const Value *V;
ExtensionKind Extension;
int64_t Scale;
+
+ bool operator==(const VariableGEPIndex &Other) const {
+ return V == Other.V && Extension == Other.Extension &&
+ Scale == Other.Scale;
+ }
+
+ bool operator!=(const VariableGEPIndex &Other) const {
+ return !operator==(Other);
+ }
};
}
/// BasicAliasAnalysis - This is the primary alias analysis implementation.
struct BasicAliasAnalysis : public ImmutablePass, public AliasAnalysis {
static char ID; // Class identification, replacement for typeinfo
- BasicAliasAnalysis() : ImmutablePass(ID),
- // AliasCache rarely has more than 1 or 2 elements,
- // so start it off fairly small so that clear()
- // doesn't have to tromp through 64 (the default)
- // elements on each alias query. This really wants
- // something like a SmallDenseMap.
- AliasCache(8) {
+ BasicAliasAnalysis() : ImmutablePass(ID) {
initializeBasicAliasAnalysisPass(*PassRegistry::getPassRegistry());
}
"BasicAliasAnalysis doesn't support interprocedural queries.");
AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.TBAATag,
LocB.Ptr, LocB.Size, LocB.TBAATag);
- AliasCache.clear();
+ // AliasCache rarely has more than 1 or 2 elements, always use
+ // shrink_and_clear so it quickly returns to the inline capacity of the
+ // SmallDenseMap if it ever grows larger.
+ // FIXME: This should really be shrink_to_inline_capacity_and_clear().
+ AliasCache.shrink_and_clear();
return Alias;
}
private:
// AliasCache - Track alias queries to guard against recursion.
typedef std::pair<Location, Location> LocPair;
- typedef DenseMap<LocPair, AliasResult> AliasCacheTy;
+ typedef SmallDenseMap<LocPair, AliasResult, 8> AliasCacheTy;
AliasCacheTy AliasCache;
// Visited - Track instructions visited by pointsToConstantMemory.
// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP
// instruction against another.
AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size,
+ const MDNode *V1TBAAInfo,
const Value *V2, uint64_t V2Size,
const MDNode *V2TBAAInfo,
const Value *UnderlyingV1, const Value *UnderlyingV2);
return ModRefResult(AliasAnalysis::getModRefInfo(CS, Loc) & Min);
}
+static bool areVarIndicesEqual(SmallVector<VariableGEPIndex, 4> &Indices1,
+ SmallVector<VariableGEPIndex, 4> &Indices2) {
+ unsigned Size1 = Indices1.size();
+ unsigned Size2 = Indices2.size();
+
+ if (Size1 != Size2)
+ return false;
+
+ for (unsigned I = 0; I != Size1; ++I)
+ if (Indices1[I] != Indices2[I])
+ return false;
+
+ return true;
+}
+
/// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction
/// against another pointer. We know that V1 is a GEP, but we don't know
/// anything about V2. UnderlyingV1 is GetUnderlyingObject(GEP1, TD),
///
AliasAnalysis::AliasResult
BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
+ const MDNode *V1TBAAInfo,
const Value *V2, uint64_t V2Size,
const MDNode *V2TBAAInfo,
const Value *UnderlyingV1,
int64_t GEP1BaseOffset;
SmallVector<VariableGEPIndex, 4> GEP1VariableIndices;
- // If we have two gep instructions with must-alias'ing base pointers, figure
- // out if the indexes to the GEP tell us anything about the derived pointer.
+ // If we have two gep instructions with must-alias or not-alias'ing base
+ // pointers, figure out if the indexes to the GEP tell us anything about the
+ // derived pointer.
if (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) {
+ // Check for geps of non-aliasing underlying pointers where the offsets are
+ // identical.
+ if (V1Size == V2Size) {
+ // Do the base pointers alias assuming type and size.
+ AliasResult PreciseBaseAlias = aliasCheck(UnderlyingV1, V1Size,
+ V1TBAAInfo, UnderlyingV2,
+ V2Size, V2TBAAInfo);
+ if (PreciseBaseAlias == NoAlias) {
+ // See if the computed offset from the common pointer tells us about the
+ // relation of the resulting pointer.
