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llvm-project/llvm/lib/Transforms/IPO/FunctionAttrs.cpp

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//===- FunctionAttrs.cpp - Pass which marks functions attributes ----------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file implements interprocedural passes which walk the
/// call-graph deducing and/or propagating function attributes.
///
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/IPO/FunctionAttrs.h"
#include "llvm/Transforms/IPO.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/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 {
typedef SmallSetVector<Function *, 8> SCCNodeSet;
}
namespace {
/// The three kinds of memory access relevant to 'readonly' and
/// 'readnone' attributes.
enum MemoryAccessKind {
MAK_ReadNone = 0,
MAK_ReadOnly = 1,
MAK_MayWrite = 2
};
}
static MemoryAccessKind checkFunctionMemoryAccess(Function &F, AAResults &AAR,
const SCCNodeSet &SCCNodes) {
FunctionModRefBehavior MRB = AAR.getModRefBehavior(&F);
if (MRB == FMRB_DoesNotAccessMemory)
// Already perfect!
return MAK_ReadNone;
// Non-exact function definitions may not be selected at link time, and an
// alternative version that writes to memory may be selected. See the comment
// on GlobalValue::isDefinitionExact for more details.
if (!F.hasExactDefinition()) {
if (AliasAnalysis::onlyReadsMemory(MRB))
return MAK_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 (inst_iterator II = inst_begin(F), E = inst_end(F); II != E; ++II) {
Instruction *I = &*II;
// 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, as long as the call sites
// don't have operand bundles. Calls with operand bundles are allowed to
// have memory effects not described by the memory effects of the call
// target.
if (!CS.hasOperandBundles() && CS.getCalledFunction() &&
SCCNodes.count(CS.getCalledFunction()))
continue;
FunctionModRefBehavior MRB = AAR.getModRefBehavior(CS);
// If the call doesn't access memory, we're done.
if (!(MRB & MRI_ModRef))
continue;
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;
}
// 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;
AAMDNodes AAInfo;
I->getAAMetadata(AAInfo);
MemoryLocation Loc(Arg, MemoryLocation::UnknownSize, AAInfo);
// 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;
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;
}
} 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;
}
} 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 MAK_MayWrite;
// 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 (Function *F : SCCNodes) {
if (F->doesNotAccessMemory())
// Already perfect!
continue;
if (F->onlyReadsMemory() && ReadsMemory)
// No change.
continue;
MadeChange = true;
// Clear out any existing attributes.
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(AttributeSet::FunctionIndex,
ReadsMemory ? Attribute::ReadOnly : Attribute::ReadNone);
if (ReadsMemory)
++NumReadOnly;
else
++NumReadNone;
}
return MadeChange;
}
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->hasExactDefinition() || !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;
ArgumentGraph AG;
AttrBuilder B;
B.addAttribute(Attribute::NoCapture);
// Check each function in turn, determining which pointer arguments are not
// captured.
for (Function *F : SCCNodes) {
// We can infer and propagate function attributes only when we know that the
// definition we'll get at link time is *exactly* the definition we see now.
// For more details, see GlobalValue::mayBeDerefined.
if (!F->hasExactDefinition())
continue;
// 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;
}
/// 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];
if (Constant *C = dyn_cast<Constant>(RetVal)) {
if (!C->isNullValue() && !isa<UndefValue>(C))
return false;
continue;
}
if (isa<Argument>(RetVal))
return false;
if (Instruction *RVI = dyn_cast<Instruction>(RetVal))
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 (Value *IncValue : PN->incoming_values())
FlowsToReturn.insert(IncValue);
continue;
}
// 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;
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 false;
}
return true;
}
/// Deduce noalias attributes for the SCC.
static bool addNoAliasAttrs(const SCCNodeSet &SCCNodes) {
// Check each function in turn, determining which functions return noalias
// pointers.
for (Function *F : SCCNodes) {
// Already noalias.
if (F->doesNotAlias(0))
continue;
// We can infer and propagate function attributes only when we know that the
// definition we'll get at link time is *exactly* the definition we see now.
// For more details, see GlobalValue::mayBeDerefined.
if (!F->hasExactDefinition())
return false;
// We annotate noalias return values, which are only applicable to
// pointer types.
if (!F->getReturnType()->isPointerTy())
continue;
if (!isFunctionMallocLike(F, SCCNodes))
return false;
}
bool MadeChange = false;
for (Function *F : SCCNodes) {
if (F->doesNotAlias(0) || !F->getReturnType()->isPointerTy())
continue;
F->setDoesNotAlias(0);
++NumNoAlias;
MadeChange = true;
}
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;
// We can infer and propagate function attributes only when we know that the
// definition we'll get at link time is *exactly* the definition we see now.
