//
// 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 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.
+// throw an exception, and marking functions 'nounwind' if they cannot throw.
+// It implements this as a bottom-up traversal of the call-graph.
//
//===----------------------------------------------------------------------===//
-#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/Instructions.h"
-#include "llvm/Analysis/CallGraph.h"
+#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
-#include "llvm/Support/CFG.h"
-#include "llvm/Support/Compiler.h"
-#include <set>
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Analysis/CallGraph.h"
+#include "llvm/Analysis/CallGraphSCCPass.h"
+#include "llvm/Analysis/EHPersonalities.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/InlineAsm.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/Transforms/Utils/Local.h"
#include <algorithm>
using namespace llvm;
+#define DEBUG_TYPE "prune-eh"
+
STATISTIC(NumRemoved, "Number of invokes removed");
STATISTIC(NumUnreach, "Number of noreturn calls optimized");
namespace {
- struct VISIBILITY_HIDDEN PruneEH : public CallGraphSCCPass {
- static char ID; // Pass identifcation, replacement for typeid
- PruneEH() : CallGraphSCCPass((intptr_t)&ID) {}
-
- /// 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;
+ struct PruneEH : public CallGraphSCCPass {
+ static char ID; // Pass identification, replacement for typeid
+ PruneEH() : CallGraphSCCPass(ID) {
+ initializePruneEHPass(*PassRegistry::getPassRegistry());
+ }
// runOnSCC - Analyze the SCC, performing the transformation if possible.
- bool runOnSCC(const std::vector<CallGraphNode *> &SCC);
+ bool runOnSCC(CallGraphSCC &SCC) override;
bool SimplifyFunction(Function *F);
void DeleteBasicBlock(BasicBlock *BB);
};
-
- char PruneEH::ID = 0;
- RegisterPass<PruneEH> X("prune-eh", "Remove unused exception handling info");
}
+char PruneEH::ID = 0;
+INITIALIZE_PASS_BEGIN(PruneEH, "prune-eh",
+ "Remove unused exception handling info", false, false)
+INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
+INITIALIZE_PASS_END(PruneEH, "prune-eh",
+ "Remove unused exception handling info", false, false)
+
Pass *llvm::createPruneEHPass() { return new PruneEH(); }
-bool PruneEH::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
- CallGraph &CG = getAnalysis<CallGraph>();
+bool PruneEH::runOnSCC(CallGraphSCC &SCC) {
+ SmallPtrSet<CallGraphNode *, 8> SCCNodes;
+ CallGraph &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
bool MadeChange = false;
+ // Fill SCCNodes with the elements of the SCC. Used for quickly
+ // looking up whether a given CallGraphNode is in this SCC.
+ for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I)
+ SCCNodes.insert(*I);
+
// 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())
+ for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I)
+ if (Function *F = (*I)->getFunction())
MadeChange |= SimplifyFunction(F);
// 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.
+ // Definitions that are weak and not declared non-throwing might be
+ // overridden at linktime with something that throws, so assume that.
// If this SCC includes the unwind instruction, we KNOW it throws, so
// obviously the SCC might throw.
//
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())) {
+ for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end();
+ (!SCCMightUnwind || !SCCMightReturn) && I != E; ++I) {
+ Function *F = (*I)->getFunction();
+ if (!F) {
SCCMightUnwind = true;
SCCMightReturn = true;
+ } else if (F->isDeclaration() || F->mayBeOverridden()) {
+ SCCMightUnwind |= !F->doesNotThrow();
+ SCCMightReturn |= !F->doesNotReturn();
} 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!
+ bool CheckUnwind = !SCCMightUnwind && !F->doesNotThrow();
+ bool CheckReturn = !SCCMightReturn && !F->doesNotReturn();
+ // Determine if we should scan for InlineAsm in a naked function as it
+ // is the only way to return without a ReturnInst. Only do this for
+ // no-inline functions as functions which may be inlined cannot
+ // meaningfully return via assembly.
