MemorySSA: Move updater to its own file
llvm-svn: 293357
diff --git a/llvm/lib/Transforms/Utils/MemorySSAUpdater.cpp b/llvm/lib/Transforms/Utils/MemorySSAUpdater.cpp
new file mode 100644
index 0000000..792ddef
--- /dev/null
+++ b/llvm/lib/Transforms/Utils/MemorySSAUpdater.cpp
@@ -0,0 +1,372 @@
+//===-- MemorySSAUpdater.cpp - Memory SSA Updater--------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------===//
+//
+// This file implements the MemorySSAUpdater class.
+//
+//===----------------------------------------------------------------===//
+#include "llvm/Transforms/Utils/MemorySSAUpdater.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Metadata.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/FormattedStream.h"
+#include "llvm/Transforms/Utils/MemorySSA.h"
+#include <algorithm>
+
+#define DEBUG_TYPE "memoryssa"
+using namespace llvm;
+namespace llvm {
+// This is the marker algorithm from "Simple and Efficient Construction of
+// Static Single Assignment Form"
+// The simple, non-marker algorithm places phi nodes at any join
+// Here, we place markers, and only place phi nodes if they end up necessary.
+// They are only necessary if they break a cycle (IE we recursively visit
+// ourselves again), or we discover, while getting the value of the operands,
+// that there are two or more definitions needing to be merged.
+// This still will leave non-minimal form in the case of irreducible control
+// flow, where phi nodes may be in cycles with themselves, but unnecessary.
+MemoryAccess *MemorySSAUpdater::getPreviousDefRecursive(BasicBlock *BB) {
+ // Single predecessor case, just recurse, we can only have one definition.
+ if (BasicBlock *Pred = BB->getSinglePredecessor()) {
+ return getPreviousDefFromEnd(Pred);
+ } else if (VisitedBlocks.count(BB)) {
+ // We hit our node again, meaning we had a cycle, we must insert a phi
+ // node to break it so we have an operand. The only case this will
+ // insert useless phis is if we have irreducible control flow.
+ return MSSA->createMemoryPhi(BB);
+ } else if (VisitedBlocks.insert(BB).second) {
+ // Mark us visited so we can detect a cycle
+ SmallVector<MemoryAccess *, 8> PhiOps;
+
+ // Recurse to get the values in our predecessors for placement of a
+ // potential phi node. This will insert phi nodes if we cycle in order to
+ // break the cycle and have an operand.
+ for (auto *Pred : predecessors(BB))
+ PhiOps.push_back(getPreviousDefFromEnd(Pred));
+
+ // Now try to simplify the ops to avoid placing a phi.
+ // This may return null if we never created a phi yet, that's okay
+ MemoryPhi *Phi = dyn_cast_or_null<MemoryPhi>(MSSA->getMemoryAccess(BB));
+ bool PHIExistsButNeedsUpdate = false;
+ // See if the existing phi operands match what we need.
+ // Unlike normal SSA, we only allow one phi node per block, so we can't just
+ // create a new one.
+ if (Phi && Phi->getNumOperands() != 0)
+ if (!std::equal(Phi->op_begin(), Phi->op_end(), PhiOps.begin())) {
+ PHIExistsButNeedsUpdate = true;
+ }
+
+ // See if we can avoid the phi by simplifying it.
+ auto *Result = tryRemoveTrivialPhi(Phi, PhiOps);
+ // If we couldn't simplify, we may have to create a phi
+ if (Result == Phi) {
+ if (!Phi)
+ Phi = MSSA->createMemoryPhi(BB);
+
+ // These will have been filled in by the recursive read we did above.
+ if (PHIExistsButNeedsUpdate) {
+ std::copy(PhiOps.begin(), PhiOps.end(), Phi->op_begin());
+ std::copy(pred_begin(BB), pred_end(BB), Phi->block_begin());
+ } else {
+ unsigned i = 0;
+ for (auto *Pred : predecessors(BB))
+ Phi->addIncoming(PhiOps[i++], Pred);
+ }
+
+ Result = Phi;
+ }
+ if (MemoryPhi *MP = dyn_cast<MemoryPhi>(Result))
+ InsertedPHIs.push_back(MP);
+ // Set ourselves up for the next variable by resetting visited state.
