New patch with PointerUnion and DenseMap is slightly faster than the previous DenseMap patch.
On Mon, Aug 27, 2012 at 9:51 PM, Ted Kremenek <[email protected]> wrote: > Thanks! Quick question before I review it in more details: what is the > performance characteristics of this patch compared to the others? > > On Aug 27, 2012, at 11:35 AM, Richard Trieu <[email protected]> wrote: > > Incorporated most of the suggestions into this patch. Still using a > double pass over the constants for the reasons outlined below. > > On Fri, Aug 17, 2012 at 10:00 PM, Ted Kremenek <[email protected]> wrote: > >> BTW, I wrote this two days ago. For some reason my mail client didn't >> send it out until now. My apologies for the delay. >> > No worries. Had some issues that cropped up on template diffing that took > my time. > >> >> On Aug 15, 2012, at 10:11 PM, Ted Kremenek <[email protected]> wrote: >> >> On Aug 15, 2012, at 6:12 PM, Richard Trieu <[email protected]> wrote: >> >> On Tue, Aug 14, 2012 at 9:48 PM, Ted Kremenek <[email protected]> wrote: >> >>> On Aug 14, 2012, at 2:32 PM, Richard Trieu <[email protected]> wrote: >>> >>> At a high level, I honestly find this logic to be more complicated >>>> than I would have expected. The sorting seems unnecessary, and will report >>>> diagnostics in an unnatural order (first based on enum constant value, then >>>> on declaration order). A straight linear pass seems more naturally to me, >>>> and DenseMap is very efficient. >>>> >>> Is there a comparison between the different containers in LLVM and the >>> STL containers? >>> >>> >>> This is a reasonable place to start: >>> >>> http://llvm.org/docs/ProgrammersManual.html#ds_map >>> >>> The key with DenseMap is that it is probed hashtable. There is one big >>> allocation for the entire table, instead of a bunch of buckets. When >>> applicable, it can be very fast, and feels like the right data structure to >>> use here. >>> >> >> Duplicate enum detection, now with DenseMap. The DenseMap maps a int64_t >> to a vector pointer. 0 and 1 were special keys for the DenseMap, so two >> separate pointers special cased for them. The vectors pointers are stored >> in another vector in declaration order. One pass is made over the enums to >> find ones without initializers. These are used to create vectors. A >> second pass through the enums populates the vectors. Finally, a pass over >> the vector of vectors is used to generate all the warnings and notes. >> >> Run time is fairly consistent with the sorted vector implementation, >> which is max %3 difference against control. >> <duplicate-enum-densemap.patch> >> >> >> Thanks for working on this. My main concern is this patch now has a lot >> of unnecessary malloc() traffic, which will certainly slow it down. >> Comments inline: >> >> + >> +static int64_t GetInt64(const llvm::APSInt& Val) { >> + return Val.isSigned() ? Val.getSExtValue() : Val.getZExtValue(); >> +} >> + >> +struct DenseMapInfoint64_t { >> + static int64_t getEmptyKey() { return 0; } >> + static int64_t getTombstoneKey() { return 1; } >> + static unsigned getHashValue(const int64_t Val) { >> + return (unsigned)(Val * 37); >> + } >> + static bool isEqual(const int64_t& LHS, const int64_t& RHS) { >> + return LHS == RHS; >> + } >> +}; >> >> >> This trait class doesn't look like it was actually used. The DenseMap >> below just uses the default trait for int64_t. >> >> I also still think we can so something a bit smarter here. What I think >> we need to distinguish between is whether or not a constant has appeared >> more than once. We're saving a bit of memory on the keys, but spending >> that savings elsewhere when we allocate the vectors unconditionally for >> each constant. >> >> + >> +// Emits a warning when an element is implicitly set a value that >> +// a previous element has already been set to. >> +static void CheckForDuplicateEnumValues(Sema &S, Decl **Elements, >> + unsigned NumElements, EnumDecl >> *Enum, >> + QualType EnumType) { >> + if (S.Diags.getDiagnosticLevel(diag::warn_duplicate_enum_values, >> + Enum->getLocation()) == >> + DiagnosticsEngine::Ignored) >> + return; >> + // Avoid anonymous enums >> + if (!Enum->getIdentifier()) >> + return; >> + >> + // Only check for small enums. >> + if (Enum->getNumPositiveBits() > 63 || Enum->getNumNegativeBits() > 64) >> + return; >> + >> + typedef llvm::SmallVector<EnumConstantDecl*, 4> SameValueVector; >> + typedef llvm::DenseMap<int64_t, SameValueVector*> ValueToVectorMap; >> + typedef llvm::SmallVector<SameValueVector*, 