+ bool CheckReturnViaAsm = CheckReturn &&
+ F->hasFnAttribute(Attribute::Naked) &&
+ F->hasFnAttribute(Attribute::NoInline);
+
+ if (!CheckUnwind && !CheckReturn)
+ continue;
+
+ for (const BasicBlock &BB : *F) {
+ const TerminatorInst *TI = BB.getTerminator();
+ if (CheckUnwind && TI->mayThrow()) {
SCCMightUnwind = true;
- } else if (isa<ReturnInst>(BB->getTerminator())) {
+ } else if (CheckReturn && isa<ReturnInst>(TI)) {
SCCMightReturn = true;
}
- // 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)) {
+ for (const Instruction &I : BB) {
+ if ((!CheckUnwind || SCCMightUnwind) &&
+ (!CheckReturnViaAsm || SCCMightReturn))
+ break;
+
+ // Check to see if this function performs an unwind or calls an
+ // unwinding function.
+ if (CheckUnwind && !SCCMightUnwind && I.mayThrow()) {
+ bool InstMightUnwind = true;
+ if (const auto *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()&&
- !DoesNotUnwind.count(CalleeNode)) {
- SCCMightUnwind = true;
- break;
- }
- } else {
- // Indirect call, it might throw.
- SCCMightUnwind = true;
- break;
+ // If the callee is outside our current SCC then we may throw
+ // because it might. If it is inside, do nothing.
+ if (SCCNodes.count(CalleeNode) > 0)
+ InstMightUnwind = false;
}
}
- if (SCCMightUnwind && SCCMightReturn) break;
+ SCCMightUnwind |= InstMightUnwind;
+ }
+ if (CheckReturnViaAsm && !SCCMightReturn)
+ if (auto ICS = ImmutableCallSite(&I))
+ if (const auto *IA = dyn_cast<InlineAsm>(ICS.getCalledValue()))
+ if (IA->hasSideEffects())
+ SCCMightReturn = true;
+ }
+
+ if (SCCMightUnwind && SCCMightReturn)
+ break;
}
}
}
// 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 (!SCCMightUnwind || !SCCMightReturn)
+ for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
+ Function *F = (*I)->getFunction();
+
+ if (!SCCMightUnwind && !F->hasFnAttribute(Attribute::NoUnwind)) {
+ F->addFnAttr(Attribute::NoUnwind);
+ MadeChange = true;
+ }
+
+ if (!SCCMightReturn && !F->hasFnAttribute(Attribute::NoReturn)) {
+ F->addFnAttr(Attribute::NoReturn);
+ MadeChange = true;
+ }
+ }
+
+ for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++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())
+ if (Function *F = (*I)->getFunction())
MadeChange |= SimplifyFunction(F);
}
// 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 (II->doesNotThrow() && canSimplifyInvokeNoUnwind(F)) {
+ BasicBlock *UnwindBlock = II->getUnwindDest();
+ removeUnwindEdge(&*BB);
- // If the unwind block is now dead, nuke it.
- if (pred_begin(UnwindBlock) == pred_end(UnwindBlock))
- DeleteBasicBlock(UnwindBlock); // Delete the new BB.
+ // If the unwind block is now dead, nuke it.
+ if (pred_empty(UnwindBlock))
+ DeleteBasicBlock(UnwindBlock); // Delete the new BB.
- ++NumRemoved;
- MadeChange = true;
- }
+ ++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;
- }
+ if (CI->doesNotReturn() && !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->getContext(), &*BB);
+ DeleteBasicBlock(New); // Delete the new BB.
+ MadeChange = true;
+ ++NumUnreach;
+ break;
+ }
}
+
return MadeChange;
}
/// 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>();
+ assert(pred_empty(BB) && "BB is not dead!");
+ CallGraph &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
+
+ Instruction *TokenInst = nullptr;
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->getType()->isTokenTy()) {
+ TokenInst = &*I;
+ break;
}
+
+ if (auto CS = CallSite (&*I)) {
+ const Function *Callee = CS.getCalledFunction();
+ if (!Callee || !Intrinsic::isLeaf(Callee->getIntrinsicID()))
+ CGN->removeCallEdgeFor(CS);
+ else if (!Callee->isIntrinsic())
+ CGN->removeCallEdgeFor(CS);
+ }
+
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));
+ if (TokenInst) {
+ if (!isa<TerminatorInst>(TokenInst))
+ changeToUnreachable(TokenInst->getNextNode(), /*UseLLVMTrap=*/false);
+ } else {
+ // 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);
+ for (unsigned i = 0, e = Succs.size(); i != e; ++i)
+ Succs[i]->removePredecessor(BB);
- BB->eraseFromParent();
+ BB->eraseFromParent();
+ }
}
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