// For more details, see GlobalValue::mayBeDerefined.
if (!F->hasExactDefinition())
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;
}
/// Remove the convergent attribute from all functions in the SCC if every
/// callsite within the SCC is not convergent (except for calls to functions
/// within the SCC). Returns true if changes were made.
static bool removeConvergentAttrs(const SCCNodeSet &SCCNodes) {
// For every function in SCC, ensure that either
// * it is not convergent, or
// * we can remove its convergent attribute.
bool HasConvergentFn = false;
for (Function *F : SCCNodes) {
if (!F->isConvergent()) continue;
HasConvergentFn = true;
// Can't remove convergent from function declarations.
if (F->isDeclaration()) return false;
// Can't remove convergent if any of our functions has a convergent call to a
// function not in the SCC.
for (Instruction &I : instructions(*F)) {
CallSite CS(&I);
// Bail if CS is a convergent call to a function not in the SCC.
if (CS && CS.isConvergent() &&
SCCNodes.count(CS.getCalledFunction()) == 0)
return false;
}
}
// If the SCC doesn't have any convergent functions, we have nothing to do.
if (!HasConvergentFn) return false;
// If we got here, all of the calls the SCC makes to functions not in the SCC
// are non-convergent. Therefore all of the SCC's functions can also be made
// non-convergent. We'll remove the attr from the callsites in
// InstCombineCalls.
for (Function *F : SCCNodes) {
if (!F->isConvergent()) continue;
DEBUG(dbgs() << "Removing convergent attr from fn " << F->getName()
<< "\n");
F->setNotConvergent();
}
return true;
}
static bool setDoesNotRecurse(Function &F) {
if (F.doesNotRecurse())
return false;
F.setDoesNotRecurse();
++NumNoRecurse;
return true;
}
static bool addNoRecurseAttrs(const SCCNodeSet &SCCNodes) {
// Try and identify functions that do not recurse.
// If the SCC contains multiple nodes we know for sure there is recursion.
if (SCCNodes.size() != 1)
return false;
Function *F = *SCCNodes.begin();
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.
for (Instruction &I : instructions(*F))
if (auto CS = CallSite(&I)) {
Function *Callee = CS.getCalledFunction();
if (!Callee || Callee == F || !Callee->doesNotRecurse())
// Function calls a potentially recursive function.
return false;
}
// Every call was to a non-recursive function other than this function, and
// we have no indirect recursion as the SCC size is one. This function cannot
// recurse.
return setDoesNotRecurse(*F);
}
PreservedAnalyses PostOrderFunctionAttrsPass::run(LazyCallGraph::SCC &C,
CGSCCAnalysisManager &AM) {
Module &M = *C.begin()->getFunction().getParent();
const ModuleAnalysisManager &MAM =
AM.getResult<ModuleAnalysisManagerCGSCCProxy>(C).getManager();
FunctionAnalysisManager &FAM =
AM.getResult<FunctionAnalysisManagerCGSCCProxy>(C).getManager();
// FIXME: Need some way to make it more reasonable to assume that this is
// always cached.
TargetLibraryInfo &TLI = *MAM.getCachedResult<TargetLibraryAnalysis>(M);
// We pass a lambda into functions to wire them up to the analysis manager
// for getting function analyses.
auto AARGetter = [&](Function &F) -> AAResults & {
return FAM.getResult<AAManager>(F);
};
// Fill SCCNodes with the elements of the 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 HasUnknownCall = false;
for (LazyCallGraph::Node &N : C) {
Function &F = N.getFunction();
if (F.hasFnAttribute(Attribute::OptimizeNone)) {
// Treat any function we're trying not to optimize as if it were an
// indirect call and omit it from the node set used below.
HasUnknownCall = true;
continue;
}
// Track whether any functions in this SCC have an unknown call edge.
// Note: if this is ever a performance hit, we can common it with
// subsequent routines which also do scans over the instructions of the
// function.
