB.begin(),
+             e = EValEBB.end(); i != e; ++i)
+      {
+        externalPhi->addIncoming(Phi->getIncomingValue(*i),
+                                 Phi->getIncomingBlock(*i));
+
+        // We make these values invalid instead of deleting them because that
+        // would shift the indices of other values... The fixPhiNodes should
+        // clean these phi nodes up later.
+        Phi->setIncomingValue(*i, 0);
+        Phi->setIncomingBlock(*i, 0);
+      }
+      PhiVal2Arg[Phi].push_back(std::make_pair(Phi->getNumIncomingValues(),
+                                               inputs.size()));
+      // We can just pass this value in as argument
+      inputs.push_back(externalPhi);
+    }
+  }
+
+  // When the value is external, but block internal...
+  // just pass it in as argument, no change to phi node
+  for (std::vector<unsigned>::iterator i = EValIBB.begin(),
+         e = EValIBB.end(); i != e; ++i)
+  {
+    // rewrite the phi input node to be an argument
+    PhiVal2Arg[Phi].push_back(std::make_pair(*i, inputs.size()));
+    inputs.push_back(Phi->getIncomingValue(*i));
+  }
+
+  // Value internal, block external
+  // this can happen if we are extracting a part of a loop
+  for (std::vector<unsigned>::iterator i = IValEBB.begin(),
+         e = IValEBB.end(); i != e; ++i)
+  {
+    assert(0 && "Cannot (YET) handle internal values via external blocks");
+  }
+}
+
+
+void CodeExtractor::findInputsOutputs(const std::vector<BasicBlock*> &code,
+                                      Values &inputs,
+                                      Values &outputs,
+                                      BasicBlock *newHeader,
+                                      BasicBlock *newRootNode)
+{
+  for (std::vector<BasicBlock*>::const_iterator ci = code.begin(), 
+       ce = code.end(); ci != ce; ++ci) {
+    BasicBlock *BB = *ci;
+    for (BasicBlock::iterator BBi = BB->begin(), BBe = BB->end();
+         BBi != BBe; ++BBi) {
+      // If a use is defined outside the region, it's an input.
+      // If a def is used outside the region, it's an output.
+      if (Instruction *I = dyn_cast<Instruction>(&*BBi)) {
+        // If it's a phi node
+        if (PHINode *Phi = dyn_cast<PHINode>(I)) {
+          processPhiNodeInputs(Phi, code, inputs, newHeader, newRootNode);
+        } else {
+          // All other instructions go through the generic input finder
+          // Loop over the operands of each instruction (inputs)
+          for (User::op_iterator op = I->op_begin(), opE = I->op_end();
+               op != opE; ++op) {
+            if (Instruction *opI = dyn_cast<Instruction>(op->get())) {
+              // Check if definition of this operand is within the loop
+              if (!contains(code, opI->getParent())) {
+                // add this operand to the inputs
+                inputs.push_back(opI);
+              }
+            }
+          }
+        }
+
+        // Consider uses of this instruction (outputs)
+        for (Value::use_iterator use = I->use_begin(), useE = I->use_end();
+             use != useE; ++use) {
+          if (Instruction* inst = dyn_cast<Instruction>(*use)) {
+            if (!contains(code, inst->getParent())) {
+              // add this op to the outputs
+              outputs.push_back(I);
+            }
+          }
+        }
+      } /* if */
+    } /* for: insts */
+  } /* for: basic blocks */
+}
+
+void CodeExtractor::rewritePhiNodes(Function *F,
+                                    BasicBlock *newFuncRoot) {
+  // Write any changes that were saved before: use function arguments as inputs
+  for (PhiVal2ArgTy::iterator i = PhiVal2Arg.begin(), e = PhiVal2Arg.end();
+       i != e; ++i)
+  {
+    PHINode *phi = (*i).first;
+    PhiValChangesTy &values = (*i).second;
+    for (unsigned cIdx = 0, ce = values.size(); cIdx != ce; ++cIdx)
+    {
+      unsigned phiValueIdx = values[cIdx].first, argNum = values[cIdx].second;
+      if (phiValueIdx < phi->getNumIncomingValues())
+        phi->setIncomingValue(phiValueIdx, getFunctionArg(F, argNum));
+      else
+        phi->addIncoming(getFunctionArg(F, argNum), newFuncRoot);
+    }
+  }
+
+  // Delete any invalid Phi node inputs that were marked as NULL previously
+  for (PhiVal2ArgTy::iterator i = PhiVal2Arg.begin(), e = PhiVal2Arg.end();
+       i != e; ++i)
+  {
+    PHINode *phi = (*i).first;
+    for (unsigned idx = 0, end = phi->getNumIncomingValues(); idx != end; ++idx)
+    {
+      if (phi->getIncomingValue(idx) == 0 && phi->getIncomingBlock(idx) == 0) {
+        phi->removeIncomingValue(idx);
+        --idx;
+        --end;
+      }
+    }
+  }
+
+  // We are done with the saved values
+  PhiVal2Arg.clear();
+}
+
+
+/// constructFunction - make a function based on inputs and outputs, as follows:
+/// f(in0, ..., inN, out0, ..., outN)
+///
+Function *CodeExtractor::constructFunction(const Values &inputs,
+                                           const Values &outputs,
+                                           BasicBlock *newRootNode,
+                                           BasicBlock *newHeader,
+                                           const std::vector<BasicBlock*> &code,
+                                           Function *oldFunction, Module *M) {
+  DEBUG(std::cerr << "inputs: " << inputs.size() << "\n");
+  DEBUG(std::cerr << "outputs: " << outputs.size() << "\n");
+  BasicBlock *header = code[0];
+
+  // This function returns unsigned, outputs will go back by reference.
