1 // Licensed to the .NET Foundation under one or more agreements.
2 // The .NET Foundation licenses this file to you under the MIT license.
3 // See the LICENSE file in the project root for more information.
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23 #include "ssaconfig.h"
24 #include "ssarenamestate.h"
25 #include "ssabuilder.h"
30 * Visits basic blocks in the depth first order and arranges them in the order of
31 * their DFS finish time.
33 * @param block The fgFirstBB or entry block.
34 * @param comp A pointer to compiler.
35 * @param visited In pointer initialized to false and of size at least fgMaxBBNum.
36 * @param count Out pointer for count of all nodes reachable by DFS.
37 * @param postOrder Out poitner to arrange the blocks and of size at least fgMaxBBNum.
39 static void TopologicalSortHelper(BasicBlock* block, Compiler* comp, bool* visited, int* count, BasicBlock** postOrder)
41 visited[block->bbNum] = true;
43 ArrayStack<BasicBlock *> blocks(comp);
44 ArrayStack<AllSuccessorIter> iterators(comp);
45 ArrayStack<AllSuccessorIter> ends(comp);
47 // there are three stacks used here and all should be same height
48 // the first is for blocks
49 // the second is the iterator to keep track of what succ of the block we are looking at
50 // and the third is the end marker iterator
52 iterators.Push(block->GetAllSuccs(comp).begin());
53 ends.Push(block->GetAllSuccs(comp).end());
55 while (blocks.Height() > 0)
62 printf("[SsaBuilder::TopologicalSortHelper] Visiting BB%02u: ", block->bbNum);
64 unsigned numSucc = block->NumSucc(comp);
65 for (unsigned i = 0; i < numSucc; ++i)
67 printf("BB%02u, ", block->GetSucc(i, comp)->bbNum);
69 EHSuccessorIter end = block->GetEHSuccs(comp).end();
70 for (EHSuccessorIter ehsi = block->GetEHSuccs(comp).begin(); ehsi != end; ++ehsi)
72 printf("[EH]BB%02u, ", (*ehsi)->bbNum);
78 if (iterators.TopRef() != ends.TopRef())
80 // if the block on TOS still has unreached successors, visit them
81 AllSuccessorIter& iter = iterators.TopRef();
82 BasicBlock* succ = *iter;
86 if (!visited[succ->bbNum])
89 iterators.Push(succ->GetAllSuccs(comp).begin());
90 ends.Push(succ->GetAllSuccs(comp).end());
91 visited[succ->bbNum] = true;
96 // all successors have been visited
101 postOrder[*count] = block;
102 block->bbPostOrderNum = *count;
105 DBG_SSA_JITDUMP("postOrder[%d] = [%p] and BB%02u\n", *count, dspPtr(block), block->bbNum);
111 * Method that finds a common IDom parent, much like least common ancestor.
113 * @param finger1 A basic block that might share IDom ancestor with finger2.
114 * @param finger2 A basic block that might share IDom ancestor with finger1.
116 * @see "A simple, fast dominance algorithm" by Keith D. Cooper, Timothy J. Harvey, Ken Kennedy.
118 * @return A basic block whose IDom is the dominator for finger1 and finger2,
119 * or else NULL. This may be called while immediate dominators are being
120 * computed, and if the input values are members of the same loop (each reachable from the other),
121 * then one may not yet have its immediate dominator computed when we are attempting
122 * to find the immediate dominator of the other. So a NULL return value means that the
123 * the two inputs are in a cycle, not that they don't have a common dominator ancestor.
125 static inline BasicBlock* IntersectDom(BasicBlock* finger1, BasicBlock* finger2)
127 while (finger1 != finger2)
129 if (finger1 == NULL || finger2 == NULL) return NULL;
130 while (finger1 != NULL && finger1->bbPostOrderNum < finger2->bbPostOrderNum)
132 finger1 = finger1->bbIDom;
134 if (finger1 == NULL) return NULL;
135 while (finger2 != NULL && finger2->bbPostOrderNum < finger1->bbPostOrderNum)
137 finger2 = finger2->bbIDom;
143 } // end of anonymous namespace.
145 // =================================================================================
147 // =================================================================================
149 void Compiler::fgSsaBuild()
151 IAllocator* pIAllocator = new (this, CMK_SSA) CompAllocator(this, CMK_SSA);
153 // If this is not the first invocation, reset data structures for SSA.
154 if (fgSsaPassesCompleted > 0)
157 SsaBuilder builder(this, pIAllocator);
159 fgSsaPassesCompleted++;
167 JITDUMP("\nAfter fgSsaBuild:\n");
168 fgDispBasicBlocks(/*dumpTrees*/true);
173 void Compiler::fgResetForSsa()
175 for (unsigned i = 0; i < lvaCount; ++i)
177 lvaTable[i].lvPerSsaData.Reset();
179 for (BasicBlock* blk = fgFirstBB; blk != nullptr; blk = blk->bbNext)
182 blk->bbHeapSsaPhiFunc = nullptr;
183 if (blk->bbTreeList != nullptr)
185 GenTreePtr last = blk->bbTreeList->gtPrev;
186 blk->bbTreeList = blk->FirstNonPhiDef();
187 if (blk->bbTreeList != nullptr)
188 blk->bbTreeList->gtPrev = last;
194 * Constructor for the SSA builder.
196 * @param pCompiler Current compiler instance.
198 * @remarks Initializes the class and member pointers/objects that use constructors.
200 SsaBuilder::SsaBuilder(Compiler* pCompiler, IAllocator* pIAllocator)
201 : m_pCompiler(pCompiler)
202 , m_allocator(pIAllocator)
204 #ifdef SSA_FEATURE_DOMARR
205 , m_pDomPreOrder(NULL)
206 , m_pDomPostOrder(NULL)
208 #ifdef SSA_FEATURE_USEDEF
209 , m_uses(jitstd::allocator<void>(pIAllocator))
210 , m_defs(jitstd::allocator<void>(pIAllocator))
216 * Topologically sort the graph and return the number of nodes visited.
218 * @param postOrder The array in which the arranged basic blocks have to be returned.
219 * @param count The size of the postOrder array.
221 * @return The number of nodes visited while performing DFS on the graph.
223 int SsaBuilder::TopologicalSort(BasicBlock** postOrder, int count)
225 // Allocate and initialize visited flags.
226 bool* visited = (bool*) alloca(count * sizeof(bool));
227 memset(visited, 0, count * sizeof(bool));
229 // Display basic blocks.
230 DBEXEC(VERBOSE, m_pCompiler->fgDispBasicBlocks());
231 DBEXEC(VERBOSE, m_pCompiler->fgDispHandlerTab());
233 // Call the recursive helper.
235 TopologicalSortHelper(m_pCompiler->fgFirstBB, m_pCompiler, visited, &postIndex, postOrder);
237 // In the absence of EH (because catch/finally have no preds), this should be valid.
238 // assert(postIndex == (count - 1));
244 * Computes the immediate dominator IDom for each block iteratively.
246 * @param postOrder The array of basic blocks arranged in postOrder.
247 * @param count The size of valid elements in the postOrder array.
249 * @see "A simple, fast dominance algorithm." paper.
251 void SsaBuilder::ComputeImmediateDom(BasicBlock** postOrder, int count)
253 JITDUMP("[SsaBuilder::ComputeImmediateDom]\n");
255 // TODO-Cleanup: We currently have two dominance computations happening. We should unify them; for
256 // now, at least forget the results of the first.
257 for (BasicBlock* blk = m_pCompiler->fgFirstBB; blk != NULL; blk = blk->bbNext)
262 // Add entry point to processed as its IDom is NULL.
263 BitVecTraits traits(m_pCompiler->fgBBNumMax + 1, m_pCompiler);
264 BitVec BITVEC_INIT_NOCOPY(processed, BitVecOps::MakeEmpty(&traits));
266 BitVecOps::AddElemD(&traits, processed, m_pCompiler->fgFirstBB->bbNum);
267 assert(postOrder[count - 1] == m_pCompiler->fgFirstBB);
274 // In reverse post order, except for the entry block (count - 1 is entry BB).
275 for (int i = count - 2; i >= 0; --i)
277 BasicBlock* block = postOrder[i];
279 DBG_SSA_JITDUMP("Visiting in reverse post order: BB%02u.\n", block->bbNum);
281 // Find the first processed predecessor block.
282 BasicBlock* predBlock = NULL;
283 for (flowList* pred = m_pCompiler->BlockPredsWithEH(block); pred; pred = pred->flNext)
285 if (BitVecOps::IsMember(&traits, processed, pred->flBlock->bbNum))
287 predBlock = pred->flBlock;
292 // There could just be a single basic block, so just check if there were any preds.
