-//===- FunctionAttrs.cpp - Pass which marks functions readnone or readonly ===//
+//===- FunctionAttrs.cpp - Pass which marks functions attributes ----------===//
//
// The LLVM Compiler Infrastructure
//
//
// This file implements a simple interprocedural pass which walks the
// call-graph, looking for functions which do not access or only read
-// non-local memory, and marking them readnone/readonly. In addition,
-// it marks function arguments (of pointer type) 'nocapture' if a call
-// to the function does not create any copies of the pointer value that
-// outlive the call. This more or less means that the pointer is only
-// dereferenced, and not returned from the function or stored in a global.
-// This pass is implemented as a bottom-up traversal of the call-graph.
+// non-local memory, and marking them readnone/readonly. It does the
+// same with function arguments independently, marking them readonly/
+// readnone/nocapture. Finally, well-known library call declarations
+// are marked with all attributes that are consistent with the
+// function's standard definition. This pass is implemented as a
+// bottom-up traversal of the call-graph.
//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "functionattrs"
#include "llvm/Transforms/IPO.h"
-#include "llvm/CallGraphSCCPass.h"
-#include "llvm/GlobalVariable.h"
-#include "llvm/IntrinsicInst.h"
-#include "llvm/LLVMContext.h"
+#include "llvm/ADT/SCCIterator.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/StringSwitch.h"
#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/AssumptionCache.h"
+#include "llvm/Analysis/BasicAliasAnalysis.h"
#include "llvm/Analysis/CallGraph.h"
+#include "llvm/Analysis/CallGraphSCCPass.h"
#include "llvm/Analysis/CaptureTracking.h"
-#include "llvm/ADT/SmallSet.h"
-#include "llvm/ADT/Statistic.h"
-#include "llvm/ADT/UniqueVector.h"
-#include "llvm/Support/InstIterator.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
using namespace llvm;
+#define DEBUG_TYPE "functionattrs"
+
STATISTIC(NumReadNone, "Number of functions marked readnone");
STATISTIC(NumReadOnly, "Number of functions marked readonly");
STATISTIC(NumNoCapture, "Number of arguments marked nocapture");
+STATISTIC(NumReadNoneArg, "Number of arguments marked readnone");
+STATISTIC(NumReadOnlyArg, "Number of arguments marked readonly");
STATISTIC(NumNoAlias, "Number of function returns marked noalias");
+STATISTIC(NumNonNullReturn, "Number of function returns marked nonnull");
+STATISTIC(NumNoRecurse, "Number of functions marked as norecurse");
namespace {
- struct FunctionAttrs : public CallGraphSCCPass {
- static char ID; // Pass identification, replacement for typeid
- FunctionAttrs() : CallGraphSCCPass(ID), AA(0) {
- initializeFunctionAttrsPass(*PassRegistry::getPassRegistry());
- }
-
- // runOnSCC - Analyze the SCC, performing the transformation if possible.
- bool runOnSCC(CallGraphSCC &SCC);
-
- // AddReadAttrs - Deduce readonly/readnone attributes for the SCC.
- bool AddReadAttrs(const CallGraphSCC &SCC);
-
- // AddNoCaptureAttrs - Deduce nocapture attributes for the SCC.
- bool AddNoCaptureAttrs(const CallGraphSCC &SCC);
-
- // IsFunctionMallocLike - Does this function allocate new memory?
- bool IsFunctionMallocLike(Function *F,
- SmallPtrSet<Function*, 8> &) const;
+typedef SmallSetVector<Function *, 8> SCCNodeSet;
+}
- // AddNoAliasAttrs - Deduce noalias attributes for the SCC.
- bool AddNoAliasAttrs(const CallGraphSCC &SCC);
+namespace {
+struct FunctionAttrs : public CallGraphSCCPass {
+ static char ID; // Pass identification, replacement for typeid
+ FunctionAttrs() : CallGraphSCCPass(ID) {
+ initializeFunctionAttrsPass(*PassRegistry::getPassRegistry());
+ }
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- AU.setPreservesCFG();
- AU.addRequired<AliasAnalysis>();
- CallGraphSCCPass::getAnalysisUsage(AU);
- }
+ bool runOnSCC(CallGraphSCC &SCC) override;
+ bool doInitialization(CallGraph &CG) override {
+ Revisit.clear();
+ return false;
+ }
+ bool doFinalization(CallGraph &CG) override;
+
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.setPreservesCFG();
+ AU.addRequired<AssumptionCacheTracker>();
+ AU.addRequired<TargetLibraryInfoWrapperPass>();
+ CallGraphSCCPass::getAnalysisUsage(AU);
+ }
- private:
- AliasAnalysis *AA;
- };
+private:
+ TargetLibraryInfo *TLI;
+ SmallVector<WeakVH,16> Revisit;
+};
}
char FunctionAttrs::ID = 0;
INITIALIZE_PASS_BEGIN(FunctionAttrs, "functionattrs",
- "Deduce function attributes", false, false)
-INITIALIZE_AG_DEPENDENCY(CallGraph)
+ "Deduce function attributes", false, false)
+INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
+INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_END(FunctionAttrs, "functionattrs",
- "Deduce function attributes", false, false)
+ "Deduce function attributes", false, false)
Pass *llvm::createFunctionAttrsPass() { return new FunctionAttrs(); }
+namespace {
+/// The three kinds of memory access relevant to 'readonly' and
+/// 'readnone' attributes.
+enum MemoryAccessKind {
+ MAK_ReadNone = 0,
+ MAK_ReadOnly = 1,
+ MAK_MayWrite = 2
+};
+}
-/// AddReadAttrs - Deduce readonly/readnone attributes for the SCC.
-bool FunctionAttrs::AddReadAttrs(const CallGraphSCC &SCC) {
- SmallPtrSet<Function*, 8> SCCNodes;
+static MemoryAccessKind checkFunctionMemoryAccess(Function &F, AAResults &AAR,
+ const SCCNodeSet &SCCNodes) {
+ FunctionModRefBehavior MRB = AAR.getModRefBehavior(&F);
+ if (MRB == FMRB_DoesNotAccessMemory)
+ // Already perfect!
