//===- 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
//
//===----------------------------------------------------------------------===//
+#define DEBUG_TYPE "prune-eh"
#include "llvm/Transforms/IPO.h"
#include "llvm/CallGraphSCCPass.h"
+#include "llvm/Constants.h"
#include "llvm/Function.h"
#include "llvm/Intrinsics.h"
-#include "llvm/iTerminators.h"
-#include "llvm/iOther.h"
+#include "llvm/Instructions.h"
#include "llvm/Analysis/CallGraph.h"
-#include "Support/Statistic.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Support/Compiler.h"
#include <set>
+#include <algorithm>
using namespace llvm;
+STATISTIC(NumRemoved, "Number of invokes removed");
+STATISTIC(NumUnreach, "Number of noreturn calls optimized");
+
namespace {
- Statistic<> NumRemoved("prune-eh", "Number of invokes removed");
+ struct VISIBILITY_HIDDEN PruneEH : public CallGraphSCCPass {
+ static char ID; // Pass identifcation, replacement for typeid
+ PruneEH() : CallGraphSCCPass((intptr_t)&ID) {}
- struct PruneEH : public CallGraphSCCPass {
- /// DoesNotThrow - This set contains all of the functions which we have
- /// determined cannot throw exceptions.
- std::set<CallGraphNode*> DoesNotThrow;
+ /// DoesNotUnwind - This set contains all of the functions which we have
+ /// determined cannot unwind.
+ std::set<CallGraphNode*> DoesNotUnwind;
+
+ /// DoesNotReturn - This set contains all of the functions which we have
+ /// determined cannot return normally (but might unwind).
+ std::set<CallGraphNode*> DoesNotReturn;
// runOnSCC - Analyze the SCC, performing the transformation if possible.
bool runOnSCC(const std::vector<CallGraphNode *> &SCC);
+
+ bool SimplifyFunction(Function *F);
+ void DeleteBasicBlock(BasicBlock *BB);
};
- RegisterOpt<PruneEH> X("prune-eh", "Remove unused exception handling info");
+
+ char PruneEH::ID = 0;
+ RegisterPass<PruneEH> X("prune-eh", "Remove unused exception handling info");
}
Pass *llvm::createPruneEHPass() { return new PruneEH(); }
bool PruneEH::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
CallGraph &CG = getAnalysis<CallGraph>();
+ bool MadeChange = false;
+
+ // First pass, scan all of the functions in the SCC, simplifying them
+ // according to what we know.
+ for (unsigned i = 0, e = SCC.size(); i != e; ++i)
+ if (Function *F = SCC[i]->getFunction())
+ MadeChange |= SimplifyFunction(F);
- // First, check to see if any callees might throw or if there are any external
+ // Next, 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)
- if (Function *F = SCC[i]->getFunction())
- if (F->isExternal()) {
- 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;
- }
+ bool SCCMightUnwind = false, SCCMightReturn = false;
+ for (unsigned i = 0, e = SCC.size();
+ (!SCCMightUnwind || !SCCMightReturn) && i != e; ++i) {
+ Function *F = SCC[i]->getFunction();
+ if (F == 0 || (F->isDeclaration() && !F->getIntrinsicID())) {
+ SCCMightUnwind = true;
+ SCCMightReturn = true;
+ } else {
+ if (F->isDeclaration())
+ SCCMightReturn = true;
+
+ // 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!
+ SCCMightUnwind = true;
+ } else if (isa<ReturnInst>(BB->getTerminator())) {
+ SCCMightReturn = true;
+ }
- // Invoke instructions don't allow unwinding to continue, so we are
- // only interested in call instructions.
+ // Invoke instructions don't allow unwinding to continue, so we are
+ // only interested in call instructions.
+ if (!SCCMightUnwind)
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
if (CallInst *CI = dyn_cast<CallInst>(I)) {
if (Function *Callee = CI->getCalledFunction()) {
// 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;
+ !DoesNotUnwind.count(CalleeNode)) {
+ SCCMightUnwind = true;
break;
}
-
} else {
// Indirect call, it might throw.
- SCCMightThrow = true;
+ SCCMightUnwind = true;
break;
}
}
- if (SCCMightThrow) break;
- }
+ if (SCCMightUnwind && SCCMightReturn) break;
}
+ }
+ }
- bool MadeChange = false;
+ // If the SCC doesn't unwind or doesn't throw, note this fact.
