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Implement switch->br and br->switch folding by ripping out the switch->switch

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and br->br code and generalizing it.  This allows us to compile code like this:

int test(Instruction *I) {
  if (isa<CastInst>(I))
    return foo(7);
  else if (isa<BranchInst>(I))
    return foo(123);
  else if (isa<UnwindInst>(I))
    return foo(1241);
  else if (isa<SetCondInst>(I))
    return foo(1);
  else if (isa<VAArgInst>(I))
    return foo(42);
  return foo(-1);
}

into:

int %_Z4testPN4llvm11InstructionE("struct.llvm::Instruction"* %I) {
entry:
        %tmp.1.i.i.i.i.i.i.i = getelementptr "struct.llvm::Instruction"* %I, long 0, ubyte 4            ; <uint*> [#uses=1]
        %tmp.2.i.i.i.i.i.i.i = load uint* %tmp.1.i.i.i.i.i.i.i          ; <uint> [#uses=2]
        %tmp.2.i.i.i.i.i.i = seteq uint %tmp.2.i.i.i.i.i.i.i, 27                ; <bool> [#uses=0]
        switch uint %tmp.2.i.i.i.i.i.i.i, label %endif.0 [
                 uint 27, label %then.0
                 uint 2, label %then.1
                 uint 5, label %then.2
                 uint 14, label %then.3
                 uint 15, label %then.3
                 uint 16, label %then.3
                 uint 17, label %then.3
                 uint 18, label %then.3
                 uint 19, label %then.3
                 uint 32, label %then.4
        ]
...

As well as handling the cases in 176.gcc and many other programs more effectively.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@11964 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-02-28 21:28:10 +00:00
parent 9ff6ba1ea1
commit 542f149f00
1 changed files with 174 additions and 178 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

352
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -328,6 +328,169 @@ static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
}
}
// isValueEqualityComparison - Return true if the specified terminator checks to
// see if a value is equal to constant integer value.
static Value *isValueEqualityComparison(TerminatorInst *TI) {
if (SwitchInst *SI = dyn_cast<SwitchInst>(TI))
return SI->getCondition();
if (BranchInst *BI = dyn_cast<BranchInst>(TI))
if (BI->isConditional() && BI->getCondition()->hasOneUse())
if (SetCondInst *SCI = dyn_cast<SetCondInst>(BI->getCondition()))
if ((SCI->getOpcode() == Instruction::SetEQ ||
SCI->getOpcode() == Instruction::SetNE) &&
isa<ConstantInt>(SCI->getOperand(1)))
return SCI->getOperand(0);
return 0;
}
// Given a value comparison instruction, decode all of the 'cases' that it
// represents and return the 'default' block.
static BasicBlock *
GetValueEqualityComparisonCases(TerminatorInst *TI,
std::vector<std::pair<ConstantInt*,
BasicBlock*> > &Cases) {
if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
Cases.reserve(SI->getNumCases());
for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
Cases.push_back(std::make_pair(cast<ConstantInt>(SI->getCaseValue(i)),
SI->getSuccessor(i)));
return SI->getDefaultDest();
}
BranchInst *BI = cast<BranchInst>(TI);
SetCondInst *SCI = cast<SetCondInst>(BI->getCondition());
Cases.push_back(std::make_pair(cast<ConstantInt>(SCI->getOperand(1)),
BI->getSuccessor(SCI->getOpcode() ==
Instruction::SetNE)));
return BI->getSuccessor(SCI->getOpcode() == Instruction::SetEQ);
}
// FoldValueComparisonIntoPredecessors - The specified terminator is a value
// equality comparison instruction (either a switch or a branch on "X == c").
// See if any of the predecessors of the terminator block are value comparisons
// on the same value. If so, and if safe to do so, fold them together.
static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
BasicBlock *BB = TI->getParent();
Value *CV = isValueEqualityComparison(TI); // CondVal
assert(CV && "Not a comparison?");
bool Changed = false;
std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
while (!Preds.empty()) {
BasicBlock *Pred = Preds.back();
Preds.pop_back();
// See if the predecessor is a comparison with the same value.