+ return MAK_ReadNone;
- // 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)->getFunction());
+ // Definitions with weak linkage may be overridden at linktime with
+ // something that writes memory, so treat them like declarations.
+ if (F.isDeclaration() || F.mayBeOverridden()) {
+ if (AliasAnalysis::onlyReadsMemory(MRB))
+ return MAK_ReadOnly;
- // Check if any of the functions in the SCC read or write memory. If they
- // write memory then they can't be marked readnone or readonly.
+ // Conservatively assume it writes to memory.
+ return MAK_MayWrite;
+ }
+
+ // Scan the function body for instructions that may read or write memory.
bool ReadsMemory = false;
- for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
- Function *F = (*I)->getFunction();
+ for (inst_iterator II = inst_begin(F), E = inst_end(F); II != E; ++II) {
+ Instruction *I = &*II;
- if (F == 0)
- // External node - may write memory. Just give up.
- return false;
+ // Some instructions can be ignored even if they read or write memory.
+ // Detect these now, skipping to the next instruction if one is found.
+ CallSite CS(cast<Value>(I));
+ if (CS) {
+ // Ignore calls to functions in the same SCC.
+ if (CS.getCalledFunction() && SCCNodes.count(CS.getCalledFunction()))
+ continue;
+ FunctionModRefBehavior MRB = AAR.getModRefBehavior(CS);
- if (F->doesNotAccessMemory())
- // Already perfect!
- continue;
+ // If the call doesn't access memory, we're done.
+ if (!(MRB & MRI_ModRef))
+ continue;
- // Definitions with weak linkage may be overridden at linktime with
- // something that writes memory, so treat them like declarations.
- if (F->isDeclaration() || F->mayBeOverridden()) {
- if (!F->onlyReadsMemory())
- // May write memory. Just give up.
- return false;
+ if (!AliasAnalysis::onlyAccessesArgPointees(MRB)) {
+ // The call could access any memory. If that includes writes, give up.
+ if (MRB & MRI_Mod)
+ return MAK_MayWrite;
+ // If it reads, note it.
+ if (MRB & MRI_Ref)
+ ReadsMemory = true;
+ continue;
+ }
- ReadsMemory = true;
- continue;
- }
+ // Check whether all pointer arguments point to local memory, and
+ // ignore calls that only access local memory.
+ for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
+ CI != CE; ++CI) {
+ Value *Arg = *CI;
+ if (!Arg->getType()->isPtrOrPtrVectorTy())
+ continue;
- // Scan the function body for instructions that may read or write memory.
- for (inst_iterator II = inst_begin(F), E = inst_end(F); II != E; ++II) {
- Instruction *I = &*II;
+ AAMDNodes AAInfo;
+ I->getAAMetadata(AAInfo);
+ MemoryLocation Loc(Arg, MemoryLocation::UnknownSize, AAInfo);
- // Some instructions can be ignored even if they read or write memory.
- // Detect these now, skipping to the next instruction if one is found.
- CallSite CS(cast<Value>(I));
- if (CS) {
- // Ignore calls to functions in the same SCC.
- if (CS.getCalledFunction() && SCCNodes.count(CS.getCalledFunction()))
- continue;
- switch (AA->getModRefBehavior(CS)) {
- case AliasAnalysis::DoesNotAccessMemory:
- // Ignore calls that don't access memory.
+ // Skip accesses to local or constant memory as they don't impact the
+ // externally visible mod/ref behavior.
+ if (AAR.pointsToConstantMemory(Loc, /*OrLocal=*/true))
continue;
- case AliasAnalysis::OnlyReadsMemory:
- // Handle calls that only read from memory.
+
+ if (MRB & MRI_Mod)
+ // Writes non-local memory. Give up.
+ return MAK_MayWrite;
+ if (MRB & MRI_Ref)
+ // Ok, it reads non-local memory.
ReadsMemory = true;
+ }
+ continue;
+ } else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
+ // Ignore non-volatile loads from local memory. (Atomic is okay here.)
+ if (!LI->isVolatile()) {
+ MemoryLocation Loc = MemoryLocation::get(LI);
+ if (AAR.pointsToConstantMemory(Loc, /*OrLocal=*/true))
continue;
- case AliasAnalysis::AccessesArguments:
- // Check whether all pointer arguments point to local memory, and
- // ignore calls that only access local memory.
- for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
- CI != CE; ++CI) {
- Value *Arg = *CI;
- if (Arg->getType()->isPointerTy()) {
- AliasAnalysis::Location Loc(Arg,
- AliasAnalysis::UnknownSize,
- I->getMetadata(LLVMContext::MD_tbaa));
- if (!AA->pointsToConstantMemory(Loc, /*OrLocal=*/true))
- // Writes memory. Just give up.
- return false;
- }
- }
- // Only reads and writes local memory.
- continue;
- case AliasAnalysis::AccessesArgumentsReadonly:
- // Check whether all pointer arguments point to local memory, and
- // ignore calls that only access local memory.
- for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
- CI != CE; ++CI) {
- Value *Arg = *CI;
- if (Arg->getType()->isPointerTy()) {
- AliasAnalysis::Location Loc(Arg,
- AliasAnalysis::UnknownSize,
- I->getMetadata(LLVMContext::MD_tbaa));
- if (!AA->pointsToConstantMemory(Loc, /*OrLocal=*/true)) {
- // Reads non-local memory.
- ReadsMemory = true;
- break;
- }
- }
- }
- // Only reads memory.
+ }
+ } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
+ // Ignore non-volatile stores to local memory. (Atomic is okay here.)
+ if (!SI->isVolatile()) {
+ MemoryLocation Loc = MemoryLocation::get(SI);
+ if (AAR.pointsToConstantMemory(Loc, /*OrLocal=*/true))
continue;
- default:
- // Otherwise, be conservative.
- break;
- }
- } else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
- // Ignore non-volatile loads from local memory.
