forked from OSchip/llvm-project
Kill some duplicated code for removing unreachable BBs.
This moves removeUnreachableBlocksFromFn from SimplifyCFGPass.cpp to Utils/Local.cpp and uses it to replace the implementation of llvm::removeUnreachableBlocks, which appears to do a strict subset of what removeUnreachableBlocksFromFn does. Differential Revision: http://llvm-reviews.chandlerc.com/D1334 llvm-svn: 188119
This commit is contained in:
Peter Collingbourne
parent
beadec4afd
commit
32090aba06
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@ -66,161 +66,6 @@ FunctionPass *llvm::createCFGSimplificationPass() {
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return new CFGSimplifyPass();
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}
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/// changeToUnreachable - Insert an unreachable instruction before the specified
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/// instruction, making it and the rest of the code in the block dead.
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static void changeToUnreachable(Instruction *I, bool UseLLVMTrap) {
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BasicBlock *BB = I->getParent();
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// Loop over all of the successors, removing BB's entry from any PHI
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// nodes.
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for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
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(*SI)->removePredecessor(BB);
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// Insert a call to llvm.trap right before this. This turns the undefined
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// behavior into a hard fail instead of falling through into random code.
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if (UseLLVMTrap) {
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Function *TrapFn =
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Intrinsic::getDeclaration(BB->getParent()->getParent(), Intrinsic::trap);
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CallInst *CallTrap = CallInst::Create(TrapFn, "", I);
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CallTrap->setDebugLoc(I->getDebugLoc());
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}
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new UnreachableInst(I->getContext(), I);
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// All instructions after this are dead.
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BasicBlock::iterator BBI = I, BBE = BB->end();
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while (BBI != BBE) {
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if (!BBI->use_empty())
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BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
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BB->getInstList().erase(BBI++);
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}
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}
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/// changeToCall - Convert the specified invoke into a normal call.
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static void changeToCall(InvokeInst *II) {
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SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
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CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args, "", II);
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NewCall->takeName(II);
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NewCall->setCallingConv(II->getCallingConv());
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NewCall->setAttributes(II->getAttributes());
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NewCall->setDebugLoc(II->getDebugLoc());
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II->replaceAllUsesWith(NewCall);
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// Follow the call by a branch to the normal destination.
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BranchInst::Create(II->getNormalDest(), II);
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// Update PHI nodes in the unwind destination
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II->getUnwindDest()->removePredecessor(II->getParent());
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II->eraseFromParent();
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}
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static bool markAliveBlocks(BasicBlock *BB,
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SmallPtrSet<BasicBlock*, 128> &Reachable) {
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SmallVector<BasicBlock*, 128> Worklist;
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Worklist.push_back(BB);
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Reachable.insert(BB);
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bool Changed = false;
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do {
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BB = Worklist.pop_back_val();
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// Do a quick scan of the basic block, turning any obviously unreachable
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// instructions into LLVM unreachable insts. The instruction combining pass
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// canonicalizes unreachable insts into stores to null or undef.
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for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E;++BBI){
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if (CallInst *CI = dyn_cast<CallInst>(BBI)) {
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if (CI->doesNotReturn()) {
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// If we found a call to a no-return function, insert an unreachable
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// instruction after it. Make sure there isn't *already* one there
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// though.
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++BBI;
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if (!isa<UnreachableInst>(BBI)) {
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// Don't insert a call to llvm.trap right before the unreachable.
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changeToUnreachable(BBI, false);
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Changed = true;
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}
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break;
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}
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}
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// Store to undef and store to null are undefined and used to signal that
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// they should be changed to unreachable by passes that can't modify the
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// CFG.
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if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
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// Don't touch volatile stores.
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if (SI->isVolatile()) continue;
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Value *Ptr = SI->getOperand(1);
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if (isa<UndefValue>(Ptr) ||
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(isa<ConstantPointerNull>(Ptr) &&
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SI->getPointerAddressSpace() == 0)) {
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changeToUnreachable(SI, true);
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Changed = true;
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break;
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}
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}
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}
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// Turn invokes that call 'nounwind' functions into ordinary calls.
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if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
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Value *Callee = II->getCalledValue();
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if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) {
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changeToUnreachable(II, true);
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Changed = true;
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} else if (II->doesNotThrow()) {
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if (II->use_empty() && II->onlyReadsMemory()) {
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// jump to the normal destination branch.
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BranchInst::Create(II->getNormalDest(), II);
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II->getUnwindDest()->removePredecessor(II->getParent());
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II->eraseFromParent();
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} else
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changeToCall(II);
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Changed = true;
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}
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}
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Changed |= ConstantFoldTerminator(BB, true);
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for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
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if (Reachable.insert(*SI))
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Worklist.push_back(*SI);
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} while (!Worklist.empty());
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return Changed;
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}
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/// removeUnreachableBlocksFromFn - Remove blocks that are not reachable, even
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/// if they are in a dead cycle. Return true if a change was made, false
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/// otherwise.
