diff options
Diffstat (limited to 'llvm/lib/Analysis/BasicAliasAnalysis.cpp')
| -rw-r--r-- | llvm/lib/Analysis/BasicAliasAnalysis.cpp | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp index 68f766edb30..06e600e8835 100644 --- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp +++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp @@ -42,6 +42,10 @@ #include <algorithm> using namespace llvm; +/// Enable analysis of recursive PHI nodes. +static cl::opt<bool> EnableRecPhiAnalysis("basicaa-recphi", + cl::Hidden, cl::init(false)); + /// Cutoff after which to stop analysing a set of phi nodes potentially involved /// in a cycle. Because we are analysing 'through' phi nodes we need to be /// careful with value equivalence. We use reachability to make sure a value @@ -1297,6 +1301,7 @@ AliasResult BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize, SmallPtrSet<Value*, 4> UniqueSrc; SmallVector<Value*, 4> V1Srcs; + bool isRecursive = false; for (Value *PV1 : PN->incoming_values()) { if (isa<PHINode>(PV1)) // If any of the source itself is a PHI, return MayAlias conservatively @@ -1304,12 +1309,33 @@ AliasResult BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize, // sides are PHI nodes. In which case, this is O(m x n) time where 'm' // and 'n' are the number of PHI sources. return MayAlias; + + if (EnableRecPhiAnalysis) + if (GEPOperator *PV1GEP = dyn_cast<GEPOperator>(PV1)) { + // Check whether the incoming value is a GEP that advances the pointer + // result of this PHI node (e.g. in a loop). If this is the case, we + // would recurse and always get a MayAlias. Handle this case specially + // below. + if (PV1GEP->getPointerOperand() == PN && PV1GEP->getNumIndices() == 1 && + isa<ConstantInt>(PV1GEP->idx_begin())) { + isRecursive = true; + continue; + } + } + if (UniqueSrc.insert(PV1).second) V1Srcs.push_back(PV1); } + // If this PHI node is recursive, set the size of the accessed memory to + // unknown to represent all the possible values the GEP could advance the + // pointer to. + if (isRecursive) + PNSize = MemoryLocation::UnknownSize; + AliasResult Alias = aliasCheck(V2, V2Size, V2AAInfo, V1Srcs[0], PNSize, PNAAInfo); + // Early exit if the check of the first PHI source against V2 is MayAlias. // Other results are not possible. if (Alias == MayAlias) |
