llvm-project/llvm/lib/Transforms/Utils/InlineFunction.cpp

//===- InlineFunction.cpp - Code to perform function inlining -------------===//
//
// This file implements inlining of a function into a call site, resolving
// parameters and the return value as appropriate.
//
// FIXME: This pass should transform alloca instructions in the called function
//        into malloc/free pairs!  Or perhaps it should refuse to inline them!
//
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Module.h"
#include "llvm/iTerminators.h"
#include "llvm/iPHINode.h"
#include "llvm/iMemory.h"
#include "llvm/iOther.h"
#include "llvm/DerivedTypes.h"

// InlineFunction - This function inlines the called function into the basic
// block of the caller.  This returns false if it is not possible to inline this
// call.  The program is still in a well defined state if this occurs though.
//
// Note that this only does one level of inlining.  For example, if the 
// instruction 'call B' is inlined, and 'B' calls 'C', then the call to 'C' now 
// exists in the instruction stream.  Similiarly this will inline a recursive
// function by one level.
//
bool InlineFunction(CallInst *CI) {
  assert(isa<CallInst>(CI) && "InlineFunction only works on CallInst nodes");
  assert(CI->getParent() && "Instruction not embedded in basic block!");
  assert(CI->getParent()->getParent() && "Instruction not in function!");

  const Function *CalledFunc = CI->getCalledFunction();
  if (CalledFunc == 0 ||          // Can't inline external function or indirect
      CalledFunc->isExternal() || // call, or call to a vararg function!
      CalledFunc->getFunctionType()->isVarArg()) return false;

  BasicBlock *OrigBB = CI->getParent();
  Function *Caller = OrigBB->getParent();

  // Call splitBasicBlock - The original basic block now ends at the instruction
  // immediately before the call.  The original basic block now ends with an
  // unconditional branch to NewBB, and NewBB starts with the call instruction.
  //
  BasicBlock *NewBB = OrigBB->splitBasicBlock(CI);
  NewBB->setName(OrigBB->getName()+".split");

  // Remove (unlink) the CallInst from the start of the new basic block.  
  NewBB->getInstList().remove(CI);

  // If we have a return value generated by this call, convert it into a PHI 
  // node that gets values from each of the old RET instructions in the original
  // function.
  //
  PHINode *PHI = 0;
  if (!CI->use_empty()) {
    // The PHI node should go at the front of the new basic block to merge all 
    // possible incoming values.
    //
    PHI = new PHINode(CalledFunc->getReturnType(), CI->getName(),
                      NewBB->begin());

    // Anything that used the result of the function call should now use the PHI
    // node as their operand.
    //
    CI->replaceAllUsesWith(PHI);
  }

  // Get an iterator to the last basic block in the function, which will have
  // the new function inlined after it.
  //
  Function::iterator LastBlock = &Caller->back();

  // Calculate the vector of arguments to pass into the function cloner...
  std::map<const Value*, Value*> ValueMap;
  assert((unsigned)std::distance(CalledFunc->abegin(), CalledFunc->aend()) == 
         CI->getNumOperands()-1 && "No varargs calls can be inlined yet!");

  unsigned i = 1;
  for (Function::const_aiterator I = CalledFunc->abegin(), E=CalledFunc->aend();
       I != E; ++I, ++i)
    ValueMap[I] = CI->getOperand(i);

  // Since we are now done with the CallInst, we can delete it.
  delete CI;

  // Make a vector to capture the return instructions in the cloned function...
  std::vector<ReturnInst*> Returns;

  // Populate the value map with all of the globals in the program.
  Module &M = *Caller->getParent();
  for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
    ValueMap[I] = I;
  for (Module::giterator I = M.gbegin(), E = M.gend(); I != E; ++I)
    ValueMap[I] = I;

  // Do all of the hard part of cloning the callee into the caller...
  CloneFunctionInto(Caller, CalledFunc, ValueMap, Returns, ".i");

  // Loop over all of the return instructions, turning them into unconditional
  // branches to the merge point now...
  for (unsigned i = 0, e = Returns.size(); i != e; ++i) {
    ReturnInst *RI = Returns[i];
    BasicBlock *BB = RI->getParent();

    // Add a branch to the merge point where the PHI node would live...
    new BranchInst(NewBB, RI);

    if (PHI) {   // The PHI node should include this value!
      assert(RI->getReturnValue() && "Ret should have value!");
      assert(RI->getReturnValue()->getType() == PHI->getType() && 
             "Ret value not consistent in function!");
      PHI->addIncoming(RI->getReturnValue(), BB);
    }

    // Delete the return instruction now
    BB->getInstList().erase(RI);
  }

  // Check to see if the PHI node only has one argument.  This is a common
  // case resulting from there only being a single return instruction in the
  // function call.  Because this is so common, eliminate the PHI node.
  //
  if (PHI && PHI->getNumIncomingValues() == 1) {
    PHI->replaceAllUsesWith(PHI->getIncomingValue(0));
    PHI->getParent()->getInstList().erase(PHI);
  }

  // Change the branch that used to go to NewBB to branch to the first basic 
  // block of the inlined function.
  //
  TerminatorInst *Br = OrigBB->getTerminator();
  assert(Br && Br->getOpcode() == Instruction::Br && 
	 "splitBasicBlock broken!");
  Br->setOperand(0, ++LastBlock);

  // If there are any alloca instructions in the block that used to be the entry
  // block for the callee, move them to the entry block of the caller.  First
  // calculate which instruction they should be inserted before.  We insert the
  // instructions at the end of the current alloca list.
  //
  BasicBlock::iterator InsertPoint = Caller->begin()->begin();
  while (isa<AllocaInst>(InsertPoint)) ++InsertPoint;

  for (BasicBlock::iterator I = LastBlock->begin(), E = LastBlock->end();
       I != E; )
    if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) {
      ++I;  // Move to the next instruction
      LastBlock->getInstList().remove(AI);
      Caller->front().getInstList().insert(InsertPoint, AI);
      
    } else {
      ++I;
    }

  // Now that the function is correct, make it a little bit nicer.  In
  // particular, move the basic blocks inserted from the end of the function
  // into the space made by splitting the source basic block.
  //
  Caller->getBasicBlockList().splice(NewBB, Caller->getBasicBlockList(), 
                                     LastBlock, Caller->end());

  return true;
}