293 if (predBlock != NULL)
295 DBG_SSA_JITDUMP("Pred block is BB%02u.\n", predBlock->bbNum);
298 // Intersect DOM, if computed, for all predecessors.
299 BasicBlock* bbIDom = predBlock;
300 for (flowList* pred = m_pCompiler->BlockPredsWithEH(block); pred; pred = pred->flNext)
302 if (predBlock != pred->flBlock)
304 BasicBlock* domAncestor = IntersectDom(pred->flBlock, bbIDom);
305 // The result may be NULL if "block" and "pred->flBlock" are part of a
306 // cycle -- neither is guaranteed ordered wrt the other in reverse postorder,
307 // so we may be computing the IDom of "block" before the IDom of "pred->flBlock" has
308 // been computed. But that's OK -- if they're in a cycle, they share the same immediate
309 // dominator, so the contribution of "pred->flBlock" is not necessary to compute
311 if (domAncestor != NULL) bbIDom = domAncestor;
315 // Did we change the bbIDom value? If so, we go around the outer loop again.
316 if (block->bbIDom != bbIDom)
320 // IDom has changed, update it.
321 DBG_SSA_JITDUMP("bbIDom of BB%02u becomes BB%02u.\n", block->bbNum, bbIDom ? bbIDom->bbNum : 0);
322 block->bbIDom = bbIDom;
325 // Mark the current block as processed.
326 BitVecOps::AddElemD(&traits, processed, block->bbNum);
328 DBG_SSA_JITDUMP("Marking block BB%02u as processed.\n", block->bbNum);
333 #ifdef SSA_FEATURE_DOMARR
335 * Walk the DOM tree and compute pre and post-order arrangement of the tree.
337 * @param curBlock The current block being operated on at some recursive level.
338 * @param domTree The DOM tree as a map (block -> set of child blocks.)
339 * @param preIndex The initial index given to the first block visited in pre order.
340 * @param postIndex The initial index given to the first block visited in post order.
342 * @remarks This would help us answer queries such as "a dom b?" in constant time.
343 * For example, if a dominated b, then Pre[a] < Pre[b] but Post[a] > Post[b]
345 void SsaBuilder::DomTreeWalk(BasicBlock* curBlock, BlkToBlkSetMap* domTree, int* preIndex, int* postIndex)
347 JITDUMP("[SsaBuilder::DomTreeWalk] block [%p], BB%02u:\n", dspPtr(curBlock), curBlock->bbNum);
349 // Store the order number at the block number in the pre order list.
350 m_pDomPreOrder[curBlock->bbNum] = *preIndex;
354 if (domTree->Lookup(curBlock, &pBlkSet))
356 for (BlkSet::KeyIterator ki = pBlkSet->Begin(); !ki.Equal(pBlkSet->End()); ++ki)
358 if (curBlock != ki.Get())
360 DomTreeWalk(ki.Get(), domTree, preIndex, postIndex);
365 // Store the order number at the block number in the post order list.
366 m_pDomPostOrder[curBlock->bbNum] = *postIndex;
372 * Using IDom of each basic block, add a mapping from block->IDom -> block.
373 * @param pCompiler Compiler instance
374 * @param block The basic block that will become the child node of it's iDom.
375 * @param domTree The output domTree which will hold the mapping "block->bbIDom" -> "block"
379 void SsaBuilder::ConstructDomTreeForBlock(Compiler* pCompiler, BasicBlock* block, BlkToBlkSetMap* domTree)
381 BasicBlock* bbIDom = block->bbIDom;
383 // bbIDom for (only) fgFirstBB will be NULL.
389 // If the bbIDom map key doesn't exist, create one.
391 if (!domTree->Lookup(bbIDom, &pBlkSet))
393 pBlkSet = new (pCompiler->getAllocator()) BlkSet(pCompiler->getAllocator());
394 domTree->Set(bbIDom, pBlkSet);
397 DBG_SSA_JITDUMP("Inserting BB%02u as dom child of BB%02u.\n", block->bbNum, bbIDom->bbNum);
398 // Insert the block into the block's set.
399 pBlkSet->Set(block, true);
403 * Using IDom of each basic block, compute the whole tree. If a block "b" has IDom "i",
404 * then, block "b" is dominated by "i". The mapping then is i -> { ..., b, ... }, in
405 * other words, "domTree" is a tree represented by nodes mapped to their children.
407 * @param pCompiler Compiler instance
408 * @param domTree The output domTree which will hold the mapping "block->bbIDom" -> "block"
412 void SsaBuilder::ComputeDominators(Compiler* pCompiler, BlkToBlkSetMap* domTree)
414 JITDUMP("*************** In SsaBuilder::ComputeDominators(Compiler*, ...)\n");
416 // Construct the DOM tree from bbIDom
417 for (BasicBlock* block = pCompiler->fgFirstBB; block != NULL; block = block->bbNext)
419 ConstructDomTreeForBlock(pCompiler, block, domTree);
422 DBEXEC(pCompiler->verboseSsa, DisplayDominators(domTree));
426 * Compute the DOM tree into a map(block -> set of blocks) adjacency representation.
428 * Using IDom of each basic block, compute the whole tree. If a block "b" has IDom "i",
429 * then, block "b" is dominated by "i". The mapping then is i -> { ..., b, ... }
431 * @param postOrder The array of basic blocks arranged in postOrder.
432 * @param count The size of valid elements in the postOrder array.
433 * @param domTree A map of (block -> set of blocks) tree representation that is empty.
436 void SsaBuilder::ComputeDominators(BasicBlock** postOrder, int count, BlkToBlkSetMap* domTree)
438 JITDUMP("*************** In SsaBuilder::ComputeDominators(BasicBlock** postOrder, int count, ...)\n");
440 // Construct the DOM tree from bbIDom
441 for (int i = 0; i < count; ++i)
443 ConstructDomTreeForBlock(m_pCompiler, postOrder[i], domTree);
446 DBEXEC(m_pCompiler->verboseSsa, DisplayDominators(domTree));
448 #ifdef SSA_FEATURE_DOMARR
449 // Allocate space for constant time computation of (a DOM b?) query.
450 unsigned bbArrSize = m_pCompiler->fgBBNumMax + 1; // We will use 1-based bbNums as indices into these arrays, so
452 m_pDomPreOrder = jitstd::utility::allocate<int>(m_allocator, bbArrSize);
453 m_pDomPostOrder = jitstd::utility::allocate<int>(m_allocator, bbArrSize);
459 // Populate the pre and post order of the tree.
460 DomTreeWalk(m_pCompiler->fgFirstBB, domTree, &preIndex, &postIndex);
467 * Display the DOM tree.
469 * @param domTree A map of (block -> set of blocks) tree representation.
472 void SsaBuilder::DisplayDominators(BlkToBlkSetMap* domTree)
474 printf("After computing dominator tree: \n");
475 for (BlkToBlkSetMap::KeyIterator nodes = domTree->Begin(); !nodes.Equal(domTree->End()); ++nodes)
477 printf("BB%02u := {", nodes.Get()->bbNum);
479 BlkSet* pBlkSet = nodes.GetValue();
480 for (BlkSet::KeyIterator ki = pBlkSet->Begin(); !ki.Equal(pBlkSet->End()); ++ki)
482 if (!ki.Equal(pBlkSet->Begin()))
486 printf("BB%02u", ki.Get()->bbNum);
494 // (Spec comment at declaration.)
495 // See "A simple, fast dominance algorithm", by Cooper, Harvey, and Kennedy.
496 // First we compute the dominance frontier for each block, then we convert these to iterated
497 // dominance frontiers by a closure operation.
498 BlkToBlkSetMap* SsaBuilder::ComputeIteratedDominanceFrontier(BasicBlock** postOrder, int count)
500 BlkToBlkSetMap* frontier = new (m_pCompiler->getAllocator()) BlkToBlkSetMap(m_pCompiler->getAllocator());
502 DBG_SSA_JITDUMP("Computing IDF: First computing DF.\n");
504 for (int i = 0; i < count; ++i)
506 BasicBlock* block = postOrder[i];
508 DBG_SSA_JITDUMP("Considering block BB%02u.\n", block->bbNum);
510 // Recall that B3 is in the dom frontier of B1 if there exists a B2
511 // such that B1 dom B2, !(B1 dom B3), and B3 is an immediate successor
512 // of B2. (Note that B1 might be the same block as B2.)
513 // In that definition, we're considering "block" to be B3, and trying
514 // to find B1's. To do so, first we consider the predecessors of "block",
515 // searching for candidate B2's -- "block" is obviously an immediate successor
516 // of its immediate predecessors. If there are zero or one preds, then there
517 // is no pred, or else the single pred dominates "block", so no B2 exists.
519 flowList* blockPreds = m_pCompiler->BlockPredsWithEH(block);
521 // If block has more 0/1 predecessor, skip.