+ VisitedBlocks.erase(BB);
+ return Result;
+ }
+ llvm_unreachable("Should have hit one of the three cases above");
+}
+
+// This starts at the memory access, and goes backwards in the block to find the
+// previous definition. If a definition is not found the block of the access,
+// it continues globally, creating phi nodes to ensure we have a single
+// definition.
+MemoryAccess *MemorySSAUpdater::getPreviousDef(MemoryAccess *MA) {
+ auto *LocalResult = getPreviousDefInBlock(MA);
+
+ return LocalResult ? LocalResult : getPreviousDefRecursive(MA->getBlock());
+}
+
+// This starts at the memory access, and goes backwards in the block to the find
+// the previous definition. If the definition is not found in the block of the
+// access, it returns nullptr.
+MemoryAccess *MemorySSAUpdater::getPreviousDefInBlock(MemoryAccess *MA) {
+ auto *Defs = MSSA->getWritableBlockDefs(MA->getBlock());
+
+ // It's possible there are no defs, or we got handed the first def to start.
+ if (Defs) {
+ // If this is a def, we can just use the def iterators.
+ if (!isa<MemoryUse>(MA)) {
+ auto Iter = MA->getReverseDefsIterator();
+ ++Iter;
+ if (Iter != Defs->rend())
+ return &*Iter;
+ } else {
+ // Otherwise, have to walk the all access iterator.
+ auto Iter = MA->getReverseIterator();
+ ++Iter;
+ while (&*Iter != &*Defs->begin()) {
+ if (!isa<MemoryUse>(*Iter))
+ return &*Iter;
+ --Iter;
+ }
+ // At this point it must be pointing at firstdef
+ assert(&*Iter == &*Defs->begin() &&
+ "Should have hit first def walking backwards");
+ return &*Iter;
+ }
+ }
+ return nullptr;
+}
+
+// This starts at the end of block
+MemoryAccess *MemorySSAUpdater::getPreviousDefFromEnd(BasicBlock *BB) {
+ auto *Defs = MSSA->getWritableBlockDefs(BB);
+
+ if (Defs)
+ return &*Defs->rbegin();
+
+ return getPreviousDefRecursive(BB);
+}
+// Recurse over a set of phi uses to eliminate the trivial ones
+MemoryAccess *MemorySSAUpdater::recursePhi(MemoryAccess *Phi) {
+ if (!Phi)
+ return nullptr;
+ TrackingVH<MemoryAccess> Res(Phi);
+ SmallVector<TrackingVH<Value>, 8> Uses;
+ std::copy(Phi->user_begin(), Phi->user_end(), std::back_inserter(Uses));
+ for (auto &U : Uses) {
+ if (MemoryPhi *UsePhi = dyn_cast<MemoryPhi>(&*U)) {
+ auto OperRange = UsePhi->operands();
+ tryRemoveTrivialPhi(UsePhi, OperRange);
+ }
+ }
+ return Res;
+}
+
+// Eliminate trivial phis
+// Phis are trivial if they are defined either by themselves, or all the same
+// argument.
+// IE phi(a, a) or b = phi(a, b) or c = phi(a, a, c)
+// We recursively try to remove them.
+template <class RangeType>
+MemoryAccess *MemorySSAUpdater::tryRemoveTrivialPhi(MemoryPhi *Phi,
+ RangeType &Operands) {
+ // Detect equal or self arguments
+ MemoryAccess *Same = nullptr;
+ for (auto &Op : Operands) {
+ // If the same or self, good so far
+ if (Op == Phi || Op == Same)
+ continue;
+ // not the same, return the phi since it's not eliminatable by us
+ if (Same)
+ return Phi;
+ Same = cast<MemoryAccess>(Op);
+ }
+ // Never found a non-self reference, the phi is undef
+ if (Same == nullptr)
+ return MSSA->getLiveOnEntryDef();
+ if (Phi) {
+ Phi->replaceAllUsesWith(Same);
+ MSSA->removeMemoryAccess(Phi);
+ }
+
+ // We should only end up recursing in case we replaced something, in which
+ // case, we may have made other Phis trivial.
