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7f0566c123
basic block clear()'s all of the operands lists, including phis. This caused removePredecessor to get confused later. Because of this, we just nuke (without prejudice) PHI nodes in unreachable blocks. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@14635 91177308-0d34-0410-b5e6-96231b3b80d8
76 lines
2.7 KiB
C++
76 lines
2.7 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/iPHINode.h"
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#include "llvm/Constant.h"
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#include "llvm/Function.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/CFG.h"
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#include "Support/DepthFirstIterator.h"
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using namespace llvm;
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namespace {
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class UnreachableBlockElim : public FunctionPass {
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virtual bool runOnFunction(Function &F);
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};
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RegisterOpt<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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