TerminatorInst *PTI = Pred->getTerminator();
Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
// Figure out which 'cases' to copy from SI to PSI.
std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
// Based on whether the default edge from PTI goes to BB or not, fill in
// PredCases and PredDefault with the new switch cases we would like to
// build.
std::vector<BasicBlock*> NewSuccessors;
if (PredDefault == BB) {
// If this is the default destination from PTI, only the edges in TI
// that don't occur in PTI, or that branch to BB will be activated.
std::set<ConstantInt*> PTIHandled;
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
if (PredCases[i].second != BB)
PTIHandled.insert(PredCases[i].first);
else {
// The default destination is BB, we don't need explicit targets.
std::swap(PredCases[i], PredCases.back());
PredCases.pop_back();
--i; --e;
}
// Reconstruct the new switch statement we will be building.
if (PredDefault != BBDefault) {
PredDefault->removePredecessor(Pred);
PredDefault = BBDefault;
NewSuccessors.push_back(BBDefault);
}
for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
if (!PTIHandled.count(BBCases[i].first) &&
BBCases[i].second != BBDefault) {
PredCases.push_back(BBCases[i]);
NewSuccessors.push_back(BBCases[i].second);
}
} else {
// If this is not the default destination from PSI, only the edges
// in SI that occur in PSI with a destination of BB will be
// activated.
std::set<ConstantInt*> PTIHandled;
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
if (PredCases[i].second == BB) {
PTIHandled.insert(PredCases[i].first);
std::swap(PredCases[i], PredCases.back());
PredCases.pop_back();
--i; --e;
}
// Okay, now we know which constants were sent to BB from the
// predecessor. Figure out where they will all go now.
for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
if (PTIHandled.count(BBCases[i].first)) {
// If this is one we are capable of getting...
PredCases.push_back(BBCases[i]);
NewSuccessors.push_back(BBCases[i].second);
PTIHandled.erase(BBCases[i].first);// This constant is taken care of
}
// If there are any constants vectored to BB that TI doesn't handle,
// they must go to the default destination of TI.
for (std::set<ConstantInt*>::iterator I = PTIHandled.begin(),
E = PTIHandled.end(); I != E; ++I) {
PredCases.push_back(std::make_pair(*I, BBDefault));
NewSuccessors.push_back(BBDefault);
}
}
// Okay, at this point, we know which new successor Pred will get. Make
// sure we update the number of entries in the PHI nodes for these
// successors.
for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
// Now that the successors are updated, create the new Switch instruction.
SwitchInst *NewSI = new SwitchInst(CV, PredDefault, PTI);
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
NewSI->addCase(PredCases[i].first, PredCases[i].second);
Pred->getInstList().erase(PTI);
// Okay, last check. If BB is still a successor of PSI, then we must
// have an infinite loop case. If so, add an infinitely looping block
// to handle the case to preserve the behavior of the code.
BasicBlock *InfLoopBlock = 0;
for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
if (NewSI->getSuccessor(i) == BB) {
if (InfLoopBlock == 0) {
// Insert it at the end of the loop, because it's either code,
// or it won't matter if it's hot. :)
InfLoopBlock = new BasicBlock("infloop", BB->getParent());
new BranchInst(InfLoopBlock, InfLoopBlock);
}
NewSI->setSuccessor(i, InfLoopBlock);
}
Changed = true;
}
}
return Changed;
}
// SimplifyCFG - This function is used to do simplification of a CFG. For
// example, it adjusts branches to branches to eliminate the extra hop, it
// eliminates unreachable basic blocks, and does other "peephole" optimization
@ -521,111 +684,18 @@ bool llvm::SimplifyCFG(BasicBlock *BB) {
}
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->begin())) {
// If the only instruction in this block is a switch instruction, see if we
// can fold the switch instruction into a switch in a predecessor block.