+  Type *retTy = Type::UShortTy;
+  std::vector<const Type*> paramTy;
+
+  // Add the types of the input values to the function's argument list
+  for (Values::const_iterator i = inputs.begin(),
+         e = inputs.end(); i != e; ++i) {
+    const Value *value = *i;
+    DEBUG(std::cerr << "value used in func: " << value << "\n");
+    paramTy.push_back(value->getType());
+  }
+
+  // Add the types of the output values to the function's argument list, but
+  // make them pointer types for scalars
+  for (Values::const_iterator i = outputs.begin(),
+         e = outputs.end(); i != e; ++i) {
+    const Value *value = *i;
+    DEBUG(std::cerr << "instr used in func: " << value << "\n");
+    const Type *valueType = value->getType();
+    // Convert scalar types into a pointer of that type
+    if (valueType->isPrimitiveType()) {
+      valueType = PointerType::get(valueType);
+    }
+    paramTy.push_back(valueType);
+  }
+
+  DEBUG(std::cerr << "Function type: " << retTy << " f(");
+  for (std::vector<const Type*>::iterator i = paramTy.begin(),
+         e = paramTy.end(); i != e; ++i)
+    DEBUG(std::cerr << (*i) << ", ");
+  DEBUG(std::cerr << ")\n");
+
+  const FunctionType *funcType = FunctionType::get(retTy, paramTy, false);
+
+  // Create the new function
+  Function *newFunction = new Function(funcType,
+                                       GlobalValue::InternalLinkage,
+                                       oldFunction->getName() + "_code", M);
+  newFunction->getBasicBlockList().push_back(newRootNode);
+
+  for (unsigned i = 0, e = inputs.size(); i != e; ++i) {
+    std::vector<User*> Users(inputs[i]->use_begin(), inputs[i]->use_end());
+    for (std::vector<User*>::iterator use = Users.begin(), useE = Users.end();
+         use != useE; ++use) {
+      if (Instruction* inst = dyn_cast<Instruction>(*use)) {
+        if (contains(code, inst->getParent())) {
+          inst->replaceUsesOfWith(inputs[i], getFunctionArg(newFunction, i));
+        }
+      }
+    }
+  }
+
+  // Rewrite branches to basic blocks outside of the loop to new dummy blocks
+  // within the new function. This must be done before we lose track of which
+  // blocks were originally in the code region.