if (!HasUnknownCall)
for (Instruction &I : instructions(F))
if (auto CS = CallSite(&I))
if (!CS.getCalledFunction()) {
HasUnknownCall = true;
break;
}
SCCNodes.insert(&F);
}
bool Changed = false;
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 (!HasUnknownCall) {
Changed |= addNoAliasAttrs(SCCNodes);
Changed |= addNonNullAttrs(SCCNodes, TLI);
Changed |= removeConvergentAttrs(SCCNodes);
Changed |= addNoRecurseAttrs(SCCNodes);
}
return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
}
namespace {
struct PostOrderFunctionAttrsLegacyPass : public CallGraphSCCPass {
static char ID; // Pass identification, replacement for typeid
PostOrderFunctionAttrsLegacyPass() : CallGraphSCCPass(ID) {
initializePostOrderFunctionAttrsLegacyPassPass(*PassRegistry::getPassRegistry());
}
bool runOnSCC(CallGraphSCC &SCC) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
AU.addRequired<AssumptionCacheTracker>();
AU.addRequired<TargetLibraryInfoWrapperPass>();
getAAResultsAnalysisUsage(AU);
CallGraphSCCPass::getAnalysisUsage(AU);
}
private:
TargetLibraryInfo *TLI;
};
}
char PostOrderFunctionAttrsLegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(PostOrderFunctionAttrsLegacyPass, "functionattrs",
"Deduce function attributes", false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_END(PostOrderFunctionAttrsLegacyPass, "functionattrs",
"Deduce function attributes", false, false)
Pass *llvm::createPostOrderFunctionAttrsLegacyPass() { return new PostOrderFunctionAttrsLegacyPass(); }
bool PostOrderFunctionAttrsLegacyPass::runOnSCC(CallGraphSCC &SCC) {
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;
}
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 |= removeConvergentAttrs(SCCNodes);
Changed |= addNoRecurseAttrs(SCCNodes);
}
return Changed;
}
namespace {
/// A pass to do RPO deduction and propagation of function attributes.
///
/// This pass provides a general RPO or "top down" propagation of
/// function attributes. For a few (rare) cases, we can deduce significantly
/// more about function attributes by working in RPO, so this pass
/// provides the compliment to the post-order pass above where the majority of
/// deduction is performed.
// FIXME: Currently there is no RPO CGSCC pass structure to slide into and so
// this is a boring module pass, but eventually it should be an RPO CGSCC pass
// when such infrastructure is available.
struct ReversePostOrderFunctionAttrs : public ModulePass {
static char ID; // Pass identification, replacement for typeid
ReversePostOrderFunctionAttrs() : ModulePass(ID) {
initializeReversePostOrderFunctionAttrsPass(*PassRegistry::getPassRegistry());
}
bool runOnModule(Module &M) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
AU.addRequired<CallGraphWrapperPass>();
}
};
}
char ReversePostOrderFunctionAttrs::ID = 0;
INITIALIZE_PASS_BEGIN(ReversePostOrderFunctionAttrs, "rpo-functionattrs",
"Deduce function attributes in RPO", false, false)
INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
INITIALIZE_PASS_END(ReversePostOrderFunctionAttrs, "rpo-functionattrs",
"Deduce function attributes in RPO", false, false)
Pass *llvm::createReversePostOrderFunctionAttrsPass() {
return new ReversePostOrderFunctionAttrs();
}
static bool addNoRecurseAttrsTopDown(Function &F) {
// We check the preconditions for the function prior to calling this to avoid
// the cost of building up a reversible post-order list. We assert them here
// to make sure none of the invariants this relies on were violated.
assert(!F.isDeclaration() && "Cannot deduce norecurse without a definition!");
assert(!F.doesNotRecurse() &&
"This function has already been deduced as norecurs!");
assert(F.hasInternalLinkage() &&
"Can only do top-down deduction for internal linkage functions!");
// If F is internal and all of its uses are calls from a non-recursive
// functions, then none of its calls could in fact recurse without going
// through a function marked norecurse, and so we can mark this function too
// as norecurse. Note that the uses must actually be calls -- otherwise
// a pointer to this function could be returned from a norecurse function but
// this function could be recursively (indirectly) called. Note that this
// also detects if F is directly recursive as F is not yet marked as
// a norecurse function.
for (auto *U : F.users()) {
auto *I = dyn_cast<Instruction>(U);
if (!I)
return false;
CallSite CS(I);
if (!CS || !CS.getParent()->getParent()->doesNotRecurse())
return false;
}
return setDoesNotRecurse(F);
}
bool ReversePostOrderFunctionAttrs::runOnModule(Module &M) {
// We only have a post-order SCC traversal (because SCCs are inherently
// discovered in post-order), so we accumulate them in a vector and then walk
// it in reverse. This is simpler than using the RPO iterator infrastructure
// because we need to combine SCC detection and the PO walk of the call
// graph. We can also cheat egregiously because we're primarily interested in
// synthesizing norecurse and so we can only save the singular SCCs as SCCs
// with multiple functions in them will clearly be recursive.
auto &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
SmallVector<Function *, 16> Worklist;
for (scc_iterator<CallGraph *> I = scc_begin(&CG); !I.isAtEnd(); ++I) {
if (I->size() != 1)
continue;
Function *F = I->front()->getFunction();
if (F && !F->isDeclaration() && !F->doesNotRecurse() &&
F->hasInternalLinkage())
Worklist.push_back(F);
}
bool Changed = false;
for (auto *F : reverse(Worklist))
Changed |= addNoRecurseAttrsTopDown(*F);
return Changed;
}
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