[llvm] r275940 - [MemorySSA] Update to the new shiny walker.
George Burgess IV via llvm-commits
llvm-commits at lists.llvm.org
Thu Jul 21 16:04:18 PDT 2016
Thanks for bringing this up! And yeah, the first thing that `def_chain`
should iterate over is `Target` itself. So, as long as `Target != nullptr`
(which should always be true), we should be fine here.
Is there something we could add to make coverity happy?
On Thu, Jul 21, 2016 at 3:50 PM, Mehdi Amini <mehdi.amini at apple.com> wrote:
>
> > On Jul 18, 2016, at 6:29 PM, George Burgess IV via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
> >
> > Author: gbiv
> > Date: Mon Jul 18 20:29:15 2016
> > New Revision: 275940
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=275940&view=rev
> > Log:
> > [MemorySSA] Update to the new shiny walker.
> >
> > This patch updates MemorySSA's use-optimizing walker to be more
> > accurate and, in some cases, faster.
> >
> > Essentially, this changed our core walking algorithm from a
> > cache-as-you-go DFS to an iteratively expanded DFS, with all of the
> > caching happening at the end. Said expansion happens when we hit a Phi,
> > P; we'll try to do the smallest amount of work possible to see if
> > optimizing above that Phi is legal in the first place. If so, we'll
> > expand the search to see if we can optimize to the next phi, etc.
> >
> > An iteratively expanded DFS lets us potentially quit earlier (because we
> > don't assume that we can optimize above all phis) than our old walker.
> > Additionally, because we don't cache as we go, we can now optimize above
> > loops.
> >
> > As an added bonus, this patch adds a ton of verification (if
> > EXPENSIVE_CHECKS are enabled), so finding bugs is easier.
> >
> > Differential Revision: https://reviews.llvm.org/D21777
> >
> > Modified:
> > llvm/trunk/include/llvm/Transforms/Utils/MemorySSA.h
> > llvm/trunk/lib/Transforms/Utils/MemorySSA.cpp
> > llvm/trunk/test/Transforms/Util/MemorySSA/cyclicphi.ll
> > llvm/trunk/test/Transforms/Util/MemorySSA/phi-translation.ll
> >
> > Modified: llvm/trunk/include/llvm/Transforms/Utils/MemorySSA.h
> > URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Transforms/Utils/MemorySSA.h?rev=275940&r1=275939&r2=275940&view=diff
> >
> ==============================================================================
> > --- llvm/trunk/include/llvm/Transforms/Utils/MemorySSA.h (original)
> > +++ llvm/trunk/include/llvm/Transforms/Utils/MemorySSA.h Mon Jul 18
> 20:29:15 2016
> > @@ -580,6 +580,10 @@ public:
> > /// whether MemoryAccess \p A dominates MemoryAccess \p B.
> > bool locallyDominates(const MemoryAccess *A, const MemoryAccess *B)
> const;
> >
> > + /// \brief Given two memory accesses in potentially different blocks,
> > + /// determine whether MemoryAccess \p A dominates MemoryAccess \p B.
> > + bool dominates(const MemoryAccess *A, const MemoryAccess *B) const;
> > +
> > /// \brief Verify that MemorySSA is self consistent (IE definitions
> dominate
> > /// all uses, uses appear in the right places). This is used by unit
> tests.
> > void verifyMemorySSA() const;
> > @@ -594,6 +598,8 @@ protected:
> >
> > private:
> > class CachingWalker;
> > +
> > + CachingWalker *getWalkerImpl();
> > void buildMemorySSA();
> > void verifyUseInDefs(MemoryAccess *, MemoryAccess *) const;
> > using AccessMap = DenseMap<const BasicBlock *,
> std::unique_ptr<AccessList>>;
> >
> > Modified: llvm/trunk/lib/Transforms/Utils/MemorySSA.cpp
> > URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/MemorySSA.cpp?rev=275940&r1=275939&r2=275940&view=diff
> >
> ==============================================================================
> > --- llvm/trunk/lib/Transforms/Utils/MemorySSA.cpp (original)
> > +++ llvm/trunk/lib/Transforms/Utils/MemorySSA.cpp Mon Jul 18 20:29:15
> 2016
> > @@ -17,6 +17,7 @@
> > #include "llvm/ADT/GraphTraits.h"
> > #include "llvm/ADT/PostOrderIterator.h"
> > #include "llvm/ADT/STLExtras.h"
> > +#include "llvm/ADT/SmallBitVector.h"
> > #include "llvm/ADT/SmallPtrSet.h"
> > #include "llvm/ADT/SmallSet.h"
> > #include "llvm/ADT/Statistic.h"
> > @@ -86,7 +87,777 @@ public:
> > OS << "; " << *MA << "\n";
> > }
> > };
> > +}
> > +
> > +namespace {
> > +struct UpwardsMemoryQuery {
> > + // True if our original query started off as a call
> > + bool IsCall;
> > + // The pointer location we started the query with. This will be empty
> if
> > + // IsCall is true.
> > + MemoryLocation StartingLoc;
> > + // This is the instruction we were querying about.
> > + const Instruction *Inst;
> > + // The MemoryAccess we actually got called with, used to test local
> domination
> > + const MemoryAccess *OriginalAccess;
> > +
> > + UpwardsMemoryQuery()
> > + : IsCall(false), Inst(nullptr), OriginalAccess(nullptr) {}
> > +
> > + UpwardsMemoryQuery(const Instruction *Inst, const MemoryAccess
> *Access)
> > + : IsCall(ImmutableCallSite(Inst)), Inst(Inst),
> OriginalAccess(Access) {
> > + if (!IsCall)
> > + StartingLoc = MemoryLocation::get(Inst);
> > + }
> > +};
> > +
> > +static bool instructionClobbersQuery(MemoryDef *MD, const
> MemoryLocation &Loc,
> > + const UpwardsMemoryQuery &Query,
> > + AliasAnalysis &AA) {
> > + Instruction *DefMemoryInst = MD->getMemoryInst();
> > + assert(DefMemoryInst && "Defining instruction not actually an
> instruction");
> > +
> > + if (!Query.IsCall)
> > + return AA.getModRefInfo(DefMemoryInst, Loc) & MRI_Mod;
> > +
> > + ModRefInfo I = AA.getModRefInfo(DefMemoryInst,
> ImmutableCallSite(Query.Inst));
> > + return I != MRI_NoModRef;
> > +}
> > +
> > +/// Cache for our caching MemorySSA walker.
> > +class WalkerCache {
> > + DenseMap<ConstMemoryAccessPair, MemoryAccess *> Accesses;
> > + DenseMap<const MemoryAccess *, MemoryAccess *> Calls;
> > +
> > +public:
> > + MemoryAccess *lookup(const MemoryAccess *MA, const MemoryLocation
> &Loc,
> > + bool IsCall) const {
> > + ++NumClobberCacheLookups;
> > + MemoryAccess *R = IsCall ? Calls.lookup(MA) : Accesses.lookup({MA,
> Loc});
> > + if (R)
> > + ++NumClobberCacheHits;
> > + return R;
> > + }
> > +
> > + bool insert(const MemoryAccess *MA, MemoryAccess *To,
> > + const MemoryLocation &Loc, bool IsCall) {
> > + // This is fine for Phis, since there are times where we can't
> optimize
> > + // them. Making a def its own clobber is never correct, though.
> > + assert((MA != To || isa<MemoryPhi>(MA)) &&
> > + "Something can't clobber itself!");
> > +
> > + ++NumClobberCacheInserts;
> > + bool Inserted;
> > + if (IsCall)
> > + Inserted = Calls.insert({MA, To}).second;
> > + else
> > + Inserted = Accesses.insert({{MA, Loc}, To}).second;
> > +
> > + return Inserted;
> > + }
> > +
> > + bool remove(const MemoryAccess *MA, const MemoryLocation &Loc, bool
> IsCall) {
> > + return IsCall ? Calls.erase(MA) : Accesses.erase({MA, Loc});
> > + }
> > +
> > + void clear() {
> > + Accesses.clear();
> > + Calls.clear();
> > + }
> > +
> > + bool contains(const MemoryAccess *MA) const {
> > + for (auto &P : Accesses)
> > + if (P.first.first == MA || P.second == MA)
> > + return true;
> > + for (auto &P : Calls)
> > + if (P.first == MA || P.second == MA)
> > + return true;
> > + return false;
> > + }
> > +};
> > +
> > +/// Walks the defining uses of MemoryDefs. Stops after we hit something
> that has
> > +/// no defining use (e.g. a MemoryPhi or liveOnEntry). Note that, when
> comparing
> > +/// against a null def_chain_iterator, this will compare equal only
> after
> > +/// walking said Phi/liveOnEntry.
