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 * Method that finds a common IDom parent, much like least common ancestor.
32 * @param finger1 A basic block that might share IDom ancestor with finger2.
33 * @param finger2 A basic block that might share IDom ancestor with finger1.
35 * @see "A simple, fast dominance algorithm" by Keith D. Cooper, Timothy J. Harvey, Ken Kennedy.
37 * @return A basic block whose IDom is the dominator for finger1 and finger2,
38 * or else NULL. This may be called while immediate dominators are being
39 * computed, and if the input values are members of the same loop (each reachable from the other),
40 * then one may not yet have its immediate dominator computed when we are attempting
41 * to find the immediate dominator of the other. So a NULL return value means that the
42 * the two inputs are in a cycle, not that they don't have a common dominator ancestor.
44 static inline BasicBlock* IntersectDom(BasicBlock* finger1, BasicBlock* finger2)
46 while (finger1 != finger2)
48 if (finger1 == nullptr || finger2 == nullptr)
52 while (finger1 != nullptr && finger1->bbPostOrderNum < finger2->bbPostOrderNum)
54 finger1 = finger1->bbIDom;
56 if (finger1 == nullptr)
60 while (finger2 != nullptr && finger2->bbPostOrderNum < finger1->bbPostOrderNum)
62 finger2 = finger2->bbIDom;
68 } // end of anonymous namespace.
70 // =================================================================================
72 // =================================================================================
74 void Compiler::fgSsaBuild()
76 IAllocator* pIAllocator = new (this, CMK_SSA) CompAllocator(this, CMK_SSA);
78 // If this is not the first invocation, reset data structures for SSA.
79 if (fgSsaPassesCompleted > 0)
84 SsaBuilder builder(this, pIAllocator);
86 fgSsaPassesCompleted++;
94 JITDUMP("\nAfter fgSsaBuild:\n");
95 fgDispBasicBlocks(/*dumpTrees*/ true);
100 void Compiler::fgResetForSsa()
102 for (unsigned i = 0; i < lvaCount; ++i)
104 lvaTable[i].lvPerSsaData.Reset();
106 for (BasicBlock* blk = fgFirstBB; blk != nullptr; blk = blk->bbNext)
109 blk->bbHeapSsaPhiFunc = nullptr;
110 if (blk->bbTreeList != nullptr)
112 GenTreePtr last = blk->bbTreeList->gtPrev;
113 blk->bbTreeList = blk->FirstNonPhiDef();
114 if (blk->bbTreeList != nullptr)
116 blk->bbTreeList->gtPrev = last;
123 * Constructor for the SSA builder.
125 * @param pCompiler Current compiler instance.
127 * @remarks Initializes the class and member pointers/objects that use constructors.
129 SsaBuilder::SsaBuilder(Compiler* pCompiler, IAllocator* pIAllocator)
130 : m_pCompiler(pCompiler)
131 , m_allocator(pIAllocator)
133 #ifdef SSA_FEATURE_DOMARR
134 , m_pDomPreOrder(NULL)
135 , m_pDomPostOrder(NULL)
137 #ifdef SSA_FEATURE_USEDEF
138 , m_uses(jitstd::allocator<void>(pIAllocator))
139 , m_defs(jitstd::allocator<void>(pIAllocator))
144 //------------------------------------------------------------------------
145 // TopologicalSort: Topologically sort the graph and return the number of nodes visited.
148 // postOrder - The array in which the arranged basic blocks have to be returned.
149 // count - The size of the postOrder array.
152 // The number of nodes visited while performing DFS on the graph.
154 int SsaBuilder::TopologicalSort(BasicBlock** postOrder, int count)
156 Compiler* comp = m_pCompiler;
158 BitVecTraits traits(comp->fgBBNumMax + 1, comp);
159 BitVec BITVEC_INIT_NOCOPY(visited, BitVecOps::MakeEmpty(&traits));
161 // Display basic blocks.
162 DBEXEC(VERBOSE, comp->fgDispBasicBlocks());
163 DBEXEC(VERBOSE, comp->fgDispHandlerTab());
167 BasicBlock* block = comp->fgFirstBB;
168 BitVecOps::AddElemD(&traits, visited, block->bbNum);
170 ArrayStack<BasicBlock *> blocks(comp);
171 ArrayStack<AllSuccessorIter> iterators(comp);
172 ArrayStack<AllSuccessorIter> ends(comp);
174 // there are three stacks used here and all should be same height
175 // the first is for blocks
176 // the second is the iterator to keep track of what succ of the block we are looking at
177 // and the third is the end marker iterator
179 iterators.Push(block->GetAllSuccs(comp).begin());
180 ends.Push(block->GetAllSuccs(comp).end());
182 while (blocks.Height() > 0)
184 block = blocks.Top();
187 if (comp->verboseSsa)
189 printf("[SsaBuilder::TopologicalSort] Visiting BB%02u: ", block->bbNum);
191 unsigned numSucc = block->NumSucc(comp);
192 for (unsigned i = 0; i < numSucc; ++i)
194 printf("BB%02u, ", block->GetSucc(i, comp)->bbNum);
196 EHSuccessorIter end = block->GetEHSuccs(comp).end();
197 for (EHSuccessorIter ehsi = block->GetEHSuccs(comp).begin(); ehsi != end; ++ehsi)
199 printf("[EH]BB%02u, ", (*ehsi)->bbNum);
205 if (iterators.TopRef() != ends.TopRef())
207 // if the block on TOS still has unreached successors, visit them
208 AllSuccessorIter& iter = iterators.TopRef();
209 BasicBlock* succ = *iter;
213 if (!BitVecOps::IsMember(&traits, visited, succ->bbNum))
216 iterators.Push(succ->GetAllSuccs(comp).begin());
217 ends.Push(succ->GetAllSuccs(comp).end());
218 BitVecOps::AddElemD(&traits, visited, succ->bbNum);
223 // all successors have been visited
228 postOrder[postIndex] = block;
229 block->bbPostOrderNum = postIndex;
232 DBG_SSA_JITDUMP("postOrder[%d] = [%p] and BB%02u\n", postIndex, dspPtr(block), block->bbNum);
236 // In the absence of EH (because catch/finally have no preds), this should be valid.
