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//===- PruneEH.cpp - Pass which deletes unused exception handlers ---------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// 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/Transforms/IPO.h"
#include "llvm/CallGraphSCCPass.h"
#include "llvm/Function.h"
#include "llvm/Intrinsics.h"
#include "llvm/Instructions.h"
#include "llvm/Analysis/CallGraph.h"
#include "llvm/ADT/Statistic.h"
#include <set>
using namespace llvm;
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");
}
ModulePass *llvm::createPruneEHPass() { return new PruneEH(); }
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 unwind instruction, we KNOW it throws, so
// obviously the SCC might throw.
//
bool SCCMightThrow = false;
for (unsigned i = 0, e = SCC.size(); !SCCMightThrow && i != e; ++i) {
Function *F = SCC[i]->getFunction();
if (F == 0 || (F->isExternal() && !F->getIntrinsicID())) {
SCCMightThrow = true;
} else {
// Check to see if this function performs an unwind or calls an
// unwinding function.
for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
if (isa<UnwindInst>(BB->getTerminator())) { // Uses unwind!
SCCMightThrow = true;
break;
}
// Invoke instructions don't allow unwinding to continue, so we are
// only interested in call instructions.
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
if (CallInst *CI = dyn_cast<CallInst>(I)) {
if (Function *Callee = CI->getCalledFunction()) {
CallGraphNode *CalleeNode = CG[Callee];
// If the callee is outside our current SCC, or if it is not
// known to throw, then we might throw also.
if (std::find(SCC.begin(), SCC.end(), CalleeNode) == SCC.end()&&
!DoesNotThrow.count(CalleeNode)) {
SCCMightThrow = true;
break;
}
} else {
// Indirect call, it might throw.
SCCMightThrow = true;
break;
}
}
if (SCCMightThrow) 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);
II->getUnwindDest()->removePredecessor(II->getParent());
// 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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