#include "llvm/Transforms/IPO.h"
#include "llvm/CallGraphSCCPass.h"
#include "llvm/GlobalVariable.h"
-#include "llvm/Instructions.h"
+#include "llvm/IntrinsicInst.h"
+#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/CallGraph.h"
-#include "llvm/ADT/PointerIntPair.h"
+#include "llvm/Analysis/CaptureTracking.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/UniqueVector.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/InstIterator.h"
using namespace llvm;
STATISTIC(NumReadNone, "Number of functions marked readnone");
STATISTIC(NumReadOnly, "Number of functions marked readonly");
STATISTIC(NumNoCapture, "Number of arguments marked nocapture");
+STATISTIC(NumNoAlias, "Number of function returns marked noalias");
namespace {
struct VISIBILITY_HIDDEN FunctionAttrs : public CallGraphSCCPass {
// AddNoCaptureAttrs - Deduce nocapture attributes for the SCC.
bool AddNoCaptureAttrs(const std::vector<CallGraphNode *> &SCC);
- // isCaptured - Return true if this pointer value may be captured.
- bool isCaptured(Function &F, Value *V);
+ // IsFunctionMallocLike - Does this function allocate new memory?
+ bool IsFunctionMallocLike(Function *F,
+ SmallPtrSet<CallGraphNode*, 8> &) const;
+
+ // AddNoAliasAttrs - Deduce noalias attributes for the SCC.
+ bool AddNoAliasAttrs(const std::vector<CallGraphNode *> &SCC);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
return MadeChange;
}
-/// isCaptured - Return true if this pointer value may be captured.
-bool FunctionAttrs::isCaptured(Function &F, Value *V) {
- typedef PointerIntPair<Use*, 2> UseWithDepth;
- SmallVector<UseWithDepth, 16> Worklist;
- SmallSet<UseWithDepth, 16> Visited;
-
- for (Value::use_iterator UI = V->use_begin(), UE = V->use_end(); UI != UE;
- ++UI) {
- UseWithDepth UD(&UI.getUse(), 0);
- Visited.insert(UD);
- Worklist.push_back(UD);
- }
-
- while (!Worklist.empty()) {
- UseWithDepth UD = Worklist.pop_back_val();
- Use *U = UD.getPointer();
- Instruction *I = cast<Instruction>(U->getUser());
- // The value V may have any type if it comes from tracking a load.
- V = U->get();
- // The depth represents the number of loads that need to be performed to
- // get back the original pointer (or a bitcast etc of it). For example,
- // if the pointer is stored to an alloca, then all uses of the alloca get
- // depth 1: if the alloca is loaded then you get the original pointer back.
- // If a load of the alloca is returned then the pointer has been captured.
- // The depth is needed in order to know which loads dereference the original
- // pointer (these do not capture), and which return a value which needs to
- // be tracked because if it is captured then so is the original pointer.
- unsigned Depth = UD.getInt();
-
- if (isa<StoreInst>(I)) {
- if (V == I->getOperand(0)) {
- // Stored the pointer - it may be captured. If it is stored to a local
- // object (alloca) then track that object. Otherwise give up.
- Value *Target = I->getOperand(1)->getUnderlyingObject();
- if (!isa<AllocaInst>(Target))
- // Didn't store to an obviously local object - captured.
- return true;
- if (Depth >= 3)
- // Alloca recursion too deep - give up.
- return true;
- // Analyze all uses of the alloca.
- for (Value::use_iterator UI = Target->use_begin(),
- UE = Target->use_end(); UI != UE; ++UI) {
- UseWithDepth NUD(&UI.getUse(), Depth + 1);
- if (Visited.insert(NUD))
- Worklist.push_back(NUD);
- }
- }
- // Storing to the pointee does not cause the pointer to be captured.
- } else if (isa<FreeInst>(I)) {
- // Freeing a pointer does not cause it to be captured.
- } else if (isa<CallInst>(I) || isa<InvokeInst>(I)) {
- CallSite CS = CallSite::get(I);
- // Not captured if the callee is readonly and doesn't return a copy
- // through its return value.
- if (CS.onlyReadsMemory() && I->getType() == Type::VoidTy)
- continue;
-
- // Not captured if only passed via 'nocapture' arguments. Note that
- // calling a function pointer does not in itself cause the pointer to
- // be captured. This is a subtle point considering that (for example)
- // the callee might return its own address. It is analogous to saying
- // that loading a value from a pointer does not cause the pointer to be
- // captured, even though the loaded value might be the pointer itself
- // (think of self-referential objects).
- CallSite::arg_iterator B = CS.arg_begin(), E = CS.arg_end();
- for (CallSite::arg_iterator A = B; A != E; ++A)
- if (A->get() == V && !CS.paramHasAttr(A - B + 1, Attribute::NoCapture))
- // The parameter is not marked 'nocapture' - captured.
- return true;
- // Only passed via 'nocapture' arguments, or is the called function - not
- // captured.
