//===- LowerSwitch.cpp - Eliminate Switch instructions --------------------===//
//
+// The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
// The LowerSwitch transformation rewrites switch statements with a sequence of
// branches, which allows targets to get away with not implementing the switch
// statement until it is convenient.
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
+#include "llvm/Constants.h"
#include "llvm/Function.h"
-#include "llvm/iTerminators.h"
-#include "llvm/iOperators.h"
-#include "llvm/iPHINode.h"
+#include "llvm/Instructions.h"
#include "llvm/Pass.h"
-#include "Support/Statistic.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/Compiler.h"
+#include <algorithm>
+using namespace llvm;
namespace {
- Statistic<> NumLowered("lowerswitch", "Number of SwitchInst's replaced");
-
/// LowerSwitch Pass - Replace all SwitchInst instructions with chained branch
/// instructions. Note that this cannot be a BasicBlock pass because it
/// modifies the CFG!
- struct LowerSwitch : public FunctionPass {
- bool runOnFunction(Function &F);
+ class VISIBILITY_HIDDEN LowerSwitch : public FunctionPass {
+ public:
+ virtual bool runOnFunction(Function &F);
+
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ // This is a cluster of orthogonal Transforms
+ AU.addPreserved<UnifyFunctionExitNodes>();
+ AU.addPreservedID(PromoteMemoryToRegisterID);
+ AU.addPreservedID(LowerSelectID);
+ AU.addPreservedID(LowerInvokePassID);
+ AU.addPreservedID(LowerAllocationsID);
+ }
+
+ typedef std::pair<Constant*, BasicBlock*> Case;
+ typedef std::vector<Case>::iterator CaseItr;
+ private:
void processSwitchInst(SwitchInst *SI);
+
+ BasicBlock* switchConvert(CaseItr Begin, CaseItr End, Value* Val,
+ BasicBlock* OrigBlock, BasicBlock* Default);
+ BasicBlock* newLeafBlock(Case& Leaf, Value* Val,
+ BasicBlock* OrigBlock, BasicBlock* Default);
+ };
+
+ /// The comparison function for sorting the switch case values in the vector.
+ struct CaseCmp {
+ bool operator () (const LowerSwitch::Case& C1,
+ const LowerSwitch::Case& C2) {
+
+ const ConstantInt* CI1 = cast<const ConstantInt>(C1.first);
+ const ConstantInt* CI2 = cast<const ConstantInt>(C2.first);
+ if (CI1->getType()->isUnsigned())
+ return CI1->getZExtValue() < CI2->getZExtValue();
+ return CI1->getSExtValue() < CI2->getSExtValue();
+ }
};
- RegisterOpt<LowerSwitch>
+ RegisterPass<LowerSwitch>
X("lowerswitch", "Lower SwitchInst's to branches");
}
+// Publically exposed interface to pass...
+const PassInfo *llvm::LowerSwitchID = X.getPassInfo();
// createLowerSwitchPass - Interface to this file...
-Pass *createLowerSwitchPass() {
+FunctionPass *llvm::createLowerSwitchPass() {
return new LowerSwitch();
}
return Changed;
}
+// operator<< - Used for debugging purposes.
+//
+std::ostream& operator<<(std::ostream &O,
+ const std::vector<LowerSwitch::Case> &C) {
+ O << "[";
+
+ for (std::vector<LowerSwitch::Case>::const_iterator B = C.begin(),
+ E = C.end(); B != E; ) {
+ O << *B->first;
+ if (++B != E) O << ", ";
+ }
+
+ return O << "]";
+}
+OStream& operator<<(OStream &O, const std::vector<LowerSwitch::Case> &C) {
+ if (O.stream()) *O.stream() << C;
+ return O;
+}
+
+// switchConvert - Convert the switch statement into a binary lookup of
+// the case values. The function recursively builds this tree.
+//
+BasicBlock* LowerSwitch::switchConvert(CaseItr Begin, CaseItr End,
+ Value* Val, BasicBlock* OrigBlock,
+ BasicBlock* Default)
+{
+ unsigned Size = End - Begin;
+
+ if (Size == 1)
+ return newLeafBlock(*Begin, Val, OrigBlock, Default);
+
+ unsigned Mid = Size / 2;
+ std::vector<Case> LHS(Begin, Begin + Mid);
+ DOUT << "LHS: " << LHS << "\n";
+ std::vector<Case> RHS(Begin + Mid, End);
+ DOUT << "RHS: " << RHS << "\n";
+
+ Case& Pivot = *(Begin + Mid);
+ DOUT << "Pivot ==> "
+ << cast<ConstantInt>(Pivot.first)->getSExtValue() << "\n";
+
+ BasicBlock* LBranch = switchConvert(LHS.begin(), LHS.end(), Val,
+ OrigBlock, Default);
+ BasicBlock* RBranch = switchConvert(RHS.begin(), RHS.end(), Val,
+ OrigBlock, Default);
+
+ // Create a new node that checks if the value is < pivot. Go to the
+ // left branch if it is and right branch if not.
+ Function* F = OrigBlock->getParent();
+ BasicBlock* NewNode = new BasicBlock("NodeBlock");
+ F->getBasicBlockList().insert(OrigBlock->getNext(), NewNode);
+
+ ICmpInst* Comp = new ICmpInst(ICmpInst::ICMP_ULT, Val, Pivot.first, "Pivot");
+ NewNode->getInstList().push_back(Comp);
+ new BranchInst(LBranch, RBranch, Comp, NewNode);
+ return NewNode;
+}
+
+// newLeafBlock - Create a new leaf block for the binary lookup tree. It
+// checks if the switch's value == the case's value. If not, then it
+// jumps to the default branch. At this point in the tree, the value
+// can't be another valid case value, so the jump to the "default" branch
+// is warranted.