std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
while (!Preds.empty()) {
BasicBlock *Pred = Preds.back();
Preds.pop_back();
// If the two blocks are switching on the same value, we can merge this
// switch into the predecessor's switch.
if (SwitchInst *PSI = dyn_cast<SwitchInst>(Pred->getTerminator()))
if (PSI->getCondition() == SI->getCondition() &&
SafeToMergeTerminators(SI, PSI)) {
// Figure out which 'cases' to copy from SI to PSI.
std::vector<std::pair<Constant*, BasicBlock*> > Cases;
BasicBlock *NewDefault = 0;
if (PSI->getDefaultDest() == BB) {
// If this is the default destination from PSI, only the edges in SI
// that don't occur in PSI, or that branch to BB will be activated.
std::set<Constant*> PSIHandled;
for (unsigned i = 1, e = PSI->getNumSuccessors(); i != e; ++i)
if (PSI->getSuccessor(i) != BB)
PSIHandled.insert(PSI->getCaseValue(i));
else {
// This entry will be replaced.
PSI->removeCase(i);
--i; --e;
}
NewDefault = SI->getDefaultDest();
for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
Constant *C = SI->getCaseValue(i);
if (!PSIHandled.count(C))
Cases.push_back(std::make_pair(C, SI->getSuccessor(i)));
}
} else {
// If this is not the default destination from PSI, only the edges
// in SI that occur in PSI with a destination of BB will be
// activated.
std::set<Constant*> PSIHandled;
for (unsigned i = 1, e = PSI->getNumSuccessors(); i != e; ++i)
if (PSI->getSuccessor(i) == BB) {
// We know that BB doesn't have any PHI nodes in it, so just
// drop the edges.
PSIHandled.insert(PSI->getCaseValue(i));
PSI->removeCase(i);
--i; --e;
}
// Okay, now we know which constants were sent to BB from the
// predecessor. Figure out where they will all go now.
for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
Constant *C = SI->getCaseValue(i);
if (PSIHandled.count(C)) {
// If this is one we are capable of getting...
Cases.push_back(std::make_pair(C, SI->getSuccessor(i)));
PSIHandled.erase(C); // This constant is taken care of
}
}
// If there are any constants vectored to BB that SI doesn't handle,
// they must go to the default destination of SI.
for (std::set<Constant*>::iterator I = PSIHandled.begin(),
E = PSIHandled.end(); I != E; ++I)
Cases.push_back(std::make_pair(*I, SI->getDefaultDest()));
}
// Okay, at this point, we know which cases need to be added to the
// PSI switch and which destinations they go to. If PSI needs its
// default destination changed, NewDefault is set. Start changing
// stuff now.
if (NewDefault) {
AddPredecessorToBlock(NewDefault, Pred, BB);
PSI->setSuccessor(0, NewDefault);
}
// Okay, add all of the cases now.
for (unsigned i = 0, e = Cases.size(); i != e; ++i) {
AddPredecessorToBlock(Cases[i].second, Pred, BB);
PSI->addCase(Cases[i].first, Cases[i].second);
}
// Okay, last check. If BB is still a successor of PSI, then we must
// have an infinite loop case. If so, add an infinitely looping block
// to handle the case to preserve the behavior of the code.
BasicBlock *InfLoopBlock = 0;
for (unsigned i = 0, e = PSI->getNumSuccessors(); i != e; ++i)
if (PSI->getSuccessor(i) == BB) {
if (InfLoopBlock == 0) {
// Insert it at the end of the loop, because it's either code,
// or it won't matter if it's hot. :)
InfLoopBlock = new BasicBlock("infloop", BB->getParent());
new BranchInst(InfLoopBlock, InfLoopBlock);
}
PSI->setSuccessor(i, InfLoopBlock);
}
Changed = true;
}
if (FoldValueComparisonIntoPredecessors(SI))
return SimplifyCFG(BB) || 1;
} else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
if (Value *CompVal = isValueEqualityComparison(BB->getTerminator())) {
// This block must be empty, except for the setcond inst, if it exists.