> > +struct def_chain_iterator
> > + : public iterator_facade_base<def_chain_iterator,
> std::forward_iterator_tag,
> > + MemoryAccess *> {
> > + def_chain_iterator() : MA(nullptr) {}
> > + def_chain_iterator(MemoryAccess *MA) : MA(MA) {}
> > +
> > + MemoryAccess *operator*() const { return MA; }
> > +
> > + def_chain_iterator &operator++() {
> > + // N.B. liveOnEntry has a null defining access.
> > + if (auto *MUD = dyn_cast<MemoryUseOrDef>(MA))
> > + MA = MUD->getDefiningAccess();
> > + else
> > + MA = nullptr;
> > + return *this;
> > + }
> > +
> > + bool operator==(const def_chain_iterator &O) const { return MA ==
> O.MA; }
> > +
> > +private:
> > + MemoryAccess *MA;
> > +};
> > +
> > +static iterator_range<def_chain_iterator>
> > +def_chain(MemoryAccess *MA, MemoryAccess *UpTo = nullptr) {
> > +#ifdef EXPENSIVE_CHECKS
> > + assert((!UpTo || find(def_chain(MA), UpTo) != def_chain_iterator()) &&
> > + "UpTo isn't in the def chain!");
> > +#endif
> > + return make_range(def_chain_iterator(MA), def_chain_iterator(UpTo));
> > +}
> > +
> > +/// Verifies that `Start` is clobbered by `ClobberAt`, and that nothing
> > +/// inbetween `Start` and `ClobberAt` can clobbers `Start`.
> > +///
> > +/// This is meant to be as simple and self-contained as possible.
> Because it
> > +/// uses no cache, etc., it can be relatively expensive.
> > +///
> > +/// \param Start The MemoryAccess that we want to walk from.
> > +/// \param ClobberAt A clobber for Start.
> > +/// \param StartLoc The MemoryLocation for Start.
> > +/// \param MSSA The MemorySSA isntance that Start and ClobberAt
> belong to.
> > +/// \param Query The UpwardsMemoryQuery we used for our search.
> > +/// \param AA The AliasAnalysis we used for our search.
> > +static void LLVM_ATTRIBUTE_UNUSED
> > +checkClobberSanity(MemoryAccess *Start, MemoryAccess *ClobberAt,
> > + const MemoryLocation &StartLoc, const MemorySSA
> &MSSA,
> > + const UpwardsMemoryQuery &Query, AliasAnalysis &AA) {
> > + assert(MSSA.dominates(ClobberAt, Start) && "Clobber doesn't dominate
> start?");
> > +
> > + if (MSSA.isLiveOnEntryDef(Start)) {
> > + assert(MSSA.isLiveOnEntryDef(ClobberAt) &&
> > + "liveOnEntry must clobber itself");
> > + return;
> > + }
> > +
> > + assert((isa<MemoryPhi>(Start) || Start != ClobberAt) &&
> > + "Start can't clobber itself!");
> > +
> > + bool FoundClobber = false;
> > + DenseSet<MemoryAccessPair> VisitedPhis;
> > + SmallVector<MemoryAccessPair, 8> Worklist;
> > + Worklist.emplace_back(Start, StartLoc);
> > + // Walk all paths from Start to ClobberAt, while looking for
> clobbers. If one
> > + // is found, complain.
> > + while (!Worklist.empty()) {
> > + MemoryAccessPair MAP = Worklist.pop_back_val();
> > + // All we care about is that nothing from Start to ClobberAt
> clobbers Start.
> > + // We learn nothing from revisiting nodes.
> > + if (!VisitedPhis.insert(MAP).second)
> > + continue;
> > +
> > + for (MemoryAccess *MA : def_chain(MAP.first)) {
> > + if (MA == ClobberAt) {
> > + if (auto *MD = dyn_cast<MemoryDef>(MA)) {
> > + // instructionClobbersQuery isn't essentially free, so don't
> use `|=`,
> > + // since it won't let us short-circuit.
> > + //
> > + // Also, note that this can't be hoisted out of the
> `Worklist` loop,
> > + // since MD may only act as a clobber for 1 of N
> MemoryLocations.
> > + FoundClobber = FoundClobber || MSSA.isLiveOnEntryDef(MD) ||
> > + instructionClobbersQuery(MD, MAP.second,
> Query, AA);
> > + }
> > + break;
> > + }
> > +
> > + // We should never hit liveOnEntry, unless it's the clobber.
> > + assert(!MSSA.isLiveOnEntryDef(MA) && "Hit liveOnEntry before
> clobber?");
> > +
> > + if (auto *MD = dyn_cast<MemoryDef>(MA)) {
> > + (void)MD;
> > + assert(!instructionClobbersQuery(MD, MAP.second, Query, AA) &&
> > + "Found clobber before reaching ClobberAt!");
> > + continue;
> > + }
> > +
> > + assert(isa<MemoryPhi>(MA));
> > + Worklist.append(upward_defs_begin({MA, MAP.second}),
> upward_defs_end());
> > + }
> > + }
> > +
> > + // If ClobberAt is a MemoryPhi, we can assume something above it
> acted as a
> > + // clobber. Otherwise, `ClobberAt` should've acted as a clobber at
> some point.
> > + assert((isa<MemoryPhi>(ClobberAt) || FoundClobber) &&
> > + "ClobberAt never acted as a clobber");
> > +}
> > +
> > +/// Our algorithm for walking (and trying to optimize) clobbers, all
> wrapped up
> > +/// in one class.
> > +class ClobberWalker {
> > + /// Save a few bytes by using unsigned instead of size_t.
> > + using ListIndex = unsigned;
> > +
> > + /// Represents a span of contiguous MemoryDefs, potentially ending in
> a
> > + /// MemoryPhi.
> > + struct DefPath {
> > + MemoryLocation Loc;
> > + // Note that, because we always walk in reverse, Last will always
> dominate
> > + // First. Also note that First and Last are inclusive.
> > + MemoryAccess *First;
> > + MemoryAccess *Last;
> > + // N.B. Blocker is currently basically unused. The goal is to use
> it to make
> > + // cache invalidation better, but we're not there yet.
> > + MemoryAccess *Blocker;
> > + Optional<ListIndex> Previous;
> > +
> > + DefPath(const MemoryLocation &Loc, MemoryAccess *First,
> MemoryAccess *Last,
> > + Optional<ListIndex> Previous)
> > + : Loc(Loc), First(First), Last(Last), Previous(Previous) {}
> > +
> > + DefPath(const MemoryLocation &Loc, MemoryAccess *Init,
> > + Optional<ListIndex> Previous)
> > + : DefPath(Loc, Init, Init, Previous) {}
> > + };
> > +
> > + const MemorySSA &MSSA;
> > + AliasAnalysis &AA;
> > + DominatorTree &DT;
> > + WalkerCache &WC;
> > + UpwardsMemoryQuery *Query;
> > + bool UseCache;
> > +
> > + // Phi optimization bookkeeping
> > + SmallVector<DefPath, 32> Paths;
> > + DenseSet<ConstMemoryAccessPair> VisitedPhis;
> > + DenseMap<const BasicBlock *, MemoryAccess *> WalkTargetCache;
> > +
> > + void setUseCache(bool Use) { UseCache = Use; }
> > + bool shouldIgnoreCache() const {
> > + // UseCache will only be false when we're debugging, or when
> expensive
> > + // checks are enabled. In either case, we don't care deeply about
> speed.
> > + return LLVM_UNLIKELY(!UseCache);
> > + }
> > +
> > + void addCacheEntry(const MemoryAccess *What, MemoryAccess *To,
> > + const MemoryLocation &Loc) const {
> > +// EXPENSIVE_CHECKS because most of these queries are redundant, and if
> What
> > +// and To are in the same BB, that gives us n^2 behavior.