237 // assert(postIndex == (count - 1));
243 * Computes the immediate dominator IDom for each block iteratively.
245 * @param postOrder The array of basic blocks arranged in postOrder.
246 * @param count The size of valid elements in the postOrder array.
248 * @see "A simple, fast dominance algorithm." paper.
250 void SsaBuilder::ComputeImmediateDom(BasicBlock** postOrder, int count)
252 JITDUMP("[SsaBuilder::ComputeImmediateDom]\n");
254 // TODO-Cleanup: We currently have two dominance computations happening. We should unify them; for
255 // now, at least forget the results of the first.
256 for (BasicBlock* blk = m_pCompiler->fgFirstBB; blk != nullptr; blk = blk->bbNext)
258 blk->bbIDom = nullptr;
261 // Add entry point to processed as its IDom is NULL.
262 BitVecTraits traits(m_pCompiler->fgBBNumMax + 1, m_pCompiler);
263 BitVec BITVEC_INIT_NOCOPY(processed, BitVecOps::MakeEmpty(&traits));
265 BitVecOps::AddElemD(&traits, processed, m_pCompiler->fgFirstBB->bbNum);
266 assert(postOrder[count - 1] == m_pCompiler->fgFirstBB);
273 // In reverse post order, except for the entry block (count - 1 is entry BB).
274 for (int i = count - 2; i >= 0; --i)
276 BasicBlock* block = postOrder[i];
278 DBG_SSA_JITDUMP("Visiting in reverse post order: BB%02u.\n", block->bbNum);
280 // Find the first processed predecessor block.
281 BasicBlock* predBlock = nullptr;
282 for (flowList* pred = m_pCompiler->BlockPredsWithEH(block); pred; pred = pred->flNext)
284 if (BitVecOps::IsMember(&traits, processed, pred->flBlock->bbNum))
286 predBlock = pred->flBlock;
291 // There could just be a single basic block, so just check if there were any preds.
292 if (predBlock != nullptr)
294 DBG_SSA_JITDUMP("Pred block is BB%02u.\n", predBlock->bbNum);
297 // Intersect DOM, if computed, for all predecessors.
298 BasicBlock* bbIDom = predBlock;
299 for (flowList* pred = m_pCompiler->BlockPredsWithEH(block); pred; pred = pred->flNext)
301 if (predBlock != pred->flBlock)
303 BasicBlock* domAncestor = IntersectDom(pred->flBlock, bbIDom);
304 // The result may be NULL if "block" and "pred->flBlock" are part of a
305 // cycle -- neither is guaranteed ordered wrt the other in reverse postorder,
306 // so we may be computing the IDom of "block" before the IDom of "pred->flBlock" has
307 // been computed. But that's OK -- if they're in a cycle, they share the same immediate
308 // dominator, so the contribution of "pred->flBlock" is not necessary to compute
310 if (domAncestor != nullptr)
312 bbIDom = domAncestor;
317 // Did we change the bbIDom value? If so, we go around the outer loop again.
318 if (block->bbIDom != bbIDom)
322 // IDom has changed, update it.
323 DBG_SSA_JITDUMP("bbIDom of BB%02u becomes BB%02u.\n", block->bbNum, bbIDom ? bbIDom->bbNum : 0);
324 block->bbIDom = bbIDom;
327 // Mark the current block as processed.
328 BitVecOps::AddElemD(&traits, processed, block->bbNum);
330 DBG_SSA_JITDUMP("Marking block BB%02u as processed.\n", block->bbNum);
335 #ifdef SSA_FEATURE_DOMARR
337 * Walk the DOM tree and compute pre and post-order arrangement of the tree.
339 * @param curBlock The current block being operated on at some recursive level.
340 * @param domTree The DOM tree as a map (block -> set of child blocks.)
341 * @param preIndex The initial index given to the first block visited in pre order.
342 * @param postIndex The initial index given to the first block visited in post order.
344 * @remarks This would help us answer queries such as "a dom b?" in constant time.
345 * For example, if a dominated b, then Pre[a] < Pre[b] but Post[a] > Post[b]
347 void SsaBuilder::DomTreeWalk(BasicBlock* curBlock, BlkToBlkSetMap* domTree, int* preIndex, int* postIndex)
349 JITDUMP("[SsaBuilder::DomTreeWalk] block [%p], BB%02u:\n", dspPtr(curBlock), curBlock->bbNum);
351 // Store the order number at the block number in the pre order list.
352 m_pDomPreOrder[curBlock->bbNum] = *preIndex;
356 if (domTree->Lookup(curBlock, &pBlkSet))
358 for (BlkSet::KeyIterator ki = pBlkSet->Begin(); !ki.Equal(pBlkSet->End()); ++ki)
360 if (curBlock != ki.Get())
362 DomTreeWalk(ki.Get(), domTree, preIndex, postIndex);
367 // Store the order number at the block number in the post order list.
368 m_pDomPostOrder[curBlock->bbNum] = *postIndex;
374 * Using IDom of each basic block, add a mapping from block->IDom -> block.