- if (!LI->isVolatile()) {
- AliasAnalysis::Location Loc(LI->getPointerOperand(),
- AA->getTypeStoreSize(LI->getType()),
- LI->getMetadata(LLVMContext::MD_tbaa));
- if (AA->pointsToConstantMemory(Loc, /*OrLocal=*/true))
- continue;
- }
- } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
- // Ignore non-volatile stores to local memory.
- if (!SI->isVolatile()) {
- const Type *StoredType = SI->getValueOperand()->getType();
- AliasAnalysis::Location Loc(SI->getPointerOperand(),
- AA->getTypeStoreSize(StoredType),
- SI->getMetadata(LLVMContext::MD_tbaa));
- if (AA->pointsToConstantMemory(Loc, /*OrLocal=*/true))
- continue;
- }
}
+ } else if (VAArgInst *VI = dyn_cast<VAArgInst>(I)) {
+ // Ignore vaargs on local memory.
+ MemoryLocation Loc = MemoryLocation::get(VI);
+ if (AAR.pointsToConstantMemory(Loc, /*OrLocal=*/true))
+ continue;
+ }
- // Any remaining instructions need to be taken seriously! Check if they
- // read or write memory.
- if (I->mayWriteToMemory())
- // Writes memory. Just give up.
- return false;
+ // Any remaining instructions need to be taken seriously! Check if they
+ // read or write memory.
+ if (I->mayWriteToMemory())
+ // Writes memory. Just give up.
+ return MAK_MayWrite;
- // If this instruction may read memory, remember that.
- ReadsMemory |= I->mayReadFromMemory();
+ // If this instruction may read memory, remember that.
+ ReadsMemory |= I->mayReadFromMemory();
+ }
+
+ return ReadsMemory ? MAK_ReadOnly : MAK_ReadNone;
+}
+
+/// Deduce readonly/readnone attributes for the SCC.
+template <typename AARGetterT>
+static bool addReadAttrs(const SCCNodeSet &SCCNodes, AARGetterT AARGetter) {
+ // Check if any of the functions in the SCC read or write memory. If they
+ // write memory then they can't be marked readnone or readonly.
+ bool ReadsMemory = false;
+ for (Function *F : SCCNodes) {
+ // Call the callable parameter to look up AA results for this function.
+ AAResults &AAR = AARGetter(*F);
+
+ switch (checkFunctionMemoryAccess(*F, AAR, SCCNodes)) {
+ case MAK_MayWrite:
+ return false;
+ case MAK_ReadOnly:
+ ReadsMemory = true;
+ break;
+ case MAK_ReadNone:
+ // Nothing to do!
+ break;
}
}
// Success! Functions in this SCC do not access memory, or only read memory.
// Give them the appropriate attribute.
bool MadeChange = false;
- for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
- Function *F = (*I)->getFunction();
-
+ for (Function *F : SCCNodes) {
if (F->doesNotAccessMemory())
// Already perfect!
continue;
MadeChange = true;
// Clear out any existing attributes.
- F->removeAttribute(~0, Attribute::ReadOnly | Attribute::ReadNone);
+ AttrBuilder B;
+ B.addAttribute(Attribute::ReadOnly).addAttribute(Attribute::ReadNone);
+ F->removeAttributes(
+ AttributeSet::FunctionIndex,
+ AttributeSet::get(F->getContext(), AttributeSet::FunctionIndex, B));
// Add in the new attribute.
- F->addAttribute(~0, ReadsMemory? Attribute::ReadOnly : Attribute::ReadNone);
+ F->addAttribute(AttributeSet::FunctionIndex,
+ ReadsMemory ? Attribute::ReadOnly : Attribute::ReadNone);
if (ReadsMemory)
++NumReadOnly;
return MadeChange;
}
-/// AddNoCaptureAttrs - Deduce nocapture attributes for the SCC.
-bool FunctionAttrs::AddNoCaptureAttrs(const CallGraphSCC &SCC) {
+namespace {
+/// For a given pointer Argument, this retains a list of Arguments of functions
+/// in the same SCC that the pointer data flows into. We use this to build an
+/// SCC of the arguments.
+struct ArgumentGraphNode {
+ Argument *Definition;
+ SmallVector<ArgumentGraphNode *, 4> Uses;
+};
+
+class ArgumentGraph {
+ // We store pointers to ArgumentGraphNode objects, so it's important that
+ // that they not move around upon insert.
+ typedef std::map<Argument *, ArgumentGraphNode> ArgumentMapTy;
+
+ ArgumentMapTy ArgumentMap;
+
+ // There is no root node for the argument graph, in fact:
+ // void f(int *x, int *y) { if (...) f(x, y); }
+ // is an example where the graph is disconnected. The SCCIterator requires a
+ // single entry point, so we maintain a fake ("synthetic") root node that
+ // uses every node. Because the graph is directed and nothing points into
+ // the root, it will not participate in any SCCs (except for its own).
+ ArgumentGraphNode SyntheticRoot;
+
+public:
+ ArgumentGraph() { SyntheticRoot.Definition = nullptr; }
+
+ typedef SmallVectorImpl<ArgumentGraphNode *>::iterator iterator;
+
+ iterator begin() { return SyntheticRoot.Uses.begin(); }
+ iterator end() { return SyntheticRoot.Uses.end(); }
+ ArgumentGraphNode *getEntryNode() { return &SyntheticRoot; }
+
+ ArgumentGraphNode *operator[](Argument *A) {
+ ArgumentGraphNode &Node = ArgumentMap[A];
+ Node.Definition = A;
+ SyntheticRoot.Uses.push_back(&Node);
+ return &Node;
+ }
+};
+
+/// This tracker checks whether callees are in the SCC, and if so it does not
+/// consider that a capture, instead adding it to the "Uses" list and
+/// continuing with the analysis.