522 if (blockPreds == NULL || blockPreds->flNext == NULL)
524 DBG_SSA_JITDUMP(" Has %d preds; skipping.\n", blockPreds == NULL ? 0 : 1);
528 // Otherwise, there are > 1 preds. Each is a candidate B2 in the definition --
529 // *unless* it dominates "block"/B3.
531 for (flowList* pred = blockPreds; pred; pred = pred->flNext)
533 DBG_SSA_JITDUMP(" Considering predecessor BB%02u.\n", pred->flBlock->bbNum);
535 // If we've found a B2, then consider the possible B1's. We start with
536 // B2, since a block dominates itself, then traverse upwards in the dominator
537 // tree, stopping when we reach the root, or the immediate dominator of "block"/B3.
538 // (Note that we are guaranteed to encounter this immediate dominator of "block"/B3:
539 // a predecessor must be dominated by B3's immediate dominator.)
540 // Along this way, make "block"/B3 part of the dom frontier of the B1.
541 // When we reach this immediate dominator, the definition no longer applies, since this
542 // potential B1 *does* dominate "block"/B3, so we stop.
543 for (BasicBlock* b1 = pred->flBlock;
544 (b1 != NULL) && (b1 != block->bbIDom); // !root && !loop
547 DBG_SSA_JITDUMP(" Adding BB%02u to dom frontier of pred dom BB%02u.\n", block->bbNum, b1->bbNum);
549 if (!frontier->Lookup(b1, &pBlkSet))
551 pBlkSet = new (m_pCompiler->getAllocator()) BlkSet(m_pCompiler->getAllocator());
552 frontier->Set(b1, pBlkSet);
554 pBlkSet->Set(block, true);
560 if (m_pCompiler->verboseSsa)
562 printf("\nComputed DF:\n");
563 for (int i = 0; i < count; ++i)
565 BasicBlock* block = postOrder[i];
566 printf("Block BB%02u := {", block->bbNum);
570 if (frontier->Lookup(block, &blkDf))
572 for (BlkSet::KeyIterator blkDfIter = blkDf->Begin(); !blkDfIter.Equal(blkDf->End()); blkDfIter++)
578 printf("BB%02u", blkDfIter.Get()->bbNum);
587 // Now do the closure operation to make the dominance frontier into an IDF.
588 // There's probably a better way to do this...
589 BlkToBlkSetMap* idf = new (m_pCompiler->getAllocator()) BlkToBlkSetMap(m_pCompiler->getAllocator());
590 for (BlkToBlkSetMap::KeyIterator kiFrontBlks = frontier->Begin();
591 !kiFrontBlks.Equal(frontier->End()); kiFrontBlks++)
594 BlkSet* blkIdf = new (m_pCompiler->getAllocator()) BlkSet(m_pCompiler->getAllocator());
595 idf->Set(kiFrontBlks.Get(), blkIdf);
597 // Keep track of what got newly added to the IDF, so we can go after their DFs.
598 BlkSet* delta = new (m_pCompiler->getAllocator()) BlkSet(m_pCompiler->getAllocator());
599 delta->Set(kiFrontBlks.Get(), true);
601 // Now transitively add DF+(delta) to IDF(b), each step gathering new "delta."
602 while (delta->GetCount() > 0)
604 // Extract a block x to be worked on.
605 BlkSet::KeyIterator ki = delta->Begin();
606 BasicBlock* curBlk = ki.Get();
607 // TODO-Cleanup: Remove(ki) doesn't work correctly in SimplerHash.
608 delta->Remove(curBlk);
612 if (frontier->Lookup(curBlk, &blkDf))
614 // Add DF(x) to IDF(b) and update "delta" i.e., new additions to IDF(b).
615 for (BlkSet::KeyIterator ki = blkDf->Begin(); !ki.Equal(blkDf->End()); ki++)
617 if (!blkIdf->Lookup(ki.Get()))
619 delta->Set(ki.Get(), true);
620 blkIdf->Set(ki.Get(), true);
628 if (m_pCompiler->verboseSsa)
630 printf("\nComputed IDF:\n");
631 for (int i = 0; i < count; ++i)
633 BasicBlock* block = postOrder[i];
634 printf("Block BB%02u := {", block->bbNum);
638 if (idf->Lookup(block, &blkIdf))
640 for (BlkSet::KeyIterator ki = blkIdf->Begin(); !ki.Equal(blkIdf->End()); ki++)
646 printf("BB%02u", ki.Get()->bbNum);
659 * Returns the phi GT_PHI node if the variable already has a phi node.
661 * @param block The block for which the existence of a phi node needs to be checked.
662 * @param lclNum The lclNum for which the occurrence of a phi node needs to be checked.
664 * @return If there is a phi node for the lclNum, returns the GT_PHI tree, else NULL.
666 static GenTree* GetPhiNode(BasicBlock* block, unsigned lclNum)
668 // Walk the statements for phi nodes.
669 for (GenTreePtr stmt = block->bbTreeList; stmt; stmt = stmt->gtNext)
671 // A prefix of the statements of the block are phi definition nodes. If we complete processing
672 // that prefix, exit.
673 if (!stmt->IsPhiDefnStmt()) break;
675 GenTreePtr tree = stmt->gtStmt.gtStmtExpr;
677 GenTreePtr phiLhs = tree->gtOp.gtOp1;
678 assert(phiLhs->OperGet() == GT_LCL_VAR);
679 if (phiLhs->gtLclVarCommon.gtLclNum == lclNum)
681 return tree->gtOp.gtOp2;
688 * Inserts phi functions at DF(b) for variables v that are live after the phi
689 * insertion point i.e., v in live-in(b).
691 * To do so, the function computes liveness, dominance frontier and inserts a phi node,
692 * if we have var v in def(b) and live-in(l) and l is in DF(b).
694 * @param postOrder The array of basic blocks arranged in postOrder.
695 * @param count The size of valid elements in the postOrder array.
697 void SsaBuilder::InsertPhiFunctions(BasicBlock** postOrder, int count)
699 JITDUMP("*************** In SsaBuilder::InsertPhiFunctions()\n");
701 // Compute liveness on the graph.
702 m_pCompiler->fgLocalVarLiveness();
703 EndPhase(PHASE_BUILD_SSA_LIVENESS);
705 // Compute dominance frontier.
706 BlkToBlkSetMap* frontier = ComputeIteratedDominanceFrontier(postOrder, count);
707 EndPhase(PHASE_BUILD_SSA_IDF);
709 JITDUMP("Inserting phi functions:\n");
711 for (int i = 0; i < count; ++i)
713 BasicBlock* block = postOrder[i];
714 DBG_SSA_JITDUMP("Considering dominance frontier of block BB%02u:\n", block->bbNum);
716 // If the block's dominance frontier is empty, go on to the next block.
718 if (!frontier->Lookup(block, &blkIdf))
723 // For each local var number "lclNum" that "block" assigns to...
724 VARSET_ITER_INIT(m_pCompiler, defVars, block->bbVarDef, varIndex);
725 while (defVars.NextElem(m_pCompiler, &varIndex))
727 unsigned lclNum = m_pCompiler->lvaTrackedToVarNum[varIndex];
728 DBG_SSA_JITDUMP(" Considering local var V%02u:\n", lclNum);
730 if (m_pCompiler->fgExcludeFromSsa(lclNum))
732 DBG_SSA_JITDUMP(" Skipping because it is excluded.\n");
737 // For each block "bbInDomFront" that is in the dominance frontier of "block"...
738 for (BlkSet::KeyIterator iterBlk = blkIdf->Begin(); !iterBlk.Equal(blkIdf->End()); ++iterBlk)
740 BasicBlock* bbInDomFront = iterBlk.Get();
741 DBG_SSA_JITDUMP(" Considering BB%02u in dom frontier of BB%02u:\n", bbInDomFront->bbNum, block->bbNum);
743 // Check if variable "lclNum" is live in block "*iterBlk".
744 if (!VarSetOps::IsMember(m_pCompiler, bbInDomFront->bbLiveIn, varIndex))
749 // Check if we've already inserted a phi node.
750 if (GetPhiNode(bbInDomFront, lclNum) == NULL)
752 // We have a variable i that is defined in block j and live at l, and l belongs to dom frontier of
753 // j. So insert a phi node at l.
754 JITDUMP("Inserting phi definition for V%02u at start of BB%02u.\n", lclNum, bbInDomFront->bbNum);
756 GenTreePtr phiLhs = m_pCompiler->gtNewLclvNode(lclNum, m_pCompiler->lvaTable[lclNum].TypeGet());
758 // Create 'phiRhs' as a GT_PHI node for 'lclNum', it will eventually hold a GT_LIST of GT_PHI_ARG
759 // nodes. However we have to construct this list so for now the gtOp1 of 'phiRhs' is a nullptr.