375 * @param pCompiler Compiler instance
376 * @param block The basic block that will become the child node of it's iDom.
377 * @param domTree The output domTree which will hold the mapping "block->bbIDom" -> "block"
381 void SsaBuilder::ConstructDomTreeForBlock(Compiler* pCompiler, BasicBlock* block, BlkToBlkSetMap* domTree)
383 BasicBlock* bbIDom = block->bbIDom;
385 // bbIDom for (only) fgFirstBB will be NULL.
386 if (bbIDom == nullptr)
391 // If the bbIDom map key doesn't exist, create one.
393 if (!domTree->Lookup(bbIDom, &pBlkSet))
395 pBlkSet = new (pCompiler->getAllocator()) BlkSet(pCompiler->getAllocator());
396 domTree->Set(bbIDom, pBlkSet);
399 DBG_SSA_JITDUMP("Inserting BB%02u as dom child of BB%02u.\n", block->bbNum, bbIDom->bbNum);
400 // Insert the block into the block's set.
401 pBlkSet->Set(block, true);
405 * Using IDom of each basic block, compute the whole tree. If a block "b" has IDom "i",
406 * then, block "b" is dominated by "i". The mapping then is i -> { ..., b, ... }, in
407 * other words, "domTree" is a tree represented by nodes mapped to their children.
409 * @param pCompiler Compiler instance
410 * @param domTree The output domTree which will hold the mapping "block->bbIDom" -> "block"
414 void SsaBuilder::ComputeDominators(Compiler* pCompiler, BlkToBlkSetMap* domTree)
416 JITDUMP("*************** In SsaBuilder::ComputeDominators(Compiler*, ...)\n");
418 // Construct the DOM tree from bbIDom
419 for (BasicBlock* block = pCompiler->fgFirstBB; block != nullptr; block = block->bbNext)
421 ConstructDomTreeForBlock(pCompiler, block, domTree);
424 DBEXEC(pCompiler->verboseSsa, DisplayDominators(domTree));
428 * Compute the DOM tree into a map(block -> set of blocks) adjacency representation.
430 * Using IDom of each basic block, compute the whole tree. If a block "b" has IDom "i",
431 * then, block "b" is dominated by "i". The mapping then is i -> { ..., b, ... }
433 * @param postOrder The array of basic blocks arranged in postOrder.
434 * @param count The size of valid elements in the postOrder array.
435 * @param domTree A map of (block -> set of blocks) tree representation that is empty.
438 void SsaBuilder::ComputeDominators(BasicBlock** postOrder, int count, BlkToBlkSetMap* domTree)
440 JITDUMP("*************** In SsaBuilder::ComputeDominators(BasicBlock** postOrder, int count, ...)\n");
442 // Construct the DOM tree from bbIDom
443 for (int i = 0; i < count; ++i)
445 ConstructDomTreeForBlock(m_pCompiler, postOrder[i], domTree);
448 DBEXEC(m_pCompiler->verboseSsa, DisplayDominators(domTree));
450 #ifdef SSA_FEATURE_DOMARR
451 // Allocate space for constant time computation of (a DOM b?) query.
452 unsigned bbArrSize = m_pCompiler->fgBBNumMax + 1; // We will use 1-based bbNums as indices into these arrays, so
454 m_pDomPreOrder = jitstd::utility::allocate<int>(m_allocator, bbArrSize);
455 m_pDomPostOrder = jitstd::utility::allocate<int>(m_allocator, bbArrSize);
461 // Populate the pre and post order of the tree.
462 DomTreeWalk(m_pCompiler->fgFirstBB, domTree, &preIndex, &postIndex);
469 * Display the DOM tree.
471 * @param domTree A map of (block -> set of blocks) tree representation.
474 void SsaBuilder::DisplayDominators(BlkToBlkSetMap* domTree)
476 printf("After computing dominator tree: \n");
477 for (BlkToBlkSetMap::KeyIterator nodes = domTree->Begin(); !nodes.Equal(domTree->End()); ++nodes)
479 printf("BB%02u := {", nodes.Get()->bbNum);
481 BlkSet* pBlkSet = nodes.GetValue();
482 for (BlkSet::KeyIterator ki = pBlkSet->Begin(); !ki.Equal(pBlkSet->End()); ++ki)
484 if (!ki.Equal(pBlkSet->Begin()))
488 printf("BB%02u", ki.Get()->bbNum);
496 // (Spec comment at declaration.)
497 // See "A simple, fast dominance algorithm", by Cooper, Harvey, and Kennedy.
498 // First we compute the dominance frontier for each block, then we convert these to iterated
499 // dominance frontiers by a closure operation.
500 BlkToBlkSetMap* SsaBuilder::ComputeIteratedDominanceFrontier(BasicBlock** postOrder, int count)
502 BlkToBlkSetMap* frontier = new (m_pCompiler->getAllocator()) BlkToBlkSetMap(m_pCompiler->getAllocator());
504 DBG_SSA_JITDUMP("Computing IDF: First computing DF.\n");
506 for (int i = 0; i < count; ++i)
508 BasicBlock* block = postOrder[i];
510 DBG_SSA_JITDUMP("Considering block BB%02u.\n", block->bbNum);
512 // Recall that B3 is in the dom frontier of B1 if there exists a B2
513 // such that B1 dom B2, !(B1 dom B3), and B3 is an immediate successor
514 // of B2. (Note that B1 might be the same block as B2.)