+struct ArgumentUsesTracker : public CaptureTracker {
+ ArgumentUsesTracker(const SCCNodeSet &SCCNodes)
+ : Captured(false), SCCNodes(SCCNodes) {}
+
+ void tooManyUses() override { Captured = true; }
+
+ bool captured(const Use *U) override {
+ CallSite CS(U->getUser());
+ if (!CS.getInstruction()) {
+ Captured = true;
+ return true;
+ }
+
+ Function *F = CS.getCalledFunction();
+ if (!F || F->isDeclaration() || F->mayBeOverridden() ||
+ !SCCNodes.count(F)) {
+ Captured = true;
+ return true;
+ }
+
+ // Note: the callee and the two successor blocks *follow* the argument
+ // operands. This means there is no need to adjust UseIndex to account for
+ // these.
+
+ unsigned UseIndex =
+ std::distance(const_cast<const Use *>(CS.arg_begin()), U);
+
+ assert(UseIndex < CS.data_operands_size() &&
+ "Indirect function calls should have been filtered above!");
+
+ if (UseIndex >= CS.getNumArgOperands()) {
+ // Data operand, but not a argument operand -- must be a bundle operand
+ assert(CS.hasOperandBundles() && "Must be!");
+
+ // CaptureTracking told us that we're being captured by an operand bundle
+ // use. In this case it does not matter if the callee is within our SCC
+ // or not -- we've been captured in some unknown way, and we have to be
+ // conservative.
+ Captured = true;
+ return true;
+ }
+
+ if (UseIndex >= F->arg_size()) {
+ assert(F->isVarArg() && "More params than args in non-varargs call");
+ Captured = true;
+ return true;
+ }
+
+ Uses.push_back(&*std::next(F->arg_begin(), UseIndex));
+ return false;
+ }
+
+ bool Captured; // True only if certainly captured (used outside our SCC).
+ SmallVector<Argument *, 4> Uses; // Uses within our SCC.
+
+ const SCCNodeSet &SCCNodes;
+};
+}
+
+namespace llvm {
+template <> struct GraphTraits<ArgumentGraphNode *> {
+ typedef ArgumentGraphNode NodeType;
+ typedef SmallVectorImpl<ArgumentGraphNode *>::iterator ChildIteratorType;
+
+ static inline NodeType *getEntryNode(NodeType *A) { return A; }
+ static inline ChildIteratorType child_begin(NodeType *N) {
+ return N->Uses.begin();
+ }
+ static inline ChildIteratorType child_end(NodeType *N) {
+ return N->Uses.end();
+ }
+};
+template <>
+struct GraphTraits<ArgumentGraph *> : public GraphTraits<ArgumentGraphNode *> {
+ static NodeType *getEntryNode(ArgumentGraph *AG) {
+ return AG->getEntryNode();
+ }
+ static ChildIteratorType nodes_begin(ArgumentGraph *AG) {
+ return AG->begin();
+ }
+ static ChildIteratorType nodes_end(ArgumentGraph *AG) { return AG->end(); }
+};
+}
+
+/// Returns Attribute::None, Attribute::ReadOnly or Attribute::ReadNone.
+static Attribute::AttrKind
+determinePointerReadAttrs(Argument *A,
+ const SmallPtrSet<Argument *, 8> &SCCNodes) {
+
+ SmallVector<Use *, 32> Worklist;
+ SmallSet<Use *, 32> Visited;
+
+ // inalloca arguments are always clobbered by the call.
+ if (A->hasInAllocaAttr())
+ return Attribute::None;
+
+ bool IsRead = false;
+ // We don't need to track IsWritten. If A is written to, return immediately.
+
+ for (Use &U : A->uses()) {
+ Visited.insert(&U);
+ Worklist.push_back(&U);
+ }
+
+ while (!Worklist.empty()) {
+ Use *U = Worklist.pop_back_val();
+ Instruction *I = cast<Instruction>(U->getUser());
+
+ switch (I->getOpcode()) {
+ case Instruction::BitCast:
+ case Instruction::GetElementPtr:
+ case Instruction::PHI:
+ case Instruction::Select:
+ case Instruction::AddrSpaceCast:
+ // The original value is not read/written via this if the new value isn't.
+ for (Use &UU : I->uses())
+ if (Visited.insert(&UU).second)
+ Worklist.push_back(&UU);
+ break;
+
+ case Instruction::Call:
+ case Instruction::Invoke: {
+ bool Captures = true;
+
+ if (I->getType()->isVoidTy())
+ Captures = false;
+
+ auto AddUsersToWorklistIfCapturing = [&] {
+ if (Captures)
+ for (Use &UU : I->uses())
+ if (Visited.insert(&UU).second)
+ Worklist.push_back(&UU);
+ };
+
+ CallSite CS(I);
+ if (CS.doesNotAccessMemory()) {
+ AddUsersToWorklistIfCapturing();
+ continue;
+ }
+
+ Function *F = CS.getCalledFunction();
+ if (!F) {
+ if (CS.onlyReadsMemory()) {
+ IsRead = true;
+ AddUsersToWorklistIfCapturing();
+ continue;
+ }
+ return Attribute::None;
+ }
+
+ // Note: the callee and the two successor blocks *follow* the argument
+ // operands. This means there is no need to adjust UseIndex to account
+ // for these.
+
+ unsigned UseIndex = std::distance(CS.arg_begin(), U);
+
+ // U cannot be the callee operand use: since we're exploring the
+ // transitive uses of an Argument, having such a use be a callee would
+ // imply the CallSite is an indirect call or invoke; and we'd take the
+ // early exit above.
+ assert(UseIndex < CS.data_operands_size() &&
+ "Data operand use expected!");
+
+ bool IsOperandBundleUse = UseIndex >= CS.getNumArgOperands();
+
+ if (UseIndex >= F->arg_size() && !IsOperandBundleUse) {
+ assert(F->isVarArg() && "More params than args in non-varargs call");
+ return Attribute::None;
+ }
+
+ Captures &= !CS.doesNotCapture(UseIndex);
+
+ // Since the optimizer (by design) cannot see the data flow corresponding
+ // to a operand bundle use, these cannot participate in the optimistic SCC
+ // analysis. Instead, we model the operand bundle uses as arguments in
+ // call to a function external to the SCC.