+//
+BasicBlock* LowerSwitch::newLeafBlock(Case& Leaf, Value* Val,
+ BasicBlock* OrigBlock,
+ BasicBlock* Default)
+{
+ Function* F = OrigBlock->getParent();
+ BasicBlock* NewLeaf = new BasicBlock("LeafBlock");
+ F->getBasicBlockList().insert(OrigBlock->getNext(), NewLeaf);
+
+ // Make the seteq instruction...
+ ICmpInst* Comp = new ICmpInst(ICmpInst::ICMP_EQ, Val,
+ Leaf.first, "SwitchLeaf");
+ NewLeaf->getInstList().push_back(Comp);
+
+ // Make the conditional branch...
+ BasicBlock* Succ = Leaf.second;
+ new BranchInst(Succ, Default, Comp, NewLeaf);
+
+ // If there were any PHI nodes in this successor, rewrite one entry
+ // from OrigBlock to come from NewLeaf.
+ for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
+ PHINode* PN = cast<PHINode>(I);
+ int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
+ assert(BlockIdx != -1 && "Switch didn't go to this successor??");
+ PN->setIncomingBlock((unsigned)BlockIdx, NewLeaf);
+ }
+
+ return NewLeaf;
+}
+
// processSwitchInst - Replace the specified switch instruction with a sequence
-// of chained basic blocks. Right now we just insert an incredibly stupid
-// linear sequence of branches. It would be better to do a balanced binary
-// search eventually. FIXME
+// of chained if-then insts in a balanced binary search.
//
void LowerSwitch::processSwitchInst(SwitchInst *SI) {
BasicBlock *CurBlock = SI->getParent();
BasicBlock *OrigBlock = CurBlock;
Function *F = CurBlock->getParent();
Value *Val = SI->getOperand(0); // The value we are switching on...
+ BasicBlock* Default = SI->getDefaultDest();
- // Unlink the switch instruction from it's block.
- CurBlock->getInstList().remove(SI);
-
- // Expand comparisons for all of the non-default cases...
- for (unsigned i = 2, e = SI->getNumOperands(); i != e; i += 2) {
- // Insert a new basic block after the current one...
- BasicBlock *NextBlock;
- if (i != e-2) {
- NextBlock = new BasicBlock("switchblock");
- F->getBasicBlockList().insert(CurBlock->getNext(), NextBlock);
- } else { // Last case, if it's not the value, go to default block.
- NextBlock = cast<BasicBlock>(SI->getDefaultDest());
- }
+ // If there is only the default destination, don't bother with the code below.
+ if (SI->getNumOperands() == 2) {
+ new BranchInst(SI->getDefaultDest(), CurBlock);
+ CurBlock->getInstList().erase(SI);
+ return;
+ }
- // Make the seteq instruction...
- Instruction *Comp = new SetCondInst(Instruction::SetEQ, Val,
- SI->getOperand(i), "switchcase");
- CurBlock->getInstList().push_back(Comp);
-
- // Make the conditional branch...
- BasicBlock *Succ = cast<BasicBlock>(SI->getOperand(i+1));
- Instruction *Br = new BranchInst(Succ, NextBlock, Comp);
- CurBlock->getInstList().push_back(Br);
-
- // If there were any PHI nodes in this successor, rewrite one entry from
- // OrigBlock to come from CurBlock.
- for (BasicBlock::iterator I = Succ->begin();
- PHINode *PN = dyn_cast<PHINode>(I); ++I) {
- int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
- assert(BlockIdx != -1 && "Switch didn't go to this successor??");
- PN->setIncomingBlock((unsigned)BlockIdx, CurBlock);
- }
+ // Create a new, empty default block so that the new hierarchy of
+ // if-then statements go to this and the PHI nodes are happy.
+ BasicBlock* NewDefault = new BasicBlock("NewDefault");
+ F->getBasicBlockList().insert(Default, NewDefault);
- if (i == e-2) { // Is this looking at the default destination?
- // If there is an entry in any PHI nodes for the default edge, make sure
- // to update them as well.
- for (BasicBlock::iterator I = NextBlock->begin();
- PHINode *PN = dyn_cast<PHINode>(I); ++I) {
- int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
- assert(BlockIdx != -1 && "Switch didn't go to this successor??");
- PN->setIncomingBlock((unsigned)BlockIdx, CurBlock);
- }
- }
+ new BranchInst(Default, NewDefault);
- CurBlock = NextBlock; // Move on to the next condition
+ // If there is an entry in any PHI nodes for the default edge, make sure
+ // to update them as well.
+ for (BasicBlock::iterator I = Default->begin(); isa<PHINode>(I); ++I) {
+ PHINode *PN = cast<PHINode>(I);
+ int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
+ assert(BlockIdx != -1 && "Switch didn't go to this successor??");
+ PN->setIncomingBlock((unsigned)BlockIdx, NewDefault);
}
+ std::vector<Case> Cases;
+
+ // Expand comparisons for all of the non-default cases...
+ for (unsigned i = 1; i < SI->getNumSuccessors(); ++i)
+ Cases.push_back(Case(SI->getSuccessorValue(i), SI->getSuccessor(i)));
+
+ std::sort(Cases.begin(), Cases.end(), CaseCmp());
+ DOUT << "Cases: " << Cases << "\n";
+ BasicBlock* SwitchBlock = switchConvert(Cases.begin(), Cases.end(), Val,
+ OrigBlock, NewDefault);
+
+ // Branch to our shiny new if-then stuff...
+ new BranchInst(SwitchBlock, OrigBlock);
+
// We are now done with the switch instruction, delete it.
- delete SI;
+ CurBlock->getInstList().erase(SI);
}
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