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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@4770 91177308-0d34-0410-b5e6-96231b3b80d8
209 lines
7.3 KiB
C++
209 lines
7.3 KiB
C++
//===- FunctionInlining.cpp - Code to perform function inlining -----------===//
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//
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// This file implements inlining of functions.
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//
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// Specifically, this:
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// * Exports functionality to inline any function call
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// * Inlines functions that consist of a single basic block
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// * Is able to inline ANY function call
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// . Has a smart heuristic for when to inline a function
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//
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// Notice that:
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// * This pass opens up a lot of opportunities for constant propogation. It
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// is a good idea to to run a constant propogation pass, then a DCE pass
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// sometime after running this pass.
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//
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// FIXME: This pass should transform alloca instructions in the called function
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// into malloc/free pairs!
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/IPO.h"
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#include "llvm/Transforms/Utils/Cloning.h"
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#include "llvm/Module.h"
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#include "llvm/Pass.h"
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#include "llvm/iTerminators.h"
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#include "llvm/iPHINode.h"
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#include "llvm/iOther.h"
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#include "llvm/Type.h"
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#include "Support/Statistic.h"
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#include <algorithm>
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static Statistic<> NumInlined("inline", "Number of functions inlined");
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using std::cerr;
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// InlineFunction - This function forcibly inlines the called function into the
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// basic block of the caller. This returns false if it is not possible to
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// inline this call. The program is still in a well defined state if this
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// occurs though.
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//
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// Note that this only does one level of inlining. For example, if the
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// instruction 'call B' is inlined, and 'B' calls 'C', then the call to 'C' now
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// exists in the instruction stream. Similiarly this will inline a recursive
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// function by one level.
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//
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bool InlineFunction(CallInst *CI) {
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assert(isa<CallInst>(CI) && "InlineFunction only works on CallInst nodes");
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assert(CI->getParent() && "Instruction not embedded in basic block!");
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assert(CI->getParent()->getParent() && "Instruction not in function!");
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const Function *CalledFunc = CI->getCalledFunction();
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if (CalledFunc == 0 || // Can't inline external function or indirect call!
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CalledFunc->isExternal()) return false;
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//cerr << "Inlining " << CalledFunc->getName() << " into "
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// << CurrentMeth->getName() << "\n";
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BasicBlock *OrigBB = CI->getParent();
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// Call splitBasicBlock - The original basic block now ends at the instruction
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// immediately before the call. The original basic block now ends with an
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// unconditional branch to NewBB, and NewBB starts with the call instruction.
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//
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BasicBlock *NewBB = OrigBB->splitBasicBlock(CI);
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NewBB->setName("InlinedFunctionReturnNode");
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// Remove (unlink) the CallInst from the start of the new basic block.
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NewBB->getInstList().remove(CI);
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// If we have a return value generated by this call, convert it into a PHI
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// node that gets values from each of the old RET instructions in the original
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// function.
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//
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PHINode *PHI = 0;
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if (!CI->use_empty()) {
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// The PHI node should go at the front of the new basic block to merge all
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// possible incoming values.
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//
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PHI = new PHINode(CalledFunc->getReturnType(), CI->getName(),
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NewBB->begin());
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// Anything that used the result of the function call should now use the PHI
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// node as their operand.
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//
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CI->replaceAllUsesWith(PHI);
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}
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// Get a pointer to the last basic block in the function, which will have the
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// new function inlined after it.
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//
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Function::iterator LastBlock = &OrigBB->getParent()->back();
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// Calculate the vector of arguments to pass into the function cloner...
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std::map<const Value*, Value*> ValueMap;
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assert((unsigned)std::distance(CalledFunc->abegin(), CalledFunc->aend()) ==
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CI->getNumOperands()-1 && "No varargs calls can be inlined yet!");
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unsigned i = 1;
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for (Function::const_aiterator I = CalledFunc->abegin(), E=CalledFunc->aend();
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I != E; ++I, ++i)
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ValueMap[I] = CI->getOperand(i);
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// Since we are now done with the CallInst, we can delete it.
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delete CI;
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// Make a vector to capture the return instructions in the cloned function...
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std::vector<ReturnInst*> Returns;
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// Do all of the hard part of cloning the callee into the caller...
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CloneFunctionInto(OrigBB->getParent(), CalledFunc, ValueMap, Returns, ".i");
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// Loop over all of the return instructions, turning them into unconditional
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// branches to the merge point now...
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for (unsigned i = 0, e = Returns.size(); i != e; ++i) {
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ReturnInst *RI = Returns[i];
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BasicBlock *BB = RI->getParent();
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// Add a branch to the merge point where the PHI node would live...
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new BranchInst(NewBB, RI);
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if (PHI) { // The PHI node should include this value!
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assert(RI->getReturnValue() && "Ret should have value!");
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assert(RI->getReturnValue()->getType() == PHI->getType() &&
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"Ret value not consistent in function!");
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PHI->addIncoming(RI->getReturnValue(), BB);
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}
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// Delete the return instruction now
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BB->getInstList().erase(RI);
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}
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// Check to see if the PHI node only has one argument. This is a common
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// case resulting from there only being a single return instruction in the
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// function call. Because this is so common, eliminate the PHI node.
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//
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if (PHI && PHI->getNumIncomingValues() == 1) {
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PHI->replaceAllUsesWith(PHI->getIncomingValue(0));
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PHI->getParent()->getInstList().erase(PHI);
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}
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// Change the branch that used to go to NewBB to branch to the first basic
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// block of the inlined function.
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//
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TerminatorInst *Br = OrigBB->getTerminator();
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assert(Br && Br->getOpcode() == Instruction::Br &&
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"splitBasicBlock broken!");
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Br->setOperand(0, ++LastBlock);
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return true;
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}
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static inline bool ShouldInlineFunction(const CallInst *CI, const Function *F) {
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assert(CI->getParent() && CI->getParent()->getParent() &&
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"Call not embedded into a function!");
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// Don't inline a recursive call.
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if (CI->getParent()->getParent() == F) return false;
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// Don't inline something too big. This is a really crappy heuristic
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if (F->size() > 3) return false;
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// Don't inline into something too big. This is a **really** crappy heuristic
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if (CI->getParent()->getParent()->size() > 10) return false;
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// Go ahead and try just about anything else.
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return true;
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}
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static inline bool DoFunctionInlining(BasicBlock *BB) {
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for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
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if (CallInst *CI = dyn_cast<CallInst>(&*I)) {
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// Check to see if we should inline this function
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Function *F = CI->getCalledFunction();
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if (F && ShouldInlineFunction(CI, F)) {
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return InlineFunction(CI);
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}
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}
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}
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return false;
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}
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// doFunctionInlining - Use a heuristic based approach to inline functions that
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// seem to look good.
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//
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static bool doFunctionInlining(Function &F) {
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bool Changed = false;
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// Loop through now and inline instructions a basic block at a time...
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for (Function::iterator I = F.begin(); I != F.end(); )
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if (DoFunctionInlining(I)) {
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++NumInlined;
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Changed = true;
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} else {
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++I;
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}
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return Changed;
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}
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namespace {
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struct FunctionInlining : public FunctionPass {
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virtual bool runOnFunction(Function &F) {
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return doFunctionInlining(F);
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}
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};
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RegisterOpt<FunctionInlining> X("inline", "Function Integration/Inlining");
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}
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Pass *createFunctionInliningPass() { return new FunctionInlining(); }
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