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Finish up the initial jump table implementation by allowing jump tables to 

not be 100% dense.  Increase the minimum threshold for the number of cases
in a switch statement from 4 to 6 in order to create a jump table.

llvm-svn: 28079
This commit is contained in:
Nate Begeman 2006-05-03 03:48:02 +00:00
parent 7bd487fe41
commit df4883971e
1 changed files with 34 additions and 26 deletions
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60
llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
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@ -836,11 +836,6 @@ void SelectionDAGLowering::visitJumpTable(SelectionDAGISel::JumpTable &JT) {
SDOperand ADD = DAG.getNode(ISD::ADD, PTy, IDX, DAG.getJumpTable(JT.JTI,PTy));
SDOperand LD = DAG.getLoad(PTy, Copy.getValue(1), ADD, DAG.getSrcValue(0));
DAG.setRoot(DAG.getNode(ISD::BRIND, MVT::Other, LD.getValue(1), LD));
// Update successor info
for (std::set<MachineBasicBlock*>::iterator ii = JT.SuccMBBs.begin(),
ee = JT.SuccMBBs.end(); ii != ee; ++ii)
JT.MBB->addSuccessor(*ii);
}
void SelectionDAGLowering::visitSwitch(SwitchInst &I) {
@ -885,22 +880,18 @@ void SelectionDAGLowering::visitSwitch(SwitchInst &I) {
const BasicBlock *LLVMBB = CurMBB->getBasicBlock();
Reloc::Model Relocs = TLI.getTargetMachine().getRelocationModel();
// If the switch has more than 3 blocks, and is 100% dense, then emit a jump
// table rather than lowering the switch to a binary tree of conditional
// If the switch has more than 5 blocks, and at least 75% dense, then emit a
// jump table rather than lowering the switch to a binary tree of conditional
// branches.
// FIXME: Make this work with 64 bit targets someday, possibly by always
// doing differences there so that entries stay 32 bits.
// FIXME: Make this work with PIC code
if (TLI.isOperationLegal(ISD::BRIND, TLI.getPointerTy()) &&
TLI.getPointerTy() == MVT::i32 &&
(Relocs == Reloc::Static || Relocs == Reloc::DynamicNoPIC) &&
Cases.size() > 3) {
Cases.size() > 5) {
uint64_t First = cast<ConstantIntegral>(Cases.front().first)->getRawValue();
uint64_t Last = cast<ConstantIntegral>(Cases.back().first)->getRawValue();
// Determine density
// FIXME: support sub-100% density
if (((Last - First) + 1ULL) == (uint64_t)Cases.size()) {
double Density = (double)Cases.size() / (double)((Last - First) + 1ULL);
if (Density >= 0.75) {
// Create a new basic block to hold the code for loading the address
// of the jump table, and jumping to it. Update successor information;
// we will either branch to the default case for the switch, or the jump
@ -938,16 +929,31 @@ void SelectionDAGLowering::visitSwitch(SwitchInst &I) {
DAG.setRoot(DAG.getNode(ISD::BRCOND, MVT::Other, CopyTo, CMP,
DAG.getBasicBlock(Default)));
// Build a sorted vector of destination BBs, corresponding to each target
// of the switch.
// FIXME: need to insert DefaultMBB for each "hole" in the jump table,
// when we support jump tables with < 100% density.
// Build a vector of destination BBs, corresponding to each target
// of the jump table. If the value of the jump table slot corresponds to
// a case statement, push the case's BB onto the vector, otherwise, push
// the default BB.
std::set<MachineBasicBlock*> UniqueBBs;
std::vector<MachineBasicBlock*> DestBBs;
for (CaseItr ii = Cases.begin(), ee = Cases.end(); ii != ee; ++ii) {
DestBBs.push_back(ii->second);
UniqueBBs.insert(ii->second);
uint64_t TEI = First;
for (CaseItr ii = Cases.begin(), ee = Cases.end(); ii != ee; ++TEI) {
if (cast<ConstantIntegral>(ii->first)->getRawValue() == TEI) {
DestBBs.push_back(ii->second);
UniqueBBs.insert(ii->second);
++ii;
} else {
DestBBs.push_back(Default);
UniqueBBs.insert(Default);
}
}
// Update successor info
for (std::set<MachineBasicBlock*>::iterator ii = UniqueBBs.begin(),
ee = UniqueBBs.end(); ii != ee; ++ii)
JumpTableBB->addSuccessor(*ii);
// Create a jump table index for this jump table, or return an existing
// one.
unsigned JTI = CurMF->getJumpTableInfo()->getJumpTableIndex(DestBBs);
// Set the jump table information so that we can codegen it as a second
@ -956,7 +962,6 @@ void SelectionDAGLowering::visitSwitch(SwitchInst &I) {
JT.JTI = JTI;
JT.MBB = JumpTableBB;
JT.Default = Default;
JT.SuccMBBs = UniqueBBs;
return;
}
}
@ -3227,10 +3232,13 @@ void SelectionDAGISel::SelectBasicBlock(BasicBlock *LLVMBB, MachineFunction &MF,
MachineBasicBlock *PHIBB = PHI->getParent();
assert(PHI->getOpcode() == TargetInstrInfo::PHI &&
"This is not a machine PHI node that we are updating!");
if (PHIBB == JT.Default || JT.SuccMBBs.find(PHIBB) != JT.SuccMBBs.end()) {
PHIBB = (PHIBB == JT.Default) ? RangeBB : BB;
if (PHIBB == JT.Default) {
PHI->addRegOperand(PHINodesToUpdate[pi].second);
PHI->addMachineBasicBlockOperand(PHIBB);
PHI->addMachineBasicBlockOperand(RangeBB);
}
if (BB->succ_end() != std::find(BB->succ_begin(),BB->succ_end(), PHIBB)) {
PHI->addRegOperand(PHINodesToUpdate[pi].second);
PHI->addMachineBasicBlockOperand(BB);
}
}
return;