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static bool removeUnreachableBlocksFromFn(Function &F) {
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SmallPtrSet<BasicBlock*, 128> Reachable;
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bool Changed = markAliveBlocks(F.begin(), Reachable);
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// If there are unreachable blocks in the CFG...
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if (Reachable.size() == F.size())
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return Changed;
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assert(Reachable.size() < F.size());
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NumSimpl += F.size()-Reachable.size();
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// Loop over all of the basic blocks that are not reachable, dropping all of
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// their internal references...
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for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) {
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if (Reachable.count(BB))
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continue;
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for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
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if (Reachable.count(*SI))
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(*SI)->removePredecessor(BB);
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BB->dropAllReferences();
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}
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for (Function::iterator I = ++F.begin(); I != F.end();)
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if (!Reachable.count(I))
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I = F.getBasicBlockList().erase(I);
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else
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++I;
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return true;
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}
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/// mergeEmptyReturnBlocks - If we have more than one empty (other than phi
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/// node) return blocks, merge them together to promote recursive block merging.
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static bool mergeEmptyReturnBlocks(Function &F) {
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@ -325,7 +170,7 @@ static bool iterativelySimplifyCFG(Function &F, const TargetTransformInfo &TTI,
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bool CFGSimplifyPass::runOnFunction(Function &F) {
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const TargetTransformInfo &TTI = getAnalysis<TargetTransformInfo>();
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const DataLayout *TD = getAnalysisIfAvailable<DataLayout>();
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bool EverChanged = removeUnreachableBlocksFromFn(F);
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bool EverChanged = removeUnreachableBlocks(F);
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EverChanged |= mergeEmptyReturnBlocks(F);
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EverChanged |= iterativelySimplifyCFG(F, TTI, TD);
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@ -333,16 +178,16 @@ bool CFGSimplifyPass::runOnFunction(Function &F) {
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if (!EverChanged) return false;
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// iterativelySimplifyCFG can (rarely) make some loops dead. If this happens,
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// removeUnreachableBlocksFromFn is needed to nuke them, which means we should
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// removeUnreachableBlocks is needed to nuke them, which means we should
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// iterate between the two optimizations. We structure the code like this to
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// avoid reruning iterativelySimplifyCFG if the second pass of
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// removeUnreachableBlocksFromFn doesn't do anything.
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if (!removeUnreachableBlocksFromFn(F))
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// removeUnreachableBlocks doesn't do anything.
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if (!removeUnreachableBlocks(F))
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return true;
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do {
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EverChanged = iterativelySimplifyCFG(F, TTI, TD);
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EverChanged |= removeUnreachableBlocksFromFn(F);
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EverChanged |= removeUnreachableBlocks(F);
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} while (EverChanged);
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return true;
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@ -16,6 +16,7 @@
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Analysis/MemoryBuiltins.h"
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@ -43,6 +44,8 @@
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#include "llvm/Support/raw_ostream.h"
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using namespace llvm;
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STATISTIC(NumRemoved, "Number of unreachable basic blocks removed");
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//===----------------------------------------------------------------------===//
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// Local constant propagation.
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//
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@ -1121,33 +1124,153 @@ bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
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return true;
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}
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bool llvm::removeUnreachableBlocks(Function &F) {
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SmallPtrSet<BasicBlock*, 16> Reachable;
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/// changeToUnreachable - Insert an unreachable instruction before the specified
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/// instruction, making it and the rest of the code in the block dead.
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static void changeToUnreachable(Instruction *I, bool UseLLVMTrap) {
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BasicBlock *BB = I->getParent();
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// Loop over all of the successors, removing BB's entry from any PHI
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// nodes.
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for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
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(*SI)->removePredecessor(BB);
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// Insert a call to llvm.trap right before this. This turns the undefined
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// behavior into a hard fail instead of falling through into random code.
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if (UseLLVMTrap) {
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Function *TrapFn =
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Intrinsic::getDeclaration(BB->getParent()->getParent(), Intrinsic::trap);
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CallInst *CallTrap = CallInst::Create(TrapFn, "", I);
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CallTrap->setDebugLoc(I->getDebugLoc());
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}
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new UnreachableInst(I->getContext(), I);
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// All instructions after this are dead.
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BasicBlock::iterator BBI = I, BBE = BB->end();
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while (BBI != BBE) {
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if (!BBI->use_empty())
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BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
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BB->getInstList().erase(BBI++);
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}
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}
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/// changeToCall - Convert the specified invoke into a normal call.
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static void changeToCall(InvokeInst *II) {
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SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
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CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args, "", II);
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NewCall->takeName(II);
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NewCall->setCallingConv(II->getCallingConv());
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NewCall->setAttributes(II->getAttributes());
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NewCall->setDebugLoc(II->getDebugLoc());
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II->replaceAllUsesWith(NewCall);
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// Follow the call by a branch to the normal destination.