+  std::vector<User*> Users(header->use_begin(), header->use_end());
+  for (std::vector<User*>::iterator i = Users.begin(), e = Users.end();
+       i != e; ++i) {
+    if (BranchInst *inst = dyn_cast<BranchInst>(*i)) {
+      BasicBlock *BB = inst->getParent();
+      if (!contains(code, BB) && BB->getParent() == oldFunction) {
+        // The BasicBlock which contains the branch is not in the region
+        // modify the branch target to a new block
+        inst->replaceUsesOfWith(header, newHeader);
+      }
+    }
+  }
+
+  return newFunction;
+}
+
+void CodeExtractor::moveCodeToFunction(const std::vector<BasicBlock*> &code,
+                                       Function *newFunction)
+{
+  for (std::vector<BasicBlock*>::const_iterator i = code.begin(), e =code.end();
+       i != e; ++i) {
+    BasicBlock *BB = *i;
+    Function *oldFunc = BB->getParent();
+    Function::BasicBlockListType &oldBlocks = oldFunc->getBasicBlockList();
+
+    // Delete the basic block from the old function, and the list of blocks
+    oldBlocks.remove(BB);
+
+    // Insert this basic block into the new function
+    Function::BasicBlockListType &newBlocks = newFunction->getBasicBlockList();
+    newBlocks.push_back(BB);
+  }
+}
+
+void
+CodeExtractor::emitCallAndSwitchStatement(Function *newFunction,
+                                          BasicBlock *codeReplacer,
+                                          const std::vector<BasicBlock*> &code,
+                                          Values &inputs,
+                                          Values &outputs)
+{
+  // Emit a call to the new function, passing allocated memory for outputs and
+  // just plain inputs for non-scalars
+  std::vector<Value*> params;
+  BasicBlock *codeReplacerTail = new BasicBlock("codeReplTail",
+                                                codeReplacer->getParent());
+  for (Values::const_iterator i = inputs.begin(),
+         e = inputs.end(); i != e; ++i)
+    params.push_back(*i);
+  for (Values::const_iterator i = outputs.begin(), 
+         e = outputs.end(); i != e; ++i) {
+    // Create allocas for scalar outputs
+    if ((*i)->getType()->isPrimitiveType()) {
+      Constant *one = ConstantUInt::get(Type::UIntTy, 1);
+      AllocaInst *alloca = new AllocaInst((*i)->getType(), one);
+      codeReplacer->getInstList().push_back(alloca);
+      params.push_back(alloca);
+
+      LoadInst *load = new LoadInst(alloca, "alloca");
+      codeReplacerTail->getInstList().push_back(load);
+      std::vector<User*> Users((*i)->use_begin(), (*i)->use_end());
+      for (std::vector<User*>::iterator use = Users.begin(), useE =Users.end();
+           use != useE; ++use) {
+        if (Instruction* inst = dyn_cast<Instruction>(*use)) {
+          if (!contains(code, inst->getParent())) {
+            inst->replaceUsesOfWith(*i, load);
+          }
+        }
+      }
+    } else {
+      params.push_back(*i);
+    }
+  }
+  CallInst *call = new CallInst(newFunction, params, "targetBlock");
+  codeReplacer->getInstList().push_back(call);
+  codeReplacer->getInstList().push_back(new BranchInst(codeReplacerTail));
+
+  // Now we can emit a switch statement using the call as a value.
+  // FIXME: perhaps instead of default being self BB, it should be a second
+  // dummy block which asserts that the value is not within the range...?
+  //BasicBlock *defaultBlock = new BasicBlock("defaultBlock", oldF);
+  //insert abort() ?
+  //defaultBlock->getInstList().push_back(new BranchInst(codeReplacer));
+
+  SwitchInst *switchInst = new SwitchInst(call, codeReplacerTail,
+                                          codeReplacerTail);
+
+  // Since there may be multiple exits from the original region, make the new
+  // function return an unsigned, switch on that number
+  unsigned switchVal = 0;
+  for (std::vector<BasicBlock*>::const_iterator i =code.begin(), e = code.end();
+       i != e; ++i) {
+    BasicBlock *BB = *i;
+
+    // rewrite the terminator of the original BasicBlock
+    Instruction *term = BB->getTerminator();
+    if (BranchInst *brInst = dyn_cast<BranchInst>(term)) {
+
+      // Restore values just before we exit
+      // FIXME: Use a GetElementPtr to bunch the outputs in a struct
+      for (unsigned outIdx = 0, outE = outputs.size(); outIdx != outE; ++outIdx)
+      {
+        new StoreInst(outputs[outIdx],
+                      getFunctionArg(newFunction, outIdx),
+                      brInst);
+      }
+
+      // Rewrite branches into exists which return a value based on which
+      // exit we take from this function
+      if (brInst->isUnconditional()) {
+        if (!contains(code, brInst->getSuccessor(0))) {
+          ConstantUInt *brVal = ConstantUInt::get(Type::UShortTy, switchVal);
+          ReturnInst *newRet = new ReturnInst(brVal);
+          // add a new target to the switch
+          switchInst->addCase(brVal, brInst->getSuccessor(0));
+          ++switchVal;
+          // rewrite the branch with a return
+          BasicBlock::iterator ii(brInst);
+          ReplaceInstWithInst(BB->getInstList(), ii, newRet);
+          delete brInst;
+        }
+      } else {
+        // Replace the conditional branch to branch
+        // to two new blocks, each of which returns a different code.
