Fix BasicAA's recursion detection so that it doesn't pessimize
queries in the case of a DAG, where a query reaches a node
visited earlier, but it's not on a cycle. This avoids
MayAlias results in cases where BasicAA is expected to
return MustAlias or PartialAlias in order to protect TBAA.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132609 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index c292999..24297d4 100644
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -465,12 +465,12 @@
virtual AliasResult alias(const Location &LocA,
const Location &LocB) {
- assert(Visited.empty() && "Visited must be cleared after use!");
+ assert(AliasCache.empty() && "AliasCache must be cleared after use!");
assert(notDifferentParent(LocA.Ptr, LocB.Ptr) &&
"BasicAliasAnalysis doesn't support interprocedural queries.");
AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.TBAATag,
LocB.Ptr, LocB.Size, LocB.TBAATag);
- Visited.clear();
+ AliasCache.clear();
return Alias;
}
@@ -506,7 +506,12 @@
}
private:
- // Visited - Track instructions visited by a aliasPHI, aliasSelect(), and aliasGEP().
+ // AliasCache - Track alias queries to guard against recursion.
+ typedef std::pair<Location, Location> LocPair;
+ typedef DenseMap<LocPair, AliasResult> AliasCacheTy;
+ AliasCacheTy AliasCache;
+
+ // Visited - Track instructions visited by pointsToConstantMemory.
SmallPtrSet<const Value*, 16> Visited;
// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP
@@ -822,13 +827,6 @@
const MDNode *V2TBAAInfo,
const Value *UnderlyingV1,
const Value *UnderlyingV2) {
- // If this GEP has been visited before, we're on a use-def cycle.
- // Such cycles are only valid when PHI nodes are involved or in unreachable
- // code. The visitPHI function catches cycles containing PHIs, but there
- // could still be a cycle without PHIs in unreachable code.
- if (!Visited.insert(GEP1))
- return MayAlias;
-
int64_t GEP1BaseOffset;
SmallVector<VariableGEPIndex, 4> GEP1VariableIndices;
@@ -969,13 +967,6 @@
const MDNode *SITBAAInfo,
const Value *V2, uint64_t V2Size,
const MDNode *V2TBAAInfo) {
- // If this select has been visited before, we're on a use-def cycle.
- // Such cycles are only valid when PHI nodes are involved or in unreachable
- // code. The visitPHI function catches cycles containing PHIs, but there
- // could still be a cycle without PHIs in unreachable code.
- if (!Visited.insert(SI))
- return MayAlias;
-
// If the values are Selects with the same condition, we can do a more precise
// check: just check for aliases between the values on corresponding arms.
if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2))
@@ -998,11 +989,6 @@
if (Alias == MayAlias)
return MayAlias;
- // If V2 is visited, the recursive case will have been caught in the
- // above aliasCheck call, so these subsequent calls to aliasCheck
- // don't need to assume that V2 is being visited recursively.
- Visited.erase(V2);
-
AliasResult ThisAlias =
aliasCheck(V2, V2Size, V2TBAAInfo, SI->getFalseValue(), SISize, SITBAAInfo);
return MergeAliasResults(ThisAlias, Alias);
@@ -1015,10 +1001,6 @@
const MDNode *PNTBAAInfo,
const Value *V2, uint64_t V2Size,
const MDNode *V2TBAAInfo) {
- // The PHI node has already been visited, avoid recursion any further.
- if (!Visited.insert(PN))
- return MayAlias;
-
// If the values are PHIs in the same block, we can do a more precise
// as well as efficient check: just check for aliases between the values
// on corresponding edges.
@@ -1068,11 +1050,6 @@
for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) {
Value *V = V1Srcs[i];
- // If V2 is visited, the recursive case will have been caught in the
- // above aliasCheck call, so these subsequent calls to aliasCheck
- // don't need to assume that V2 is being visited recursively.
- Visited.erase(V2);
-
AliasResult ThisAlias = aliasCheck(V2, V2Size, V2TBAAInfo,
V, PNSize, PNTBAAInfo);
Alias = MergeAliasResults(ThisAlias, Alias);
@@ -1162,6 +1139,17 @@
(V2Size != UnknownSize && isObjectSmallerThan(O1, V2Size, *TD)))
return NoAlias;
+ // Check the cache before climbing up use-def chains. This also terminates
+ // otherwise infinitely recursive queries.
+ LocPair Locs(Location(V1, V1Size, V1TBAAInfo),
+ Location(V2, V2Size, V2TBAAInfo));
+ if (V1 > V2)
+ std::swap(Locs.first, Locs.second);
+ std::pair<AliasCacheTy::iterator, bool> Pair =
+ AliasCache.insert(std::make_pair(Locs, MayAlias));
+ if (!Pair.second)
+ return Pair.first->second;
+
// FIXME: This isn't aggressively handling alias(GEP, PHI) for example: if the
// GEP can't simplify, we don't even look at the PHI cases.
if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) {
@@ -1171,7 +1159,7 @@
}
if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) {
AliasResult Result = aliasGEP(GV1, V1Size, V2, V2Size, V2TBAAInfo, O1, O2);
- if (Result != MayAlias) return Result;
+ if (Result != MayAlias) return AliasCache[Locs] = Result;
}
if (isa<PHINode>(V2) && !isa<PHINode>(V1)) {
@@ -1181,7 +1169,7 @@
if (const PHINode *PN = dyn_cast<PHINode>(V1)) {
AliasResult Result = aliasPHI(PN, V1Size, V1TBAAInfo,
V2, V2Size, V2TBAAInfo);
- if (Result != MayAlias) return Result;
+ if (Result != MayAlias) return AliasCache[Locs] = Result;
}
if (isa<SelectInst>(V2) && !isa<SelectInst>(V1)) {
@@ -1191,7 +1179,7 @@
if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) {
AliasResult Result = aliasSelect(S1, V1Size, V1TBAAInfo,
V2, V2Size, V2TBAAInfo);
- if (Result != MayAlias) return Result;
+ if (Result != MayAlias) return AliasCache[Locs] = Result;
}
// If both pointers are pointing into the same object and one of them
@@ -1200,8 +1188,10 @@
if (TD && O1 == O2)
if ((V1Size != UnknownSize && isObjectSize(O1, V1Size, *TD)) ||
(V2Size != UnknownSize && isObjectSize(O2, V2Size, *TD)))
- return PartialAlias;
+ return AliasCache[Locs] = PartialAlias;
- return AliasAnalysis::alias(Location(V1, V1Size, V1TBAAInfo),
- Location(V2, V2Size, V2TBAAInfo));
+ AliasResult Result =
+ AliasAnalysis::alias(Location(V1, V1Size, V1TBAAInfo),
+ Location(V2, V2Size, V2TBAAInfo));
+ return AliasCache[Locs] = Result;
}