760 // It will get replaced with a GT_LIST of GT_PHI_ARG nodes in
761 // SsaBuilder::AssignPhiNodeRhsVariables() and in SsaBuilder::AddDefToHandlerPhis()
763 GenTreePtr phiRhs = m_pCompiler->gtNewOperNode(GT_PHI, m_pCompiler->lvaTable[lclNum].TypeGet(), nullptr);
765 GenTreePtr phiAsg = m_pCompiler->gtNewAssignNode(phiLhs, phiRhs);
767 GenTreePtr stmt = m_pCompiler->fgInsertStmtAtBeg(bbInDomFront, phiAsg);
768 m_pCompiler->gtSetStmtInfo(stmt);
769 m_pCompiler->fgSetStmtSeq(stmt);
774 // Now make a similar phi definition if the block defines Heap.
775 if (block->bbHeapDef)
777 // For each block "bbInDomFront" that is in the dominance frontier of "block".
778 for (BlkSet::KeyIterator iterBlk = blkIdf->Begin(); !iterBlk.Equal(blkIdf->End()); ++iterBlk)
780 BasicBlock* bbInDomFront = iterBlk.Get();
781 DBG_SSA_JITDUMP(" Considering BB%02u in dom frontier of BB%02u for Heap phis:\n", bbInDomFront->bbNum, block->bbNum);
783 // Check if Heap is live into block "*iterBlk".
784 if (!bbInDomFront->bbHeapLiveIn)
787 // Check if we've already inserted a phi node.
788 if (bbInDomFront->bbHeapSsaPhiFunc == NULL)
790 // We have a variable i that is defined in block j and live at l, and l belongs to dom frontier of
791 // j. So insert a phi node at l.
792 JITDUMP("Inserting phi definition for Heap at start of BB%02u.\n", bbInDomFront->bbNum);
793 bbInDomFront->bbHeapSsaPhiFunc = BasicBlock::EmptyHeapPhiDef;
798 EndPhase(PHASE_BUILD_SSA_INSERT_PHIS);
801 #ifdef SSA_FEATURE_USEDEF
803 * Record a use point of a variable.
805 * The use point is just the tree that is a local variable use.
807 * @param tree Tree node where an SSA variable is used.
809 * @remarks The result is in the m_uses map :: [lclNum, ssaNum] -> tree.
811 void SsaBuilder::AddUsePoint(GenTree* tree)
813 assert(tree->IsLocal());
814 SsaVarName key(tree->gtLclVarCommon.gtLclNum, tree->gtLclVarCommon.gtSsaNum);
815 VarToUses::iterator iter = m_uses.find(key);
816 if (iter == m_uses.end())
818 iter = m_uses.insert(key, VarToUses::mapped_type(m_uses.get_allocator()));
820 (*iter).second.push_back(tree);
822 #endif // !SSA_FEATURE_USEDEF
825 * Record a def point of a variable.
827 * The def point is just the tree that is a local variable def.
829 * @param tree Tree node where an SSA variable is def'ed.
831 * @remarks The result is in the m_defs map :: [lclNum, ssaNum] -> tree.
833 void SsaBuilder::AddDefPoint(GenTree* tree, BasicBlock* blk)
835 Compiler::IndirectAssignmentAnnotation* pIndirAnnot;
836 // In the case of an "indirect assignment", where the LHS is IND of a byref to the local actually being assigned,
837 // we make the ASG tree the def point.
838 assert(tree->IsLocal() || IsIndirectAssign(tree, &pIndirAnnot));
843 lclNum = tree->gtLclVarCommon.gtLclNum;
844 defSsaNum = m_pCompiler->GetSsaNumForLocalVarDef(tree);
848 bool b = m_pCompiler->GetIndirAssignMap()->Lookup(tree, &pIndirAnnot);
850 lclNum = pIndirAnnot->m_lclNum;
851 defSsaNum = pIndirAnnot->m_defSsaNum;
854 // Record that there's a new SSA def.
855 m_pCompiler->lvaTable[lclNum].lvNumSsaNames++;
857 // Record where the defn happens.
858 LclSsaVarDsc* ssaDef = m_pCompiler->lvaTable[lclNum].GetPerSsaData(defSsaNum);
859 ssaDef->m_defLoc.m_blk = blk;
860 ssaDef->m_defLoc.m_tree = tree;
862 #ifdef SSA_FEATURE_USEDEF
863 SsaVarName key(lclNum, defSsaNum);
864 VarToDef::iterator iter = m_defs.find(key);
865 if (iter == m_defs.end())
867 iter = m_defs.insert(key, tree);
870 // There can only be a single definition for an SSA var.
875 bool SsaBuilder::IsIndirectAssign(GenTreePtr tree, Compiler::IndirectAssignmentAnnotation** ppIndirAssign)
877 return tree->OperGet() == GT_ASG && m_pCompiler->m_indirAssignMap != NULL && m_pCompiler->GetIndirAssignMap()->Lookup(tree, ppIndirAssign);
881 * Rename the local variable tree node.
883 * If the given tree node is a local variable, then for a def give a new count, if use,
884 * then give the count in the top of stack, i.e., current count (used for last def.)
886 * @param tree Tree node where an SSA variable is used or def'ed.
887 * @param pRenameState The incremental rename information stored during renaming process.
889 * @remarks This method has to maintain parity with TreePopStacks corresponding to pushes
892 void SsaBuilder::TreeRenameVariables(GenTree* tree, BasicBlock* block, SsaRenameState* pRenameState, bool isPhiDefn)
894 // This is perhaps temporary -- maybe should be done elsewhere. Label GT_INDs on LHS of assignments, so we
895 // can skip these during (at least) value numbering.
896 if (tree->OperIsAssignment())
898 GenTreePtr lhs = tree->gtOp.gtOp1->gtEffectiveVal(/*commaOnly*/true);
899 GenTreePtr trueLhs = lhs->gtEffectiveVal(/*commaOnly*/true);
900 if (trueLhs->OperGet() == GT_IND)
902 trueLhs->gtFlags |= GTF_IND_ASG_LHS;
904 else if (trueLhs->OperGet() == GT_CLS_VAR)
906 trueLhs->gtFlags |= GTF_CLS_VAR_ASG_LHS;
910 // Figure out if "tree" may make a new heap state (if we care for this block).
911 if (!block->bbHeapHavoc)
913 if (tree->OperIsAssignment() ||
916 if (m_pCompiler->ehBlockHasExnFlowDsc(block))
918 GenTreeLclVarCommon* lclVarNode;
919 if (!tree->DefinesLocal(m_pCompiler, &lclVarNode))
921 // It *may* define the heap in a non-havoc way. Make a new SSA # -- associate with this node.
922 unsigned count = pRenameState->CountForHeapDef();
923 pRenameState->PushHeap(block, count);
924 m_pCompiler->GetHeapSsaMap()->Set(tree, count);
926 if (JitTls::GetCompiler()->verboseSsa)
929 Compiler::printTreeID(tree);
930 printf(" (in try block) may define heap; ssa # = %d.\n", count);
934 // Now add this SSA # to all phis of the reachable catch blocks.
935 AddHeapDefToHandlerPhis(block, count);
941 Compiler::IndirectAssignmentAnnotation* pIndirAssign = NULL;
942 if (!tree->IsLocal() && !IsIndirectAssign(tree, &pIndirAssign))
947 if (pIndirAssign != NULL)
949 unsigned lclNum = pIndirAssign->m_lclNum;
950 // Is this a variable we exclude from SSA?
951 if (m_pCompiler->fgExcludeFromSsa(lclNum))
953 pIndirAssign->m_defSsaNum = SsaConfig::RESERVED_SSA_NUM;
957 if (!pIndirAssign->m_isEntire)
959 pIndirAssign->m_useSsaNum = pRenameState->CountForUse(lclNum);
961 unsigned count = pRenameState->CountForDef(lclNum);
962 pIndirAssign->m_defSsaNum = count;
963 pRenameState->Push(block, lclNum, count);
964 AddDefPoint(tree, block);
968 unsigned lclNum = tree->gtLclVarCommon.gtLclNum;
969 // Is this a variable we exclude from SSA?
970 if (m_pCompiler->fgExcludeFromSsa(lclNum))
972 tree->gtLclVarCommon.SetSsaNum(SsaConfig::RESERVED_SSA_NUM);
976 if (tree->gtFlags & GTF_VAR_DEF)
978 if (tree->gtFlags & GTF_VAR_USEASG)
980 // This the "x" in something like "x op= y"; it is both a use (first), then a def.
981 // The def will define a new SSA name, and record that in "x". If we need the SSA
982 // name of the use, we record it in a map reserved for that purpose.