+ return recursePhi(Same);
+}
+
+void MemorySSAUpdater::insertUse(MemoryUse *MU) {
+ InsertedPHIs.clear();
+ MU->setDefiningAccess(getPreviousDef(MU));
+ // Unlike for defs, there is no extra work to do. Because uses do not create
+ // new may-defs, there are only two cases:
+ //
+ // 1. There was a def already below us, and therefore, we should not have
+ // created a phi node because it was already needed for the def.
+ //
+ // 2. There is no def below us, and therefore, there is no extra renaming work
+ // to do.
+}
+
+void setMemoryPhiValueForBlock(MemoryPhi *MP, const BasicBlock *BB,
+ MemoryAccess *NewDef) {
+ // Replace any operand with us an incoming block with the new defining
+ // access.
+ int i = MP->getBasicBlockIndex(BB);
+ assert(i != -1 && "Should have found the basic block in the phi");
+ while (MP->getIncomingBlock(i) == BB) {
+ // Unlike above, there is already a phi node here, so we only need
+ // to set the right value.
+ MP->setIncomingValue(i, NewDef);
+ ++i;
+ }
+}
+
+// A brief description of the algorithm:
+// First, we compute what should define the new def, using the SSA
+// construction algorithm.
+// Then, we update the defs below us (and any new phi nodes) in the graph to
+// point to the correct new defs, to ensure we only have one variable, and no
+// disconnected stores.
+void MemorySSAUpdater::insertDef(MemoryDef *MD) {
+ InsertedPHIs.clear();
+
+ // See if we had a local def, and if not, go hunting.
+ MemoryAccess *DefBefore = getPreviousDefInBlock(MD);
+ bool DefBeforeSameBlock = DefBefore != nullptr;
+ if (!DefBefore)
+ DefBefore = getPreviousDefRecursive(MD->getBlock());
+
+ // There is a def before us, which means we can replace any store/phi uses
+ // of that thing with us, since we are in the way of whatever was there
+ // before.
+ // We now define that def's memorydefs and memoryphis
+ for (auto UI = DefBefore->use_begin(), UE = DefBefore->use_end(); UI != UE;) {
+ Use &U = *UI++;
+ // Leave the uses alone
+ if (isa<MemoryUse>(U.getUser()))
+ continue;
+ U.set(MD);
+ }
+ // and that def is now our defining access.
+ // We change them in this order otherwise we will appear in the use list
+ // above and reset ourselves.
+ MD->setDefiningAccess(DefBefore);
+
+ SmallVector<MemoryAccess *, 8> FixupList(InsertedPHIs.begin(),
+ InsertedPHIs.end());
+ if (!DefBeforeSameBlock) {
+ // If there was a local def before us, we must have the same effect it
+ // did. Because every may-def is the same, any phis/etc we would create, it
+ // would also have created. If there was no local def before us, we
+ // performed a global update, and have to search all successors and make
+ // sure we update the first def in each of them (following all paths until
+ // we hit the first def along each path). This may also insert phi nodes.
+ // TODO: There are other cases we can skip this work, such as when we have a
+ // single successor, and only used a straight line of single pred blocks
+ // backwards to find the def. To make that work, we'd have to track whether
+ // getDefRecursive only ever used the single predecessor case. These types
+ // of paths also only exist in between CFG simplifications.