+        for (unsigned idx = 0; idx < 2; ++idx) {
+          BasicBlock *oldTarget = brInst->getSuccessor(idx);
+          if (!contains(code, oldTarget)) {
+            // add a new basic block which returns the appropriate value
+            BasicBlock *newTarget = new BasicBlock("newTarget", newFunction);
+            ConstantUInt *brVal = ConstantUInt::get(Type::UShortTy, switchVal);
+            ReturnInst *newRet = new ReturnInst(brVal);
+            newTarget->getInstList().push_back(newRet);
+            // rewrite the original branch instruction with this new target
+            brInst->setSuccessor(idx, newTarget);
+            // the switch statement knows what to do with this value
+            switchInst->addCase(brVal, oldTarget);
+            ++switchVal;
+          }
+        }
+      }
+    } else if (ReturnInst *retTerm = dyn_cast<ReturnInst>(term)) {
+      assert(0 && "Cannot handle return instructions just yet.");
+      // FIXME: what if the terminator is a return!??!
+      // Need to rewrite: add new basic block, move the return there
+      // treat the original as an unconditional branch to that basicblock
+    } else if (SwitchInst *swTerm = dyn_cast<SwitchInst>(term)) {
+      assert(0 && "Cannot handle switch instructions just yet.");
+    } else if (InvokeInst *invInst = dyn_cast<InvokeInst>(term)) {
+      assert(0 && "Cannot handle invoke instructions just yet.");
+    } else {
+      assert(0 && "Unrecognized terminator, or badly-formed BasicBlock.");
+    }
+  }
+}
+
+
+/// ExtractRegion - Removes a loop from a function, replaces it with a call to
+/// new function. Returns pointer to the new function.
+///
+/// algorithm:
+///
+/// find inputs and outputs for the region
+///
+/// for inputs: add to function as args, map input instr* to arg# 
+/// for outputs: add allocas for scalars, 
+///             add to func as args, map output instr* to arg#
+///
+/// rewrite func to use argument #s instead of instr*
+///
+/// for each scalar output in the function: at every exit, store intermediate 
+/// computed result back into memory.
+///
+Function *CodeExtractor::ExtractCodeRegion(const std::vector<BasicBlock*> &code)
+{
+  // 1) Find inputs, outputs
+  // 2) Construct new function
+  //  * Add allocas for defs, pass as args by reference
+  //  * Pass in uses as args
+  // 3) Move code region, add call instr to func
+  // 
+
+  Values inputs, outputs;
+
+  // Assumption: this is a single-entry code region, and the header is the first
+  // block in the region. FIXME: is this true for a list of blocks from a
+  // natural function?
+  BasicBlock *header = code[0];
+  Function *oldFunction = header->getParent();
+  Module *module = oldFunction->getParent();
+
+  // This takes place of the original loop
+  BasicBlock *codeReplacer = new BasicBlock("codeRepl", oldFunction);
+
+  // The new function needs a root node because other nodes can branch to the
+  // head of the loop, and the root cannot have predecessors
+  BasicBlock *newFuncRoot = new BasicBlock("newFuncRoot");
+  newFuncRoot->getInstList().push_back(new BranchInst(header));
+
+  // Find inputs to, outputs from the code region
+  //
+  // If one of the inputs is coming from a different basic block and it's in a
+  // phi node, we need to rewrite the phi node:
+  //
+  // * All the inputs which involve basic blocks OUTSIDE of this region go into
+  //   a NEW phi node that takes care of finding which value really came in.
+  //   The result of this phi is passed to the function as an argument. 
+  //
+  // * All the other phi values stay.
+  //
+  // FIXME: PHI nodes' incoming blocks aren't being rewritten to accomodate for
+  // blocks moving to a new function.
+  // SOLUTION: move Phi nodes out of the loop header into the codeReplacer, pass
+  // the values as parameters to the function
+  findInputsOutputs(code, inputs, outputs, codeReplacer, newFuncRoot);
+
+  // Step 2: Construct new function based on inputs/outputs,
+  // Add allocas for all defs
+  Function *newFunction = constructFunction(inputs, outputs, newFuncRoot, 
+                                            codeReplacer, code, 
+                                            oldFunction, module);
+
+  rewritePhiNodes(newFunction, newFuncRoot);
+
+  emitCallAndSwitchStatement(newFunction, codeReplacer, code, inputs, outputs);
+
+  moveCodeToFunction(code, newFunction);
+
+  return newFunction;
+}
+
+Function* llvm::ExtractLoop(Loop *L) {
+  CodeExtractor CE;
+  return CE.ExtractCodeRegion(L->getBlocks());
+}
+