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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@36873 91177308-0d34-0410-b5e6-96231b3b80d8
82 lines
2.9 KiB
C++
82 lines
2.9 KiB
C++
//===-- UnreachableBlockElim.cpp - Remove unreachable blocks for codegen --===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass is an extremely simple version of the SimplifyCFG pass. Its sole
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// job is to delete LLVM basic blocks that are not reachable from the entry
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// node. To do this, it performs a simple depth first traversal of the CFG,
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// then deletes any unvisited nodes.
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//
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// Note that this pass is really a hack. In particular, the instruction
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// selectors for various targets should just not generate code for unreachable
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// blocks. Until LLVM has a more systematic way of defining instruction
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// selectors, however, we cannot really expect them to handle additional
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// complexity.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/Constant.h"
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#include "llvm/Instructions.h"
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#include "llvm/Function.h"
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#include "llvm/Pass.h"
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#include "llvm/Type.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/ADT/DepthFirstIterator.h"
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using namespace llvm;
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namespace {
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class VISIBILITY_HIDDEN UnreachableBlockElim : public FunctionPass {
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virtual bool runOnFunction(Function &F);
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public:
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static char ID; // Pass identification, replacement for typeid
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UnreachableBlockElim() : FunctionPass((intptr_t)&ID) {}
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};
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char UnreachableBlockElim::ID = 0;
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RegisterPass<UnreachableBlockElim>
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X("unreachableblockelim", "Remove unreachable blocks from the CFG");
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}
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FunctionPass *llvm::createUnreachableBlockEliminationPass() {
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return new UnreachableBlockElim();
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}
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bool UnreachableBlockElim::runOnFunction(Function &F) {
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std::set<BasicBlock*> Reachable;
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// Mark all reachable blocks.
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for (df_ext_iterator<Function*> I = df_ext_begin(&F, Reachable),
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E = df_ext_end(&F, Reachable); I != E; ++I)
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/* Mark all reachable blocks */;
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// Loop over all dead blocks, remembering them and deleting all instructions
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// in them.
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std::vector<BasicBlock*> DeadBlocks;
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for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
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if (!Reachable.count(I)) {
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BasicBlock *BB = I;
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DeadBlocks.push_back(BB);
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while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
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PN->replaceAllUsesWith(Constant::getNullValue(PN->getType()));
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BB->getInstList().pop_front();
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}
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for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
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(*SI)->removePredecessor(BB);
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BB->dropAllReferences();
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}
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if (DeadBlocks.empty()) return false;
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// Actually remove the blocks now.
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for (unsigned i = 0, e = DeadBlocks.size(); i != e; ++i)
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F.getBasicBlockList().erase(DeadBlocks[i]);
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return true;
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}
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