> > +#ifdef EXPENSIVE_CHECKS
> > + assert(MSSA.dominates(To, What));
> > +#endif
> > + if (shouldIgnoreCache())
> > + return;
> > + WC.insert(What, To, Loc, Query->IsCall);
> > + }
> > +
> > + MemoryAccess *lookupCache(const MemoryAccess *MA, const
> MemoryLocation &Loc) {
> > + return shouldIgnoreCache() ? nullptr : WC.lookup(MA, Loc,
> Query->IsCall);
> > + }
> > +
> > + void cacheDefPath(const DefPath &DN, MemoryAccess *Target) const {
> > + if (shouldIgnoreCache())
> > + return;
> > +
> > + for (MemoryAccess *MA : def_chain(DN.First, DN.Last))
> > + addCacheEntry(MA, Target, DN.Loc);
> > +
> > + // DefPaths only express the path we walked. So, DN.Last could
> either be a
> > + // thing we want to cache, or not.
> > + if (DN.Last != Target)
> > + addCacheEntry(DN.Last, Target, DN.Loc);
> > + }
> > +
> > + /// Find the nearest def or phi that `From` can legally be optimized
> to.
> > + ///
> > + /// FIXME: Deduplicate this with MSSA::findDominatingDef. Ideally,
> MSSA should
> > + /// keep track of this information for us, and allow us O(1) lookups
> of this
> > + /// info.
> > + MemoryAccess *getWalkTarget(const MemoryPhi *From) {
> > + assert(!MSSA.isLiveOnEntryDef(From) && "liveOnEntry has no
> target.");
> > + assert(From->getNumOperands() && "Phi with no operands?");
> > +
> > + BasicBlock *BB = From->getBlock();
> > + auto At = WalkTargetCache.find(BB);
> > + if (At != WalkTargetCache.end())
> > + return At->second;
> > +
> > + SmallVector<const BasicBlock *, 8> ToCache;
> > + ToCache.push_back(BB);
> > +
> > + MemoryAccess *Result = MSSA.getLiveOnEntryDef();
> > + DomTreeNode *Node = DT.getNode(BB);
> > + while ((Node = Node->getIDom())) {
> > + auto At = WalkTargetCache.find(BB);
> > + if (At != WalkTargetCache.end()) {
> > + Result = At->second;
> > + break;
> > + }
> > +
> > + auto *Accesses = MSSA.getBlockAccesses(Node->getBlock());
> > + if (Accesses) {
> > + auto Iter = find_if(reverse(*Accesses), [](const MemoryAccess
> &MA) {
> > + return !isa<MemoryUse>(MA);
> > + });
> > + if (Iter != Accesses->rend()) {
> > + Result = const_cast<MemoryAccess *>(&*Iter);
> > + break;
> > + }
> > + }
> > +
> > + ToCache.push_back(Node->getBlock());
> > + }
> > +
> > + for (const BasicBlock *BB : ToCache)
> > + WalkTargetCache.insert({BB, Result});
> > + return Result;
> > + }
> > +
> > + /// Result of calling walkToPhiOrClobber.
> > + struct UpwardsWalkResult {
> > + /// The "Result" of the walk. Either a clobber, the last thing we
> walked, or
> > + /// both.
> > + MemoryAccess *Result;
> > + bool IsKnownClobber;
> > + bool FromCache;
> > + };
> > +
> > + /// Walk to the next Phi or Clobber in the def chain starting at
> Desc.Last.
> > + /// This will update Desc.Last as it walks. It will (optionally) also
> stop at
> > + /// StopAt.
> > + ///
> > + /// This does not test for whether StopAt is a clobber
> > + UpwardsWalkResult walkToPhiOrClobber(DefPath &Desc,
> > + MemoryAccess *StopAt = nullptr) {
> > + assert(!isa<MemoryUse>(Desc.Last) && "Uses don't exist in my
> world");
> > +
> > + for (MemoryAccess *Current : def_chain(Desc.Last)) {
> > + Desc.Last = Current;
> > + if (Current == StopAt)
> > + return {Current, false, false};
> > +
> > + if (auto *MD = dyn_cast<MemoryDef>(Current))
> > + if (MSSA.isLiveOnEntryDef(MD) ||
> > + instructionClobbersQuery(MD, Desc.Loc, *Query, AA))
> > + return {MD, true, false};
> > +
> > + // Cache checks must be done last, because if Current is a
> clobber, the
> > + // cache will contain the clobber for Current.
> > + if (MemoryAccess *MA = lookupCache(Current, Desc.Loc))
> > + return {MA, true, true};
> > + }
> > +
> > + assert(isa<MemoryPhi>(Desc.Last) &&
> > + "Ended at a non-clobber that's not a phi?");
> > + return {Desc.Last, false, false};
> > + }
> > +
> > + void addSearches(MemoryPhi *Phi, SmallVectorImpl<ListIndex>
> &PausedSearches,
> > + ListIndex PriorNode) {
> > + auto UpwardDefs = make_range(upward_defs_begin({Phi,
> Paths[PriorNode].Loc}),
> > + upward_defs_end());
> > + for (const MemoryAccessPair &P : UpwardDefs) {
> > + PausedSearches.push_back(Paths.size());
> > + Paths.emplace_back(P.second, P.first, PriorNode);
> > + }
> > + }
> > +
> > + /// Represents a search that terminated after finding a clobber. This
> clobber
> > + /// may or may not be present in the path of defs from
> LastNode..SearchStart,
> > + /// since it may have been retrieved from cache.
> > + struct TerminatedPath {
> > + MemoryAccess *Clobber;
> > + ListIndex LastNode;
> > + };
> > +
> > + /// Get an access that keeps us from optimizing to the given phi.
> > + ///
> > + /// PausedSearches is an array of indices into the Paths array. Its
> incoming
> > + /// value is the indices of searches that stopped at the last phi
> optimization
> > + /// target. It's left in an unspecified state.
> > + ///
> > + /// If this returns None, NewPaused is a vector of searches that
> terminated
> > + /// at StopWhere. Otherwise, NewPaused is left in an unspecified
> state.
> > + Optional<ListIndex>
> > + getBlockingAccess(MemoryAccess *StopWhere,
> > + SmallVectorImpl<ListIndex> &PausedSearches,
> > + SmallVectorImpl<ListIndex> &NewPaused,
> > + SmallVectorImpl<TerminatedPath> &Terminated) {
> > + assert(!PausedSearches.empty() && "No searches to continue?");
> > +
> > + // BFS vs DFS really doesn't make a difference here, so just do a
> DFS with
> > + // PausedSearches as our stack.
> > + while (!PausedSearches.empty()) {
> > + ListIndex PathIndex = PausedSearches.pop_back_val();
> > + DefPath &Node = Paths[PathIndex];
> > +
> > + // If we've already visited this path with this MemoryLocation,
> we don't
> > + // need to do so again.
> > + //
> > + // NOTE: That we just drop these paths on the ground makes caching
> > + // behavior sporadic. e.g. given a diamond:
> > + // A
> > + // B C
> > + // D
> > + //
> > + // ...If we walk D, B, A, C, we'll only cache the result of phi
> > + // optimization for A, B, and D; C will be skipped because it
> dies here.
> > + // This arguably isn't the worst thing ever, since:
> > + // - We generally query things in a top-down order, so if we
> got below D
> > + // without needing cache entries for {C, MemLoc}, then
> chances are
> > + // that those cache entries would end up ultimately unused.
> > + // - We still cache things for A, so C only needs to walk up a
> bit.
> > + // If this behavior becomes problematic, we can fix without a ton
> of extra
> > + // work.
> > + if (!VisitedPhis.insert({Node.Last, Node.Loc}).second)
> > + continue;
> > +
> > + UpwardsWalkResult Res = walkToPhiOrClobber(Node,
> /*StopAt=*/StopWhere);
> > + if (Res.IsKnownClobber) {
> > + assert(Res.Result != StopWhere || Res.FromCache);
> > + // If this wasn't a cache hit, we hit a clobber when walking.
> That's a
> > + // failure.
> > + if (!Res.FromCache || !MSSA.dominates(Res.Result, StopWhere))
> > + return PathIndex;
> > +
> > + // Otherwise, it's a valid thing to potentially optimize to.
> > + Terminated.push_back({Res.Result, PathIndex});
> > + continue;
> > + }
> > +
> > + if (Res.Result == StopWhere) {
> > + // We've hit our target. Save this path off for if we want to
> continue
> > + // walking.
