[llvm-commits] CVS: llvm/lib/Transforms/Utils/CodeExtractor.cpp
Chris Lattner
lattner at cs.uiuc.edu
Tue May 11 23:14:01 PDT 2004
Changes in directory llvm/lib/Transforms/Utils:
CodeExtractor.cpp updated: 1.18 -> 1.19
---
Log message:
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.
---
Diffs of the changes: (+61 -22)
Index: llvm/lib/Transforms/Utils/CodeExtractor.cpp
diff -u llvm/lib/Transforms/Utils/CodeExtractor.cpp:1.18 llvm/lib/Transforms/Utils/CodeExtractor.cpp:1.19
--- llvm/lib/Transforms/Utils/CodeExtractor.cpp:1.18 Tue May 11 22:22:33 2004
+++ llvm/lib/Transforms/Utils/CodeExtractor.cpp Tue May 11 23:14:24 2004
@@ -44,9 +44,11 @@
std::set<BasicBlock*> BlocksToExtract;
DominatorSet *DS;
bool AggregateArgs;
+ unsigned NumExitBlocks;
+ const Type *RetTy;
public:
CodeExtractor(DominatorSet *ds = 0, bool AggArgs = false)
- : DS(ds), AggregateArgs(AggregateArgsOpt) {}
+ : DS(ds), AggregateArgs(AggregateArgsOpt), NumExitBlocks(~0U) {}
Function *ExtractCodeRegion(const std::vector<BasicBlock*> &code);
@@ -76,6 +78,7 @@
void CodeExtractor::findInputsOutputs(Values &inputs, Values &outputs,
BasicBlock *newHeader,
BasicBlock *newRootNode) {
+ std::set<BasicBlock*> ExitBlocks;
for (std::set<BasicBlock*>::const_iterator ci = BlocksToExtract.begin(),
ce = BlocksToExtract.end(); ci != ce; ++ci) {
BasicBlock *BB = *ci;
@@ -116,7 +119,14 @@
break;
}
} // for: insts
+
+ TerminatorInst *TI = BB->getTerminator();
+ for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
+ if (!BlocksToExtract.count(TI->getSuccessor(i)))
+ ExitBlocks.insert(TI->getSuccessor(i));
} // for: basic blocks
+
+ NumExitBlocks = ExitBlocks.size();
}
/// constructFunction - make a function based on inputs and outputs, as follows:
@@ -133,7 +143,13 @@
DEBUG(std::cerr << "outputs: " << outputs.size() << "\n");
// This function returns unsigned, outputs will go back by reference.
- Type *retTy = Type::UShortTy;
+ switch (NumExitBlocks) {
+ case 0:
+ case 1: RetTy = Type::VoidTy; break;
+ case 2: RetTy = Type::BoolTy; break;
+ default: RetTy = Type::UShortTy; break;
+ }
+
std::vector<const Type*> paramTy;
// Add the types of the input values to the function's argument list
@@ -154,7 +170,7 @@
paramTy.push_back(PointerType::get((*I)->getType()));
}
- DEBUG(std::cerr << "Function type: " << retTy << " f(");
+ DEBUG(std::cerr << "Function type: " << RetTy << " f(");
DEBUG(for (std::vector<const Type*>::iterator i = paramTy.begin(),
e = paramTy.end(); i != e; ++i) std::cerr << *i << ", ");
DEBUG(std::cerr << ")\n");
@@ -164,7 +180,7 @@
paramTy.clear();
paramTy.push_back(StructPtr);
}
- const FunctionType *funcType = FunctionType::get(retTy, paramTy, false);
+ const FunctionType *funcType = FunctionType::get(RetTy, paramTy, false);
// Create the new function
Function *newFunction = new Function(funcType,
@@ -296,7 +312,8 @@
}
// Emit the call to the function
- CallInst *call = new CallInst(newFunction, params, "targetBlock");
+ CallInst *call = new CallInst(newFunction, params,
+ NumExitBlocks > 1 ? "targetBlock": "");
codeReplacer->getInstList().push_back(call);
Function::aiterator OutputArgBegin = newFunction->abegin();
@@ -330,7 +347,9 @@
}
// Now we can emit a switch statement using the call as a value.
- SwitchInst *TheSwitch = new SwitchInst(call, codeReplacer, codeReplacer);
+ SwitchInst *TheSwitch =
+ new SwitchInst(ConstantUInt::getNullValue(Type::UShortTy),
+ codeReplacer, codeReplacer);
// Since there may be multiple exits from the original region, make the new
// function return an unsigned, switch on that number. This loop iterates
@@ -353,12 +372,25 @@
// destination, create one now!
NewTarget = new BasicBlock(OldTarget->getName() + ".exitStub",
newFunction);
+ unsigned SuccNum = switchVal++;
+
+ Value *brVal = 0;
+ switch (NumExitBlocks) {
+ case 0:
+ case 1: break; // No value needed.
+ case 2: // Conditional branch, return a bool
+ brVal = SuccNum ? ConstantBool::False : ConstantBool::True;
+ break;
+ default:
+ brVal = ConstantUInt::get(Type::UShortTy, SuccNum);
+ break;
+ }
- ConstantUInt *brVal = ConstantUInt::get(Type::UShortTy, switchVal++);
ReturnInst *NTRet = new ReturnInst(brVal, NewTarget);
// Update the switch instruction.
- TheSwitch->addCase(brVal, OldTarget);
+ TheSwitch->addCase(ConstantUInt::get(Type::UShortTy, SuccNum),
+ OldTarget);
// Restore values just before we exit
Function::aiterator OAI = OutputArgBegin;
@@ -391,20 +423,8 @@
}
// Now that we've done the deed, simplify the switch instruction.
- unsigned NumSuccs = TheSwitch->getNumSuccessors();
- if (NumSuccs > 1) {
- if (NumSuccs-1 == 1) {
- // Only a single destination, change the switch into an unconditional
- // branch.
- new BranchInst(TheSwitch->getSuccessor(1), TheSwitch);
- TheSwitch->getParent()->getInstList().erase(TheSwitch);
- } else {
- // Otherwise, make the default destination of the switch instruction be
- // one of the other successors.
- TheSwitch->setSuccessor(0, TheSwitch->getSuccessor(NumSuccs-1));
- TheSwitch->removeCase(NumSuccs-1); // Remove redundant case
- }
- } else {
+ switch (NumExitBlocks) {
+ case 0:
// There is only 1 successor (the block containing the switch itself), which
// means that previously this was the last part of the function, and hence
// this should be rewritten as a `ret'
@@ -420,6 +440,25 @@
new ReturnInst(0, TheSwitch);
TheSwitch->getParent()->getInstList().erase(TheSwitch);
+ break;
+ case 1:
+ // Only a single destination, change the switch into an unconditional
+ // branch.
+ new BranchInst(TheSwitch->getSuccessor(1), TheSwitch);
+ TheSwitch->getParent()->getInstList().erase(TheSwitch);
+ break;
+ case 2:
+ new BranchInst(TheSwitch->getSuccessor(1), TheSwitch->getSuccessor(2),
+ call, TheSwitch);
+ TheSwitch->getParent()->getInstList().erase(TheSwitch);
+ break;
+ default:
+ // Otherwise, make the default destination of the switch instruction be one
+ // of the other successors.
+ TheSwitch->setOperand(0, call);
+ TheSwitch->setSuccessor(0, TheSwitch->getSuccessor(NumExitBlocks));
+ TheSwitch->removeCase(NumExitBlocks); // Remove redundant case
+ break;
}
}
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