BasicBlock::iterator I = BB->begin();
if (&*I == BI ||
(&*I == cast<Instruction>(BI->getCondition()) &&
&*++I == BI))
if (FoldValueComparisonIntoPredecessors(BI))
return SimplifyCFG(BB) || 1;
}
// If we removed all predecessors of this block, recursively call
// SimplifyCFG to remove it.
if (pred_begin(BB) == pred_end(BB))
return SimplifyCFG(BB);
}
// Merge basic blocks into their predecessor if there is only one distinct
@ -690,80 +760,6 @@ bool llvm::SimplifyCFG(BasicBlock *BB) {
return true;
}
// If there is a single predecessor for this block, and if this block is a
// simple value comparison block (ie, contains X == C), see if we can fold
// this comparison into the comparison in our predecessor block, making the
// predecessor block terminator into a switch (or adding cases to a
// preexisting switch).
if (OnlyPred) {
if (SetCondInst *SCI = dyn_cast<SetCondInst>(BB->begin()))
if (SCI->getOpcode() == Instruction::SetEQ && SCI->hasOneUse() &&
isa<BranchInst>(SCI->use_back()) &&
SCI->getNext() == cast<BranchInst>(SCI->use_back())) {
// Okay, we know we have a block containing (only) a seteq and a
// conditional branch instruction. If an integer value is being
// compared, if the comparison value is a constant, then check the
// predecessor.
BranchInst *BBBr = cast<BranchInst>(BB->getTerminator());
Value *CompVal = SCI->getOperand(0);
if (ConstantInt *CVal = dyn_cast<ConstantInt>(SCI->getOperand(1))) {
// We can do the merge if the predecessor contains either a
// conditional branch or a switch instruction which is operating on
// the CompVal.
if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator())){
// If it is a branch, then it must be a conditional branch,
// otherwise we would have merged it in before. We can only handle
// this if the block we are looking at is the 'false' branch.
assert(BI->isConditional() &&
"Should have previously merged blocks!");
if (SetCondInst *PredSCC= dyn_cast<SetCondInst>(BI->getCondition()))
if (PredSCC->getOperand(0) == CompVal &&
PredSCC->getOpcode() == Instruction::SetEQ &&
isa<ConstantInt>(PredSCC->getOperand(1)) &&
BB == BI->getSuccessor(1) &&
SafeToMergeTerminators(BI, BBBr)) {
// If the constants being compared are the same, then the
// comparison in this block could never come true.
if (SCI->getOperand(1) == PredSCC->getOperand(1)) {
// Tell the block to skip over us, making us dead.
BI->setSuccessor(1, BBBr->getSuccessor(1));
AddPredecessorToBlock(BBBr->getSuccessor(1), OnlyPred, BB);
return SimplifyCFG(BB);
}
// Otherwise, create the switch instruction!
SwitchInst *SI = new SwitchInst(CompVal, BBBr->getSuccessor(1),
BI);
// Add the edge from our predecessor, and remove the
// predecessors (now obsolete branch instruction). This makes
// the current block dead.
SI->addCase(cast<Constant>(PredSCC->getOperand(1)),
BI->getSuccessor(0));
OnlyPred->getInstList().erase(BI);
if (PredSCC->use_empty())
PredSCC->getParent()->getInstList().erase(PredSCC);
// Add our case...
SI->addCase(cast<Constant>(SCI->getOperand(1)),
BBBr->getSuccessor(0));
AddPredecessorToBlock(BBBr->getSuccessor(0), OnlyPred, BB);
AddPredecessorToBlock(BBBr->getSuccessor(1), OnlyPred, BB);
//std::cerr << "Formed Switch: " << SI;
// Made a big change! Now this block is dead, so remove it.
return SimplifyCFG(BB);
}
} else if (SwitchInst *SI =
dyn_cast<SwitchInst>(OnlyPred->getTerminator())) {
}
}
}
}
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
// Change br (X == 0 | X == 1), T, F into a switch instruction.