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//===- FunctionInlining.cpp - Code to perform function inlining -----------===//
//
// This file implements inlining of functions.
//
// Specifically, this:
// * Exports functionality to inline any function call
// * Inlines functions that consist of a single basic block
// * Is able to inline ANY function call
// . Has a smart heuristic for when to inline a function
//
// Notice that:
// * This pass opens up a lot of opportunities for constant propogation. It
// is a good idea to to run a constant propogation pass, then a DCE pass
// sometime after running this pass.
//
// FIXME: This pass should transform alloca instructions in the called function
// into malloc/free pairs!
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/IPO.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/iTerminators.h"
#include "llvm/iPHINode.h"
#include "llvm/iOther.h"
#include "llvm/Type.h"
#include "Support/Statistic.h"
#include <algorithm>
static Statistic<> NumInlined("inline", "Number of functions inlined");
using std::cerr;
// InlineFunction - This function forcibly 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 call!
CalledFunc->isExternal()) return false;
//cerr << "Inlining " << CalledFunc->getName() << " into "
// << CurrentMeth->getName() << "\n";
BasicBlock *OrigBB = CI->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("InlinedFunctionReturnNode");
// 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 a pointer to the last basic block in the function, which will have the
// new function inlined after it.
//
Function::iterator LastBlock = &OrigBB->getParent()->back();
// Calculate the vector of arguments to pass into the function cloner...
std::vector<Value*> ArgVector;
for (unsigned i = 1, e = CI->getNumOperands(); i != e; ++i)
ArgVector.push_back(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;
// Do all of the hard part of cloning the callee into the caller...
CloneFunctionInto(OrigBB->getParent(), CalledFunc, ArgVector, 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);
return true;
}
static inline bool ShouldInlineFunction(const CallInst *CI, const Function *F) {
assert(CI->getParent() && CI->getParent()->getParent() &&
"Call not embedded into a function!");
// Don't inline a recursive call.
if (CI->getParent()->getParent() == F) return false;
// Don't inline something too big. This is a really crappy heuristic
if (F->size() > 3) return false;
// Don't inline into something too big. This is a **really** crappy heuristic
if (CI->getParent()->getParent()->size() > 10) return false;
// Go ahead and try just about anything else.
return true;
}
static inline bool DoFunctionInlining(BasicBlock *BB) {
for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
if (CallInst *CI = dyn_cast<CallInst>(&*I)) {
// Check to see if we should inline this function
Function *F = CI->getCalledFunction();
if (F && ShouldInlineFunction(CI, F)) {
return InlineFunction(CI);
}
}
}
return false;
}
// doFunctionInlining - Use a heuristic based approach to inline functions that
// seem to look good.
//
static bool doFunctionInlining(Function &F) {
bool Changed = false;
// Loop through now and inline instructions a basic block at a time...
for (Function::iterator I = F.begin(); I != F.end(); )
if (DoFunctionInlining(I)) {
++NumInlined;
Changed = true;
} else {
++I;
}
return Changed;
}
namespace {
struct FunctionInlining : public FunctionPass {
virtual bool runOnFunction(Function &F) {
return doFunctionInlining(F);
}
};
RegisterOpt<FunctionInlining> X("inline", "Function Integration/Inlining");
}
Pass *createFunctionInliningPass() { return new FunctionInlining(); }
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