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