515 // In that definition, we're considering "block" to be B3, and trying
516 // to find B1's. To do so, first we consider the predecessors of "block",
517 // searching for candidate B2's -- "block" is obviously an immediate successor
518 // of its immediate predecessors. If there are zero or one preds, then there
519 // is no pred, or else the single pred dominates "block", so no B2 exists.
521 flowList* blockPreds = m_pCompiler->BlockPredsWithEH(block);
523 // If block has more 0/1 predecessor, skip.
524 if (blockPreds == nullptr || blockPreds->flNext == nullptr)
526 DBG_SSA_JITDUMP(" Has %d preds; skipping.\n", blockPreds == nullptr ? 0 : 1);
530 // Otherwise, there are > 1 preds. Each is a candidate B2 in the definition --
531 // *unless* it dominates "block"/B3.
533 for (flowList* pred = blockPreds; pred; pred = pred->flNext)
535 DBG_SSA_JITDUMP(" Considering predecessor BB%02u.\n", pred->flBlock->bbNum);
537 // If we've found a B2, then consider the possible B1's. We start with
538 // B2, since a block dominates itself, then traverse upwards in the dominator
539 // tree, stopping when we reach the root, or the immediate dominator of "block"/B3.
540 // (Note that we are guaranteed to encounter this immediate dominator of "block"/B3:
541 // a predecessor must be dominated by B3's immediate dominator.)
542 // Along this way, make "block"/B3 part of the dom frontier of the B1.
543 // When we reach this immediate dominator, the definition no longer applies, since this
544 // potential B1 *does* dominate "block"/B3, so we stop.
545 for (BasicBlock* b1 = pred->flBlock; (b1 != nullptr) && (b1 != block->bbIDom); // !root && !loop
548 DBG_SSA_JITDUMP(" Adding BB%02u to dom frontier of pred dom BB%02u.\n", block->bbNum, b1->bbNum);
550 if (!frontier->Lookup(b1, &pBlkSet))
552 pBlkSet = new (m_pCompiler->getAllocator()) BlkSet(m_pCompiler->getAllocator());
553 frontier->Set(b1, pBlkSet);
555 pBlkSet->Set(block, true);
561 if (m_pCompiler->verboseSsa)
563 printf("\nComputed DF:\n");
564 for (int i = 0; i < count; ++i)
566 BasicBlock* block = postOrder[i];
567 printf("Block BB%02u := {", block->bbNum);
571 if (frontier->Lookup(block, &blkDf))
573 for (BlkSet::KeyIterator blkDfIter = blkDf->Begin(); !blkDfIter.Equal(blkDf->End()); blkDfIter++)
579 printf("BB%02u", blkDfIter.Get()->bbNum);
588 // Now do the closure operation to make the dominance frontier into an IDF.
589 // There's probably a better way to do this...
590 BlkToBlkSetMap* idf = new (m_pCompiler->getAllocator()) BlkToBlkSetMap(m_pCompiler->getAllocator());
591 for (BlkToBlkSetMap::KeyIterator kiFrontBlks = frontier->Begin(); !kiFrontBlks.Equal(frontier->End());
595 BlkSet* blkIdf = new (m_pCompiler->getAllocator()) BlkSet(m_pCompiler->getAllocator());
596 idf->Set(kiFrontBlks.Get(), blkIdf);
598 // Keep track of what got newly added to the IDF, so we can go after their DFs.
599 BlkSet* delta = new (m_pCompiler->getAllocator()) BlkSet(m_pCompiler->getAllocator());
600 delta->Set(kiFrontBlks.Get(), true);
602 // Now transitively add DF+(delta) to IDF(b), each step gathering new "delta."
603 while (delta->GetCount() > 0)
605 // Extract a block x to be worked on.
606 BlkSet::KeyIterator ki = delta->Begin();
607 BasicBlock* curBlk = ki.Get();
608 // TODO-Cleanup: Remove(ki) doesn't work correctly in SimplerHash.
609 delta->Remove(curBlk);
613 if (frontier->Lookup(curBlk, &blkDf))
615 // Add DF(x) to IDF(b) and update "delta" i.e., new additions to IDF(b).
616 for (BlkSet::KeyIterator ki = blkDf->Begin(); !ki.Equal(blkDf->End()); ki++)
618 if (!blkIdf->Lookup(ki.Get()))
620 delta->Set(ki.Get(), true);
621 blkIdf->Set(ki.Get(), true);
629 if (m_pCompiler->verboseSsa)
631 printf("\nComputed IDF:\n");
632 for (int i = 0; i < count; ++i)
634 BasicBlock* block = postOrder[i];
635 printf("Block BB%02u := {", block->bbNum);
639 if (idf->Lookup(block, &blkIdf))
641 for (BlkSet::KeyIterator ki = blkIdf->Begin(); !ki.Equal(blkIdf->End()); ki++)
647 printf("BB%02u", ki.Get()->bbNum);
660 * Returns the phi GT_PHI node if the variable already has a phi node.
662 * @param block The block for which the existence of a phi node needs to be checked.
663 * @param lclNum The lclNum for which the occurrence of a phi node needs to be checked.
665 * @return If there is a phi node for the lclNum, returns the GT_PHI tree, else NULL.
667 static GenTree* GetPhiNode(BasicBlock* block, unsigned lclNum)
669 // Walk the statements for phi nodes.
670 for (GenTreePtr stmt = block->bbTreeList; stmt; stmt = stmt->gtNext)
672 // A prefix of the statements of the block are phi definition nodes. If we complete processing
673 // that prefix, exit.