+ FixupList.push_back(MD);
+ }
+
+ while (!FixupList.empty()) {
+ unsigned StartingPHISize = InsertedPHIs.size();
+ fixupDefs(FixupList);
+ FixupList.clear();
+ // Put any new phis on the fixup list, and process them
+ FixupList.append(InsertedPHIs.end() - StartingPHISize, InsertedPHIs.end());
+ }
+}
+
+void MemorySSAUpdater::fixupDefs(const SmallVectorImpl<MemoryAccess *> &Vars) {
+ SmallPtrSet<const BasicBlock *, 8> Seen;
+ SmallVector<const BasicBlock *, 16> Worklist;
+ for (auto *NewDef : Vars) {
+ // First, see if there is a local def after the operand.
+ auto *Defs = MSSA->getWritableBlockDefs(NewDef->getBlock());
+ auto DefIter = NewDef->getDefsIterator();
+
+ // If there is a local def after us, we only have to rename that.
+ if (++DefIter != Defs->end()) {
+ cast<MemoryDef>(DefIter)->setDefiningAccess(NewDef);
+ continue;
+ }
+
+ // Otherwise, we need to search down through the CFG.
+ // For each of our successors, handle it directly if their is a phi, or
+ // place on the fixup worklist.
+ for (const auto *S : successors(NewDef->getBlock())) {
+ if (auto *MP = MSSA->getMemoryAccess(S))
+ setMemoryPhiValueForBlock(MP, NewDef->getBlock(), NewDef);
+ else
+ Worklist.push_back(S);
+ }
+
+ while (!Worklist.empty()) {
+ const BasicBlock *FixupBlock = Worklist.back();
+ Worklist.pop_back();
+
+ // Get the first def in the block that isn't a phi node.
+ if (auto *Defs = MSSA->getWritableBlockDefs(FixupBlock)) {
+ auto *FirstDef = &*Defs->begin();
+ // The loop above and below should have taken care of phi nodes
+ assert(!isa<MemoryPhi>(FirstDef) &&
+ "Should have already handled phi nodes!");
+ // We are now this def's defining access, make sure we actually dominate
+ // it
+ assert(MSSA->dominates(NewDef, FirstDef) &&
+ "Should have dominated the new access");
+
+ // This may insert new phi nodes, because we are not guaranteed the
+ // block we are processing has a single pred, and depending where the
+ // store was inserted, it may require phi nodes below it.
+ cast<MemoryDef>(FirstDef)->setDefiningAccess(getPreviousDef(FirstDef));
+ return;
+ }
+ // We didn't find a def, so we must continue.
+ for (const auto *S : successors(FixupBlock)) {
+ // If there is a phi node, handle it.
+ // Otherwise, put the block on the worklist
+ if (auto *MP = MSSA->getMemoryAccess(S))
+ setMemoryPhiValueForBlock(MP, FixupBlock, NewDef);
+ else {
+ // If we cycle, we should have ended up at a phi node that we already
+ // processed. FIXME: Double check this
+ if (!Seen.insert(S).second)
+ continue;
+ Worklist.push_back(S);
+ }
+ }
+ }
+ }
+}
+
+// Move What before Where in the MemorySSA IR.
+void MemorySSAUpdater::moveTo(MemoryUseOrDef *What, BasicBlock *BB,
+ MemorySSA::AccessList::iterator Where) {
+ // Replace all our users with our defining access.
+ What->replaceAllUsesWith(What->getDefiningAccess());
+
+ // Let MemorySSA take care of moving it around in the lists.
+ MSSA->moveTo(What, BB, Where);
+
+ // Now reinsert it into the IR and do whatever fixups needed.
+ if (auto *MD = dyn_cast<MemoryDef>(What))
+ insertDef(MD);
+ else
+ insertUse(cast<MemoryUse>(What));
+}
+// Move What before Where in the MemorySSA IR.
+void MemorySSAUpdater::moveBefore(MemoryUseOrDef *What, MemoryUseOrDef *Where) {
+ moveTo(What, Where->getBlock(), Where->getIterator());
+}
+
+// Move What after Where in the MemorySSA IR.
+void MemorySSAUpdater::moveAfter(MemoryUseOrDef *What, MemoryUseOrDef *Where) {
+ moveTo(What, Where->getBlock(), ++Where->getIterator());
+}
+
+} // namespace llvm