+ if (!SCCNodes.count(&*std::next(F->arg_begin(), UseIndex)) ||
+ IsOperandBundleUse) {
+
+ // The accessors used on CallSite here do the right thing for calls and
+ // invokes with operand bundles.
+
+ if (!CS.onlyReadsMemory() && !CS.onlyReadsMemory(UseIndex))
+ return Attribute::None;
+ if (!CS.doesNotAccessMemory(UseIndex))
+ IsRead = true;
+ }
+
+ AddUsersToWorklistIfCapturing();
+ break;
+ }
+
+ case Instruction::Load:
+ IsRead = true;
+ break;
+
+ case Instruction::ICmp:
+ case Instruction::Ret:
+ break;
+
+ default:
+ return Attribute::None;
+ }
+ }
+
+ return IsRead ? Attribute::ReadOnly : Attribute::ReadNone;
+}
+
+/// Deduce nocapture attributes for the SCC.
+static bool addArgumentAttrs(const SCCNodeSet &SCCNodes) {
bool Changed = false;
- // Check each function in turn, determining which pointer arguments are not
- // captured.
- for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
- Function *F = (*I)->getFunction();
+ ArgumentGraph AG;
- if (F == 0)
- // External node - skip it;
- continue;
+ AttrBuilder B;
+ B.addAttribute(Attribute::NoCapture);
+ // Check each function in turn, determining which pointer arguments are not
+ // captured.
+ for (Function *F : SCCNodes) {
// Definitions with weak linkage may be overridden at linktime with
- // something that writes memory, so treat them like declarations.
+ // something that captures pointers, so treat them like declarations.
if (F->isDeclaration() || F->mayBeOverridden())
continue;
- for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end(); A!=E; ++A)
- if (A->getType()->isPointerTy() && !A->hasNoCaptureAttr() &&
- !PointerMayBeCaptured(A, true, /*StoreCaptures=*/false)) {
- A->addAttr(Attribute::NoCapture);
+ // Functions that are readonly (or readnone) and nounwind and don't return
+ // a value can't capture arguments. Don't analyze them.
+ if (F->onlyReadsMemory() && F->doesNotThrow() &&
+ F->getReturnType()->isVoidTy()) {
+ for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end(); A != E;
+ ++A) {
+ if (A->getType()->isPointerTy() && !A->hasNoCaptureAttr()) {
+ A->addAttr(AttributeSet::get(F->getContext(), A->getArgNo() + 1, B));
+ ++NumNoCapture;
+ Changed = true;
+ }
+ }
+ continue;
+ }
+
+ for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end(); A != E;
+ ++A) {
+ if (!A->getType()->isPointerTy())
+ continue;
+ bool HasNonLocalUses = false;
+ if (!A->hasNoCaptureAttr()) {
+ ArgumentUsesTracker Tracker(SCCNodes);
+ PointerMayBeCaptured(&*A, &Tracker);
+ if (!Tracker.Captured) {
+ if (Tracker.Uses.empty()) {
+ // If it's trivially not captured, mark it nocapture now.
+ A->addAttr(
+ AttributeSet::get(F->getContext(), A->getArgNo() + 1, B));
+ ++NumNoCapture;
+ Changed = true;
+ } else {
+ // If it's not trivially captured and not trivially not captured,
+ // then it must be calling into another function in our SCC. Save
+ // its particulars for Argument-SCC analysis later.
+ ArgumentGraphNode *Node = AG[&*A];
+ for (SmallVectorImpl<Argument *>::iterator
+ UI = Tracker.Uses.begin(),
+ UE = Tracker.Uses.end();
+ UI != UE; ++UI) {
+ Node->Uses.push_back(AG[*UI]);
+ if (*UI != A)
+ HasNonLocalUses = true;
+ }
+ }
+ }
+ // Otherwise, it's captured. Don't bother doing SCC analysis on it.
+ }
+ if (!HasNonLocalUses && !A->onlyReadsMemory()) {
+ // Can we determine that it's readonly/readnone without doing an SCC?
+ // Note that we don't allow any calls at all here, or else our result
+ // will be dependent on the iteration order through the functions in the
+ // SCC.
+ SmallPtrSet<Argument *, 8> Self;
+ Self.insert(&*A);
+ Attribute::AttrKind R = determinePointerReadAttrs(&*A, Self);
+ if (R != Attribute::None) {
+ AttrBuilder B;
+ B.addAttribute(R);
+ A->addAttr(AttributeSet::get(A->getContext(), A->getArgNo() + 1, B));
+ Changed = true;
+ R == Attribute::ReadOnly ? ++NumReadOnlyArg : ++NumReadNoneArg;
+ }
+ }
+ }
+ }
+
+ // The graph we've collected is partial because we stopped scanning for
+ // argument uses once we solved the argument trivially. These partial nodes
+ // show up as ArgumentGraphNode objects with an empty Uses list, and for
+ // these nodes the final decision about whether they capture has already been
+ // made. If the definition doesn't have a 'nocapture' attribute by now, it
+ // captures.
+
+ for (scc_iterator<ArgumentGraph *> I = scc_begin(&AG); !I.isAtEnd(); ++I) {
+ const std::vector<ArgumentGraphNode *> &ArgumentSCC = *I;
+ if (ArgumentSCC.size() == 1) {
+ if (!ArgumentSCC[0]->Definition)
+ continue; // synthetic root node
+
+ // eg. "void f(int* x) { if (...) f(x); }"
+ if (ArgumentSCC[0]->Uses.size() == 1 &&
+ ArgumentSCC[0]->Uses[0] == ArgumentSCC[0]) {
+ Argument *A = ArgumentSCC[0]->Definition;
+ A->addAttr(AttributeSet::get(A->getContext(), A->getArgNo() + 1, B));
++NumNoCapture;
Changed = true;
}
+ continue;
+ }
+
+ bool SCCCaptured = false;
+ for (auto I = ArgumentSCC.begin(), E = ArgumentSCC.end();
+ I != E && !SCCCaptured; ++I) {
+ ArgumentGraphNode *Node = *I;
+ if (Node->Uses.empty()) {
+ if (!Node->Definition->hasNoCaptureAttr())
+ SCCCaptured = true;
+ }
+ }
+ if (SCCCaptured)
+ continue;
+
+ SmallPtrSet<Argument *, 8> ArgumentSCCNodes;
+ // Fill ArgumentSCCNodes with the elements of the ArgumentSCC. Used for
+ // quickly looking up whether a given Argument is in this ArgumentSCC.