674 if (!stmt->IsPhiDefnStmt())
679 GenTreePtr tree = stmt->gtStmt.gtStmtExpr;
681 GenTreePtr phiLhs = tree->gtOp.gtOp1;
682 assert(phiLhs->OperGet() == GT_LCL_VAR);
683 if (phiLhs->gtLclVarCommon.gtLclNum == lclNum)
685 return tree->gtOp.gtOp2;
692 * Inserts phi functions at DF(b) for variables v that are live after the phi
693 * insertion point i.e., v in live-in(b).
695 * To do so, the function computes liveness, dominance frontier and inserts a phi node,
696 * if we have var v in def(b) and live-in(l) and l is in DF(b).
698 * @param postOrder The array of basic blocks arranged in postOrder.
699 * @param count The size of valid elements in the postOrder array.
701 void SsaBuilder::InsertPhiFunctions(BasicBlock** postOrder, int count)
703 JITDUMP("*************** In SsaBuilder::InsertPhiFunctions()\n");
705 // Compute liveness on the graph.
706 m_pCompiler->fgLocalVarLiveness();
707 EndPhase(PHASE_BUILD_SSA_LIVENESS);
709 // Compute dominance frontier.
710 BlkToBlkSetMap* frontier = ComputeIteratedDominanceFrontier(postOrder, count);
711 EndPhase(PHASE_BUILD_SSA_IDF);
713 JITDUMP("Inserting phi functions:\n");
715 for (int i = 0; i < count; ++i)
717 BasicBlock* block = postOrder[i];
718 DBG_SSA_JITDUMP("Considering dominance frontier of block BB%02u:\n", block->bbNum);
720 // If the block's dominance frontier is empty, go on to the next block.
722 if (!frontier->Lookup(block, &blkIdf))
727 // For each local var number "lclNum" that "block" assigns to...
728 VARSET_ITER_INIT(m_pCompiler, defVars, block->bbVarDef, varIndex);
729 while (defVars.NextElem(m_pCompiler, &varIndex))
731 unsigned lclNum = m_pCompiler->lvaTrackedToVarNum[varIndex];
732 DBG_SSA_JITDUMP(" Considering local var V%02u:\n", lclNum);
734 if (m_pCompiler->fgExcludeFromSsa(lclNum))
736 DBG_SSA_JITDUMP(" Skipping because it is excluded.\n");
740 // For each block "bbInDomFront" that is in the dominance frontier of "block"...
741 for (BlkSet::KeyIterator iterBlk = blkIdf->Begin(); !iterBlk.Equal(blkIdf->End()); ++iterBlk)
743 BasicBlock* bbInDomFront = iterBlk.Get();
744 DBG_SSA_JITDUMP(" Considering BB%02u in dom frontier of BB%02u:\n", bbInDomFront->bbNum,
747 // Check if variable "lclNum" is live in block "*iterBlk".
748 if (!VarSetOps::IsMember(m_pCompiler, bbInDomFront->bbLiveIn, varIndex))
753 // Check if we've already inserted a phi node.
754 if (GetPhiNode(bbInDomFront, lclNum) == nullptr)
756 // We have a variable i that is defined in block j and live at l, and l belongs to dom frontier of
757 // j. So insert a phi node at l.
758 JITDUMP("Inserting phi definition for V%02u at start of BB%02u.\n", lclNum, bbInDomFront->bbNum);
760 GenTreePtr phiLhs = m_pCompiler->gtNewLclvNode(lclNum, m_pCompiler->lvaTable[lclNum].TypeGet());
762 // Create 'phiRhs' as a GT_PHI node for 'lclNum', it will eventually hold a GT_LIST of GT_PHI_ARG
763 // nodes. However we have to construct this list so for now the gtOp1 of 'phiRhs' is a nullptr.
764 // It will get replaced with a GT_LIST of GT_PHI_ARG nodes in
765 // SsaBuilder::AssignPhiNodeRhsVariables() and in SsaBuilder::AddDefToHandlerPhis()
768 m_pCompiler->gtNewOperNode(GT_PHI, m_pCompiler->lvaTable[lclNum].TypeGet(), nullptr);
770 GenTreePtr phiAsg = m_pCompiler->gtNewAssignNode(phiLhs, phiRhs);
772 GenTreePtr stmt = m_pCompiler->fgInsertStmtAtBeg(bbInDomFront, phiAsg);
773 m_pCompiler->gtSetStmtInfo(stmt);
774 m_pCompiler->fgSetStmtSeq(stmt);
779 // Now make a similar phi definition if the block defines Heap.
780 if (block->bbHeapDef)
782 // For each block "bbInDomFront" that is in the dominance frontier of "block".
783 for (BlkSet::KeyIterator iterBlk = blkIdf->Begin(); !iterBlk.Equal(blkIdf->End()); ++iterBlk)
785 BasicBlock* bbInDomFront = iterBlk.Get();
786 DBG_SSA_JITDUMP(" Considering BB%02u in dom frontier of BB%02u for Heap phis:\n",
787 bbInDomFront->bbNum, block->bbNum);
789 // Check if Heap is live into block "*iterBlk".
790 if (!bbInDomFront->bbHeapLiveIn)
795 // Check if we've already inserted a phi node.
796 if (bbInDomFront->bbHeapSsaPhiFunc == nullptr)
798 // We have a variable i that is defined in block j and live at l, and l belongs to dom frontier of
799 // j. So insert a phi node at l.
800 JITDUMP("Inserting phi definition for Heap at start of BB%02u.\n", bbInDomFront->bbNum);
801 bbInDomFront->bbHeapSsaPhiFunc = BasicBlock::EmptyHeapPhiDef;
806 EndPhase(PHASE_BUILD_SSA_INSERT_PHIS);
809 #ifdef SSA_FEATURE_USEDEF
811 * Record a use point of a variable.
