1 //===- InlineFunction.cpp - Code to perform function inlining -------------===//
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 inlining of a function into a call site, resolving
11 // parameters and the return value as appropriate.
13 // FIXME: This pass should transform alloca instructions in the called function
14 // into malloc/free pairs! Or perhaps it should refuse to inline them!
16 //===----------------------------------------------------------------------===//
18 #include "llvm/Transforms/Utils/Cloning.h"
19 #include "llvm/Constant.h"
20 #include "llvm/DerivedTypes.h"
21 #include "llvm/Module.h"
22 #include "llvm/Instructions.h"
23 #include "llvm/Intrinsics.h"
24 #include "llvm/Support/CallSite.h"
25 #include "llvm/Transforms/Utils/Local.h"
27 bool InlineFunction(CallInst *CI) { return InlineFunction(CallSite(CI)); }
28 bool InlineFunction(InvokeInst *II) { return InlineFunction(CallSite(II)); }
30 // InlineFunction - This function inlines the called function into the basic
31 // block of the caller. This returns false if it is not possible to inline this
32 // call. The program is still in a well defined state if this occurs though.
34 // Note that this only does one level of inlining. For example, if the
35 // instruction 'call B' is inlined, and 'B' calls 'C', then the call to 'C' now
36 // exists in the instruction stream. Similiarly this will inline a recursive
37 // function by one level.
39 bool InlineFunction(CallSite CS) {
40 Instruction *TheCall = CS.getInstruction();
41 assert(TheCall->getParent() && TheCall->getParent()->getParent() &&
42 "Instruction not in function!");
44 const Function *CalledFunc = CS.getCalledFunction();
45 if (CalledFunc == 0 || // Can't inline external function or indirect
46 CalledFunc->isExternal() || // call, or call to a vararg function!
47 CalledFunc->getFunctionType()->isVarArg()) return false;
49 BasicBlock *OrigBB = TheCall->getParent();
50 Function *Caller = OrigBB->getParent();
52 // We want to clone the entire callee function into the whole between the
53 // "starter" and "ender" blocks. How we accomplish this depends on whether
54 // this is an invoke instruction or a call instruction.
56 BasicBlock *InvokeDest = 0; // Exception handling destination
57 std::vector<Value*> InvokeDestPHIValues; // Values for PHI nodes in InvokeDest
58 BasicBlock *AfterCallBB;
60 if (InvokeInst *II = dyn_cast<InvokeInst>(TheCall)) {
61 InvokeDest = II->getExceptionalDest();
63 // If there are PHI nodes in the exceptional destination block, we need to
64 // keep track of which values came into them from this invoke, then remove
65 // the entry for this block.
66 for (BasicBlock::iterator I = InvokeDest->begin();
67 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
68 // Save the value to use for this edge...
69 InvokeDestPHIValues.push_back(PN->getIncomingValueForBlock(OrigBB));
72 // Add an unconditional branch to make this look like the CallInst case...
73 BranchInst *NewBr = new BranchInst(II->getNormalDest(), TheCall);
75 // Split the basic block. This guarantees that no PHI nodes will have to be
76 // updated due to new incoming edges, and make the invoke case more
77 // symmetric to the call case.
78 AfterCallBB = OrigBB->splitBasicBlock(NewBr,
79 CalledFunc->getName()+".entry");
81 // Remove (unlink) the InvokeInst from the function...
82 OrigBB->getInstList().remove(TheCall);
84 } else { // It's a call
85 // If this is a call instruction, we need to split the basic block that the
88 AfterCallBB = OrigBB->splitBasicBlock(TheCall,
89 CalledFunc->getName()+".entry");
90 // Remove (unlink) the CallInst from the function...
91 AfterCallBB->getInstList().remove(TheCall);
94 // If we have a return value generated by this call, convert it into a PHI
95 // node that gets values from each of the old RET instructions in the original
99 if (!TheCall->use_empty()) {
100 // The PHI node should go at the front of the new basic block to merge all
101 // possible incoming values.
103 PHI = new PHINode(CalledFunc->getReturnType(), TheCall->getName(),
104 AfterCallBB->begin());
106 // Anything that used the result of the function call should now use the PHI
107 // node as their operand.
109 TheCall->replaceAllUsesWith(PHI);
112 // Get an iterator to the last basic block in the function, which will have
113 // the new function inlined after it.
115 Function::iterator LastBlock = &Caller->back();
117 // Calculate the vector of arguments to pass into the function cloner...
118 std::map<const Value*, Value*> ValueMap;
119 assert(std::distance(CalledFunc->abegin(), CalledFunc->aend()) ==
120 std::distance(CS.arg_begin(), CS.arg_end()) &&
121 "No varargs calls can be inlined!");
123 CallSite::arg_iterator AI = CS.arg_begin();
124 for (Function::const_aiterator I = CalledFunc->abegin(), E=CalledFunc->aend();
128 // Since we are now done with the Call/Invoke, we can delete it.
131 // Make a vector to capture the return instructions in the cloned function...
132 std::vector<ReturnInst*> Returns;
134 // Do all of the hard part of cloning the callee into the caller...
135 CloneFunctionInto(Caller, CalledFunc, ValueMap, Returns, ".i");
137 // Loop over all of the return instructions, turning them into unconditional
138 // branches to the merge point now...
139 for (unsigned i = 0, e = Returns.size(); i != e; ++i) {
140 ReturnInst *RI = Returns[i];
141 BasicBlock *BB = RI->getParent();
143 // Add a branch to the merge point where the PHI node lives if it exists.