983 unsigned count = pRenameState->CountForUse(lclNum);
984 tree->gtLclVarCommon.SetSsaNum(count);
985 #ifdef SSA_FEATURE_USEDEF
990 // Give a count and increment.
991 unsigned count = pRenameState->CountForDef(lclNum);
992 if (tree->gtFlags & GTF_VAR_USEASG)
994 m_pCompiler->GetOpAsgnVarDefSsaNums()->Set(tree, count);
998 tree->gtLclVarCommon.SetSsaNum(count);
1000 pRenameState->Push(block, lclNum, count);
1001 AddDefPoint(tree, block);
1003 // If necessary, add "lclNum/count" to the arg list of a phi def in any
1004 // handlers for try blocks that "block" is within. (But only do this for "real" definitions,
1005 // not phi definitions.)
1007 AddDefToHandlerPhis(block, lclNum, count);
1009 else if (!isPhiDefn) // Phi args already have ssa numbers.
1011 // This case is obviated by the short-term "early-out" above...but it's in the right direction.
1012 // Is it a promoted struct local?
1013 if (m_pCompiler->lvaTable[lclNum].lvPromoted)
1015 assert(tree->TypeGet() == TYP_STRUCT);
1016 LclVarDsc* varDsc = &m_pCompiler->lvaTable[lclNum];
1017 // If has only a single field var, treat this as a use of that field var.
1018 // Otherwise, we don't give SSA names to uses of promoted struct vars.
1019 if (varDsc->lvFieldCnt == 1)
1021 lclNum = varDsc->lvFieldLclStart;
1025 tree->gtLclVarCommon.SetSsaNum(SsaConfig::RESERVED_SSA_NUM);
1029 // Give the count as top of stack.
1030 unsigned count = pRenameState->CountForUse(lclNum);
1031 tree->gtLclVarCommon.SetSsaNum(count);
1032 #ifdef SSA_FEATURE_USEDEF
1039 void SsaBuilder::AddDefToHandlerPhis(BasicBlock* block, unsigned lclNum, unsigned count)
1041 assert(m_pCompiler->lvaTable[lclNum].lvTracked); // Precondition.
1042 unsigned lclIndex = m_pCompiler->lvaTable[lclNum].lvVarIndex;
1044 EHblkDsc* tryBlk = m_pCompiler->ehGetBlockExnFlowDsc(block);
1045 if (tryBlk != nullptr)
1047 DBG_SSA_JITDUMP("Definition of local V%02u/d:%d in block BB%02u has exn handler; adding as phi arg to handlers.\n", lclNum, count, block->bbNum);
1050 BasicBlock* handler = tryBlk->ExFlowBlock();
1052 // Is "lclNum" live on entry to the handler?
1053 if (VarSetOps::IsMember(m_pCompiler, handler->bbLiveIn, lclIndex))
1056 bool phiFound = false;
1058 // A prefix of blocks statements will be SSA definitions. Search those for "lclNum".
1059 for (GenTreePtr stmt = handler->bbTreeList; stmt; stmt = stmt->gtNext)
1061 // If the tree is not an SSA def, break out of the loop: we're done.
1062 if (!stmt->IsPhiDefnStmt()) break;
1064 GenTreePtr tree = stmt->gtStmt.gtStmtExpr;
1066 assert(tree->IsPhiDefn());
1068 if (tree->gtOp.gtOp1->gtLclVar.gtLclNum == lclNum)
1070 // It's the definition for the right local. Add "count" to the RHS.
1071 GenTreePtr phi = tree->gtOp.gtOp2;
1072 GenTreeArgList* args = NULL;
1073 if (phi->gtOp.gtOp1 != NULL) args = phi->gtOp.gtOp1->AsArgList();
1075 // Make sure it isn't already present: we should only add each definition once.
1076 for (GenTreeArgList* curArgs = args; curArgs != NULL; curArgs = curArgs->Rest())
1078 GenTreePhiArg* phiArg = curArgs->Current()->AsPhiArg();
1079 assert(phiArg->gtSsaNum != count);
1082 var_types typ = m_pCompiler->lvaTable[lclNum].TypeGet();
1083 GenTreePhiArg* newPhiArg =
1084 new (m_pCompiler, GT_PHI_ARG) GenTreePhiArg(typ, lclNum, count, block);
1086 phi->gtOp.gtOp1 = new (m_pCompiler, GT_LIST) GenTreeArgList(newPhiArg, args );
1087 m_pCompiler->gtSetStmtInfo(stmt);
1088 m_pCompiler->fgSetStmtSeq(stmt);
1092 DBG_SSA_JITDUMP(" Added phi arg u:%d for V%02u to phi defn in handler block BB%02u.\n", count, lclNum, handler->bbNum);
1099 unsigned nextTryIndex = tryBlk->ebdEnclosingTryIndex;
1100 if (nextTryIndex == EHblkDsc::NO_ENCLOSING_INDEX)
1105 tryBlk = m_pCompiler->ehGetDsc(nextTryIndex);
1110 void SsaBuilder::AddHeapDefToHandlerPhis(BasicBlock* block, unsigned count)
1112 if (m_pCompiler->ehBlockHasExnFlowDsc(block))
1114 // Don't do anything for a compiler-inserted BBJ_ALWAYS that is a "leave helper".
1115 if ( block->bbJumpKind == BBJ_ALWAYS
1116 && (block->bbFlags & BBF_INTERNAL)
1117 && (block->bbPrev->isBBCallAlwaysPair()))
1121 DBG_SSA_JITDUMP("Definition of Heap/d:%d in block BB%02u has exn handler; adding as phi arg to handlers.\n", count, block->bbNum);
1122 EHblkDsc* tryBlk = m_pCompiler->ehGetBlockExnFlowDsc(block);
1125 BasicBlock* handler = tryBlk->ExFlowBlock();
1127 // Is Heap live on entry to the handler?
1128 if (handler->bbHeapLiveIn)
1130 assert(handler->bbHeapSsaPhiFunc != NULL);
1132 // Add "count" to the phi args of Heap.
1133 if (handler->bbHeapSsaPhiFunc == BasicBlock::EmptyHeapPhiDef)
1135 handler->bbHeapSsaPhiFunc = new (m_pCompiler) BasicBlock::HeapPhiArg(count);
1140 BasicBlock::HeapPhiArg* curArg = handler->bbHeapSsaPhiFunc;
1141 while (curArg != NULL)
1143 assert(curArg->GetSsaNum() != count);
1144 curArg = curArg->m_nextArg;
1147 handler->bbHeapSsaPhiFunc = new (m_pCompiler) BasicBlock::HeapPhiArg(count, handler->bbHeapSsaPhiFunc);
1150 DBG_SSA_JITDUMP(" Added phi arg u:%d for Heap to phi defn in handler block BB%02u.\n", count, handler->bbNum);
1152 unsigned tryInd = tryBlk->ebdEnclosingTryIndex;
1153 if (tryInd == EHblkDsc::NO_ENCLOSING_INDEX)
1157 tryBlk = m_pCompiler->ehGetDsc(tryInd);
1163 * Walk the block's tree in the evaluation order and give var definitions and uses their
1166 * @param block Block for which SSA variables have to be renamed.
1167 * @param pRenameState The incremental rename information stored during renaming process.
1170 void SsaBuilder::BlockRenameVariables(BasicBlock* block, SsaRenameState* pRenameState)
1172 // Walk the statements of the block and rename the tree variables.
1174 // First handle the incoming Heap state.
1176 // Is there an Phi definition for heap at the start of this block?
1177 if (block->bbHeapSsaPhiFunc != NULL)
1179 unsigned count = pRenameState->CountForHeapDef();
1180 pRenameState->PushHeap(block, count);
1182 DBG_SSA_JITDUMP("Ssa # for Heap phi on entry to BB%02u is %d.\n", block->bbNum, count);
1185 // Record the "in" Ssa # for Heap.
1186 block->bbHeapSsaNumIn = pRenameState->CountForHeapUse();
1189 // We need to iterate over phi definitions, to give them SSA names, but we need
1190 // to know which are which, so we don't add phi definitions to handler phi arg lists.
1191 // Statements are phi defns until they aren't.
1192 bool isPhiDefn = true;
1193 GenTreePtr firstNonPhi = block->FirstNonPhiDef();
1194 for (GenTreePtr stmt = block->bbTreeList; stmt; stmt = stmt->gtNext)
1196 if (stmt == firstNonPhi) isPhiDefn = false;
1198 for (GenTreePtr tree = stmt->gtStmt.gtStmtList; tree; tree = tree->gtNext)
1200 TreeRenameVariables(tree, block, pRenameState, isPhiDefn);
1204 // Now handle the final heap state.
1206 // If the block defines Heap, allocate an SSA variable for the final heap state in the block.