813 * The use point is just the tree that is a local variable use.
815 * @param tree Tree node where an SSA variable is used.
817 * @remarks The result is in the m_uses map :: [lclNum, ssaNum] -> tree.
819 void SsaBuilder::AddUsePoint(GenTree* tree)
821 assert(tree->IsLocal());
822 SsaVarName key(tree->gtLclVarCommon.gtLclNum, tree->gtLclVarCommon.gtSsaNum);
823 VarToUses::iterator iter = m_uses.find(key);
824 if (iter == m_uses.end())
826 iter = m_uses.insert(key, VarToUses::mapped_type(m_uses.get_allocator()));
828 (*iter).second.push_back(tree);
830 #endif // !SSA_FEATURE_USEDEF
833 * Record a def point of a variable.
835 * The def point is just the tree that is a local variable def.
837 * @param tree Tree node where an SSA variable is def'ed.
839 * @remarks The result is in the m_defs map :: [lclNum, ssaNum] -> tree.
841 void SsaBuilder::AddDefPoint(GenTree* tree, BasicBlock* blk)
843 Compiler::IndirectAssignmentAnnotation* pIndirAnnot;
844 // In the case of an "indirect assignment", where the LHS is IND of a byref to the local actually being assigned,
845 // we make the ASG tree the def point.
846 assert(tree->IsLocal() || IsIndirectAssign(tree, &pIndirAnnot));
851 lclNum = tree->gtLclVarCommon.gtLclNum;
852 defSsaNum = m_pCompiler->GetSsaNumForLocalVarDef(tree);
856 bool b = m_pCompiler->GetIndirAssignMap()->Lookup(tree, &pIndirAnnot);
858 lclNum = pIndirAnnot->m_lclNum;
859 defSsaNum = pIndirAnnot->m_defSsaNum;
862 // Record that there's a new SSA def.
863 m_pCompiler->lvaTable[lclNum].lvNumSsaNames++;
865 // Record where the defn happens.
866 LclSsaVarDsc* ssaDef = m_pCompiler->lvaTable[lclNum].GetPerSsaData(defSsaNum);
867 ssaDef->m_defLoc.m_blk = blk;
868 ssaDef->m_defLoc.m_tree = tree;
870 #ifdef SSA_FEATURE_USEDEF
871 SsaVarName key(lclNum, defSsaNum);
872 VarToDef::iterator iter = m_defs.find(key);
873 if (iter == m_defs.end())
875 iter = m_defs.insert(key, tree);
878 // There can only be a single definition for an SSA var.
883 bool SsaBuilder::IsIndirectAssign(GenTreePtr tree, Compiler::IndirectAssignmentAnnotation** ppIndirAssign)
885 return tree->OperGet() == GT_ASG && m_pCompiler->m_indirAssignMap != nullptr &&
886 m_pCompiler->GetIndirAssignMap()->Lookup(tree, ppIndirAssign);
890 * Rename the local variable tree node.
892 * If the given tree node is a local variable, then for a def give a new count, if use,
893 * then give the count in the top of stack, i.e., current count (used for last def.)
895 * @param tree Tree node where an SSA variable is used or def'ed.
896 * @param pRenameState The incremental rename information stored during renaming process.
898 * @remarks This method has to maintain parity with TreePopStacks corresponding to pushes
901 void SsaBuilder::TreeRenameVariables(GenTree* tree, BasicBlock* block, SsaRenameState* pRenameState, bool isPhiDefn)
903 // This is perhaps temporary -- maybe should be done elsewhere. Label GT_INDs on LHS of assignments, so we
904 // can skip these during (at least) value numbering.
905 if (tree->OperIsAssignment())
907 GenTreePtr lhs = tree->gtOp.gtOp1->gtEffectiveVal(/*commaOnly*/ true);
908 GenTreePtr trueLhs = lhs->gtEffectiveVal(/*commaOnly*/ true);
909 if (trueLhs->OperIsIndir())
911 trueLhs->gtFlags |= GTF_IND_ASG_LHS;
913 else if (trueLhs->OperGet() == GT_CLS_VAR)
915 trueLhs->gtFlags |= GTF_CLS_VAR_ASG_LHS;
919 // Figure out if "tree" may make a new heap state (if we care for this block).
920 if (!block->bbHeapHavoc)
922 if (tree->OperIsAssignment() || tree->OperIsBlkOp())
924 if (m_pCompiler->ehBlockHasExnFlowDsc(block))
926 GenTreeLclVarCommon* lclVarNode;
927 if (!tree->DefinesLocal(m_pCompiler, &lclVarNode))
929 // It *may* define the heap in a non-havoc way. Make a new SSA # -- associate with this node.
930 unsigned count = pRenameState->CountForHeapDef();
931 pRenameState->PushHeap(block, count);
932 m_pCompiler->GetHeapSsaMap()->Set(tree, count);
934 if (JitTls::GetCompiler()->verboseSsa)
937 Compiler::printTreeID(tree);
938 printf(" (in try block) may define heap; ssa # = %d.\n", count);
942 // Now add this SSA # to all phis of the reachable catch blocks.
943 AddHeapDefToHandlerPhis(block, count);
949 Compiler::IndirectAssignmentAnnotation* pIndirAssign = nullptr;
950 if (!tree->IsLocal() && !IsIndirectAssign(tree, &pIndirAssign))
955 if (pIndirAssign != nullptr)
957 unsigned lclNum = pIndirAssign->m_lclNum;
958 // Is this a variable we exclude from SSA?
