1 //===- PruneEH.cpp - Pass which deletes unused exception handlers ---------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements a simple interprocedural pass which walks the
11 // call-graph, turning invoke instructions into calls, iff the callee cannot
12 // throw an exception. It implements this as a bottom-up traversal of the
15 //===----------------------------------------------------------------------===//
17 #include "llvm/Transforms/IPO.h"
18 #include "llvm/CallGraphSCCPass.h"
19 #include "llvm/Function.h"
20 #include "llvm/Intrinsics.h"
21 #include "llvm/iTerminators.h"
22 #include "llvm/iOther.h"
23 #include "llvm/Analysis/CallGraph.h"
24 #include "Support/Statistic.h"
29 Statistic<> NumRemoved("prune-eh", "Number of invokes removed");
31 struct PruneEH : public CallGraphSCCPass {
32 /// DoesNotThrow - This set contains all of the functions which we have
33 /// determined cannot throw exceptions.
34 std::set<CallGraphNode*> DoesNotThrow;
36 // runOnSCC - Analyze the SCC, performing the transformation if possible.
37 bool runOnSCC(const std::vector<CallGraphNode *> &SCC);
39 RegisterOpt<PruneEH> X("prune-eh", "Remove unused exception handling info");
42 Pass *llvm::createPruneEHPass() { return new PruneEH(); }
45 bool PruneEH::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
46 CallGraph &CG = getAnalysis<CallGraph>();
48 // First, check to see if any callees might throw or if there are any external
49 // functions in this SCC: if so, we cannot prune any functions in this SCC.
50 // If this SCC includes the unwind instruction, we KNOW it throws, so
51 // obviously the SCC might throw.
53 bool SCCMightThrow = false;
54 for (unsigned i = 0, e = SCC.size(); !SCCMightThrow && i != e; ++i)
55 if (Function *F = SCC[i]->getFunction())
56 if (F->isExternal() && !F->getIntrinsicID()) {
59 // Check to see if this function performs an unwind or calls an
60 // unwinding function.
61 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
62 if (isa<UnwindInst>(BB->getTerminator())) { // Uses unwind!
67 // Invoke instructions don't allow unwinding to continue, so we are
68 // only interested in call instructions.
69 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
70 if (CallInst *CI = dyn_cast<CallInst>(I)) {
71 if (Function *Callee = CI->getCalledFunction()) {
72 CallGraphNode *CalleeNode = CG[Callee];
73 // If the callee is outside our current SCC, or if it is not
74 // known to throw, then we might throw also.
75 if (std::find(SCC.begin(), SCC.end(), CalleeNode) == SCC.end()&&
76 !DoesNotThrow.count(CalleeNode)) {
82 // Indirect call, it might throw.
87 if (SCCMightThrow) break;
91 bool MadeChange = false;
93 for (unsigned i = 0, e = SCC.size(); i != e; ++i) {
94 // If the SCC can't throw, remember this for callers...
96 DoesNotThrow.insert(SCC[i]);
98 // Convert any invoke instructions to non-throwing functions in this node
99 // into call instructions with a branch. This makes the exception blocks
101 if (Function *F = SCC[i]->getFunction())
102 for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I)
103 if (InvokeInst *II = dyn_cast<InvokeInst>(I->getTerminator()))
104 if (Function *F = II->getCalledFunction())
105 if (DoesNotThrow.count(CG[F])) {
106 // Insert a call instruction before the invoke...
107 std::string Name = II->getName(); II->setName("");
108 Value *Call = new CallInst(II->getCalledValue(),
109 std::vector<Value*>(II->op_begin()+3,
113 // Anything that used the value produced by the invoke instruction
114 // now uses the value produced by the call instruction.
115 II->replaceAllUsesWith(Call);
116 II->getUnwindDest()->removePredecessor(II->getParent());
118 // Insert a branch to the normal destination right before the
120 new BranchInst(II->getNormalDest(), II);
122 // Finally, delete the invoke instruction!
123 I->getInstList().pop_back();