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100 lines
3.8 KiB
C++
100 lines
3.8 KiB
C++
//===- PruneEH.cpp - Pass which deletes unused exception handlers ---------===//
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//
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// This file implements a simple interprocedural pass which walks the
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// call-graph, turning invoke instructions into calls, iff the callee cannot
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// throw an exception. It implements this as a bottom-up traversal of the
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// call-graph.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CallGraphSCCPass.h"
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#include "llvm/Function.h"
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#include "llvm/Intrinsics.h"
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#include "llvm/iTerminators.h"
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#include "llvm/iOther.h"
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#include "llvm/Analysis/CallGraph.h"
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#include "Support/Statistic.h"
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#include <set>
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namespace {
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Statistic<> NumRemoved("prune-eh", "Number of invokes removed");
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struct PruneEH : public CallGraphSCCPass {
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/// DoesNotThrow - This set contains all of the functions which we have
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/// determined cannot throw exceptions.
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std::set<CallGraphNode*> DoesNotThrow;
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// runOnSCC - Analyze the SCC, performing the transformation if possible.
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bool runOnSCC(const std::vector<CallGraphNode *> &SCC);
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};
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RegisterOpt<PruneEH> X("prune-eh", "Remove unused exception handling info");
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}
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Pass *createPruneEHPass() { return new PruneEH(); }
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bool PruneEH::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
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CallGraph &CG = getAnalysis<CallGraph>();
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// First, check to see if any callees might throw or if there are any external
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// functions in this SCC: if so, we cannot prune any functions in this SCC.
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// If this SCC includes the unwind instruction, we KNOW it throws, so
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// obviously the SCC might throw.
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//
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bool SCCMightThrow = false;
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for (unsigned i = 0, e = SCC.size(); i != e; ++i)
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if (!DoesNotThrow.count(SCC[i]) && // Calls maybe throwing fn
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// Make sure this is not one of the fn's in the SCC.
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std::find(SCC.begin(), SCC.end(), SCC[i]) == SCC.end()) {
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SCCMightThrow = true; break;
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} else if (Function *F = SCC[i]->getFunction())
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if (F->isExternal()) {
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SCCMightThrow = true; break;
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} else {
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for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I)
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if (isa<UnwindInst>(I->getTerminator())) { // Uses unwind!
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SCCMightThrow = true; break;
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}
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}
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bool MadeChange = false;
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for (unsigned i = 0, e = SCC.size(); i != e; ++i) {
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// If the SCC can't throw, remember this for callers...
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if (!SCCMightThrow)
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DoesNotThrow.insert(SCC[i]);
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// Convert any invoke instructions to non-throwing functions in this node
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// into call instructions with a branch. This makes the exception blocks
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// dead.
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if (Function *F = SCC[i]->getFunction())
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for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I)
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if (InvokeInst *II = dyn_cast<InvokeInst>(I->getTerminator()))
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if (Function *F = II->getCalledFunction())
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if (DoesNotThrow.count(CG[F])) {
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// Insert a call instruction before the invoke...
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std::string Name = II->getName(); II->setName("");
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Value *Call = new CallInst(II->getCalledValue(),
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std::vector<Value*>(II->op_begin()+3,
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II->op_end()),
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Name, II);
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// Anything that used the value produced by the invoke instruction
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// now uses the value produced by the call instruction.
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II->replaceAllUsesWith(Call);
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// Insert a branch to the normal destination right before the
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// invoke.
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new BranchInst(II->getNormalDest(), II);
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// Finally, delete the invoke instruction!
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I->getInstList().pop_back();
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++NumRemoved;
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MadeChange = true;
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}
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}
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return MadeChange;
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}
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