> > + NewPaused.push_back(PathIndex);
> > + continue;
> > + }
> > +
> > + assert(!MSSA.isLiveOnEntryDef(Res.Result) && "liveOnEntry is a
> clobber");
> > + addSearches(cast<MemoryPhi>(Res.Result), PausedSearches,
> PathIndex);
> > + }
> > +
> > + return None;
> > + }
> > +
> > + template <typename T, typename Walker>
> > + struct generic_def_path_iterator
> > + : public iterator_facade_base<generic_def_path_iterator<T,
> Walker>,
> > + std::forward_iterator_tag, T *> {
> > + generic_def_path_iterator() : W(nullptr), N(None) {}
> > + generic_def_path_iterator(Walker *W, ListIndex N) : W(W), N(N) {}
> > +
> > + T &operator*() const { return curNode(); }
> > +
> > + generic_def_path_iterator &operator++() {
> > + N = curNode().Previous;
> > + return *this;
> > + }
> > +
> > + bool operator==(const generic_def_path_iterator &O) const {
> > + if (N.hasValue() != O.N.hasValue())
> > + return false;
> > + return !N.hasValue() || *N == *O.N;
> > + }
> > +
> > + private:
> > + T &curNode() const { return W->Paths[*N]; }
> > +
> > + Walker *W;
> > + Optional<ListIndex> N;
> > + };
> > +
> > + using def_path_iterator = generic_def_path_iterator<DefPath,
> ClobberWalker>;
> > + using const_def_path_iterator =
> > + generic_def_path_iterator<const DefPath, const ClobberWalker>;
> > +
> > + iterator_range<def_path_iterator> def_path(ListIndex From) {
> > + return make_range(def_path_iterator(this, From),
> def_path_iterator());
> > + }
> > +
> > + iterator_range<const_def_path_iterator> const_def_path(ListIndex
> From) const {
> > + return make_range(const_def_path_iterator(this, From),
> > + const_def_path_iterator());
> > + }
> > +
> > + struct OptznResult {
> > + /// The path that contains our result.
> > + TerminatedPath PrimaryClobber;
> > + /// The paths that we can legally cache back from, but that aren't
> > + /// necessarily the result of the Phi optimization.
> > + SmallVector<TerminatedPath, 4> OtherClobbers;
> > + };
> > +
> > + ListIndex defPathIndex(const DefPath &N) const {
> > + // The assert looks nicer if we don't need to do &N
> > + const DefPath *NP = &N;
> > + assert(!Paths.empty() && NP >= &Paths.front() && NP <=
> &Paths.back() &&
> > + "Out of bounds DefPath!");
> > + return NP - &Paths.front();
> > + }
> > +
> > + /// Try to optimize a phi as best as we can. Returns a SmallVector of
> Paths
> > + /// that act as legal clobbers. Note that this won't return *all*
> clobbers.
> > + ///
> > + /// Phi optimization algorithm tl;dr:
> > + /// - Find the earliest def/phi, A, we can optimize to
> > + /// - Find if all paths from the starting memory access ultimately
> reach A
> > + /// - If not, optimization isn't possible.
> > + /// - Otherwise, walk from A to another clobber or phi, A'.
> > + /// - If A' is a def, we're done.
> > + /// - If A' is a phi, try to optimize it.
> > + ///
> > + /// A path is a series of {MemoryAccess, MemoryLocation} pairs. A path
> > + /// terminates when a MemoryAccess that clobbers said MemoryLocation
> is found.
> > + OptznResult tryOptimizePhi(MemoryPhi *Phi, MemoryAccess *Start,
> > + const MemoryLocation &Loc) {
> > + assert(Paths.empty() && VisitedPhis.empty() &&
> > + "Reset the optimization state.");
> > +
> > + Paths.emplace_back(Loc, Start, Phi, None);
> > + // Stores how many "valid" optimization nodes we had prior to
> calling
> > + // addSearches/getBlockingAccess. Necessary for caching if we had a
> blocker.
> > + auto PriorPathsSize = Paths.size();
> > +
> > + SmallVector<ListIndex, 16> PausedSearches;
> > + SmallVector<ListIndex, 8> NewPaused;
> > + SmallVector<TerminatedPath, 4> TerminatedPaths;
> > +
> > + addSearches(Phi, PausedSearches, 0);
> > +
> > + // Moves the TerminatedPath with the "most dominated" Clobber to
> the end of
> > + // Paths.
> > + auto MoveDominatedPathToEnd = [&](SmallVectorImpl<TerminatedPath>
> &Paths) {
> > + assert(!Paths.empty() && "Need a path to move");
> > + // FIXME: This is technically n^2 (n = distance(DefPath.First,
> > + // DefPath.Last)) because of local dominance checks.
> > + auto Dom = Paths.begin();
> > + for (auto I = std::next(Dom), E = Paths.end(); I != E; ++I)
> > + if (!MSSA.dominates(I->Clobber, Dom->Clobber))
> > + Dom = I;
> > + auto Last = Paths.end() - 1;
> > + if (Last != Dom)
> > + std::iter_swap(Last, Dom);
> > + };
> > +
> > + MemoryPhi *Current = Phi;
> > + while (1) {
> > + assert(!MSSA.isLiveOnEntryDef(Current) &&
> > + "liveOnEntry wasn't treated as a clobber?");
> > +
> > + MemoryAccess *Target = getWalkTarget(Current);
> > + // If a TerminatedPath doesn't dominate Target, then it wasn't a
> legal
> > + // optimization for the prior phi.
> > + assert(all_of(TerminatedPaths, [&](const TerminatedPath &P) {
> > + return MSSA.dominates(P.Clobber, Target);
> > + }));
> > +
> > + // FIXME: This is broken, because the Blocker may be reported to
> be
> > + // liveOnEntry, and we'll happily wait for that to disappear
> (read: never)
> > + // For the moment, this is fine, since we do basically nothing
> with
> > + // blocker info.
> > + if (Optional<ListIndex> Blocker = getBlockingAccess(
> > + Target, PausedSearches, NewPaused, TerminatedPaths)) {
> > + MemoryAccess *BlockingAccess = Paths[*Blocker].Last;
> > + // Cache our work on the blocking node, since we know that's
> correct.
> > + cacheDefPath(Paths[*Blocker], BlockingAccess);
> > +
> > + // Find the node we started at. We can't search based on
> N->Last, since
> > + // we may have gone around a loop with a different
> MemoryLocation.
> > + auto Iter = find_if(def_path(*Blocker), [&](const DefPath &N) {
> > + return defPathIndex(N) < PriorPathsSize;
> > + });
> > + assert(Iter != def_path_iterator());
> > +
> > + DefPath &CurNode = *Iter;
> > + assert(CurNode.Last == Current);
> > + CurNode.Blocker = BlockingAccess;
> > +
> > + // Two things:
> > + // A. We can't reliably cache all of NewPaused back. Consider a
> case
> > + // where we have two paths in NewPaused; one of which can't
> optimize
> > + // above this phi, whereas the other can. If we cache the
> second path
> > + // back, we'll end up with suboptimal cache entries. We can
> handle
> > + // cases like this a bit better when we either try to find
> all
> > + // clobbers that block phi optimization, or when our cache
> starts
> > + // supporting unfinished searches.
> > + // B. We can't reliably cache TerminatedPaths back here without
> doing
> > + // extra checks; consider a case like:
> > + // T
> > + // / \
> > + // D C
> > + // \ /
> > + // S
> > + // Where T is our target, C is a node with a clobber on it,
> D is a
> > + // diamond (with a clobber *only* on the left or right node,
> N), and
> > + // S is our start. Say we walk to D, through the node
> opposite N
> > + // (read: ignoring the clobber), and see a cache entry in
> the top
> > + // node of D. That cache entry gets put into
> TerminatedPaths. We then
> > + // walk up to C (N is later in our worklist), find the
> clobber, and
> > + // quit. If we append TerminatedPaths to OtherClobbers,
> we'll cache
> > + // the bottom part of D to the cached clobber, ignoring the
> clobber
> > + // in N. Again, this problem goes away if we start tracking
> all
> > + // blockers for a given phi optimization.
> > + TerminatedPath Result{CurNode.Last, defPathIndex(CurNode)};
> > + return {Result, {}};
> > + }
> > +
> > + // If there's nothing left to search, then all paths led to valid
> clobbers
> > + // that we got from our cache; pick the nearest to the start, and
> allow
> > + // the rest to be cached back.
> > + if (NewPaused.empty()) {
> > + MoveDominatedPathToEnd(TerminatedPaths);
> > + TerminatedPath Result = TerminatedPaths.pop_back_val();
> > + return {Result, std::move(TerminatedPaths)};
> > + }
> > +
> > + MemoryAccess *DefChainEnd = nullptr;
> > + SmallVector<TerminatedPath, 4> Clobbers;
> > + for (ListIndex Paused : NewPaused) {
> > + UpwardsWalkResult WR = walkToPhiOrClobber(Paths[Paused]);
> > + if (WR.IsKnownClobber)
> > + Clobbers.push_back({WR.Result, Paused});
> > + else
> > + // Micro-opt: If we hit the end of the chain, save it.