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BranchInst::Create(II->getNormalDest(), II);
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// Update PHI nodes in the unwind destination
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II->getUnwindDest()->removePredecessor(II->getParent());
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II->eraseFromParent();
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}
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static bool markAliveBlocks(BasicBlock *BB,
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SmallPtrSet<BasicBlock*, 128> &Reachable) {
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SmallVector<BasicBlock*, 128> Worklist;
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Worklist.push_back(&F.getEntryBlock());
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Reachable.insert(&F.getEntryBlock());
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Worklist.push_back(BB);
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Reachable.insert(BB);
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bool Changed = false;
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do {
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BasicBlock *BB = Worklist.pop_back_val();
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BB = Worklist.pop_back_val();
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// Do a quick scan of the basic block, turning any obviously unreachable
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// instructions into LLVM unreachable insts. The instruction combining pass
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// canonicalizes unreachable insts into stores to null or undef.
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for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E;++BBI){
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if (CallInst *CI = dyn_cast<CallInst>(BBI)) {
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if (CI->doesNotReturn()) {
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// If we found a call to a no-return function, insert an unreachable
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// instruction after it. Make sure there isn't *already* one there
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// though.
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++BBI;
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if (!isa<UnreachableInst>(BBI)) {
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// Don't insert a call to llvm.trap right before the unreachable.
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changeToUnreachable(BBI, false);
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Changed = true;
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}
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break;
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}
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}
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// Store to undef and store to null are undefined and used to signal that
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// they should be changed to unreachable by passes that can't modify the
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// CFG.
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if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
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// Don't touch volatile stores.
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if (SI->isVolatile()) continue;
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Value *Ptr = SI->getOperand(1);
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if (isa<UndefValue>(Ptr) ||
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(isa<ConstantPointerNull>(Ptr) &&
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SI->getPointerAddressSpace() == 0)) {
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changeToUnreachable(SI, true);
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Changed = true;
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break;
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}
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}
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}
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// Turn invokes that call 'nounwind' functions into ordinary calls.
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if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
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Value *Callee = II->getCalledValue();
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if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) {
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changeToUnreachable(II, true);
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Changed = true;
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} else if (II->doesNotThrow()) {
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if (II->use_empty() && II->onlyReadsMemory()) {
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// jump to the normal destination branch.
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BranchInst::Create(II->getNormalDest(), II);
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II->getUnwindDest()->removePredecessor(II->getParent());
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II->eraseFromParent();
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} else
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changeToCall(II);
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Changed = true;
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}
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}
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Changed |= ConstantFoldTerminator(BB, true);
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for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
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if (Reachable.insert(*SI))
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Worklist.push_back(*SI);
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} while (!Worklist.empty());
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return Changed;
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}
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/// removeUnreachableBlocksFromFn - Remove blocks that are not reachable, even
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/// if they are in a dead cycle. Return true if a change was made, false
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/// otherwise.
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bool llvm::removeUnreachableBlocks(Function &F) {
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SmallPtrSet<BasicBlock*, 128> Reachable;
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bool Changed = markAliveBlocks(F.begin(), Reachable);
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// If there are unreachable blocks in the CFG...
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if (Reachable.size() == F.size())
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return false;
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return Changed;
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assert(Reachable.size() < F.size());
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for (Function::iterator I = llvm::next(F.begin()), E = F.end(); I != E; ++I) {
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if (Reachable.count(I))
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NumRemoved += F.size()-Reachable.size();
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// Loop over all of the basic blocks that are not reachable, dropping all of
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// their internal references...
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for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) {
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if (Reachable.count(BB))
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continue;
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for (succ_iterator SI = succ_begin(I), SE = succ_end(I); SI != SE; ++SI)
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for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
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if (Reachable.count(*SI))
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(*SI)->removePredecessor(I);
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I->dropAllReferences();
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(*SI)->removePredecessor(BB);
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BB->dropAllReferences();
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}
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for (Function::iterator I = llvm::next(F.begin()), E=F.end(); I != E;)
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for (Function::iterator I = ++F.begin(); I != F.end();)
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if (!Reachable.count(I))
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I = F.getBasicBlockList().erase(I);
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else
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@ -1,8 +1,8 @@
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; RUN: opt < %s -dfsan -verify -dfsan-args-abi -S | FileCheck %s
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target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
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define i8 @unreachable_bb() {
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; CHECK: @unreachable_bb
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; CHECK-LABEL: @unreachable_bb1
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define i8 @unreachable_bb1() {
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; CHECK: ret { i8, i16 } { i8 1, i16 0 }
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; CHECK-NOT: bb2:
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; CHECK-NOT: bb3:
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@ -18,3 +18,13 @@ bb3:
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bb4:
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br label %bb3
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}
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declare void @abort() noreturn
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; CHECK-LABEL: @unreachable_bb2
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define i8 @unreachable_bb2() {
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call void @abort() noreturn
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; CHECK-NOT: i8 12
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; CHECK: unreachable
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ret i8 12
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}
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