959 if (m_pCompiler->fgExcludeFromSsa(lclNum))
961 pIndirAssign->m_defSsaNum = SsaConfig::RESERVED_SSA_NUM;
965 if (!pIndirAssign->m_isEntire)
967 pIndirAssign->m_useSsaNum = pRenameState->CountForUse(lclNum);
969 unsigned count = pRenameState->CountForDef(lclNum);
970 pIndirAssign->m_defSsaNum = count;
971 pRenameState->Push(block, lclNum, count);
972 AddDefPoint(tree, block);
976 unsigned lclNum = tree->gtLclVarCommon.gtLclNum;
977 // Is this a variable we exclude from SSA?
978 if (m_pCompiler->fgExcludeFromSsa(lclNum))
980 tree->gtLclVarCommon.SetSsaNum(SsaConfig::RESERVED_SSA_NUM);
984 if (tree->gtFlags & GTF_VAR_DEF)
986 if (tree->gtFlags & GTF_VAR_USEASG)
988 // This the "x" in something like "x op= y"; it is both a use (first), then a def.
989 // The def will define a new SSA name, and record that in "x". If we need the SSA
990 // name of the use, we record it in a map reserved for that purpose.
991 unsigned count = pRenameState->CountForUse(lclNum);
992 tree->gtLclVarCommon.SetSsaNum(count);
993 #ifdef SSA_FEATURE_USEDEF
998 // Give a count and increment.
999 unsigned count = pRenameState->CountForDef(lclNum);
1000 if (tree->gtFlags & GTF_VAR_USEASG)
1002 m_pCompiler->GetOpAsgnVarDefSsaNums()->Set(tree, count);
1006 tree->gtLclVarCommon.SetSsaNum(count);
1008 pRenameState->Push(block, lclNum, count);
1009 AddDefPoint(tree, block);
1011 // If necessary, add "lclNum/count" to the arg list of a phi def in any
1012 // handlers for try blocks that "block" is within. (But only do this for "real" definitions,
1013 // not phi definitions.)
1016 AddDefToHandlerPhis(block, lclNum, count);
1019 else if (!isPhiDefn) // Phi args already have ssa numbers.
1021 // This case is obviated by the short-term "early-out" above...but it's in the right direction.
1022 // Is it a promoted struct local?
1023 if (m_pCompiler->lvaTable[lclNum].lvPromoted)
1025 assert(tree->TypeGet() == TYP_STRUCT);
1026 LclVarDsc* varDsc = &m_pCompiler->lvaTable[lclNum];
1027 // If has only a single field var, treat this as a use of that field var.
1028 // Otherwise, we don't give SSA names to uses of promoted struct vars.
1029 if (varDsc->lvFieldCnt == 1)
1031 lclNum = varDsc->lvFieldLclStart;
1035 tree->gtLclVarCommon.SetSsaNum(SsaConfig::RESERVED_SSA_NUM);
1039 // Give the count as top of stack.
1040 unsigned count = pRenameState->CountForUse(lclNum);
1041 tree->gtLclVarCommon.SetSsaNum(count);
1042 #ifdef SSA_FEATURE_USEDEF
1049 void SsaBuilder::AddDefToHandlerPhis(BasicBlock* block, unsigned lclNum, unsigned count)
1051 assert(m_pCompiler->lvaTable[lclNum].lvTracked); // Precondition.
1052 unsigned lclIndex = m_pCompiler->lvaTable[lclNum].lvVarIndex;
1054 EHblkDsc* tryBlk = m_pCompiler->ehGetBlockExnFlowDsc(block);
1055 if (tryBlk != nullptr)
1058 "Definition of local V%02u/d:%d in block BB%02u has exn handler; adding as phi arg to handlers.\n", lclNum,
1059 count, block->bbNum);
1062 BasicBlock* handler = tryBlk->ExFlowBlock();
1064 // Is "lclNum" live on entry to the handler?
1065 if (VarSetOps::IsMember(m_pCompiler, handler->bbLiveIn, lclIndex))
1068 bool phiFound = false;
1070 // A prefix of blocks statements will be SSA definitions. Search those for "lclNum".
1071 for (GenTreePtr stmt = handler->bbTreeList; stmt; stmt = stmt->gtNext)
1073 // If the tree is not an SSA def, break out of the loop: we're done.
1074 if (!stmt->IsPhiDefnStmt())
1079 GenTreePtr tree = stmt->gtStmt.gtStmtExpr;
1081 assert(tree->IsPhiDefn());
1083 if (tree->gtOp.gtOp1->gtLclVar.gtLclNum == lclNum)
1085 // It's the definition for the right local. Add "count" to the RHS.
1086 GenTreePtr phi = tree->gtOp.gtOp2;
1087 GenTreeArgList* args = nullptr;
1088 if (phi->gtOp.gtOp1 != nullptr)
1090 args = phi->gtOp.gtOp1->AsArgList();
1093 // Make sure it isn't already present: we should only add each definition once.