> > + DefChainEnd = WR.Result;
> > + }
> > +
> > + if (!TerminatedPaths.empty()) {
> > + // If we couldn't find the dominating phi/liveOnEntry in the
> above loop,
> > + // do it now.
> > + if (!DefChainEnd)
> > + for (MemoryAccess *MA : def_chain(Target)))
> > + DefChainEnd = MA;
>
> Is it guaranteed that `def_chain(Target)` isn’t empty?
> Otherwise you have nullptr deref on the next line (Reported by coverity
> who can’t know this invariant).
>
> —
> Mehdi
>
> > +
> > + // If any of the terminated paths don't dominate the phi we'll
> try to
> > + // optimize, we need to figure out what they are and quit.
> > + const BasicBlock *ChainBB = DefChainEnd->getBlock();
> > + for (const TerminatedPath &TP : TerminatedPaths) {
> > + // Because we know that DefChainEnd is as "high" as we can
> go, we
> > + // don't need local dominance checks; BB dominance is
> sufficient.
> > + if (DT.dominates(ChainBB, TP.Clobber->getBlock()))
> > + Clobbers.push_back(TP);
> > + }
> > + }
> > +
> > + // If we have clobbers in the def chain, find the one closest to
> Current
> > + // and quit.
> > + if (!Clobbers.empty()) {
> > + MoveDominatedPathToEnd(Clobbers);
> > + TerminatedPath Result = Clobbers.pop_back_val();
> > + return {Result, std::move(Clobbers)};
> > + }
> > +
> > + assert(all_of(NewPaused,
> > + [&](ListIndex I) { return Paths[I].Last ==
> DefChainEnd; }));
> > +
> > + // Because liveOnEntry is a clobber, this must be a phi.
> > + auto *DefChainPhi = cast<MemoryPhi>(DefChainEnd);
> > +
> > + PriorPathsSize = Paths.size();
> > + PausedSearches.clear();
> > + for (ListIndex I : NewPaused)
> > + addSearches(DefChainPhi, PausedSearches, I);
> > + NewPaused.clear();
> > +
> > + Current = DefChainPhi;
> > + }
> > + }
> > +
> > + /// Caches everything in an OptznResult.
> > + void cacheOptResult(const OptznResult &R) {
> > + if (R.OtherClobbers.empty()) {
> > + // If we're not going to be caching OtherClobbers, don't bother
> with
> > + // marking visited/etc.
> > + for (const DefPath &N : const_def_path(R.PrimaryClobber.LastNode))
> > + cacheDefPath(N, R.PrimaryClobber.Clobber);
> > + return;
> > + }
> > +
> > + // PrimaryClobber is our answer. If we can cache anything back, we
> need to
> > + // stop caching when we visit PrimaryClobber.
> > + SmallBitVector Visited(Paths.size());
> > + for (const DefPath &N : const_def_path(R.PrimaryClobber.LastNode)) {
> > + Visited[defPathIndex(N)] = true;
> > + cacheDefPath(N, R.PrimaryClobber.Clobber);
> > + }
> > +
> > + for (const TerminatedPath &P : R.OtherClobbers) {
> > + for (const DefPath &N : const_def_path(P.LastNode)) {
> > + ListIndex NIndex = defPathIndex(N);
> > + if (Visited[NIndex])
> > + break;
> > + Visited[NIndex] = true;
> > + cacheDefPath(N, P.Clobber);
> > + }
> > + }
> > + }
> > +
> > + void verifyOptResult(const OptznResult &R) const {
> > + assert(all_of(R.OtherClobbers, [&](const TerminatedPath &P) {
> > + return MSSA.dominates(P.Clobber, R.PrimaryClobber.Clobber);
> > + }));
> > + }
> > +
> > + void resetPhiOptznState() {
> > + Paths.clear();
> > + VisitedPhis.clear();
> > + }
> > +
> > +public:
> > + ClobberWalker(const MemorySSA &MSSA, AliasAnalysis &AA, DominatorTree
> &DT,
> > + WalkerCache &WC)
> > + : MSSA(MSSA), AA(AA), DT(DT), WC(WC), UseCache(true) {}
> > +
> > + void reset() { WalkTargetCache.clear(); }
> > +
> > + /// Finds the nearest clobber for the given query, optimizing phis if
> > + /// possible.
> > + MemoryAccess *findClobber(MemoryAccess *Start, UpwardsMemoryQuery &Q,
> > + bool UseWalkerCache = true) {
> > + setUseCache(UseWalkerCache);
> > + Query = &Q;
> > +
> > + MemoryAccess *Current = Start;
> > + // This walker pretends uses don't exist. If we're handed one,
> silently grab
> > + // its def. (This has the nice side-effect of ensuring we never
> cache uses)
> > + if (auto *MU = dyn_cast<MemoryUse>(Start))
> > + Current = MU->getDefiningAccess();
> > +
> > + DefPath FirstDesc(Q.StartingLoc, Current, Current, None);
> > + // Fast path for the overly-common case (no crazy phi optimization
> > + // necessary)
> > + UpwardsWalkResult WalkResult = walkToPhiOrClobber(FirstDesc);
> > + if (WalkResult.IsKnownClobber) {
> > + cacheDefPath(FirstDesc, WalkResult.Result);
> > + return WalkResult.Result;
> > + }
> > +
> > + OptznResult OptRes =
> > + tryOptimizePhi(cast<MemoryPhi>(FirstDesc.Last), Current,
> Q.StartingLoc);
> > + verifyOptResult(OptRes);
> > + cacheOptResult(OptRes);
> > + resetPhiOptznState();
> > +
> > +#ifdef EXPENSIVE_CHECKS
> > + checkClobberSanity(Current, OptRes.PrimaryClobber.Clobber,
> Q.StartingLoc,
> > + MSSA, Q, AA);
> > +#endif
> > + return OptRes.PrimaryClobber.Clobber;
> > + }
> > +};
> > +
> > +struct RenamePassData {
> > + DomTreeNode *DTN;
> > + DomTreeNode::const_iterator ChildIt;
> > + MemoryAccess *IncomingVal;
> >
> > + RenamePassData(DomTreeNode *D, DomTreeNode::const_iterator It,
> > + MemoryAccess *M)
> > + : DTN(D), ChildIt(It), IncomingVal(M) {}
> > + void swap(RenamePassData &RHS) {
> > + std::swap(DTN, RHS.DTN);
> > + std::swap(ChildIt, RHS.ChildIt);
> > + std::swap(IncomingVal, RHS.IncomingVal);
> > + }
> > +};
> > +} // anonymous namespace
> > +
> > +namespace llvm {
> > /// \brief A MemorySSAWalker that does AA walks and caching of lookups to
> > /// disambiguate accesses.
> > ///
> > @@ -121,6 +892,13 @@ public:
> > /// ret i32 %r
> > /// }
> > class MemorySSA::CachingWalker final : public MemorySSAWalker {
> > + WalkerCache Cache;
> > + ClobberWalker Walker;
> > + bool AutoResetWalker;
> > +
> > + MemoryAccess *getClobberingMemoryAccess(MemoryAccess *,
> UpwardsMemoryQuery &);
> > + void verifyRemoved(MemoryAccess *);
> > +
> > public:
> > CachingWalker(MemorySSA *, AliasAnalysis *, DominatorTree *);
> > ~CachingWalker() override;
> > @@ -130,50 +908,17 @@ public:
> > MemoryLocation &) override;
> > void invalidateInfo(MemoryAccess *) override;
> >
> > -protected:
> > - struct UpwardsMemoryQuery;
> > - MemoryAccess *doCacheLookup(const MemoryAccess *, const
> UpwardsMemoryQuery &,
> > - const MemoryLocation &);
> > -
> > - void doCacheInsert(const MemoryAccess *, MemoryAccess *,
> > - const UpwardsMemoryQuery &, const MemoryLocation
> &);
> > -
> > - void doCacheRemove(const MemoryAccess *, const UpwardsMemoryQuery &,
> > - const MemoryLocation &);
> > -
> > -private:
> > - MemoryAccessPair UpwardsDFSWalk(MemoryAccess *, const MemoryLocation
> &,
> > - UpwardsMemoryQuery &, bool);
> > - MemoryAccess *getClobberingMemoryAccess(MemoryAccess *,
> UpwardsMemoryQuery &);
> > - bool instructionClobbersQuery(const MemoryDef *, UpwardsMemoryQuery &,
> > - const MemoryLocation &Loc) const;
> > - void verifyRemoved(MemoryAccess *);
> > - SmallDenseMap<ConstMemoryAccessPair, MemoryAccess *>
> > - CachedUpwardsClobberingAccess;
> > - DenseMap<const MemoryAccess *, MemoryAccess *>
> CachedUpwardsClobberingCall;
> > - AliasAnalysis *AA;
> > - DominatorTree *DT;
> > + /// Whether we call resetClobberWalker() after each time we
> *actually* walk to
> > + /// answer a clobber query.