10> DoubleVector; >> + ValueToVectorMap EnumMap; >> + DoubleVector EnumVector; >> + SameValueVector *ZeroVector = 0, *OneVector = 0; >> >> >> It took me a while to understand what this was doing, so I feel it could >> really benefit from a comment. This also appears to result in a ton of >> malloc traffic below. Here's my suggestion: >> >> typedef llvm::SmallVector<EnumConstantDecl*, 3> ECDVector; >> typedef llvm::SmallVector<ECDVector *, 3> DuplicatesVector; >> >> typedef llvm::PointerUnion<EnumConstantDecl*, ECDVector *> DeclOrVector; >> typedef llvm::DenseMap<int64_t, DeclOrVector> ValueToVectorMap; >> >> DuplicatesVector DupVector; >> ValueToVectorMap EnumMap; >> >> The trick here is that the DenseMap maps from a constant to the first >> EnumConstantDecl it encounters. Only if we encounter a second >> EnumConstantDecl with the same enum value do we pay the cost of allocating >> another vector. This will drastically optimize in the common case, as >> calling malloc() is really slow. Right now the code appears to be doing a >> malloc() for every enum constant, which is going to really penalize us here. >> >> + >> + for (unsigned i = 0; i < NumElements; ++i) { >> + EnumConstantDecl *ECD = cast<EnumConstantDecl>(Elements[i]); >> + if (!ECD) { >> + for (DoubleVector::iterator I = EnumVector.begin(), E = >> EnumVector.end(); >> + I != E; ++I) >> + delete *I; >> + return; >> + } >> >> >> I don't quite understand this loop through DoubleVector here, but it >> looks like logic in case we want to return early and cleanup. Is there a >> case where the EnumConstantDecl can be null? >> >> According to ActOnEnumBody, EnumConstantDecl is null if a diagnostic has > previously been emitted for the constant. Since the enum > is possibly ill-formed, skip checking it. > >> >> + >> + if (ECD->getInitExpr()) >> + continue; >> + >> + int64_t Val = GetInt64(ECD->getInitVal()); >> + >> >> >> Looks good. >> >> + if (Val == 0) { >> + if (ZeroVector) continue; >> + ZeroVector = new SameValueVector(); >> + ZeroVector->push_back(ECD); >> + EnumVector.push_back(ZeroVector); >> + } else if (Val == 1) { >> + if (OneVector) continue; >> + OneVector = new SameValueVector(); >> + OneVector->push_back(ECD); >> + EnumVector.push_back(OneVector); >> + } else { >> + if (EnumMap.find(Val) != EnumMap.end()) >> + continue; >> + SameValueVector *ValueVector = new SameValueVector(); >> + ValueVector->push_back(ECD); >> + EnumVector.push_back(ValueVector); >> + EnumMap.insert(std::make_pair(Val, ValueVector)); >> >> >> The "find()" followed by the "insert()" is wasteful. It results in two >> lookups to the hash table when we could have just used one. More on that >> later. >> >> + } >> + } >> >> >> IMO, this looks like a lot of complexity just to handle the fact that 0 >> and 1 are special values for the DenseMap. I don't really see this as the >> right tradeoff; the code is more complicated with marginal impact on memory >> usage or performance. >> >> If you humor me for a bit, consider using something else for the key, >> e.g.: >> >> struct DupKey { >> int64_t val; >> bool isTombstoneOrEmptyKey; >> }; >> >> The idea is if 'isTombStoneOrEmptyKey' is true, we can use val = 0 or val >> = 1 to represent empty keys or tombstone entries. Otherwise, it's an >> int64_t, with the full range of values. We can define a DenseMap trait to >> do the right thing. Yes, this costs a tiny bit more in storage, but it >> allows the data structure to handle the complete set of values in your >> domain, instead of resorting to complicating the core algorithm. What I >> see here now is the same code essentially duplicated twice, which makes it >> harder to read and more error prone. >> >> If we use DupKey as our key for the DenseMap, we can instead do something >> like this: >> >> DeclOrVector &entry = EnumMap[Val]; // Use default construction of >> 'entry'. >> // Is the first time we encountered this constant? >> if (entry.isNull()) { >> entry = ECD; >> continue; >> } >> // Is this the second time we encountered this constant? If so, >> // push the previous decl encountered and the one just encountered >> // to a vector of duplicates. >> if (EnumConstantDecl *D = entry.dyn_cast<EnumConstantDecl*>()) { >> ECDVector *Vec = new ECDVector(); >> Vec->push_back(D); >> Vec->push_back(ECD); >> >> // Update the entry to refer to the duplicates. >> entry = Vec; >> >> // Store the duplicates in a vector we can consult later for >> // quick emission of diagnostics. >> DupVector.push_back(Vec); >> >> // On to the next constant. >> continue; >> } >> // Is