+ for (auto I = ArgumentSCC.begin(), E = ArgumentSCC.end(); I != E; ++I) {
+ ArgumentSCCNodes.insert((*I)->Definition);
+ }
+
+ for (auto I = ArgumentSCC.begin(), E = ArgumentSCC.end();
+ I != E && !SCCCaptured; ++I) {
+ ArgumentGraphNode *N = *I;
+ for (SmallVectorImpl<ArgumentGraphNode *>::iterator UI = N->Uses.begin(),
+ UE = N->Uses.end();
+ UI != UE; ++UI) {
+ Argument *A = (*UI)->Definition;
+ if (A->hasNoCaptureAttr() || ArgumentSCCNodes.count(A))
+ continue;
+ SCCCaptured = true;
+ break;
+ }
+ }
+ if (SCCCaptured)
+ continue;
+
+ for (unsigned i = 0, e = ArgumentSCC.size(); i != e; ++i) {
+ Argument *A = ArgumentSCC[i]->Definition;
+ A->addAttr(AttributeSet::get(A->getContext(), A->getArgNo() + 1, B));
+ ++NumNoCapture;
+ Changed = true;
+ }
+
+ // We also want to compute readonly/readnone. With a small number of false
+ // negatives, we can assume that any pointer which is captured isn't going
+ // to be provably readonly or readnone, since by definition we can't
+ // analyze all uses of a captured pointer.
+ //
+ // The false negatives happen when the pointer is captured by a function
+ // that promises readonly/readnone behaviour on the pointer, then the
+ // pointer's lifetime ends before anything that writes to arbitrary memory.
+ // Also, a readonly/readnone pointer may be returned, but returning a
+ // pointer is capturing it.
+
+ Attribute::AttrKind ReadAttr = Attribute::ReadNone;
+ for (unsigned i = 0, e = ArgumentSCC.size(); i != e; ++i) {
+ Argument *A = ArgumentSCC[i]->Definition;
+ Attribute::AttrKind K = determinePointerReadAttrs(A, ArgumentSCCNodes);
+ if (K == Attribute::ReadNone)
+ continue;
+ if (K == Attribute::ReadOnly) {
+ ReadAttr = Attribute::ReadOnly;
+ continue;
+ }
+ ReadAttr = K;
+ break;
+ }
+
+ if (ReadAttr != Attribute::None) {
+ AttrBuilder B, R;
+ B.addAttribute(ReadAttr);
+ R.addAttribute(Attribute::ReadOnly).addAttribute(Attribute::ReadNone);
+ for (unsigned i = 0, e = ArgumentSCC.size(); i != e; ++i) {
+ Argument *A = ArgumentSCC[i]->Definition;
+ // Clear out existing readonly/readnone attributes
+ A->removeAttr(AttributeSet::get(A->getContext(), A->getArgNo() + 1, R));
+ A->addAttr(AttributeSet::get(A->getContext(), A->getArgNo() + 1, B));
+ ReadAttr == Attribute::ReadOnly ? ++NumReadOnlyArg : ++NumReadNoneArg;
+ Changed = true;
+ }
+ }
}
return Changed;
}
-/// IsFunctionMallocLike - A function is malloc-like if it returns either null
-/// or a pointer that doesn't alias any other pointer visible to the caller.
-bool FunctionAttrs::IsFunctionMallocLike(Function *F,
- SmallPtrSet<Function*, 8> &SCCNodes) const {
- UniqueVector<Value *> FlowsToReturn;
+/// Tests whether a function is "malloc-like".
+///
+/// A function is "malloc-like" if it returns either null or a pointer that
+/// doesn't alias any other pointer visible to the caller.
+static bool isFunctionMallocLike(Function *F, const SCCNodeSet &SCCNodes) {
+ SmallSetVector<Value *, 8> FlowsToReturn;
for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I)
if (ReturnInst *Ret = dyn_cast<ReturnInst>(I->getTerminator()))
FlowsToReturn.insert(Ret->getReturnValue());
for (unsigned i = 0; i != FlowsToReturn.size(); ++i) {
- Value *RetVal = FlowsToReturn[i+1]; // UniqueVector[0] is reserved.
+ Value *RetVal = FlowsToReturn[i];
if (Constant *C = dyn_cast<Constant>(RetVal)) {
if (!C->isNullValue() && !isa<UndefValue>(C))
if (Instruction *RVI = dyn_cast<Instruction>(RetVal))
switch (RVI->getOpcode()) {
- // Extend the analysis by looking upwards.
- case Instruction::BitCast:
- case Instruction::GetElementPtr:
- FlowsToReturn.insert(RVI->getOperand(0));
- continue;
- case Instruction::Select: {
- SelectInst *SI = cast<SelectInst>(RVI);
- FlowsToReturn.insert(SI->getTrueValue());
- FlowsToReturn.insert(SI->getFalseValue());
- continue;
- }
- case Instruction::PHI: {
- PHINode *PN = cast<PHINode>(RVI);
- for (int i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
- FlowsToReturn.insert(PN->getIncomingValue(i));
- continue;
- }
+ // Extend the analysis by looking upwards.
+ case Instruction::BitCast:
+ case Instruction::GetElementPtr:
+ case Instruction::AddrSpaceCast:
+ FlowsToReturn.insert(RVI->getOperand(0));
+ continue;
+ case Instruction::Select: {
+ SelectInst *SI = cast<SelectInst>(RVI);
+ FlowsToReturn.insert(SI->getTrueValue());
+ FlowsToReturn.insert(SI->getFalseValue());
+ continue;
+ }
+ case Instruction::PHI: {
+ PHINode *PN = cast<PHINode>(RVI);
+ for (Value *IncValue : PN->incoming_values())
+ FlowsToReturn.insert(IncValue);
+ continue;
+ }
- // Check whether the pointer came from an allocation.