1207 // (This may be redundant with the last SSA var explicitly created, but there's no harm in that.)
1208 if (block->bbHeapDef)
1210 unsigned count = pRenameState->CountForHeapDef();
1211 pRenameState->PushHeap(block, count);
1212 AddHeapDefToHandlerPhis(block, count);
1215 // Record the "out" Ssa" # for Heap.
1216 block->bbHeapSsaNumOut = pRenameState->CountForHeapUse();
1218 DBG_SSA_JITDUMP("Ssa # for Heap on entry to BB%02u is %d; on exit is %d.\n",
1219 block->bbNum, block->bbHeapSsaNumIn, block->bbHeapSsaNumOut);
1223 * Walk through the phi nodes of a given block and assign rhs variables to them.
1225 * Also renumber the rhs variables from top of the stack.
1227 * @param block Block for which phi nodes have to be assigned their rhs arguments.
1228 * @param pRenameState The incremental rename information stored during renaming process.
1231 void SsaBuilder::AssignPhiNodeRhsVariables(BasicBlock* block, SsaRenameState* pRenameState)
1233 BasicBlock::AllSuccs allSuccs = block->GetAllSuccs(m_pCompiler);
1234 AllSuccessorIter allSuccsEnd = allSuccs.end();
1235 for (AllSuccessorIter allSuccsIter = allSuccs.begin(); allSuccsIter != allSuccsEnd; ++allSuccsIter)
1237 BasicBlock* succ = (*allSuccsIter);
1238 // Walk the statements for phi nodes.
1239 for (GenTreePtr stmt = succ->bbTreeList; stmt != nullptr && stmt->IsPhiDefnStmt(); stmt = stmt->gtNext)
1241 GenTreePtr tree = stmt->gtStmt.gtStmtExpr;
1242 assert(tree->IsPhiDefn());
1244 // Get the phi node from GT_ASG.
1245 GenTreePtr phiNode = tree->gtOp.gtOp2;
1246 assert(phiNode->gtOp.gtOp1 == NULL || phiNode->gtOp.gtOp1->OperGet() == GT_LIST);
1248 unsigned lclNum = tree->gtOp.gtOp1->gtLclVar.gtLclNum;
1249 unsigned ssaNum = pRenameState->CountForUse(lclNum);
1250 // Search the arglist for an existing definition for ssaNum.
1251 // (Can we assert that its the head of the list? This should only happen when we add
1252 // during renaming for a definition that occurs within a try, and then that's the last
1253 // value of the var within that basic block.)
1254 GenTreeArgList* argList = (phiNode->gtOp.gtOp1 == nullptr ? nullptr : phiNode->gtOp.gtOp1->AsArgList());
1256 while (argList != nullptr)
1258 if (argList->Current()->AsLclVarCommon()->GetSsaNum() == ssaNum)
1263 argList = argList->Rest();
1267 GenTreePtr newPhiArg = new (m_pCompiler, GT_PHI_ARG) GenTreePhiArg(tree->gtOp.gtOp1->TypeGet(), lclNum, ssaNum, block);
1268 argList = (phiNode->gtOp.gtOp1 == nullptr ? nullptr : phiNode->gtOp.gtOp1->AsArgList());
1269 phiNode->gtOp.gtOp1 = new (m_pCompiler, GT_LIST) GenTreeArgList(newPhiArg, argList);
1270 DBG_SSA_JITDUMP(" Added phi arg u:%d for V%02u from BB%02u in BB%02u.\n", ssaNum, lclNum, block->bbNum, succ->bbNum);
1273 m_pCompiler->gtSetStmtInfo(stmt);
1274 m_pCompiler->fgSetStmtSeq(stmt);
1278 if (succ->bbHeapSsaPhiFunc != NULL)
1280 if (succ->bbHeapSsaPhiFunc == BasicBlock::EmptyHeapPhiDef)
1282 succ->bbHeapSsaPhiFunc = new (m_pCompiler) BasicBlock::HeapPhiArg(block);
1286 BasicBlock::HeapPhiArg* curArg = succ->bbHeapSsaPhiFunc;
1288 // This is a quadratic algorithm. We might need to consider some switch over to a hash table
1289 // representation for the arguments of a phi node, to make this linear.
1290 while (curArg != NULL)
1292 if (curArg->m_predBB == block)
1297 curArg = curArg->m_nextArg;
1301 succ->bbHeapSsaPhiFunc = new (m_pCompiler) BasicBlock::HeapPhiArg(block, succ->bbHeapSsaPhiFunc);
1304 DBG_SSA_JITDUMP(" Added phi arg for Heap from BB%02u in BB%02u.\n", block->bbNum, succ->bbNum);
1307 // If "succ" is the first block of a try block (and "block" is not also in that try block)
1308 // then we must look at the vars that have phi defs in the corresponding handler;
1309 // the current SSA name for such vars must be included as an argument to that phi.
1310 if (m_pCompiler->bbIsTryBeg(succ))
1312 assert(succ->hasTryIndex());
1313 unsigned tryInd = succ->getTryIndex();
1315 while (tryInd != EHblkDsc::NO_ENCLOSING_INDEX)
1317 // Check if the predecessor "block" is within the same try block.
1318 if (block->hasTryIndex())
1320 for (unsigned blockTryInd = block->getTryIndex();
1321 blockTryInd != EHblkDsc::NO_ENCLOSING_INDEX;
1322 blockTryInd = m_pCompiler->ehGetEnclosingTryIndex(blockTryInd))
1324 if (blockTryInd == tryInd)
1326 // It is; don't execute the loop below.
1327 tryInd = EHblkDsc::NO_ENCLOSING_INDEX;
1332 // The loop just above found that the predecessor "block" is within the same
1333 // try block as "succ." So we don't need to process this try, or any
1334 // further outer try blocks here, since they would also contain both "succ"
1336 if (tryInd == EHblkDsc::NO_ENCLOSING_INDEX)
1341 EHblkDsc* succTry = m_pCompiler->ehGetDsc(tryInd);
1342 // This is necessarily true on the first iteration, but not
1343 // necessarily on the second and subsequent.
1344 if (succTry->ebdTryBeg != succ)
1347 // succ is the first block of this try. Look at phi defs in the handler.
1348 // For a filter, we consider the filter to be the "real" handler.
1349 BasicBlock* handlerStart = succTry->ExFlowBlock();
1351 for (GenTreePtr stmt = handlerStart->bbTreeList; stmt; stmt = stmt->gtNext)
1353 GenTreePtr tree = stmt->gtStmt.gtStmtExpr;
1355 // Check if the first n of the statements are phi nodes. If not, exit.
1356 if (tree->OperGet() != GT_ASG ||
1357 tree->gtOp.gtOp2 == NULL || tree->gtOp.gtOp2->OperGet() != GT_PHI)
1362 // Get the phi node from GT_ASG.
1363 GenTreePtr lclVar = tree->gtOp.gtOp1;
1364 unsigned lclNum = lclVar->gtLclVar.gtLclNum;
1366 // If the variable is live-out of "blk", and is therefore live on entry to the try-block-start
1367 // "succ", then we make sure the current SSA name for the
1368 // var is one of the args of the phi node. If not, go on.
1369 LclVarDsc* lclVarDsc = &m_pCompiler->lvaTable[lclNum];
1370 if (!lclVarDsc->lvTracked || !VarSetOps::IsMember(m_pCompiler, block->bbLiveOut, lclVarDsc->lvVarIndex)) continue;
1372 GenTreePtr phiNode = tree->gtOp.gtOp2;
1373 assert(phiNode->gtOp.gtOp1 == NULL || phiNode->gtOp.gtOp1->OperGet() == GT_LIST);
1374 GenTreeArgList* argList = reinterpret_cast<GenTreeArgList*>(phiNode->gtOp.gtOp1);
1376 // What is the current SSAName from the predecessor for this local?
1377 unsigned ssaNum = pRenameState->CountForUse(lclNum);
1379 // See if this ssaNum is already an arg to the phi.
1380 bool alreadyArg = false;
1381 for (GenTreeArgList* curArgs = argList; curArgs != NULL; curArgs = curArgs->Rest())
1383 if (curArgs->Current()->gtPhiArg.gtSsaNum == ssaNum)
1391 // Add the new argument.