this the third (or greater) time we encountered the constant? >> If so, >> // continue to add it to the existing vector. >> ECDVector *Vec = entry.get<ECDVector*>(); >> Vec->push_back(ECD); >> >> >> With this code, we only allocate memory (beyond the DenseMap) when we >> encounter a duplicate that would be worth reporting. In the common case, >> this savings in malloc traffic should be noticeable. >> >> Notice also that I used: >> >> DeclOrVector &entry = EnumMap[Val]; // Use default construction of >> 'entry'. >> >> This results in a single lookup in the hashtable. Since we plan on >> adding a value for a key no matter what, by using this idiom we allow the >> DenseMap to default construct an entry if it doesn't exist. This results >> in a single hashtable lookup, from which we can modify the value in place. >> This is obviously faster than doing a hashtable lookup twice. >> >> + >> + for (unsigned i = 0; i < NumElements; ++i) { >> + EnumConstantDecl *ECD = cast<EnumConstantDecl>(Elements[i]); >> + if (!ValidDuplicateEnum(ECD, Enum)) >> + continue; >> + >> + int64_t Val = GetInt64(ECD->getInitVal()); >> + >> + if (Val == 0) { >> + if (!ZeroVector || *ZeroVector->begin() == ECD) >> + continue; >> + ZeroVector->push_back(ECD); >> + } else if (Val == 1) { >> + if (!OneVector || *OneVector->begin() == ECD) >> + continue; >> + OneVector->push_back(ECD); >> + } else { >> + ValueToVectorMap::iterator I = EnumMap.find(Val); >> + if (I == EnumMap.end()) >> + continue; >> + SameValueVector *V = I->second; >> + if (*V->begin() == ECD) >> + continue; >> + V->push_back(ECD); >> + } >> + } >> >> >> This second loop looks unnecessary. I think we can do everything we need >> to count duplicates with one loop. Of course the ValidDuplicateEnum() >> would need to be hoisted to the first loop. >> >> Using two traverses allows two things to happen. One, the first element > in the ECDVector will not have an initializer and will work with the > warning. Otherwise, the vector needs to be searched for a proper enum > constant to use. Two, it prevents unneeded creation of ECDVectors. If we > have enum A { A1 = 2, A2 = 2, A3 = 1, A4 = 1, A5}; vectors for values 1 and > 2 are created using a single pass while only a vector for 2 will be created > using a double pass. > >> >> + >> + for (DoubleVector::iterator DoubleVectorIter = EnumVector.begin(), >> + DoubleVectorEnd = EnumVector.end(); >> + DoubleVectorIter != DoubleVectorEnd; ++DoubleVectorIter) { >> + SameValueVector *V = *DoubleVectorIter; >> + if (V->size() == 1) >> + continue; >> + >> + SameValueVector::iterator I = V->begin(); >> + S.Diag((*I)->getLocation(), diag::warn_duplicate_enum_values) >> + << (*I)->getName() << (*I)->getInitVal().toString(10) >> + << (*I)->getSourceRange(); >> + ++I; >> + for (SameValueVector::iterator E = V->end(); I != E; ++I) >> + S.Diag((*I)->getLocation(), diag::note_duplicate_element) >> + << (*I)->getName() << (*I)->getInitVal().toString(10) >> + << (*I)->getSourceRange(); >> + delete V; >> + } >> >> >> >> This is more or less the same, essentially it becomes: >> >> for (DuplicateVector::iterator I = DupVector.begin(), E = >> DupVector.end(); I != E; ++I) { >> ECDVector *Vec = *I; >> // do the diagnostic logic ... >> delete *I; >> } >> >> Note that with my suggestions the vector has size on order of the number >> of duplicate constants, not the number of total constants. If there are no >> duplicates, no work is required (including free'ing memory). >> >> +} >> + >> void Sema::ActOnEnumBody(SourceLocation EnumLoc, SourceLocation >> LBraceLoc, >> SourceLocation RBraceLoc, Decl *EnumDeclX, >> Decl **Elements, unsigned NumElements, >> @@ -10709,6 +10868,7 @@ >> DeclsInPrototypeScope.push_back(Enum); >> >> CheckForUniqueEnumValues(*this, Elements, NumElements, Enum, EnumType); >> + CheckForDuplicateEnumValues(*this, Elements, NumElements, Enum, >> EnumType); >> } >> >> Decl *Sema::ActOnFileScopeAsmDecl(Expr *expr, >> >> >> I know this may all be nit-picky, but I really think trying to reduce the >> malloc() traffic is worth looking at to get a real understanding of the >> performance improvement that can be found here. >> >> Thanks for forging ahead on this. >> _______________________________________________ >> cfe-commits mailing list >> [email protected] >> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits >> >> >> > <duplicate-enum-densemap2.patch> > > >
_______________________________________________ cfe-commits mailing list [email protected] http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
