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-rw-r--r--llvm/lib/Analysis/LoopAccessAnalysis.cpp22
-rw-r--r--llvm/lib/Analysis/ValueTracking.cpp46
2 files changed, 57 insertions, 11 deletions
diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index cd94583c9e2..cfa8fbe4a8c 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -199,9 +199,9 @@ public:
typedef PointerIntPair<Value *, 1, bool> MemAccessInfo;
typedef SmallPtrSet<MemAccessInfo, 8> MemAccessInfoSet;
- AccessAnalysis(const DataLayout &Dl, AliasAnalysis *AA,
+ AccessAnalysis(const DataLayout &Dl, AliasAnalysis *AA, LoopInfo *LI,
MemoryDepChecker::DepCandidates &DA)
- : DL(Dl), AST(*AA), DepCands(DA), IsRTCheckNeeded(false) {}
+ : DL(Dl), AST(*AA), LI(LI), DepCands(DA), IsRTCheckNeeded(false) {}
/// \brief Register a load and whether it is only read from.
void addLoad(AliasAnalysis::Location &Loc, bool IsReadOnly) {
@@ -261,6 +261,8 @@ private:
//intrinsic property (such as TBAA metadata).
AliasSetTracker AST;
+ LoopInfo *LI;
+
/// Sets of potentially dependent accesses - members of one set share an
/// underlying pointer. The set "CheckDeps" identfies which sets really need a
/// dependence check.
@@ -477,7 +479,9 @@ void AccessAnalysis::processMemAccesses() {
// underlying object.
typedef SmallVector<Value *, 16> ValueVector;
ValueVector TempObjects;
- GetUnderlyingObjects(Ptr, TempObjects, DL);
+
+ GetUnderlyingObjects(Ptr, TempObjects, DL, LI);
+ DEBUG(dbgs() << "Underlying objects for pointer " << *Ptr << "\n");
for (Value *UnderlyingObj : TempObjects) {
UnderlyingObjToAccessMap::iterator Prev =
ObjToLastAccess.find(UnderlyingObj);
@@ -485,6 +489,7 @@ void AccessAnalysis::processMemAccesses() {
DepCands.unionSets(Access, Prev->second);
ObjToLastAccess[UnderlyingObj] = Access;
+ DEBUG(dbgs() << " " << *UnderlyingObj << "\n");
}
}
}
@@ -1035,7 +1040,7 @@ void LoopAccessInfo::analyzeLoop(const ValueToValueMap &Strides) {
MemoryDepChecker::DepCandidates DependentAccesses;
AccessAnalysis Accesses(TheLoop->getHeader()->getModule()->getDataLayout(),
- AA, DependentAccesses);
+ AA, LI, DependentAccesses);
// Holds the analyzed pointers. We don't want to call GetUnderlyingObjects
// multiple times on the same object. If the ptr is accessed twice, once
@@ -1306,10 +1311,10 @@ std::pair<Instruction *, Instruction *> LoopAccessInfo::addRuntimeCheck(
LoopAccessInfo::LoopAccessInfo(Loop *L, ScalarEvolution *SE,
const DataLayout &DL,
const TargetLibraryInfo *TLI, AliasAnalysis *AA,
- DominatorTree *DT,
+ DominatorTree *DT, LoopInfo *LI,
const ValueToValueMap &Strides)
: DepChecker(SE, L), NumComparisons(0), TheLoop(L), SE(SE), DL(DL),
- TLI(TLI), AA(AA), DT(DT), NumLoads(0), NumStores(0),
+ TLI(TLI), AA(AA), DT(DT), LI(LI), NumLoads(0), NumStores(0),
MaxSafeDepDistBytes(-1U), CanVecMem(false),
StoreToLoopInvariantAddress(false) {
if (canAnalyzeLoop())
@@ -1356,7 +1361,8 @@ LoopAccessAnalysis::getInfo(Loop *L, const ValueToValueMap &Strides) {
if (!LAI) {
const DataLayout &DL = L->getHeader()->getModule()->getDataLayout();
- LAI = llvm::make_unique<LoopAccessInfo>(L, SE, DL, TLI, AA, DT, Strides);
+ LAI = llvm::make_unique<LoopAccessInfo>(L, SE, DL, TLI, AA, DT, LI,
+ Strides);
#ifndef NDEBUG
LAI->NumSymbolicStrides = Strides.size();
#endif
@@ -1367,7 +1373,6 @@ LoopAccessAnalysis::getInfo(Loop *L, const ValueToValueMap &Strides) {
