X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FAnalysis%2FCaptureTracking.cpp;h=f2f8877af1a280dd44b49c1badf1aa5b6951eaf1;hb=1cb132f921c55f9584d06787b849ef0f255403b2;hp=8364d81497c2f5b9af1190cb0909f388ddedce26;hpb=837be07979723fb05ef47c828da014ce9ed1ba34;p=oota-llvm.git diff --git a/lib/Analysis/CaptureTracking.cpp b/lib/Analysis/CaptureTracking.cpp index 8364d81497c..f2f8877af1a 100644 --- a/lib/Analysis/CaptureTracking.cpp +++ b/lib/Analysis/CaptureTracking.cpp @@ -16,15 +16,102 @@ // //===----------------------------------------------------------------------===// -#include "llvm/Analysis/CaptureTracking.h" -#include "llvm/Instructions.h" -#include "llvm/Value.h" -#include "llvm/Analysis/AliasAnalysis.h" #include "llvm/ADT/SmallSet.h" #include "llvm/ADT/SmallVector.h" -#include "llvm/Support/CallSite.h" +#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/Analysis/CaptureTracking.h" +#include "llvm/Analysis/CFG.h" +#include "llvm/IR/CallSite.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/Instructions.h" + using namespace llvm; +CaptureTracker::~CaptureTracker() {} + +bool CaptureTracker::shouldExplore(const Use *U) { return true; } + +namespace { + struct SimpleCaptureTracker : public CaptureTracker { + explicit SimpleCaptureTracker(bool ReturnCaptures) + : ReturnCaptures(ReturnCaptures), Captured(false) {} + + void tooManyUses() override { Captured = true; } + + bool captured(const Use *U) override { + if (isa(U->getUser()) && !ReturnCaptures) + return false; + + Captured = true; + return true; + } + + bool ReturnCaptures; + + bool Captured; + }; + + /// Only find pointer captures which happen before the given instruction. Uses + /// the dominator tree to determine whether one instruction is before another. + /// Only support the case where the Value is defined in the same basic block + /// as the given instruction and the use. + struct CapturesBefore : public CaptureTracker { + CapturesBefore(bool ReturnCaptures, const Instruction *I, DominatorTree *DT, + bool IncludeI) + : BeforeHere(I), DT(DT), ReturnCaptures(ReturnCaptures), + IncludeI(IncludeI), Captured(false) {} + + void tooManyUses() override { Captured = true; } + + bool shouldExplore(const Use *U) override { + Instruction *I = cast(U->getUser()); + if (BeforeHere == I && !IncludeI) + return false; + + BasicBlock *BB = I->getParent(); + // We explore this usage only if the usage can reach "BeforeHere". + // If use is not reachable from entry, there is no need to explore. + if (BeforeHere != I && !DT->isReachableFromEntry(BB)) + return false; + // If the value is defined in the same basic block as use and BeforeHere, + // there is no need to explore the use if BeforeHere dominates use. + // Check whether there is a path from I to BeforeHere. + if (BeforeHere != I && DT->dominates(BeforeHere, I) && + !isPotentiallyReachable(I, BeforeHere, DT)) + return false; + return true; + } + + bool captured(const Use *U) override { + if (isa(U->getUser()) && !ReturnCaptures) + return false; + + Instruction *I = cast(U->getUser()); + if (BeforeHere == I && !IncludeI) + return false; + + BasicBlock *BB = I->getParent(); + // Same logic as in shouldExplore. + if (BeforeHere != I && !DT->isReachableFromEntry(BB)) + return false; + if (BeforeHere != I && DT->dominates(BeforeHere, I) && + !isPotentiallyReachable(I, BeforeHere, DT)) + return false; + Captured = true; + return true; + } + + const Instruction *BeforeHere; + DominatorTree *DT; + + bool ReturnCaptures; + bool IncludeI; + + bool Captured; + }; +} + /// PointerMayBeCaptured - Return true if this pointer value may be captured /// by the enclosing function (which is required to exist). This routine can /// be expensive, so consider caching the results. The boolean ReturnCaptures @@ -34,26 +121,77 @@ using namespace llvm; /// counts as capturing it or not. bool llvm::PointerMayBeCaptured(const Value *V, bool ReturnCaptures, bool StoreCaptures) { - assert(isa(V->getType()) && "Capture is for pointers only!"); - SmallVector Worklist; - SmallSet Visited; - - for (Value::use_const_iterator UI = V->use_begin(), UE = V->use_end(); - UI != UE; ++UI) { - Use *U = &UI.getUse(); - Visited.insert(U); - Worklist.push_back(U); + assert(!isa(V) && + "It doesn't make sense to ask whether a global is captured."); + + // TODO: If StoreCaptures is not true, we could do Fancy analysis + // to determine whether this store is not actually an escape point. + // In that case, BasicAliasAnalysis should be updated as well to + // take advantage of this. + (void)StoreCaptures; + + SimpleCaptureTracker SCT(ReturnCaptures); + PointerMayBeCaptured(V, &SCT); + return SCT.Captured; +} + +/// PointerMayBeCapturedBefore - Return true if this pointer value may be +/// captured by the enclosing function (which is required to exist). If a +/// DominatorTree is provided, only captures which happen before