1392 GenTreePtr newPhiArg =
1393 new (m_pCompiler, GT_PHI_ARG) GenTreePhiArg(lclVar->TypeGet(), lclNum, ssaNum, block);
1394 phiNode->gtOp.gtOp1 =
1395 new (m_pCompiler, GT_LIST) GenTreeArgList(newPhiArg, argList );
1397 DBG_SSA_JITDUMP(" Added phi arg u:%d for V%02u from BB%02u in BB%02u.\n", ssaNum, lclNum, block->bbNum, handlerStart->bbNum);
1399 m_pCompiler->gtSetStmtInfo(stmt);
1400 m_pCompiler->fgSetStmtSeq(stmt);
1405 if (handlerStart->bbHeapSsaPhiFunc != NULL)
1407 if (handlerStart->bbHeapSsaPhiFunc == BasicBlock::EmptyHeapPhiDef)
1409 handlerStart->bbHeapSsaPhiFunc = new (m_pCompiler) BasicBlock::HeapPhiArg(block);
1414 BasicBlock::HeapPhiArg* curArg = handlerStart->bbHeapSsaPhiFunc;
1415 while (curArg != NULL)
1417 assert(curArg->m_predBB != block);
1418 curArg = curArg->m_nextArg;
1421 handlerStart->bbHeapSsaPhiFunc = new (m_pCompiler) BasicBlock::HeapPhiArg(block, handlerStart->bbHeapSsaPhiFunc);
1423 DBG_SSA_JITDUMP(" Added phi arg for Heap from BB%02u in BB%02u.\n", block->bbNum, handlerStart->bbNum);
1426 tryInd = succTry->ebdEnclosingTryIndex;
1433 * Walk the block's tree in the evaluation order and reclaim rename stack for var definitions.
1435 * @param block Block for which SSA variables have to be renamed.
1436 * @param pRenameState The incremental rename information stored during renaming process.
1439 void SsaBuilder::BlockPopStacks(BasicBlock* block, SsaRenameState* pRenameState)
1441 // Pop the names given to the non-phi nodes.
1442 pRenameState->PopBlockStacks(block);
1445 pRenameState->PopBlockHeapStack(block);
1449 * Perform variable renaming.
1451 * Walks the blocks and renames all var defs with ssa numbers and all uses with the
1452 * current count that is in the top of the stack. Assigns phi node rhs variables
1453 * (i.e., the arguments to the phi.) Then, calls the function recursively on child
1454 * nodes in the DOM tree to continue the renaming process.
1456 * @param block Block for which SSA variables have to be renamed.
1457 * @param pRenameState The incremental rename information stored during renaming process.
1459 * @remarks At the end of the method, m_uses and m_defs should be populated linking the
1462 * @see Briggs, Cooper, Harvey and Simpson "Practical Improvements to the Construction
1463 * and Destruction of Static Single Assignment Form."
1466 void SsaBuilder::RenameVariables(BlkToBlkSetMap* domTree, SsaRenameState* pRenameState)
1468 JITDUMP("*************** In SsaBuilder::RenameVariables()\n");
1470 // The first thing we do is treat parameters and must-init variables as if they have a
1471 // virtual definition before entry -- they start out at SSA name 1.
1472 for (unsigned i = 0; i < m_pCompiler->lvaCount; i++)
1474 LclVarDsc* varDsc = &m_pCompiler->lvaTable[i];
1477 varDsc->lvNumSsaNames = SsaConfig::UNINIT_SSA_NUM; // Start off fresh...
1480 if (varDsc->lvIsParam || m_pCompiler->info.compInitMem || varDsc->lvMustInit ||
1481 (varDsc->lvTracked && VarSetOps::IsMember(m_pCompiler, m_pCompiler->fgFirstBB->bbLiveIn, varDsc->lvVarIndex)))
1483 unsigned count = pRenameState->CountForDef(i);
1485 // In ValueNum we'd assume un-inited variables get FIRST_SSA_NUM.
1486 assert(count == SsaConfig::FIRST_SSA_NUM);
1488 varDsc->lvNumSsaNames++;
1490 pRenameState->Push(NULL, i, count);
1493 // In ValueNum we'd assume un-inited heap gets FIRST_SSA_NUM.
1494 // The heap is a parameter. Use FIRST_SSA_NUM as first SSA name.
1495 unsigned initHeapCount = pRenameState->CountForHeapDef();
1496 assert(initHeapCount == SsaConfig::FIRST_SSA_NUM);
1497 pRenameState->PushHeap(m_pCompiler->fgFirstBB, initHeapCount);
1499 // Initialize the heap ssa numbers for unreachable blocks. ValueNum expects
1500 // heap ssa numbers to have some intitial value.
1501 for (BasicBlock* block = m_pCompiler->fgFirstBB; block; block = block->bbNext)
1503 if (block->bbIDom == NULL)
1505 block->bbHeapSsaNumIn = initHeapCount;
1506 block->bbHeapSsaNumOut = initHeapCount;
1513 bool m_processed; // Whether the this block have already been processed: its var renamed, and children processed.
1514 // If so, awaiting only BlockPopStacks.
1515 BlockWork(BasicBlock* blk, bool processed = false) : m_blk(blk), m_processed(processed) {}
1517 typedef jitstd::vector<BlockWork> BlockWorkStack;
1518 BlockWorkStack* blocksToDo = new (jitstd::utility::allocate<BlockWorkStack>(m_allocator), jitstd::placement_t()) BlockWorkStack(m_allocator);
1520 blocksToDo->push_back(BlockWork(m_pCompiler->fgFirstBB)); // Probably have to include other roots of dom tree.
1522 while (blocksToDo->size() != 0)
1524 BlockWork blockWrk = blocksToDo->back();
1525 blocksToDo->pop_back();
1526 BasicBlock* block = blockWrk.m_blk;
1528 DBG_SSA_JITDUMP("[SsaBuilder::RenameVariables](BB%02u, processed = %d)\n", block->bbNum, blockWrk.m_processed);
1530 if (!blockWrk.m_processed)
1532 // Push the block back on the stack with "m_processed" true, to record the fact that when its children have
1533 // been (recursively) processed, we still need to call BlockPopStacks on it.
1534 blocksToDo->push_back(BlockWork(block, true));
1536 // Walk the block give counts to DEFs and give top of stack count for USEs.
1537 BlockRenameVariables(block, pRenameState);
1539 // Assign arguments to the phi node of successors, corresponding to the block's index.
1540 AssignPhiNodeRhsVariables(block, pRenameState);
1542 // Recurse with the block's DOM children.
1544 if (domTree->Lookup(block, &pBlkSet))
1546 for (BlkSet::KeyIterator child = pBlkSet->Begin(); !child.Equal(pBlkSet->End()); ++child)
1548 DBG_SSA_JITDUMP("[SsaBuilder::RenameVariables](pushing dom child BB%02u)\n", child.Get()->bbNum);
1549 blocksToDo->push_back(BlockWork(child.Get()));
1555 // Done, pop all the stack count, if there is one for this block.
1556 BlockPopStacks(block, pRenameState);
1557 DBG_SSA_JITDUMP("[SsaBuilder::RenameVariables] done with BB%02u\n", block->bbNum);
1561 // Remember the number of Heap SSA names.
1562 m_pCompiler->lvHeapNumSsaNames = pRenameState->HeapCount();
1567 * Print the blocks, the phi nodes get printed as well.
1570 * [0027CC0C] ----------- stmtExpr void (IL 0x019...0x01B)
1571 * N001 ( 1, 1) [0027CB70] ----------- const int 23
1572 * N003 ( 3, 3) [0027CBD8] -A------R-- = int
1573 * N002 ( 1, 1) [0027CBA4] D------N--- lclVar int V01 arg1 d:5
1576 * [0027D530] ----------- stmtExpr void (IL ???... ???)
1577 * N002 ( 0, 0) [0027D4C8] ----------- phi int
1578 * [0027D8CC] ----------- lclVar int V01 arg1 u:5
1579 * [0027D844] ----------- lclVar int V01 arg1 u:4
1580 * N004 ( 2, 2) [0027D4FC] -A------R-- = int
1581 * N003 ( 1, 1) [0027D460] D------N--- lclVar int V01 arg1 d:3
1583 void SsaBuilder::Print(BasicBlock** postOrder, int count)
1585 for (int i = count - 1; i >= 0; --i)
1587 printf("After SSA BB%02u:\n", postOrder[i]->bbNum);
1588 m_pCompiler->gtDispTreeList(postOrder[i]->bbTreeList);
1596 * Sorts the graph topologically.
1597 * - Collects them in postOrder array.
1599 * Identifies each block's immediate dominator.
1600 * - Computes this in bbIDom of each BasicBlock.
1602 * Computes DOM tree relation.
1603 * - Computes domTree as block -> set of blocks.
1604 * - Computes pre/post order traversal of the DOM tree.
1606 * Inserts phi nodes.
1607 * - Computes dominance frontier as block -> set of blocks.
1608 * - Allocates block use/def/livein/liveout and computes it.
1609 * - Inserts phi nodes with only rhs at the beginning of the blocks.
1611 * Renames variables.
1612 * - Walks blocks in evaluation order and gives uses and defs names.
1613 * - Gives empty phi nodes their rhs arguments as they become known while renaming.
1615 * @return true if successful, for now, this must always be true.