void LoopAccessAnalysis::print(raw_ostream &OS, const Module *M) const {
LoopAccessAnalysis &LAA = *const_cast<LoopAccessAnalysis *>(this);
- LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
ValueToValueMap NoSymbolicStrides;
for (Loop *TopLevelLoop : *LI)
@@ -1384,6 +1389,7 @@ bool LoopAccessAnalysis::runOnFunction(Function &F) {
TLI = TLIP ? &TLIP->getTLI() : nullptr;
AA = &getAnalysis<AliasAnalysis>();
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+ LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
return false;
}
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index de175fc523d..52a8c69688f 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -17,6 +17,7 @@
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/MemoryBuiltins.h"
+#include "llvm/Analysis/LoopInfo.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/ConstantRange.h"
#include "llvm/IR/Constants.h"
@@ -2737,6 +2738,32 @@ uint64_t llvm::GetStringLength(Value *V) {
return Len == ~0ULL ? 1 : Len;
}
+/// \brief \p PN defines a loop-variant pointer to an object. Check if the
+/// previous iteration of the loop was referring to the same object as \p PN.
+static bool isSameUnderlyingObjectInLoop(PHINode *PN, LoopInfo *LI) {
+ // Find the loop-defined value.
+ Loop *L = LI->getLoopFor(PN->getParent());
+ if (PN->getNumIncomingValues() != 2)
+ return true;
+
+ // Find the value from previous iteration.
+ auto *PrevValue = dyn_cast<Instruction>(PN->getIncomingValue(0));
+ if (!PrevValue || LI->getLoopFor(PrevValue->getParent()) != L)
+ PrevValue = dyn_cast<Instruction>(PN->getIncomingValue(1));
+ if (!PrevValue || LI->getLoopFor(PrevValue->getParent()) != L)
+ return true;
+
+ // If a new pointer is loaded in the loop, the pointer references a different
+ // object in every iteration. E.g.:
+ // for (i)
+ // int *p = a[i];
+ // ...
+ if (auto *Load = dyn_cast<LoadInst>(PrevValue))
+ if (!L->isLoopInvariant(Load->getPointerOperand()))
+ return false;
+ return true;
+}
+
Value *llvm::GetUnderlyingObject(Value *V, const DataLayout &DL,
unsigned MaxLookup) {
if (!V->getType()->isPointerTy())
@@ -2768,7 +2795,8 @@ Value *llvm::GetUnderlyingObject(Value *V, const DataLayout &DL,
}
void llvm::GetUnderlyingObjects(Value *V, SmallVectorImpl<Value *> &Objects,
- const DataLayout &DL, unsigned MaxLookup) {
+ const DataLayout &DL, LoopInfo *LI,
+ unsigned MaxLookup) {
SmallPtrSet<Value *, 4> Visited;
SmallVector<Value *, 4> Worklist;
Worklist.push_back(V);
@@ -2786,8 +2814,20 @@ void llvm::GetUnderlyingObjects(Value *V, SmallVectorImpl<Value *> &Objects,
}
if (PHINode *PN = dyn_cast<PHINode>(P)) {
- for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
- Worklist.push_back(PN->getIncomingValue(i));
+ // If this PHI changes the underlying object in every iteration of the
+ // loop, don't look through it. Consider:
+ // int **A;
+ // for (i) {
+ // Prev = Curr; // Prev = PHI (Prev_0, Curr)
+ // Curr = A[i];
+ // *Prev, *Curr;
+ //
+ // Prev is tracking Curr one iteration behind so they refer to different
+ // underlying objects.
+ if (!LI || !LI->isLoopHeader(PN->getParent()) ||
+ isSameUnderlyingObjectInLoop(PN, LI))
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+ Worklist.push_back(PN->getIncomingValue(i));
continue;
}
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