the given +/// instruction are considered. This routine can be expensive, so consider +/// caching the results. The boolean ReturnCaptures specifies whether +/// returning the value (or part of it) from the function counts as capturing +/// it or not. The boolean StoreCaptures specified whether storing the value +/// (or part of it) into memory anywhere automatically counts as capturing it +/// or not. +bool llvm::PointerMayBeCapturedBefore(const Value *V, bool ReturnCaptures, + bool StoreCaptures, const Instruction *I, + DominatorTree *DT, bool IncludeI) { + assert(!isa(V) && + "It doesn't make sense to ask whether a global is captured."); + + if (!DT) + return PointerMayBeCaptured(V, ReturnCaptures, StoreCaptures); + + // TODO: See comment in PointerMayBeCaptured regarding what could be done + // with StoreCaptures. + + CapturesBefore CB(ReturnCaptures, I, DT, IncludeI); + PointerMayBeCaptured(V, &CB); + return CB.Captured; +} + +/// TODO: Write a new FunctionPass AliasAnalysis so that it can keep +/// a cache. Then we can move the code from BasicAliasAnalysis into +/// that path, and remove this threshold. +static int const Threshold = 20; + +void llvm::PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker) { + assert(V->getType()->isPointerTy() && "Capture is for pointers only!"); + SmallVector Worklist; + SmallSet Visited; + int Count = 0; + + for (const Use &U : V->uses()) { + // If there are lots of uses, conservatively say that the value + // is captured to avoid taking too much compile time. + if (Count++ >= Threshold) + return Tracker->tooManyUses(); + + if (!Tracker->shouldExplore(&U)) continue; + Visited.insert(&U); + Worklist.push_back(&U); } while (!Worklist.empty()) { - Use *U = Worklist.pop_back_val(); + const Use *U = Worklist.pop_back_val(); Instruction *I = cast(U->getUser()); V = U->get(); switch (I->getOpcode()) { case Instruction::Call: case Instruction::Invoke: { - CallSite CS = CallSite::get(I); + CallSite CS(I); // Not captured if the callee is readonly, doesn't return a copy through // its return value and doesn't unwind (a readonly function can leak bits // by throwing an exception or not depending on the input value). @@ -69,60 +207,64 @@ bool llvm::PointerMayBeCaptured(const Value *V, // (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)) + if (A->get() == V && !CS.doesNotCapture(A - B)) // The parameter is not marked 'nocapture' - captured. - return true; - // Only passed via 'nocapture' arguments, or is the called function - not - // captured. + if (Tracker->captured(U)) + return; break; } case Instruction::Load: // Loading from a pointer does not cause it to be captured. break; - case Instruction::Ret: - if (ReturnCaptures) - return true; + case Instruction::VAArg: + // "va-arg" from a pointer does not cause it to be captured. break; case Instruction::Store: if (V == I->getOperand(0)) // Stored the pointer - conservatively assume it may be captured. - // TODO: If StoreCaptures is not true, we could do Fancy analysis - // to determine whether this store is not actually an escape point. - // In that case, BasicAliasAnalysis should be updated as well to - // take advantage of this. - return true; + if (Tracker->captured(U)) + return; // Storing to the pointee does not cause the pointer to be captured. break; case Instruction::BitCast: case Instruction::GetElementPtr: case Instruction::PHI: case Instruction::Select: + case Instruction::AddrSpaceCast: // The original value is not captured via this if the new value isn't. - for (Instruction::use_iterator UI = I->use_begin(), UE = I->use_end(); - UI != UE; ++UI) { - Use *U = &UI.getUse(); - if (Visited.insert(U)) - Worklist.push_back(U); + Count = 0; + for (Use &UU : I->uses()) { + // If there are lots of uses, conservatively say that the value + // is captured to avoid taking too much compile time. + if (Count++ >= Threshold) + return Tracker->tooManyUses(); + + if (Visited.insert(&UU)) + if (Tracker->shouldExplore(&UU)) + Worklist.push_back(&UU); } break; case Instruction::ICmp: // Don't count comparisons of a no-alias return value against null as // captures. This allows us to ignore comparisons of malloc results // with null, for example. - if (isNoAliasCall(V)) - if (ConstantPointerNull *CPN = - dyn_cast(I->getOperand(1))) - if (CPN->getType()->getAddressSpace() == 0) + if (ConstantPointerNull *CPN = + dyn_cast(I->getOperand(1))) + if (CPN->getType()->getAddressSpace() == 0) + if (isNoAliasCall(V->stripPointerCasts())) break; // Otherwise, be conservative. There are crazy ways to capture pointers // using comparisons. - return true; + if (Tracker->captured(U)) + return; + break; default: // Something else - be conservative and say it is captured. - return true; + if (Tracker->captured(U)) + return; + break; } } - // All uses examined - not captured. - return false; + // All uses examined. }