> > + void setAutoResetWalker(bool AutoReset) { AutoResetWalker =
> AutoReset; }
> > +
> > + /// Drop the walker's persistent data structures. At the moment, this
> means
> > + /// "drop the walker's cache of BasicBlocks ->
> > + /// earliest-MemoryAccess-we-can-optimize-to". This is necessary if
> we're
> > + /// going to have DT updates, if we remove MemoryAccesses, etc.
> > + void resetClobberWalker() { Walker.reset(); }
> > };
> > -}
> >
> > -namespace {
> > -struct RenamePassData {
> > - DomTreeNode *DTN;
> > - DomTreeNode::const_iterator ChildIt;
> > - MemoryAccess *IncomingVal;
> > -
> > - RenamePassData(DomTreeNode *D, DomTreeNode::const_iterator It,
> > - MemoryAccess *M)
> > - : DTN(D), ChildIt(It), IncomingVal(M) {}
> > - void swap(RenamePassData &RHS) {
> > - std::swap(DTN, RHS.DTN);
> > - std::swap(ChildIt, RHS.ChildIt);
> > - std::swap(IncomingVal, RHS.IncomingVal);
> > - }
> > -};
> > -}
> > -
> > -namespace llvm {
> > /// \brief Rename a single basic block into MemorySSA form.
> > /// Uses the standard SSA renaming algorithm.
> > /// \returns The new incoming value.
> > @@ -417,7 +1162,10 @@ void MemorySSA::buildMemorySSA() {
> > SmallPtrSet<BasicBlock *, 16> Visited;
> > renamePass(DT->getRootNode(), LiveOnEntryDef.get(), Visited);
> >
> > - MemorySSAWalker *Walker = getWalker();
> > + CachingWalker *Walker = getWalkerImpl();
> > +
> > + // We're doing a batch of updates; don't drop useful caches between
> them.
> > + Walker->setAutoResetWalker(false);
> >
> > // Now optimize the MemoryUse's defining access to point to the nearest
> > // dominating clobbering def.
> > @@ -437,6 +1185,9 @@ void MemorySSA::buildMemorySSA() {
> > }
> > }
> >
> > + Walker->setAutoResetWalker(true);
> > + Walker->resetClobberWalker();
> > +
> > // Mark the uses in unreachable blocks as live on entry, so that they
> go
> > // somewhere.
> > for (auto &BB : F)
> > @@ -444,7 +1195,9 @@ void MemorySSA::buildMemorySSA() {
> > markUnreachableAsLiveOnEntry(&BB);
> > }
> >
> > -MemorySSAWalker *MemorySSA::getWalker() {
> > +MemorySSAWalker *MemorySSA::getWalker() { return getWalkerImpl(); }
> > +
> > +MemorySSA::CachingWalker *MemorySSA::getWalkerImpl() {
> > if (Walker)
> > return Walker.get();
> >
> > @@ -820,7 +1573,6 @@ MemoryPhi *MemorySSA::getMemoryAccess(co
> > /// \returns True if \p Dominator dominates \p Dominatee.
> > bool MemorySSA::locallyDominates(const MemoryAccess *Dominator,
> > const MemoryAccess *Dominatee) const {
> > -
> > assert((Dominator->getBlock() == Dominatee->getBlock()) &&
> > "Asking for local domination when accesses are in different
> blocks!");
> >
> > @@ -848,6 +1600,19 @@ bool MemorySSA::locallyDominates(const M
> > [&](const MemoryAccess &MA) { return &MA ==
> Dominatee; });
> > }
> >
> > +bool MemorySSA::dominates(const MemoryAccess *Dominator,
> > + const MemoryAccess *Dominatee) const {
> > + if (Dominator == Dominatee)
> > + return true;
> > +
> > + if (isLiveOnEntryDef(Dominatee))
> > + return false;
> > +
> > + if (Dominator->getBlock() != Dominatee->getBlock())
> > + return DT->dominates(Dominator->getBlock(), Dominatee->getBlock());
> > + return locallyDominates(Dominator, Dominatee);
> > +}
> > +
> > const static char LiveOnEntryStr[] = "liveOnEntry";
> >
> > void MemoryDef::print(raw_ostream &OS) const {
> > @@ -978,41 +1743,12 @@ MemorySSAWalker::MemorySSAWalker(MemoryS
> >
> > MemorySSA::CachingWalker::CachingWalker(MemorySSA *M, AliasAnalysis *A,
> > DominatorTree *D)
> > - : MemorySSAWalker(M), AA(A), DT(D) {}
> > + : MemorySSAWalker(M), Walker(*M, *A, *D, Cache),
> > + AutoResetWalker(true) {}
> >
> > MemorySSA::CachingWalker::~CachingWalker() {}
> >
> > -struct MemorySSA::CachingWalker::UpwardsMemoryQuery {
> > - // True if we saw a phi whose predecessor was a backedge
> > - bool SawBackedgePhi;
> > - // True if our original query started off as a call
> > - bool IsCall;
> > - // The pointer location we started the query with. This will be empty
> if
> > - // IsCall is true.
> > - MemoryLocation StartingLoc;
> > - // This is the instruction we were querying about.
> > - const Instruction *Inst;
> > - // Set of visited Instructions for this query.
> > - DenseSet<MemoryAccessPair> Visited;
> > - // Vector of visited call accesses for this query. This is separated
> out
> > - // because you can always cache and lookup the result of call queries
> (IE when
> > - // IsCall == true) for every call in the chain. The calls have no AA
> location
> > - // associated with them with them, and thus, no context dependence.
> > - SmallVector<const MemoryAccess *, 32> VisitedCalls;
> > - // The MemoryAccess we actually got called with, used to test local
> domination
> > - const MemoryAccess *OriginalAccess;
> > -
> > - UpwardsMemoryQuery()
> > - : SawBackedgePhi(false), IsCall(false), Inst(nullptr),
> > - OriginalAccess(nullptr) {}
> > -
> > - UpwardsMemoryQuery(const Instruction *Inst, const MemoryAccess
> *Access)
> > - : SawBackedgePhi(false), IsCall(ImmutableCallSite(Inst)),
> Inst(Inst),
> > - OriginalAccess(Access) {}
> > -};
> > -
> > void MemorySSA::CachingWalker::invalidateInfo(MemoryAccess *MA) {
> > -
> > // TODO: We can do much better cache invalidation with differently
> stored
> > // caches. For now, for MemoryUses, we simply remove them
> > // from the cache, and kill the entire call/non-call cache for
> everything
> > @@ -1026,217 +1762,33 @@ void MemorySSA::CachingWalker::invalidat
> > // itself.
> >
> > if (MemoryUse *MU = dyn_cast<MemoryUse>(MA)) {
> > - UpwardsMemoryQuery Q;
> > - Instruction *I = MU->getMemoryInst();
> > - Q.IsCall = bool(ImmutableCallSite(I));
> > - Q.Inst = I;
> > - if (!Q.IsCall)
> > - Q.StartingLoc = MemoryLocation::get(I);
> > - doCacheRemove(MA, Q, Q.StartingLoc);
> > + UpwardsMemoryQuery Q(MU->getMemoryInst(), MU);
> > + Cache.remove(MU, Q.StartingLoc, Q.IsCall);
> > } else {
> > // If it is not a use, the best we can do right now is destroy the
> cache.
> > - CachedUpwardsClobberingCall.clear();
> > - CachedUpwardsClobberingAccess.clear();
> > + Cache.clear();
> > }
> >
> > #ifdef EXPENSIVE_CHECKS
> > - // Run this only when expensive checks are enabled.
