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//===-- LowerSwitch.cpp - Eliminate Switch instructions -------------------===//
//
// The KLEE Symbolic Virtual Machine
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Derived from LowerSwitch.cpp in LLVM, heavily modified by piotrek
// to get rid of the binary search transform, as it was creating
// multiple paths through the program (i.e., extra paths that didn't
// exist in the original program).
//
//===----------------------------------------------------------------------===//
#include "Passes.h"
#include <algorithm>
using namespace llvm;
namespace klee {
char LowerSwitchPass::ID = 0;
// The comparison function for sorting the switch case values in the vector.
struct SwitchCaseCmp {
bool operator () (const LowerSwitchPass::SwitchCase& C1,
const LowerSwitchPass::SwitchCase& C2) {
const ConstantInt* CI1 = cast<const ConstantInt>(C1.value);
const ConstantInt* CI2 = cast<const ConstantInt>(C2.value);
return CI1->getValue().slt(CI2->getValue());
}
};
bool LowerSwitchPass::runOnFunction(Function &F) {
bool changed = false;
for (Function::iterator I = F.begin(), E = F.end(); I != E; ) {
BasicBlock *cur = I++; // Advance over block so we don't traverse new blocks
if (SwitchInst *SI = dyn_cast<SwitchInst>(cur->getTerminator())) {
changed = true;
processSwitchInst(SI);
}
}
return changed;
}
// switchConvert - Convert the switch statement into a linear scan
// through all the case values
void LowerSwitchPass::switchConvert(CaseItr begin, CaseItr end,
Value* value, BasicBlock* origBlock,
BasicBlock* defaultBlock)
{
BasicBlock *curHead = defaultBlock;
Function *F = origBlock->getParent();
// iterate through all the cases, creating a new BasicBlock for each
for (CaseItr it = begin; it < end; ++it) {
BasicBlock *newBlock = BasicBlock::Create(getGlobalContext(), "NodeBlock");
Function::iterator FI = origBlock;
F->getBasicBlockList().insert(++FI, newBlock);
ICmpInst *cmpInst =
new ICmpInst(*newBlock, ICmpInst::ICMP_EQ, value, it->value, "case.cmp");
BranchInst::Create(it->block, curHead, cmpInst, newBlock);
// If there were any PHI nodes in this successor, rewrite one entry
// from origBlock to come from newBlock.
for (BasicBlock::iterator bi = it->block->begin(); isa<PHINode>(bi); ++bi) {
PHINode* PN = cast<PHINode>(bi);
int blockIndex = PN->getBasicBlockIndex(origBlock);
assert(blockIndex != -1 && "Switch didn't go to this successor??");
PN->setIncomingBlock((unsigned)blockIndex, newBlock);
}
curHead = newBlock;
}
// Branch to our shiny new if-then stuff...
BranchInst::Create(curHead, origBlock);
}
// processSwitchInst - Replace the specified switch instruction with a sequence
// of chained if-then instructions.
//
void LowerSwitchPass::processSwitchInst(SwitchInst *SI) {
BasicBlock *origBlock = SI->getParent();
BasicBlock *defaultBlock = SI->getDefaultDest();
Function *F = origBlock->getParent();
Value *switchValue = SI->getOperand(0);
// 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 = BasicBlock::Create(getGlobalContext(), "newDefault");
F->getBasicBlockList().insert(defaultBlock, newDefault);
BranchInst::Create(defaultBlock, newDefault);
// If there is an entry in any PHI nodes for the default edge, make sure
// to update them as well.
for (BasicBlock::iterator I = defaultBlock->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);
}
CaseVector cases;
for (unsigned i = 1; i < SI->getNumSuccessors(); ++i)
cases.push_back(SwitchCase(SI->getSuccessorValue(i),
SI->getSuccessor(i)));
// reverse cases, as switchConvert constructs a chain of
// basic blocks by appending to the front. if we reverse,
// the if comparisons will happen in the same order
// as the cases appear in the switch
std::reverse(cases.begin(), cases.end());
switchConvert(cases.begin(), cases.end(), switchValue, origBlock, newDefault);
// We are now done with the switch instruction, so delete it
origBlock->getInstList().erase(SI);
}
}
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