1617 * @see "A simple, fast dominance algorithm" by Keith D. Cooper, Timothy J. Harvey, Ken Kennedy.
1618 * @see Briggs, Cooper, Harvey and Simpson "Practical Improvements to the Construction
1619 * and Destruction of Static Single Assignment Form."
1621 void SsaBuilder::Build()
1624 if (m_pCompiler->verbose)
1626 printf("*************** In SsaBuilder::Build()\n");
1630 // Ensure that there's a first block outside a try, so that the dominator tree has a unique root.
1633 // Just to keep block no. & index same add 1.
1634 int blockCount = m_pCompiler->fgBBNumMax + 1;
1636 JITDUMP("[SsaBuilder] Max block count is %d.\n", blockCount);
1638 // Allocate the postOrder array for the graph.
1639 BasicBlock** postOrder = (BasicBlock**) alloca(blockCount * sizeof(BasicBlock*));
1641 // Topologically sort the graph.
1642 int count = TopologicalSort(postOrder, blockCount);
1643 JITDUMP("[SsaBuilder] Topologically sorted the graph.\n");
1644 EndPhase(PHASE_BUILD_SSA_TOPOSORT);
1647 ComputeImmediateDom(postOrder, count);
1649 // Compute the dominator tree.
1650 BlkToBlkSetMap* domTree = new (m_pCompiler->getAllocator()) BlkToBlkSetMap(m_pCompiler->getAllocator());
1651 ComputeDominators(postOrder, count, domTree);
1652 EndPhase(PHASE_BUILD_SSA_DOMS);
1654 // Insert phi functions.
1655 InsertPhiFunctions(postOrder, count);
1657 // Rename local variables and collect UD information for each ssa var.
1658 SsaRenameState* pRenameState = new (jitstd::utility::allocate<SsaRenameState>(m_allocator), jitstd::placement_t()) SsaRenameState(m_allocator, m_pCompiler->lvaCount);
1659 RenameVariables(domTree, pRenameState);
1660 EndPhase(PHASE_BUILD_SSA_RENAME);
1663 // At this point we are in SSA form. Print the SSA form.
1664 if (m_pCompiler->verboseSsa) Print(postOrder, count);
1668 void SsaBuilder::SetupBBRoot()
1670 // Allocate a bbroot, if necessary.
1671 // We need a unique block to be the root of the dominator tree.
1672 // This can be violated if the first block is in a try, or if it is the first block of
1673 // a loop (which would necessarily be an infinite loop) -- i.e., it has a predecessor.
1675 // If neither condition holds, no reason to make a new block.
1676 if (!m_pCompiler->fgFirstBB->hasTryIndex()
1677 && m_pCompiler->fgFirstBB->bbPreds == NULL)
1680 BasicBlock* bbRoot = m_pCompiler->bbNewBasicBlock(BBJ_NONE);
1681 bbRoot->bbFlags |= BBF_INTERNAL;
1683 // May need to fix up preds list, so remember the old first block.
1684 BasicBlock* oldFirst = m_pCompiler->fgFirstBB;
1686 // Copy the liveness information from the first basic block.
1687 if (m_pCompiler->fgLocalVarLivenessDone)
1689 VarSetOps::Assign(m_pCompiler, bbRoot->bbLiveIn, oldFirst->bbLiveIn);
1690 VarSetOps::Assign(m_pCompiler, bbRoot->bbLiveOut, oldFirst->bbLiveIn);
1693 // Copy the bbWeight. (This is technically wrong, if the first block is a loop head, but
1694 // it shouldn't matter...)
1695 bbRoot->inheritWeight(oldFirst);
1697 // There's an artifical incoming reference count for the first BB. We're about to make it no longer
1698 // the first BB, so decrement that.
1699 assert(oldFirst->bbRefs > 0);
1702 m_pCompiler->fgInsertBBbefore(m_pCompiler->fgFirstBB, bbRoot);
1704 assert(m_pCompiler->fgFirstBB == bbRoot);
1705 if (m_pCompiler->fgComputePredsDone)
1707 m_pCompiler->fgAddRefPred(oldFirst, bbRoot);
1712 // This method asserts that SSA name constraints specified are satisfied.
1713 void Compiler::JitTestCheckSSA()
1720 static unsigned GetHashCode(SSAName ssaNm)
1722 return ssaNm.m_lvNum << 16 | ssaNm.m_ssaNum;
1725 static bool Equals(SSAName ssaNm1, SSAName ssaNm2)
1727 return ssaNm1.m_lvNum == ssaNm2.m_lvNum && ssaNm1.m_ssaNum == ssaNm2.m_ssaNum;
1731 typedef SimplerHashTable<ssize_t, SmallPrimitiveKeyFuncs<ssize_t>, SSAName, JitSimplerHashBehavior> LabelToSSANameMap;
1732 typedef SimplerHashTable<SSAName, SSAName, ssize_t, JitSimplerHashBehavior> SSANameToLabelMap;
1734 // If we have no test data, early out.
1735 if (m_nodeTestData == NULL) return;
1737 NodeToTestDataMap* testData = GetNodeTestData();
1739 // First we have to know which nodes in the tree are reachable.
1740 NodeToIntMap* reachable = FindReachableNodesInNodeTestData();
1742 LabelToSSANameMap* labelToSSA = new (getAllocatorDebugOnly()) LabelToSSANameMap(getAllocatorDebugOnly());
1743 SSANameToLabelMap* ssaToLabel = new (getAllocatorDebugOnly()) SSANameToLabelMap(getAllocatorDebugOnly());
1747 printf("\nJit Testing: SSA names.\n");
1749 for (NodeToTestDataMap::KeyIterator ki = testData->Begin(); !ki.Equal(testData->End()); ++ki)
1751 TestLabelAndNum tlAndN;
1752 GenTreePtr node = ki.Get();
1753 bool b = testData->Lookup(node, &tlAndN);
1755 if (tlAndN.m_tl == TL_SsaName)
1757 if (node->OperGet() != GT_LCL_VAR)
1759 printf("SSAName constraint put on non-lcl-var expression ");
1761 printf(" (of type %s).\n", varTypeName(node->TypeGet()));
1764 GenTreeLclVarCommon* lcl = node->AsLclVarCommon();
1767 if (!reachable->Lookup(lcl, &dummy))
1771 printf(" had a test constraint declared, but has become unreachable at the time the constraint is tested.\n"
1772 "(This is probably as a result of some optimization -- \n"
1773 "you may need to modify the test case to defeat this opt.)\n");
1781 printf(", SSA name = <%d, %d> -- SSA name class %d.\n",
1782 lcl->gtLclNum, lcl->gtSsaNum, tlAndN.m_num);
1785 if (labelToSSA->Lookup(tlAndN.m_num, &ssaNm))
1789 printf(" Already in hash tables.\n");
1791 // The mapping(s) must be one-to-one: if the label has a mapping, then the ssaNm must, as well.
1793 bool b = ssaToLabel->Lookup(ssaNm, &num2);
1794 // And the mappings must be the same.
1795 if (tlAndN.m_num != num2)
1799 printf(", SSA name = <%d, %d> was declared in SSA name class %d,\n",
1800 lcl->gtLclNum, lcl->gtSsaNum, tlAndN.m_num);
1801 printf("but this SSA name <%d,%d> has already been associated with a different SSA name class: %d.\n",
1802 ssaNm.m_lvNum, ssaNm.m_ssaNum, num2);
1805 // And the current node must be of the specified SSA family.
1806 if (!(lcl->gtLclNum == ssaNm.m_lvNum
1807 && lcl->gtSsaNum == ssaNm.m_ssaNum))
1811 printf(", SSA name = <%d, %d> was declared in SSA name class %d,\n",
1812 lcl->gtLclNum, lcl->gtSsaNum, tlAndN.m_num);
1813 printf("but that name class was previously bound to a different SSA name: <%d,%d>.\n",
1814 ssaNm.m_lvNum, ssaNm.m_ssaNum);
1820 ssaNm.m_lvNum = lcl->gtLclNum;
1821 ssaNm.m_ssaNum = lcl->gtSsaNum;
1823 // The mapping(s) must be one-to-one: if the label has no mapping, then the ssaNm may not, either.
1824 if (ssaToLabel->Lookup(ssaNm, &num))
1828 printf(", SSA name = <%d, %d> was declared in SSA name class %d,\n",
1829 lcl->gtLclNum, lcl->gtSsaNum, tlAndN.m_num);
1830 printf("but this SSA name has already been associated with a different name class: %d.\n", num);
1833 // Add to both mappings.
1834 labelToSSA->Set(tlAndN.m_num, ssaNm);
1835 ssaToLabel->Set(ssaNm, tlAndN.m_num);
1838 printf(" added to hash tables.\n");