> > verifyRemoved(MA);
> > #endif
> > }
> >
> > -void MemorySSA::CachingWalker::doCacheRemove(const MemoryAccess *M,
> > - const UpwardsMemoryQuery
> &Q,
> > - const MemoryLocation &Loc)
> {
> > - if (Q.IsCall)
> > - CachedUpwardsClobberingCall.erase(M);
> > - else
> > - CachedUpwardsClobberingAccess.erase({M, Loc});
> > -}
> > -
> > -void MemorySSA::CachingWalker::doCacheInsert(const MemoryAccess *M,
> > - MemoryAccess *Result,
> > - const UpwardsMemoryQuery
> &Q,
> > - const MemoryLocation &Loc)
> {
> > - // This is fine for Phis, since there are times where we can't
> optimize them.
> > - // Making a def its own clobber is never correct, though.
> > - assert((Result != M || isa<MemoryPhi>(M)) &&
> > - "Something can't clobber itself!");
> > - ++NumClobberCacheInserts;
> > - if (Q.IsCall)
> > - CachedUpwardsClobberingCall[M] = Result;
> > - else
> > - CachedUpwardsClobberingAccess[{M, Loc}] = Result;
> > -}
> > -
> > -MemoryAccess *
> > -MemorySSA::CachingWalker::doCacheLookup(const MemoryAccess *M,
> > - const UpwardsMemoryQuery &Q,
> > - const MemoryLocation &Loc) {
> > - ++NumClobberCacheLookups;
> > - MemoryAccess *Result;
> > -
> > - if (Q.IsCall)
> > - Result = CachedUpwardsClobberingCall.lookup(M);
> > - else
> > - Result = CachedUpwardsClobberingAccess.lookup({M, Loc});
> > -
> > - if (Result)
> > - ++NumClobberCacheHits;
> > - return Result;
> > -}
> > -
> > -bool MemorySSA::CachingWalker::instructionClobbersQuery(
> > - const MemoryDef *MD, UpwardsMemoryQuery &Q,
> > - const MemoryLocation &Loc) const {
> > - Instruction *DefMemoryInst = MD->getMemoryInst();
> > - assert(DefMemoryInst && "Defining instruction not actually an
> instruction");
> > -
> > - if (!Q.IsCall)
> > - return AA->getModRefInfo(DefMemoryInst, Loc) & MRI_Mod;
> > -
> > - // If this is a call, mark it for caching
> > - if (ImmutableCallSite(DefMemoryInst))
> > - Q.VisitedCalls.push_back(MD);
> > - ModRefInfo I = AA->getModRefInfo(DefMemoryInst,
> ImmutableCallSite(Q.Inst));
> > - return I != MRI_NoModRef;
> > -}
> > -
> > -MemoryAccessPair MemorySSA::CachingWalker::UpwardsDFSWalk(
> > - MemoryAccess *StartingAccess, const MemoryLocation &Loc,
> > - UpwardsMemoryQuery &Q, bool FollowingBackedge) {
> > - MemoryAccess *ModifyingAccess = nullptr;
> > -
> > - auto DFI = df_begin(StartingAccess);
> > - for (auto DFE = df_end(StartingAccess); DFI != DFE;) {
> > - MemoryAccess *CurrAccess = *DFI;
> > - if (MSSA->isLiveOnEntryDef(CurrAccess))
> > - return {CurrAccess, Loc};
> > - // If this is a MemoryDef, check whether it clobbers our current
> query. This
> > - // needs to be done before consulting the cache, because the cache
> reports
> > - // the clobber for CurrAccess. If CurrAccess is a clobber for this
> query,
> > - // and we ask the cache for information first, then we might skip
> this
> > - // clobber, which is bad.
> > - if (auto *MD = dyn_cast<MemoryDef>(CurrAccess)) {
> > - // If we hit the top, stop following this path.
> > - // While we can do lookups, we can't sanely do inserts here
> unless we were
> > - // to track everything we saw along the way, since we don't know
> where we
> > - // will stop.
> > - if (instructionClobbersQuery(MD, Q, Loc)) {
> > - ModifyingAccess = CurrAccess;
> > - break;
> > - }
> > - }
> > - if (auto CacheResult = doCacheLookup(CurrAccess, Q, Loc))
> > - return {CacheResult, Loc};
> > -
> > - // We need to know whether it is a phi so we can track backedges.
> > - // Otherwise, walk all upward defs.
> > - if (!isa<MemoryPhi>(CurrAccess)) {
> > - ++DFI;
> > - continue;
> > - }
> > -
> > -#ifndef NDEBUG
> > - // The loop below visits the phi's children for us. Because phis
> are the
> > - // only things with multiple edges, skipping the children should
> always lead
> > - // us to the end of the loop.
> > - //
> > - // Use a copy of DFI because skipChildren would kill our search
> stack, which
> > - // would make caching anything on the way back impossible.
> > - auto DFICopy = DFI;
> > - assert(DFICopy.skipChildren() == DFE &&
> > - "Skipping phi's children doesn't end the DFS?");
> > -#endif
> > -
> > - const MemoryAccessPair PHIPair(CurrAccess, Loc);
> > -
> > - // Don't try to optimize this phi again if we've already tried to
> do so.
> > - if (!Q.Visited.insert(PHIPair).second) {
> > - ModifyingAccess = CurrAccess;
> > - break;
> > - }
> > -
> > - std::size_t InitialVisitedCallSize = Q.VisitedCalls.size();
> > -
> > - // Recurse on PHI nodes, since we need to change locations.
> > - // TODO: Allow graphtraits on pairs, which would turn this whole
> function
> > - // into a normal single depth first walk.
> > - MemoryAccess *FirstDef = nullptr;
> > - for (auto MPI = upward_defs_begin(PHIPair), MPE = upward_defs_end();
> > - MPI != MPE; ++MPI) {
> > - bool Backedge =
> > - !FollowingBackedge &&
> > - DT->dominates(CurrAccess->getBlock(), MPI.getPhiArgBlock());
> > -
> > - MemoryAccessPair CurrentPair =
> > - UpwardsDFSWalk(MPI->first, MPI->second, Q, Backedge);
> > - // All the phi arguments should reach the same point if we can
> bypass
> > - // this phi. The alternative is that they hit this phi node, which
> > - // means we can skip this argument.
> > - if (FirstDef && CurrentPair.first != PHIPair.first &&
> > - CurrentPair.first != FirstDef) {
> > - ModifyingAccess = CurrAccess;
> > - break;
> > - }
> > -
> > - if (!FirstDef)
> > - FirstDef = CurrentPair.first;
> > - }
> > -
> > - // If we exited the loop early, go with the result it gave us.
> > - if (!ModifyingAccess) {
> > - assert(FirstDef && "Found a Phi with no upward defs?");
> > - ModifyingAccess = FirstDef;
> > - } else {
> > - // If we can't optimize this Phi, then we can't safely cache any
> of the
> > - // calls we visited when trying to optimize it. Wipe them out now.
> > - Q.VisitedCalls.resize(InitialVisitedCallSize);
> > - }
> > - break;
> > - }
> > -
> > - if (!ModifyingAccess)
> > - return {MSSA->getLiveOnEntryDef(), Q.StartingLoc};
> > -
> > - const BasicBlock *OriginalBlock = StartingAccess->getBlock();
> > - assert(DFI.getPathLength() > 0 && "We dropped our path?");
> > - unsigned N = DFI.getPathLength();
> > - // If we found a clobbering def, the last element in the path will be
> our
> > - // clobber, so we don't want to cache that to itself. OTOH, if we
> optimized a
> > - // phi, we can add the last thing in the path to the cache, since
> that won't
> > - // be the result.
> > - if (DFI.getPath(N - 1) == ModifyingAccess)
> > - --N;
> > - for (; N > 1; --N) {
> > - MemoryAccess *CacheAccess = DFI.getPath(N - 1);
> > - BasicBlock *CurrBlock = CacheAccess->getBlock();
> > - if (!FollowingBackedge)
> > - doCacheInsert(CacheAccess, ModifyingAccess, Q, Loc);
> > - if (DT->dominates(CurrBlock, OriginalBlock) &&
> > - (CurrBlock != OriginalBlock || !FollowingBackedge ||
> > - MSSA->locallyDominates(CacheAccess, StartingAccess)))
> > - break;
> > - }
> > -
> > - // Cache everything else on the way back. The caller should cache
> > - // StartingAccess for us.