+ int64_t GEP2BaseOffset;
+ SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
+ const Value *GEP2BasePtr =
+ DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD);
+ const Value *GEP1BasePtr =
+ DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD);
+ // DecomposeGEPExpression and GetUnderlyingObject should return the
+ // same result except when DecomposeGEPExpression has no TargetData.
+ if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
+ assert(TD == 0 &&
+ "DecomposeGEPExpression and GetUnderlyingObject disagree!");
+ return MayAlias;
+ }
+ // Same offsets.
+ if (GEP1BaseOffset == GEP2BaseOffset &&
+ areVarIndicesEqual(GEP1VariableIndices, GEP2VariableIndices))
+ return NoAlias;
+ GEP1VariableIndices.clear();
+ }
+ }
+
// Do the base pointers alias?
AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, 0,
UnderlyingV2, UnknownSize, 0);
const Value *GEP2BasePtr =
DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD);
- // If DecomposeGEPExpression isn't able to look all the way through the
- // addressing operation, we must not have TD and this is too complex for us
- // to handle without it.
+ // DecomposeGEPExpression and GetUnderlyingObject should return the
+ // same result except when DecomposeGEPExpression has no TargetData.
if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
assert(TD == 0 &&
"DecomposeGEPExpression and GetUnderlyingObject disagree!");
const Value *GEP1BasePtr =
DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD);
- // If DecomposeGEPExpression isn't able to look all the way through the
- // addressing operation, we must not have TD and this is too complex for us
- // to handle without it.
+ // DecomposeGEPExpression and GetUnderlyingObject should return the
+ // same result except when DecomposeGEPExpression has no TargetData.
if (GEP1BasePtr != UnderlyingV1) {
assert(TD == 0 &&
"DecomposeGEPExpression and GetUnderlyingObject disagree!");
// on corresponding edges.
if (const PHINode *PN2 = dyn_cast<PHINode>(V2))
if (PN2->getParent() == PN->getParent()) {
+ LocPair Locs(Location(PN, PNSize, PNTBAAInfo),
+ Location(V2, V2Size, V2TBAAInfo));
+ if (PN > V2)
+ std::swap(Locs.first, Locs.second);
+
AliasResult Alias =
aliasCheck(PN->getIncomingValue(0), PNSize, PNTBAAInfo,
PN2->getIncomingValueForBlock(PN->getIncomingBlock(0)),
V2Size, V2TBAAInfo);
if (Alias == MayAlias)
return MayAlias;
+
+ // If the first source of the PHI nodes NoAlias and the other inputs are
+ // the PHI node itself through some amount of recursion this does not add
+ // any new information so just return NoAlias.
+ // bb:
+ // ptr = ptr2 + 1
+ // loop:
+ // ptr_phi = phi [bb, ptr], [loop, ptr_plus_one]
+ // ptr2_phi = phi [bb, ptr2], [loop, ptr2_plus_one]
+ // ...
+ // ptr_plus_one = gep ptr_phi, 1
+ // ptr2_plus_one = gep ptr2_phi, 1
+ // We assume for the recursion that the the phis (ptr_phi, ptr2_phi) do
+ // not alias each other.
+ bool ArePhisAssumedNoAlias = false;
+ AliasResult OrigAliasResult = NoAlias;
+ if (Alias == NoAlias) {
+ // Pretend the phis do not alias.
+ assert(AliasCache.count(Locs) &&
+ "There must exist an entry for the phi node");
+ OrigAliasResult = AliasCache[Locs];
+ AliasCache[Locs] = NoAlias;
+ ArePhisAssumedNoAlias = true;
+ }
+
for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) {
AliasResult ThisAlias =
aliasCheck(PN->getIncomingValue(i), PNSize, PNTBAAInfo,
if (Alias == MayAlias)
break;
}
+
+ // Reset if speculation failed.
+ if (ArePhisAssumedNoAlias && Alias != NoAlias)
+ AliasCache[Locs] = OrigAliasResult;
+
return Alias;
}
std::swap(O1, O2);
}
if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) {
- AliasResult Result = aliasGEP(GV1, V1Size, V2, V2Size, V2TBAAInfo, O1, O2);
+ AliasResult Result = aliasGEP(GV1, V1Size, V1TBAAInfo, V2, V2Size, V2TBAAInfo, O1, O2);
if (Result != MayAlias) return AliasCache[Locs] = Result;
}
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