- } else if (isa<BitCastInst>(I) || isa<LoadInst>(I) || isa<PHINode>(I) ||
- // Play safe and exclude GEP indices.
- (isa<GetElementPtrInst>(I) && V == I->getOperand(0)) ||
- // Play safe and exclude the select condition.
- (isa<SelectInst>(I) && V != I->getOperand(0))) {
-
- // Usually loads can be ignored because they dereference the original
- // pointer. However the loaded value needs to be tracked if loading
- // from an object that the original pointer was stored to.
- if (isa<LoadInst>(I)) {
- if (Depth == 0)
- // Loading the original pointer or a variation of it. This does not
- // cause the pointer to be captured. Note that the loaded value might
- // be the pointer itself (think of self-referential objects), but that
- // is fine as long as it's not this function that stored it there.
- continue;
- // Loading a pointer to (a pointer to...) the original pointer or a
- // variation of it. Track uses of the loaded value, noting that one
- // dereference was performed. Note that the loaded value need not be
- // of pointer type. For example, an alloca may have been bitcast to
- // a pointer to another type, which was then loaded.
- --Depth;
- }
-
- // The original value is not captured via this if the instruction isn't.
- for (Instruction::use_iterator UI = I->use_begin(), UE = I->use_end();
- UI != UE; ++UI) {
- UseWithDepth UD(&UI.getUse(), Depth);
- if (Visited.insert(UD))
- Worklist.push_back(UD);
- }
- } else {
- // Something else - be conservative and say it is captured.
- return true;
- }
- }
-
- // All uses examined - not captured.
- return false;
-}
-
/// AddNoCaptureAttrs - Deduce nocapture attributes for the SCC.
bool FunctionAttrs::AddNoCaptureAttrs(const std::vector<CallGraphNode *> &SCC) {
bool Changed = false;
for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end(); A!=E; ++A)
if (isa<PointerType>(A->getType()) && !A->hasNoCaptureAttr() &&
- !isCaptured(*F, A)) {
+ !PointerMayBeCaptured(A, true)) {
A->addAttr(Attribute::NoCapture);
++NumNoCapture;
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<CallGraphNode*, 8> &SCCNodes) const {
+ CallGraph &CG = getAnalysis<CallGraph>();
+
+ UniqueVector<Value *> 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.
+
+ 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::GetElementPtr:
+ case Instruction::BitCast:
+ 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;
+
+ // Check whether the pointer came from an allocation.
+ case Instruction::Alloca:
+ case Instruction::Malloc:
+ break;
+ case Instruction::Call:
+ case Instruction::Invoke: {
+ CallSite CS(RVI);
+ if (CS.paramHasAttr(0, Attribute::NoAlias))
+ break;
+ if (CS.getCalledFunction() &&
+ SCCNodes.count(CG[CS.getCalledFunction()]))
+ break;
+ } // fall-through
+ default:
+ return false; // Did not come from an allocation.
+ }
+
+ if (PointerMayBeCaptured(RetVal, false))
+ return false;
+ }
+
+ return true;
+}
+
+/// AddNoAliasAttrs - Deduce noalias attributes for the SCC.
+bool FunctionAttrs::AddNoAliasAttrs(const std::vector<CallGraphNode *> &SCC) {
+ SmallPtrSet<CallGraphNode*, 8> SCCNodes;
+
+ // Fill SCCNodes with the elements of the SCC. Used for quickly
+ // looking up whether a given CallGraphNode is in this SCC.
+ for (unsigned i = 0, e = SCC.size(); i != e; ++i)
+ SCCNodes.insert(SCC[i]);
+
+ // Check each function in turn, determining which functions return noalias
+ // pointers.
+ for (unsigned i = 0, e = SCC.size(); i != e; ++i) {
+ Function *F = SCC[i]->getFunction();
+
+ if (F == 0)
+ // External node - skip it;
+ return false;
+
+ // Already noalias.
+ if (F->doesNotAlias(0))
+ continue;
+
+ // Definitions with weak linkage may be overridden at linktime, so
+ // treat them like declarations.
+ if (F->isDeclaration() || F->mayBeOverridden())
+ return false;
+
+ // We annotate noalias return values, which are only applicable to
+ // pointer types.
+ if (!isa<PointerType>(F->getReturnType()))
+ continue;
+
+ if (!IsFunctionMallocLike(F, SCCNodes))
+ return false;
+ }
+
+ bool MadeChange = false;
+ for (unsigned i = 0, e = SCC.size(); i != e; ++i) {
+ Function *F = SCC[i]->getFunction();
+ if (F->doesNotAlias(0) || !isa<PointerType>(F->getReturnType()))
+ continue;
+
+ F->setDoesNotAlias(0);
+ ++NumNoAlias;
+ MadeChange = true;
+ }
+
+ return MadeChange;
+}
+
bool FunctionAttrs::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
bool Changed = AddReadAttrs(SCC);
Changed |= AddNoCaptureAttrs(SCC);
+ Changed |= AddNoAliasAttrs(SCC);
return Changed;
}
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