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Generate substantially better code when there are a limited number of exits
from the extracted region. If the return has 0 or 1 exit blocks, the new function returns void. If it has 2 exits, it returns bool, otherwise it returns a ushort as before. This allows us to use a conditional branch instruction when there are two exit blocks, as often happens during block extraction. llvm-svn: 13481
This commit is contained in:
Chris Lattner
parent
7f4cd3b0be
commit
67e58adb41
@ -44,9 +44,11 @@ namespace {
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std::set<BasicBlock*> BlocksToExtract;
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DominatorSet *DS;
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bool AggregateArgs;
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unsigned NumExitBlocks;
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const Type *RetTy;
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public:
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CodeExtractor(DominatorSet *ds = 0, bool AggArgs = false)
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: DS(ds), AggregateArgs(AggregateArgsOpt) {}
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: DS(ds), AggregateArgs(AggregateArgsOpt), NumExitBlocks(~0U) {}
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Function *ExtractCodeRegion(const std::vector<BasicBlock*> &code);
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@ -76,6 +78,7 @@ namespace {
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void CodeExtractor::findInputsOutputs(Values &inputs, Values &outputs,
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BasicBlock *newHeader,
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BasicBlock *newRootNode) {
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std::set<BasicBlock*> ExitBlocks;
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for (std::set<BasicBlock*>::const_iterator ci = BlocksToExtract.begin(),
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ce = BlocksToExtract.end(); ci != ce; ++ci) {
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BasicBlock *BB = *ci;
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@ -116,7 +119,14 @@ void CodeExtractor::findInputsOutputs(Values &inputs, Values &outputs,
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break;
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}
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} // for: insts
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TerminatorInst *TI = BB->getTerminator();
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for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
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if (!BlocksToExtract.count(TI->getSuccessor(i)))
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ExitBlocks.insert(TI->getSuccessor(i));
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} // for: basic blocks
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NumExitBlocks = ExitBlocks.size();
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}
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/// constructFunction - make a function based on inputs and outputs, as follows:
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@ -133,7 +143,13 @@ Function *CodeExtractor::constructFunction(const Values &inputs,
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DEBUG(std::cerr << "outputs: " << outputs.size() << "\n");
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// This function returns unsigned, outputs will go back by reference.
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Type *retTy = Type::UShortTy;
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switch (NumExitBlocks) {
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case 0:
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case 1: RetTy = Type::VoidTy; break;
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case 2: RetTy = Type::BoolTy; break;
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default: RetTy = Type::UShortTy; break;
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}
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std::vector<const Type*> paramTy;
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// Add the types of the input values to the function's argument list
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@ -154,7 +170,7 @@ Function *CodeExtractor::constructFunction(const Values &inputs,
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paramTy.push_back(PointerType::get((*I)->getType()));
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}
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DEBUG(std::cerr << "Function type: " << retTy << " f(");
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DEBUG(std::cerr << "Function type: " << RetTy << " f(");
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DEBUG(for (std::vector<const Type*>::iterator i = paramTy.begin(),
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e = paramTy.end(); i != e; ++i) std::cerr << *i << ", ");
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DEBUG(std::cerr << ")\n");
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@ -164,7 +180,7 @@ Function *CodeExtractor::constructFunction(const Values &inputs,
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paramTy.clear();
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paramTy.push_back(StructPtr);
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}
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const FunctionType *funcType = FunctionType::get(retTy, paramTy, false);
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const FunctionType *funcType = FunctionType::get(RetTy, paramTy, false);
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// Create the new function
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Function *newFunction = new Function(funcType,
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@ -296,7 +312,8 @@ CodeExtractor::emitCallAndSwitchStatement(Function *newFunction,
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}
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// Emit the call to the function
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CallInst *call = new CallInst(newFunction, params, "targetBlock");
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CallInst *call = new CallInst(newFunction, params,
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NumExitBlocks > 1 ? "targetBlock": "");
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codeReplacer->getInstList().push_back(call);
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Function::aiterator OutputArgBegin = newFunction->abegin();
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@ -330,7 +347,9 @@ CodeExtractor::emitCallAndSwitchStatement(Function *newFunction,
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}
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// Now we can emit a switch statement using the call as a value.
