[llvm-commits] CVS: llvm/lib/Transforms/Utils/SimplifyCFG.cpp
Chris Lattner
lattner at cs.uiuc.edu
Sat Feb 28 15:29:01 PST 2004
Changes in directory llvm/lib/Transforms/Utils:
SimplifyCFG.cpp updated: 1.28 -> 1.29
---
Log message:
Implement switch->br and br->switch folding by ripping out the switch->switch
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.
---
Diffs of the changes: (+174 -178)
Index: llvm/lib/Transforms/Utils/SimplifyCFG.cpp
diff -u llvm/lib/Transforms/Utils/SimplifyCFG.cpp:1.28 llvm/lib/Transforms/Utils/SimplifyCFG.cpp:1.29
--- llvm/lib/Transforms/Utils/SimplifyCFG.cpp:1.28 Thu Feb 26 01:13:46 2004
+++ llvm/lib/Transforms/Utils/SimplifyCFG.cpp Sat Feb 28 15:28:10 2004
@@ -328,6 +328,169 @@
}
}
+// 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 @@
}
} 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
@@ -688,80 +758,6 @@
OnlyPred->setName(OldName);
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)
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