144 new BranchInst(AfterCallBB, RI);
146 if (PHI) { // The PHI node should include this value!
147 assert(RI->getReturnValue() && "Ret should have value!");
148 assert(RI->getReturnValue()->getType() == PHI->getType() &&
149 "Ret value not consistent in function!");
150 PHI->addIncoming(RI->getReturnValue(), BB);
153 // Delete the return instruction now
154 BB->getInstList().erase(RI);
157 // Check to see if the PHI node only has one argument. This is a common
158 // case resulting from there only being a single return instruction in the
159 // function call. Because this is so common, eliminate the PHI node.
161 if (PHI && PHI->getNumIncomingValues() == 1) {
162 PHI->replaceAllUsesWith(PHI->getIncomingValue(0));
163 PHI->getParent()->getInstList().erase(PHI);
166 // Change the branch that used to go to AfterCallBB to branch to the first
167 // basic block of the inlined function.
169 TerminatorInst *Br = OrigBB->getTerminator();
170 assert(Br && Br->getOpcode() == Instruction::Br &&
171 "splitBasicBlock broken!");
172 Br->setOperand(0, ++LastBlock);
174 // If there are any alloca instructions in the block that used to be the entry
175 // block for the callee, move them to the entry block of the caller. First
176 // calculate which instruction they should be inserted before. We insert the
177 // instructions at the end of the current alloca list.
179 if (isa<AllocaInst>(LastBlock->begin())) {
180 BasicBlock::iterator InsertPoint = Caller->begin()->begin();
181 while (isa<AllocaInst>(InsertPoint)) ++InsertPoint;
183 for (BasicBlock::iterator I = LastBlock->begin(), E = LastBlock->end();
185 if (AllocaInst *AI = dyn_cast<AllocaInst>(I++))
186 if (isa<Constant>(AI->getArraySize())) {
187 LastBlock->getInstList().remove(AI);
188 Caller->front().getInstList().insert(InsertPoint, AI);
192 // If we just inlined a call due to an invoke instruction, scan the inlined
193 // function checking for function calls that should now be made into invoke
194 // instructions, and for unwind's which should be turned into branches.
196 for (Function::iterator BB = LastBlock, E = Caller->end(); BB != E; ++BB) {
197 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
198 // We only need to check for function calls: inlined invoke instructions
199 // require no special handling...
200 if (CallInst *CI = dyn_cast<CallInst>(I)) {
201 // Convert this function call into an invoke instruction...
203 // First, split the basic block...
204 BasicBlock *Split = BB->splitBasicBlock(CI, CI->getName()+".noexc");
206 // Next, create the new invoke instruction, inserting it at the end
207 // of the old basic block.
209 new InvokeInst(CI->getCalledValue(), Split, InvokeDest,
210 std::vector<Value*>(CI->op_begin()+1, CI->op_end()),
211 CI->getName(), BB->getTerminator());
213 // Make sure that anything using the call now uses the invoke!
214 CI->replaceAllUsesWith(II);
216 // Delete the unconditional branch inserted by splitBasicBlock
217 BB->getInstList().pop_back();
218 Split->getInstList().pop_front(); // Delete the original call
220 // Update any PHI nodes in the exceptional block to indicate that
221 // there is now a new entry in them.
223 for (BasicBlock::iterator I = InvokeDest->begin();
224 PHINode *PN = dyn_cast<PHINode>(I); ++I, ++i)
225 PN->addIncoming(InvokeDestPHIValues[i], BB);
227 // This basic block is now complete, start scanning the next one.
234 if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
235 // An UnwindInst requires special handling when it gets inlined into an
236 // invoke site. Once this happens, we know that the unwind would cause
237 // a control transfer to the invoke exception destination, so we can
238 // transform it into a direct branch to the exception destination.
239 BranchInst *BI = new BranchInst(InvokeDest, UI);
241 // Delete the unwind instruction!
242 UI->getParent()->getInstList().pop_back();
244 // Update any PHI nodes in the exceptional block to indicate that
245 // there is now a new entry in them.
247 for (BasicBlock::iterator I = InvokeDest->begin();
248 PHINode *PN = dyn_cast<PHINode>(I); ++I, ++i)
249 PN->addIncoming(InvokeDestPHIValues[i], BB);
253 // Now that everything is happy, we have one final detail. The PHI nodes in
254 // the exception destination block still have entries due to the original
255 // invoke instruction. Eliminate these entries (which might even delete the
257 for (BasicBlock::iterator I = InvokeDest->begin();
258 PHINode *PN = dyn_cast<PHINode>(I); ++I)
259 PN->removeIncomingValue(AfterCallBB);
261 // Now that the function is correct, make it a little bit nicer. In
262 // particular, move the basic blocks inserted from the end of the function
263 // into the space made by splitting the source basic block.
265 Caller->getBasicBlockList().splice(AfterCallBB, Caller->getBasicBlockList(),
266 LastBlock, Caller->end());
268 // We should always be able to fold the entry block of the function into the
269 // single predecessor of the block...
270 assert(cast<BranchInst>(Br)->isUnconditional() && "splitBasicBlock broken!");
271 BasicBlock *CalleeEntry = cast<BranchInst>(Br)->getSuccessor(0);
272 SimplifyCFG(CalleeEntry);
274 // Okay, continue the CFG cleanup. It's often the case that there is only a
275 // single return instruction in the callee function. If this is the case,
276 // then we have an unconditional branch from the return block to the
277 // 'AfterCallBB'. Check for this case, and eliminate the branch is possible.
278 SimplifyCFG(AfterCallBB);