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SwitchInst *TheSwitch = new SwitchInst(call, codeReplacer, codeReplacer);
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SwitchInst *TheSwitch =
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new SwitchInst(ConstantUInt::getNullValue(Type::UShortTy),
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codeReplacer, codeReplacer);
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// Since there may be multiple exits from the original region, make the new
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// function return an unsigned, switch on that number. This loop iterates
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@ -353,12 +372,25 @@ CodeExtractor::emitCallAndSwitchStatement(Function *newFunction,
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// destination, create one now!
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NewTarget = new BasicBlock(OldTarget->getName() + ".exitStub",
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newFunction);
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unsigned SuccNum = switchVal++;
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Value *brVal = 0;
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switch (NumExitBlocks) {
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case 0:
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case 1: break; // No value needed.
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case 2: // Conditional branch, return a bool
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brVal = SuccNum ? ConstantBool::False : ConstantBool::True;
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break;
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default:
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brVal = ConstantUInt::get(Type::UShortTy, SuccNum);
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break;
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}
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ConstantUInt *brVal = ConstantUInt::get(Type::UShortTy, switchVal++);
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ReturnInst *NTRet = new ReturnInst(brVal, NewTarget);
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// Update the switch instruction.
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TheSwitch->addCase(brVal, OldTarget);
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TheSwitch->addCase(ConstantUInt::get(Type::UShortTy, SuccNum),
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OldTarget);
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// Restore values just before we exit
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Function::aiterator OAI = OutputArgBegin;
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@ -391,20 +423,8 @@ CodeExtractor::emitCallAndSwitchStatement(Function *newFunction,
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}
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// Now that we've done the deed, simplify the switch instruction.
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unsigned NumSuccs = TheSwitch->getNumSuccessors();
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if (NumSuccs > 1) {
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if (NumSuccs-1 == 1) {
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// Only a single destination, change the switch into an unconditional
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// branch.
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new BranchInst(TheSwitch->getSuccessor(1), TheSwitch);
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TheSwitch->getParent()->getInstList().erase(TheSwitch);
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} else {
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// Otherwise, make the default destination of the switch instruction be
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// one of the other successors.
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TheSwitch->setSuccessor(0, TheSwitch->getSuccessor(NumSuccs-1));
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TheSwitch->removeCase(NumSuccs-1); // Remove redundant case
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}
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} else {
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switch (NumExitBlocks) {
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case 0:
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// There is only 1 successor (the block containing the switch itself), which
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// means that previously this was the last part of the function, and hence
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// this should be rewritten as a `ret'
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@ -420,6 +440,25 @@ CodeExtractor::emitCallAndSwitchStatement(Function *newFunction,
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new ReturnInst(0, TheSwitch);
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TheSwitch->getParent()->getInstList().erase(TheSwitch);
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break;
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case 1:
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// Only a single destination, change the switch into an unconditional
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// branch.
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new BranchInst(TheSwitch->getSuccessor(1), TheSwitch);
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TheSwitch->getParent()->getInstList().erase(TheSwitch);
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break;
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case 2:
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new BranchInst(TheSwitch->getSuccessor(1), TheSwitch->getSuccessor(2),
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call, TheSwitch);
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TheSwitch->getParent()->getInstList().erase(TheSwitch);
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break;
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default:
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// Otherwise, make the default destination of the switch instruction be one
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// of the other successors.
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TheSwitch->setOperand(0, call);
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TheSwitch->setSuccessor(0, TheSwitch->getSuccessor(NumExitBlocks));
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TheSwitch->removeCase(NumExitBlocks); // Remove redundant case
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break;
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}
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}
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