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/Instructions.h"
22 #include "llvm/Analysis/CallGraph.h"
23 #include "Support/Statistic.h"
28 Statistic<> NumRemoved("prune-eh", "Number of invokes removed");
30 struct PruneEH : public CallGraphSCCPass {
31 /// DoesNotThrow - This set contains all of the functions which we have
32 /// determined cannot throw exceptions.
33 std::set<CallGraphNode*> DoesNotThrow;
35 // runOnSCC - Analyze the SCC, performing the transformation if possible.
36 bool runOnSCC(const std::vector<CallGraphNode *> &SCC);
38 RegisterOpt<PruneEH> X("prune-eh", "Remove unused exception handling info");
41 Pass *llvm::createPruneEHPass() { return new PruneEH(); }
44 bool PruneEH::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
45 CallGraph &CG = getAnalysis<CallGraph>();
47 // First, check to see if any callees might throw or if there are any external
48 // functions in this SCC: if so, we cannot prune any functions in this SCC.
49 // If this SCC includes the unwind instruction, we KNOW it throws, so
50 // obviously the SCC might throw.
52 bool SCCMightThrow = false;
53 for (unsigned i = 0, e = SCC.size(); !SCCMightThrow && i != e; ++i) {
54 Function *F = SCC[i]->getFunction();
55 if (F == 0 || (F->isExternal() && !F->getIntrinsicID())) {
58 // Check to see if this function performs an unwind or calls an
59 // unwinding function.
60 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
61 if (isa<UnwindInst>(BB->getTerminator())) { // Uses unwind!
66 // Invoke instructions don't allow unwinding to continue, so we are
67 // only interested in call instructions.
68 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
69 if (CallInst *CI = dyn_cast<CallInst>(I)) {
70 if (Function *Callee = CI->getCalledFunction()) {
71 CallGraphNode *CalleeNode = CG[Callee];
72 // If the callee is outside our current SCC, or if it is not
73 // known to throw, then we might throw also.
74 if (std::find(SCC.begin(), SCC.end(), CalleeNode) == SCC.end()&&
75 !DoesNotThrow.count(CalleeNode)) {
81 // Indirect call, it might throw.
86 if (SCCMightThrow) break;
90 bool MadeChange = false;
92 for (unsigned i = 0, e = SCC.size(); i != e; ++i) {
93 // If the SCC can't throw, remember this for callers...
95 DoesNotThrow.insert(SCC[i]);
97 // Convert any invoke instructions to non-throwing functions in this node
98 // into call instructions with a branch. This makes the exception blocks
100 if (Function *F = SCC[i]->getFunction())
101 for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I)
102 if (InvokeInst *II = dyn_cast<InvokeInst>(I->getTerminator()))
103 if (Function *F = II->getCalledFunction())
104 if (DoesNotThrow.count(CG[F])) {
105 // Insert a call instruction before the invoke...
106 std::string Name = II->getName(); II->setName("");
107 Value *Call = new CallInst(II->getCalledValue(),
108 std::vector<Value*>(II->op_begin()+3,
112 // Anything that used the value produced by the invoke instruction
113 // now uses the value produced by the call instruction.
114 II->replaceAllUsesWith(Call);
115 II->getUnwindDest()->removePredecessor(II->getParent());
117 // Insert a branch to the normal destination right before the
119 new BranchInst(II->getNormalDest(), II);
121 // Finally, delete the invoke instruction!
122 I->getInstList().pop_back();