//
// 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/LLVMContext.h"
#include "llvm/Instructions.h"
+#include "llvm/IntrinsicInst.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 <set>
#include <algorithm>
using namespace llvm;
-namespace {
- Statistic<> NumRemoved("prune-eh", "Number of invokes removed");
+STATISTIC(NumRemoved, "Number of invokes removed");
+STATISTIC(NumUnreach, "Number of noreturn calls optimized");
+namespace {
struct PruneEH : public CallGraphSCCPass {
- /// DoesNotUnwind - This set contains all of the functions which we have
- /// determined cannot throw exceptions.
- std::set<CallGraphNode*> DoesNotUnwind;
+ static char ID; // Pass identification, replacement for typeid
+ PruneEH() : CallGraphSCCPass(ID) {}
// runOnSCC - Analyze the SCC, performing the transformation if possible.
- bool runOnSCC(const std::vector<CallGraphNode *> &SCC);
+ bool runOnSCC(CallGraphSCC &SCC);
+
+ bool SimplifyFunction(Function *F);
+ void DeleteBasicBlock(BasicBlock *BB);
};
- RegisterOpt<PruneEH> X("prune-eh", "Remove unused exception handling info");
}
-ModulePass *llvm::createPruneEHPass() { return new PruneEH(); }
+char PruneEH::ID = 0;
+INITIALIZE_PASS(PruneEH, "prune-eh",
+ "Remove unused exception handling info", false, false);
+Pass *llvm::createPruneEHPass() { return new PruneEH(); }
-bool PruneEH::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
+
+bool PruneEH::runOnSCC(CallGraphSCC &SCC) {
+ SmallPtrSet<CallGraphNode *, 8> SCCNodes;
CallGraph &CG = getAnalysis<CallGraph>();
+ bool MadeChange = false;
- // First, check to see if any callees might throw or if there are any external
+ // 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 (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;
- for (unsigned i = 0, e = SCC.size(); !SCCMightUnwind && i != e; ++i) {
- Function *F = SCC[i]->getFunction();
- if (F == 0 || (F->isExternal() && !F->getIntrinsicID())) {
+ bool SCCMightUnwind = false, SCCMightReturn = false;
+ for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end();
+ (!SCCMightUnwind || !SCCMightReturn) && I != E; ++I) {
+ Function *F = (*I)->getFunction();
+ if (F == 0) {
SCCMightUnwind = true;
+ SCCMightReturn = true;
+ } else if (F->isDeclaration() || F->mayBeOverridden()) {
+ SCCMightUnwind |= !F->doesNotThrow();
+ SCCMightReturn |= !F->doesNotReturn();
} else {
+ bool CheckUnwind = !SCCMightUnwind && !F->doesNotThrow();
+ bool CheckReturn = !SCCMightReturn && !F->doesNotReturn();
+
+ if (!CheckUnwind && !CheckReturn)
+ continue;
+
// 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!
+ if (CheckUnwind && isa<UnwindInst>(BB->getTerminator())) {
+ // Uses unwind!
SCCMightUnwind = true;
- break;
+ } else if (CheckReturn && isa<ReturnInst>(BB->getTerminator())) {
+ SCCMightReturn = true;
}
// 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()&&
- !DoesNotUnwind.count(CalleeNode)) {
+ if (CheckUnwind && !SCCMightUnwind)
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
+ if (CallInst *CI = dyn_cast<CallInst>(I)) {
+ if (CI->doesNotThrow()) {
+ // This call cannot throw.
+ } else if (Function *Callee = CI->getCalledFunction()) {
+ CallGraphNode *CalleeNode = CG[Callee];
+ // If the callee is outside our current SCC then we may
+ // throw because it might.
+ if (!SCCNodes.count(CalleeNode)) {
+ SCCMightUnwind = true;
+ break;
+ }
+ } else {
+ // Indirect call, it might throw.
SCCMightUnwind = true;
break;
}
-
- } else {
- // Indirect call, it might throw.
- SCCMightUnwind = true;
- break;
}
- }
- if (SCCMightUnwind) break;
+ if (SCCMightUnwind && SCCMightReturn) 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 (!SCCMightUnwind)
- DoesNotUnwind.insert(SCC[i]);
+ // If the SCC doesn't unwind or doesn't throw, note this fact.
+ if (!SCCMightUnwind || !SCCMightReturn)
+ for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
+ Attributes NewAttributes = Attribute::None;
+
+ if (!SCCMightUnwind)
+ NewAttributes |= Attribute::NoUnwind;
+ if (!SCCMightReturn)
+ NewAttributes |= Attribute::NoReturn;
+
+ Function *F = (*I)->getFunction();
+ const AttrListPtr &PAL = F->getAttributes();
+ const AttrListPtr &NPAL = PAL.addAttr(~0, NewAttributes);
+ if (PAL != NPAL) {
+ MadeChange = true;
+ F->setAttributes(NPAL);
+ }
+ }
+ 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())
- 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 (DoesNotUnwind.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;
- }
+ if (Function *F = (*I)->getFunction())
+ MadeChange |= SimplifyFunction(F);
}
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) {
+ bool MadeChange = false;
+ for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
+ if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator()))
+ if (II->doesNotThrow()) {
+ SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
+ // Insert a call instruction before the invoke.
+ CallInst *Call = CallInst::Create(II->getCalledValue(),
+ Args.begin(), Args.end(), "", II);
+ Call->takeName(II);
+ Call->setCallingConv(II->getCallingConv());
+ Call->setAttributes(II->getAttributes());
+
+ // Anything that used the value produced by the invoke instruction
+ // now uses the value produced by the call instruction. Note that we
+ // do this even for void functions and calls with no uses so that the
+ // callgraph edge is updated.
+ II->replaceAllUsesWith(Call);
+ BasicBlock *UnwindBlock = II->getUnwindDest();
+ UnwindBlock->removePredecessor(II->getParent());
+
+ // Insert a branch to the normal destination right before the
+ // invoke.
+ BranchInst::Create(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 (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;
+}
+
+/// 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 (!isa<DbgInfoIntrinsic>(I))
+ CGN->removeCallEdgeFor(CI);
+ } else if (InvokeInst *II = dyn_cast<InvokeInst>(I))
+ CGN->removeCallEdgeFor(II);
+ 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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