1 //===- FunctionInlining.cpp - Code to perform function inlining -----------===//
3 // This file implements inlining of functions.
6 // * Exports functionality to inline any function call
7 // * Inlines functions that consist of a single basic block
8 // * Is able to inline ANY function call
9 // . Has a smart heuristic for when to inline a function
12 // * This pass opens up a lot of opportunities for constant propogation. It
13 // is a good idea to to run a constant propogation pass, then a DCE pass
14 // sometime after running this pass.
16 // FIXME: This pass should transform alloca instructions in the called function
17 // into malloc/free pairs!
19 //===----------------------------------------------------------------------===//
21 #include "llvm/Transforms/IPO.h"
22 #include "llvm/Transforms/Utils/Cloning.h"
23 #include "llvm/Module.h"
24 #include "llvm/Pass.h"
25 #include "llvm/iTerminators.h"
26 #include "llvm/iPHINode.h"
27 #include "llvm/iOther.h"
28 #include "llvm/Type.h"
29 #include "Support/Statistic.h"
32 static Statistic<> NumInlined("inline", "Number of functions inlined");
35 // InlineFunction - This function forcibly inlines the called function into the
36 // basic block of the caller. This returns false if it is not possible to
37 // inline this call. The program is still in a well defined state if this
40 // Note that this only does one level of inlining. For example, if the
41 // instruction 'call B' is inlined, and 'B' calls 'C', then the call to 'C' now
42 // exists in the instruction stream. Similiarly this will inline a recursive
43 // function by one level.
45 bool InlineFunction(CallInst *CI) {
46 assert(isa<CallInst>(CI) && "InlineFunction only works on CallInst nodes");
47 assert(CI->getParent() && "Instruction not embedded in basic block!");
48 assert(CI->getParent()->getParent() && "Instruction not in function!");
50 const Function *CalledFunc = CI->getCalledFunction();
51 if (CalledFunc == 0 || // Can't inline external function or indirect call!
52 CalledFunc->isExternal()) return false;
54 //cerr << "Inlining " << CalledFunc->getName() << " into "
55 // << CurrentMeth->getName() << "\n";
57 BasicBlock *OrigBB = CI->getParent();
59 // Call splitBasicBlock - The original basic block now ends at the instruction
60 // immediately before the call. The original basic block now ends with an
61 // unconditional branch to NewBB, and NewBB starts with the call instruction.
63 BasicBlock *NewBB = OrigBB->splitBasicBlock(CI);
64 NewBB->setName("InlinedFunctionReturnNode");
66 // Remove (unlink) the CallInst from the start of the new basic block.
67 NewBB->getInstList().remove(CI);
69 // If we have a return value generated by this call, convert it into a PHI
70 // node that gets values from each of the old RET instructions in the original
74 if (!CI->use_empty()) {
75 // The PHI node should go at the front of the new basic block to merge all
76 // possible incoming values.
78 PHI = new PHINode(CalledFunc->getReturnType(), CI->getName(),
81 // Anything that used the result of the function call should now use the PHI
82 // node as their operand.
84 CI->replaceAllUsesWith(PHI);
87 // Get a pointer to the last basic block in the function, which will have the
88 // new function inlined after it.
90 Function::iterator LastBlock = &OrigBB->getParent()->back();
92 // Calculate the vector of arguments to pass into the function cloner...
93 std::vector<Value*> ArgVector;
94 for (unsigned i = 1, e = CI->getNumOperands(); i != e; ++i)
95 ArgVector.push_back(CI->getOperand(i));
97 // Since we are now done with the CallInst, we can delete it.
100 // Make a vector to capture the return instructions in the cloned function...
101 std::vector<ReturnInst*> Returns;
103 // Do all of the hard part of cloning the callee into the caller...
104 CloneFunctionInto(OrigBB->getParent(), CalledFunc, ArgVector, Returns, ".i");
106 // Loop over all of the return instructions, turning them into unconditional
107 // branches to the merge point now...
108 for (unsigned i = 0, e = Returns.size(); i != e; ++i) {
109 ReturnInst *RI = Returns[i];
110 BasicBlock *BB = RI->getParent();
112 // Add a branch to the merge point where the PHI node would live...
113 new BranchInst(NewBB, RI);
115 if (PHI) { // The PHI node should include this value!
116 assert(RI->getReturnValue() && "Ret should have value!");
117 assert(RI->getReturnValue()->getType() == PHI->getType() &&
118 "Ret value not consistent in function!");
119 PHI->addIncoming(RI->getReturnValue(), BB);
122 // Delete the return instruction now
123 BB->getInstList().erase(RI);
126 // Check to see if the PHI node only has one argument. This is a common
127 // case resulting from there only being a single return instruction in the
128 // function call. Because this is so common, eliminate the PHI node.
130 if (PHI && PHI->getNumIncomingValues() == 1) {
131 PHI->replaceAllUsesWith(PHI->getIncomingValue(0));
132 PHI->getParent()->getInstList().erase(PHI);
135 // Change the branch that used to go to NewBB to branch to the first basic
136 // block of the inlined function.
138 TerminatorInst *Br = OrigBB->getTerminator();
139 assert(Br && Br->getOpcode() == Instruction::Br &&
140 "splitBasicBlock broken!");
141 Br->setOperand(0, ++LastBlock);
145 static inline bool ShouldInlineFunction(const CallInst *CI, const Function *F) {
146 assert(CI->getParent() && CI->getParent()->getParent() &&
147 "Call not embedded into a function!");
149 // Don't inline a recursive call.
150 if (CI->getParent()->getParent() == F) return false;
152 // Don't inline something too big. This is a really crappy heuristic
153 if (F->size() > 3) return false;
155 // Don't inline into something too big. This is a **really** crappy heuristic
156 if (CI->getParent()->getParent()->size() > 10) return false;
158 // Go ahead and try just about anything else.
163 static inline bool DoFunctionInlining(BasicBlock *BB) {
164 for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
165 if (CallInst *CI = dyn_cast<CallInst>(&*I)) {
166 // Check to see if we should inline this function
167 Function *F = CI->getCalledFunction();
168 if (F && ShouldInlineFunction(CI, F)) {
169 return InlineFunction(CI);
176 // doFunctionInlining - Use a heuristic based approach to inline functions that
177 // seem to look good.
179 static bool doFunctionInlining(Function &F) {
180 bool Changed = false;
182 // Loop through now and inline instructions a basic block at a time...
183 for (Function::iterator I = F.begin(); I != F.end(); )
184 if (DoFunctionInlining(I)) {
195 struct FunctionInlining : public FunctionPass {
196 virtual bool runOnFunction(Function &F) {
197 return doFunctionInlining(F);
200 RegisterOpt<FunctionInlining> X("inline", "Function Integration/Inlining");
203 Pass *createFunctionInliningPass() { return new FunctionInlining(); }