- case Instruction::Alloca:
+ // Check whether the pointer came from an allocation.
+ case Instruction::Alloca:
+ break;
+ case Instruction::Call:
+ case Instruction::Invoke: {
+ CallSite CS(RVI);
+ if (CS.paramHasAttr(0, Attribute::NoAlias))
break;
- case Instruction::Call:
- case Instruction::Invoke: {
- CallSite CS(RVI);
- if (CS.paramHasAttr(0, Attribute::NoAlias))
- break;
- if (CS.getCalledFunction() &&
- SCCNodes.count(CS.getCalledFunction()))
- break;
- } // fall-through
- default:
- return false; // Did not come from an allocation.
+ if (CS.getCalledFunction() && SCCNodes.count(CS.getCalledFunction()))
+ break;
+ } // fall-through
+ default:
+ return false; // Did not come from an allocation.
}
if (PointerMayBeCaptured(RetVal, false, /*StoreCaptures=*/false))
return true;
}
-/// AddNoAliasAttrs - Deduce noalias attributes for the SCC.
-bool FunctionAttrs::AddNoAliasAttrs(const CallGraphSCC &SCC) {
- SmallPtrSet<Function*, 8> SCCNodes;
-
- // 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)->getFunction());
-
+/// Deduce noalias attributes for the SCC.
+static bool addNoAliasAttrs(const SCCNodeSet &SCCNodes) {
// Check each function in turn, determining which functions return noalias
// pointers.
- for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
- Function *F = (*I)->getFunction();
-
- if (F == 0)
- // External node - skip it;
- return false;
-
+ for (Function *F : SCCNodes) {
// Already noalias.
if (F->doesNotAlias(0))
continue;
if (F->isDeclaration() || F->mayBeOverridden())
return false;
- // We annotate noalias return values, which are only applicable to
+ // We annotate noalias return values, which are only applicable to
// pointer types.
if (!F->getReturnType()->isPointerTy())
continue;
- if (!IsFunctionMallocLike(F, SCCNodes))
+ if (!isFunctionMallocLike(F, SCCNodes))
return false;
}
bool MadeChange = false;
- for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
- Function *F = (*I)->getFunction();
+ for (Function *F : SCCNodes) {
if (F->doesNotAlias(0) || !F->getReturnType()->isPointerTy())
continue;
return MadeChange;
}
+/// Tests whether this function is known to not return null.
+///
+/// Requires that the function returns a pointer.
+///
+/// Returns true if it believes the function will not return a null, and sets
+/// \p Speculative based on whether the returned conclusion is a speculative
+/// conclusion due to SCC calls.
+static bool isReturnNonNull(Function *F, const SCCNodeSet &SCCNodes,
+ const TargetLibraryInfo &TLI, bool &Speculative) {
+ assert(F->getReturnType()->isPointerTy() &&
+ "nonnull only meaningful on pointer types");
+ Speculative = false;
+
+ SmallSetVector<Value *, 8> FlowsToReturn;
+ for (BasicBlock &BB : *F)
+ if (auto *Ret = dyn_cast<ReturnInst>(BB.getTerminator()))
+ FlowsToReturn.insert(Ret->getReturnValue());
+
+ for (unsigned i = 0; i != FlowsToReturn.size(); ++i) {
+ Value *RetVal = FlowsToReturn[i];
+
+ // If this value is locally known to be non-null, we're good
+ if (isKnownNonNull(RetVal, &TLI))
+ continue;
+
+ // Otherwise, we need to look upwards since we can't make any local
+ // conclusions.
+ Instruction *RVI = dyn_cast<Instruction>(RetVal);
+ if (!RVI)
+ return false;
+ switch (RVI->getOpcode()) {
+ // Extend the analysis by looking upwards.
+ case Instruction::BitCast:
+ case Instruction::GetElementPtr:
+ case Instruction::AddrSpaceCast:
+ FlowsToReturn.insert(RVI->getOperand(0));
+ continue;
+ case Instruction::Select: {
+ SelectInst *SI = cast<SelectInst>(RVI);
+ FlowsToReturn.insert(SI->getTrueValue());
+ FlowsToReturn.insert(SI->getFalseValue());
+ continue;
+ }
+ case Instruction::PHI: {
+ PHINode *PN = cast<PHINode>(RVI);
+ for (int i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+ FlowsToReturn.insert(PN->getIncomingValue(i));
+ continue;
+ }
+ case Instruction::Call:
+ case Instruction::Invoke: {
+ CallSite CS(RVI);
+ Function *Callee = CS.getCalledFunction();
+ // A call to a node within the SCC is assumed to return null until
+ // proven otherwise
+ if (Callee && SCCNodes.count(Callee)) {
+ Speculative = true;
+ continue;
+ }
+ return false;
+ }
+ default:
+ return false; // Unknown source, may be null
+ };
+ llvm_unreachable("should have either continued or returned");
+ }
+
+ return true;
+}
+
+/// Deduce nonnull attributes for the SCC.
+static bool addNonNullAttrs(const SCCNodeSet &SCCNodes,
+ const TargetLibraryInfo &TLI) {
+ // Speculative that all functions in the SCC return only nonnull
+ // pointers. We may refute this as we analyze functions.
+ bool SCCReturnsNonNull = true;
+
+ bool MadeChange = false;
+
+ // Check each function in turn, determining which functions return nonnull
+ // pointers.
+ for (Function *F : SCCNodes) {
+ // Already nonnull.
+ if (F->getAttributes().hasAttribute(AttributeSet::ReturnIndex,
+ Attribute::NonNull))
+ continue;
+
+ // Definitions with weak linkage may be overridden at linktime, so
+ // treat them like declarations.
+ if (F->isDeclaration() || F->mayBeOverridden())
+ return false;
+
+ // We annotate nonnull return values, which are only applicable to
+ // pointer types.