> > - for (; N > 1; --N) {
> > - MemoryAccess *CacheAccess = DFI.getPath(N - 1);
> > - doCacheInsert(CacheAccess, ModifyingAccess, Q, Loc);
> > - }
> > - assert(Q.Visited.size() < 1000 && "Visited too much");
> > -
> > - return {ModifyingAccess, Loc};
> > -}
> > -
> > /// \brief Walk the use-def chains starting at \p MA and find
> > /// the MemoryAccess that actually clobbers Loc.
> > ///
> > /// \returns our clobbering memory access
> > MemoryAccess *MemorySSA::CachingWalker::getClobberingMemoryAccess(
> > MemoryAccess *StartingAccess, UpwardsMemoryQuery &Q) {
> > - return UpwardsDFSWalk(StartingAccess, Q.StartingLoc, Q, false).first;
> > + MemoryAccess *New = Walker.findClobber(StartingAccess, Q);
> > +#ifdef EXPENSIVE_CHECKS
> > + MemoryAccess *NewNoCache =
> > + Walker.findClobber(StartingAccess, Q, /*UseWalkerCache=*/false);
> > + assert(NewNoCache == New && "Cache made us hand back a different
> result?");
> > +#endif
> > + if (AutoResetWalker)
> > + resetClobberWalker();
> > + return New;
> > }
> >
> > MemoryAccess *MemorySSA::CachingWalker::getClobberingMemoryAccess(
> > @@ -1258,10 +1810,10 @@ MemoryAccess *MemorySSA::CachingWalker::
> > UpwardsMemoryQuery Q;
> > Q.OriginalAccess = StartingUseOrDef;
> > Q.StartingLoc = Loc;
> > - Q.Inst = StartingUseOrDef->getMemoryInst();
> > + Q.Inst = I;
> > Q.IsCall = false;
> >
> > - if (auto CacheResult = doCacheLookup(StartingUseOrDef, Q,
> Q.StartingLoc))
> > + if (auto *CacheResult = Cache.lookup(StartingUseOrDef, Loc, Q.IsCall))
> > return CacheResult;
> >
> > // Unlike the other function, do not walk to the def of a def, because
> we are
> > @@ -1271,9 +1823,6 @@ MemoryAccess *MemorySSA::CachingWalker::
> > : StartingUseOrDef;
> >
> > MemoryAccess *Clobber = getClobberingMemoryAccess(DefiningAccess, Q);
> > - // Only cache this if it wouldn't make Clobber point to itself.
> > - if (Clobber != StartingAccess)
> > - doCacheInsert(Q.OriginalAccess, Clobber, Q, Q.StartingLoc);
> > DEBUG(dbgs() << "Starting Memory SSA clobber for " << *I << " is ");
> > DEBUG(dbgs() << *StartingUseOrDef << "\n");
> > DEBUG(dbgs() << "Final Memory SSA clobber for " << *I << " is ");
> > @@ -1287,21 +1836,14 @@ MemorySSA::CachingWalker::getClobberingM
> > // access, since we only map BB's to PHI's. So, this must be a use or
> def.
> > auto *StartingAccess = cast<MemoryUseOrDef>(MSSA->getMemoryAccess(I));
> >
> > - bool IsCall = bool(ImmutableCallSite(I));
> > -
> > + UpwardsMemoryQuery Q(I, StartingAccess);
> > // We can't sanely do anything with a fences, they conservatively
> > // clobber all memory, and have no locations to get pointers from to
> > // try to disambiguate.
> > - if (!IsCall && I->isFenceLike())
> > + if (!Q.IsCall && I->isFenceLike())
> > return StartingAccess;
> >
> > - UpwardsMemoryQuery Q;
> > - Q.OriginalAccess = StartingAccess;
> > - Q.IsCall = IsCall;
> > - if (!Q.IsCall)
> > - Q.StartingLoc = MemoryLocation::get(I);
> > - Q.Inst = I;
> > - if (auto CacheResult = doCacheLookup(StartingAccess, Q,
> Q.StartingLoc))
> > + if (auto *CacheResult = Cache.lookup(StartingAccess, Q.StartingLoc,
> Q.IsCall))
> > return CacheResult;
> >
> > // Start with the thing we already think clobbers this location
> > @@ -1313,18 +1855,6 @@ MemorySSA::CachingWalker::getClobberingM
> > return DefiningAccess;
> >
> > MemoryAccess *Result = getClobberingMemoryAccess(DefiningAccess, Q);
> > - // DFS won't cache a result for DefiningAccess. So, if DefiningAccess
> isn't
> > - // our clobber, be sure that it gets a cache entry, too.
> > - if (Result != DefiningAccess)
> > - doCacheInsert(DefiningAccess, Result, Q, Q.StartingLoc);
> > - doCacheInsert(Q.OriginalAccess, Result, Q, Q.StartingLoc);
> > - // TODO: When this implementation is more mature, we may want to
> figure out
> > - // what this additional caching buys us. It's most likely A Good
> Thing.
> > - if (Q.IsCall)
> > - for (const MemoryAccess *MA : Q.VisitedCalls)
> > - if (MA != Result)
> > - doCacheInsert(MA, Result, Q, Q.StartingLoc);
> > -
> > DEBUG(dbgs() << "Starting Memory SSA clobber for " << *I << " is ");
> > DEBUG(dbgs() << *DefiningAccess << "\n");
> > DEBUG(dbgs() << "Final Memory SSA clobber for " << *I << " is ");
> > @@ -1335,14 +1865,7 @@ MemorySSA::CachingWalker::getClobberingM
> >
> > // Verify that MA doesn't exist in any of the caches.
> > void MemorySSA::CachingWalker::verifyRemoved(MemoryAccess *MA) {
> > -#ifndef NDEBUG
> > - for (auto &P : CachedUpwardsClobberingAccess)
> > - assert(P.first.first != MA && P.second != MA &&
> > - "Found removed MemoryAccess in cache.");
> > - for (auto &P : CachedUpwardsClobberingCall)
> > - assert(P.first != MA && P.second != MA &&
> > - "Found removed MemoryAccess in cache.");
> > -#endif // !NDEBUG
> > + assert(!Cache.contains(MA) && "Found removed MemoryAccess in cache.");
> > }
> >
> > MemoryAccess *
> > @@ -1359,4 +1882,4 @@ MemoryAccess *DoNothingMemorySSAWalker::
> > return Use->getDefiningAccess();
> > return StartingAccess;
> > }
> > -}
> > +} // namespace llvm
> >
> > Modified: llvm/trunk/test/Transforms/Util/MemorySSA/cyclicphi.ll
> > URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/Util/MemorySSA/cyclicphi.ll?rev=275940&r1=275939&r2=275940&view=diff
> >
> ==============================================================================
> > --- llvm/trunk/test/Transforms/Util/MemorySSA/cyclicphi.ll (original)
> > +++ llvm/trunk/test/Transforms/Util/MemorySSA/cyclicphi.ll Mon Jul 18
> 20:29:15 2016
> > @@ -56,8 +56,7 @@ bb68:
> >
> > bb77: ; preds = %bb68, %bb26
> > ; CHECK: 2 = MemoryPhi({bb26,3},{bb68,1})
> > -; FIXME: This should be MemoryUse(liveOnEntry)
> > -; CHECK: MemoryUse(3)
> > +; CHECK: MemoryUse(liveOnEntry)
> > ; CHECK-NEXT: %tmp78 = load i64*, i64** %tmp25, align 8
> > %tmp78 = load i64*, i64** %tmp25, align 8
> > br label %bb26
> >
> > Modified: llvm/trunk/test/Transforms/Util/MemorySSA/phi-translation.ll
> > URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/Util/MemorySSA/phi-translation.ll?rev=275940&r1=275939&r2=275940&view=diff
> >
> ==============================================================================
> > --- llvm/trunk/test/Transforms/Util/MemorySSA/phi-translation.ll
> (original)
> > +++ llvm/trunk/test/Transforms/Util/MemorySSA/phi-translation.ll Mon Jul
> 18 20:29:15 2016
> > @@ -138,8 +138,7 @@ loop.3:
> > ; CHECK: 4 = MemoryDef(5)
> > ; CHECK-NEXT: store i8 2, i8* %p2
> > store i8 2, i8* %p2
> > -; FIXME: This should be MemoryUse(1)
> > -; CHECK: MemoryUse(5)
> > +; CHECK: MemoryUse(1)
> > ; CHECK-NEXT: load i8, i8* %p1
> > load i8, i8* %p1
> > br i1 undef, label %loop.2, label %loop.1
> >
> >
> > _______________________________________________
> > llvm-commits mailing list
> > llvm-commits at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>
>
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