[llvm] r275940 - [MemorySSA] Update to the new shiny walker.
Mehdi Amini via llvm-commits
llvm-commits at lists.llvm.org
Thu Jul 21 15:50:39 PDT 2016
> 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
>
>
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