+ if (!F->getReturnType()->isPointerTy())
+ continue;
+
+ bool Speculative = false;
+ if (isReturnNonNull(F, SCCNodes, TLI, Speculative)) {
+ if (!Speculative) {
+ // Mark the function eagerly since we may discover a function
+ // which prevents us from speculating about the entire SCC
+ DEBUG(dbgs() << "Eagerly marking " << F->getName() << " as nonnull\n");
+ F->addAttribute(AttributeSet::ReturnIndex, Attribute::NonNull);
+ ++NumNonNullReturn;
+ MadeChange = true;
+ }
+ continue;
+ }
+ // At least one function returns something which could be null, can't
+ // speculate any more.
+ SCCReturnsNonNull = false;
+ }
+
+ if (SCCReturnsNonNull) {
+ for (Function *F : SCCNodes) {
+ if (F->getAttributes().hasAttribute(AttributeSet::ReturnIndex,
+ Attribute::NonNull) ||
+ !F->getReturnType()->isPointerTy())
+ continue;
+
+ DEBUG(dbgs() << "SCC marking " << F->getName() << " as nonnull\n");
+ F->addAttribute(AttributeSet::ReturnIndex, Attribute::NonNull);
+ ++NumNonNullReturn;
+ MadeChange = true;
+ }
+ }
+
+ return MadeChange;
+}
+
+static bool setDoesNotRecurse(Function &F) {
+ if (F.doesNotRecurse())
+ return false;
+ F.setDoesNotRecurse();
+ ++NumNoRecurse;
+ return true;
+}
+
+static bool addNoRecurseAttrs(const CallGraphSCC &SCC,
+ SmallVectorImpl<WeakVH> &Revisit) {
+ // Try and identify functions that do not recurse.
+
+ // If the SCC contains multiple nodes we know for sure there is recursion.
+ if (!SCC.isSingular())
+ return false;
+
+ const CallGraphNode *CGN = *SCC.begin();
+ Function *F = CGN->getFunction();
+ if (!F || F->isDeclaration() || F->doesNotRecurse())
+ return false;
+
+ // If all of the calls in F are identifiable and are to norecurse functions, F
+ // is norecurse. This check also detects self-recursion as F is not currently
+ // marked norecurse, so any called from F to F will not be marked norecurse.
+ if (std::all_of(CGN->begin(), CGN->end(),
+ [](const CallGraphNode::CallRecord &CR) {
+ Function *F = CR.second->getFunction();
+ return F && F->doesNotRecurse();
+ }))
+ // Function calls a potentially recursive function.
+ return setDoesNotRecurse(*F);
+
+ // We know that F is not obviously recursive, but we haven't been able to
+ // prove that it doesn't actually recurse. Add it to the Revisit list to try
+ // again top-down later.
+ Revisit.push_back(F);
+ return false;
+}
+
+static bool addNoRecurseAttrsTopDownOnly(Function *F) {
+ // If F is internal and all uses are in norecurse functions, then F is also
+ // norecurse.
+ if (F->doesNotRecurse())
+ return false;
+ if (F->hasInternalLinkage()) {
+ for (auto *U : F->users())
+ if (auto *I = dyn_cast<Instruction>(U)) {
+ if (!I->getParent()->getParent()->doesNotRecurse())
+ return false;
+ } else {
+ return false;
+ }
+ return setDoesNotRecurse(*F);
+ }
+ return false;
+}
+
bool FunctionAttrs::runOnSCC(CallGraphSCC &SCC) {
- AA = &getAnalysis<AliasAnalysis>();
+ TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
+ bool Changed = false;
+
+ // We compute dedicated AA results for each function in the SCC as needed. We
+ // use a lambda referencing external objects so that they live long enough to
+ // be queried, but we re-use them each time.
+ Optional<BasicAAResult> BAR;
+ Optional<AAResults> AAR;
+ auto AARGetter = [&](Function &F) -> AAResults & {
+ BAR.emplace(createLegacyPMBasicAAResult(*this, F));
+ AAR.emplace(createLegacyPMAAResults(*this, F, *BAR));
+ return *AAR;
+ };
+
+ // Fill SCCNodes with the elements of the SCC. Used for quickly looking up
+ // whether a given CallGraphNode is in this SCC. Also track whether there are
+ // any external or opt-none nodes that will prevent us from optimizing any
+ // part of the SCC.
+ SCCNodeSet SCCNodes;
+ bool ExternalNode = false;
+ for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
+ Function *F = (*I)->getFunction();
+ if (!F || F->hasFnAttribute(Attribute::OptimizeNone)) {
+ // External node or function we're trying not to optimize - we both avoid
+ // transform them and avoid leveraging information they provide.
+ ExternalNode = true;
+ continue;
+ }
- bool Changed = AddReadAttrs(SCC);
- Changed |= AddNoCaptureAttrs(SCC);
- Changed |= AddNoAliasAttrs(SCC);
+ SCCNodes.insert(F);
+ }
+
+ Changed |= addReadAttrs(SCCNodes, AARGetter);
+ Changed |= addArgumentAttrs(SCCNodes);
+
+ // If we have no external nodes participating in the SCC, we can deduce some
+ // more precise attributes as well.
+ if (!ExternalNode) {
+ Changed |= addNoAliasAttrs(SCCNodes);
+ Changed |= addNonNullAttrs(SCCNodes, *TLI);
+ }
+
+ Changed |= addNoRecurseAttrs(SCC, Revisit);
+ return Changed;
+}
+
+bool FunctionAttrs::doFinalization(CallGraph &CG) {
+ bool Changed = false;
+ // When iterating over SCCs we visit functions in a bottom-up fashion. Some of
+ // the rules we have for identifying norecurse functions work best with a
+ // top-down walk, so look again at all the functions we previously marked as
+ // worth revisiting, in top-down order.
+ for (auto &F : reverse(Revisit))
+ if (F)
+ Changed |= addNoRecurseAttrsTopDownOnly(cast<Function>((Value*)F));
return Changed;
}
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