+ if (!SCCMightUnwind)
+ for (unsigned i = 0, e = SCC.size(); i != e; ++i)
+ DoesNotUnwind.insert(SCC[i]);
+ if (!SCCMightReturn)
+ for (unsigned i = 0, e = SCC.size(); i != e; ++i)
+ DoesNotReturn.insert(SCC[i]);
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;
- }
+ MadeChange |= SimplifyFunction(F);
}
- return MadeChange;
+ return MadeChange;
+}
+
+
+// SimplifyFunction - Given information about callees, simplify the specified
+// function if we have invokes to non-unwinding functions or code after calls to
+// no-return functions.
+bool PruneEH::SimplifyFunction(Function *F) {
+ CallGraph &CG = getAnalysis<CallGraph>();
+ bool MadeChange = false;
+ for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
+ if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator()))
+ if (Function *F = II->getCalledFunction())
+ if (DoesNotUnwind.count(CG[F])) {
+ SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
+ // Insert a call instruction before the invoke.
+ CallInst *Call = new CallInst(II->getCalledValue(),
+ &Args[0], Args.size(), "", II);
+ Call->takeName(II);
+ Call->setCallingConv(II->getCallingConv());
+
+ // Anything that used the value produced by the invoke instruction
+ // now uses the value produced by the call instruction.
+ II->replaceAllUsesWith(Call);
+ BasicBlock *UnwindBlock = II->getUnwindDest();
+ UnwindBlock->removePredecessor(II->getParent());
+
+ // Insert a branch to the normal destination right before the
+ // invoke.
+ new BranchInst(II->getNormalDest(), II);
+
+ // Finally, delete the invoke instruction!
+ BB->getInstList().pop_back();
+
+ // If the unwind block is now dead, nuke it.
+ if (pred_begin(UnwindBlock) == pred_end(UnwindBlock))
+ DeleteBasicBlock(UnwindBlock); // Delete the new BB.
+
+ ++NumRemoved;
+ MadeChange = true;
+ }
+
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; )
+ if (CallInst *CI = dyn_cast<CallInst>(I++))
+ if (Function *Callee = CI->getCalledFunction())
+ if (DoesNotReturn.count(CG[Callee]) && !isa<UnreachableInst>(I)) {
+ // This call calls a function that cannot return. Insert an
+ // unreachable instruction after it and simplify the code. Do this
+ // by splitting the BB, adding the unreachable, then deleting the
+ // new BB.
+ BasicBlock *New = BB->splitBasicBlock(I);
+
+ // Remove the uncond branch and add an unreachable.
+ BB->getInstList().pop_back();
+ new UnreachableInst(BB);
+
+ DeleteBasicBlock(New); // Delete the new BB.
+ MadeChange = true;
+ ++NumUnreach;
+ break;
+ }
+
+ }
+ return MadeChange;
}
+/// DeleteBasicBlock - remove the specified basic block from the program,
+/// updating the callgraph to reflect any now-obsolete edges due to calls that
+/// exist in the BB.
+void PruneEH::DeleteBasicBlock(BasicBlock *BB) {
+ assert(pred_begin(BB) == pred_end(BB) && "BB is not dead!");
+ CallGraph &CG = getAnalysis<CallGraph>();
+
+ CallGraphNode *CGN = CG[BB->getParent()];
+ for (BasicBlock::iterator I = BB->end(), E = BB->begin(); I != E; ) {
+ --I;
+ if (CallInst *CI = dyn_cast<CallInst>(I)) {
+ if (Function *Callee = CI->getCalledFunction())
+ CGN->removeCallEdgeTo(CG[Callee]);
+ } else if (InvokeInst *II = dyn_cast<InvokeInst>(I)) {
+ if (Function *Callee = II->getCalledFunction())
+ CGN->removeCallEdgeTo(CG[Callee]);
+ }
+ if (!I->use_empty())
+ I->replaceAllUsesWith(UndefValue::get(I->getType()));
+ }
+
+ // Get the list of successors of this block.
+ std::vector<BasicBlock*> Succs(succ_begin(BB), succ_end(BB));
+
+ for (unsigned i = 0, e = Succs.size(); i != e; ++i)
+ Succs[i]->removePredecessor(BB);
+
+ BB->eraseFromParent();
+}
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