1094 for (GenTreeArgList* curArgs = args; curArgs != nullptr; curArgs = curArgs->Rest())
1096 GenTreePhiArg* phiArg = curArgs->Current()->AsPhiArg();
1097 assert(phiArg->gtSsaNum != count);
1100 var_types typ = m_pCompiler->lvaTable[lclNum].TypeGet();
1101 GenTreePhiArg* newPhiArg =
1102 new (m_pCompiler, GT_PHI_ARG) GenTreePhiArg(typ, lclNum, count, block);
1104 phi->gtOp.gtOp1 = new (m_pCompiler, GT_LIST) GenTreeArgList(newPhiArg, args);
1105 m_pCompiler->gtSetStmtInfo(stmt);
1106 m_pCompiler->fgSetStmtSeq(stmt);
1110 DBG_SSA_JITDUMP(" Added phi arg u:%d for V%02u to phi defn in handler block BB%02u.\n", count,
1111 lclNum, handler->bbNum);
1118 unsigned nextTryIndex = tryBlk->ebdEnclosingTryIndex;
1119 if (nextTryIndex == EHblkDsc::NO_ENCLOSING_INDEX)
1124 tryBlk = m_pCompiler->ehGetDsc(nextTryIndex);
1129 void SsaBuilder::AddHeapDefToHandlerPhis(BasicBlock* block, unsigned count)
1131 if (m_pCompiler->ehBlockHasExnFlowDsc(block))
1133 // Don't do anything for a compiler-inserted BBJ_ALWAYS that is a "leave helper".
1134 if (block->bbJumpKind == BBJ_ALWAYS && (block->bbFlags & BBF_INTERNAL) && (block->bbPrev->isBBCallAlwaysPair()))
1140 DBG_SSA_JITDUMP("Definition of Heap/d:%d in block BB%02u has exn handler; adding as phi arg to handlers.\n",
1141 count, block->bbNum);
1142 EHblkDsc* tryBlk = m_pCompiler->ehGetBlockExnFlowDsc(block);
1145 BasicBlock* handler = tryBlk->ExFlowBlock();
1147 // Is Heap live on entry to the handler?
1148 if (handler->bbHeapLiveIn)
1150 assert(handler->bbHeapSsaPhiFunc != nullptr);
1152 // Add "count" to the phi args of Heap.
1153 if (handler->bbHeapSsaPhiFunc == BasicBlock::EmptyHeapPhiDef)
1155 handler->bbHeapSsaPhiFunc = new (m_pCompiler) BasicBlock::HeapPhiArg(count);
1160 BasicBlock::HeapPhiArg* curArg = handler->bbHeapSsaPhiFunc;
1161 while (curArg != nullptr)
1163 assert(curArg->GetSsaNum() != count);
1164 curArg = curArg->m_nextArg;
1167 handler->bbHeapSsaPhiFunc =
1168 new (m_pCompiler) BasicBlock::HeapPhiArg(count, handler->bbHeapSsaPhiFunc);
1171 DBG_SSA_JITDUMP(" Added phi arg u:%d for Heap to phi defn in handler block BB%02u.\n", count,
1174 unsigned tryInd = tryBlk->ebdEnclosingTryIndex;
1175 if (tryInd == EHblkDsc::NO_ENCLOSING_INDEX)
1179 tryBlk = m_pCompiler->ehGetDsc(tryInd);
1185 * Walk the block's tree in the evaluation order and give var definitions and uses their
1188 * @param block Block for which SSA variables have to be renamed.
1189 * @param pRenameState The incremental rename information stored during renaming process.
1192 void SsaBuilder::BlockRenameVariables(BasicBlock* block, SsaRenameState* pRenameState)
1194 // Walk the statements of the block and rename the tree variables.
1196 // First handle the incoming Heap state.
1198 // Is there an Phi definition for heap at the start of this block?
1199 if (block->bbHeapSsaPhiFunc != nullptr)
1201 unsigned count = pRenameState->CountForHeapDef();
1202 pRenameState->PushHeap(block, count);
1204 DBG_SSA_JITDUMP("Ssa # for Heap phi on entry to BB%02u is %d.\n", block->bbNum, count);
1207 // Record the "in" Ssa # for Heap.
1208 block->bbHeapSsaNumIn = pRenameState->CountForHeapUse();
1210 // We need to iterate over phi definitions, to give them SSA names, but we need
1211 // to know which are which, so we don't add phi definitions to handler phi arg lists.
1212 // Statements are phi defns until they aren't.
1213 bool isPhiDefn = true;
1214 GenTreePtr firstNonPhi = block->FirstNonPhiDef();
1215 for (GenTreePtr stmt = block->bbTreeList; stmt; stmt = stmt->gtNext)
1217 if (stmt == firstNonPhi)
1222 for (GenTreePtr tree = stmt->gtStmt.gtStmtList; tree; tree = tree->gtNext)
1224 TreeRenameVariables(tree, block, pRenameState, isPhiDefn);
1228 // Now handle the final heap state.
1230 // If the block defines Heap, allocate an SSA variable for the final heap state in the block.
1231 // (This may be redundant with the last SSA var explicitly created, but there's no harm in that.)
1232 if (block->bbHeapDef)
1234 unsigned count = pRenameState->CountForHeapDef();
1235 pRenameState->PushHeap(block, count);
1236 AddHeapDefToHandlerPhis(block, count);
1239 // Record the "out" Ssa" # for Heap.
1240 block->bbHeapSsaNumOut = pRenameState->CountForHeapUse();
1242 DBG_SSA_JITDUMP("Ssa # for Heap on entry to BB%02u is %d; on exit is %d.\n", block->bbNum, block->bbHeapSsaNumIn,
1243 block->bbHeapSsaNumOut);
1247 * Walk through the phi nodes of a given block and assign rhs variables to them.
1249 * Also renumber the rhs variables from top of the stack.
1251 * @param block Block for which phi nodes have to be assigned their rhs arguments.
1252 * @param pRenameState The incremental rename information stored during renaming process.
1255 void SsaBuilder::AssignPhiNodeRhsVariables(BasicBlock* block, SsaRenameState* pRenameState)
1257 BasicBlock::AllSuccs allSuccs = block->GetAllSuccs(m_pCompiler);
1258 AllSuccessorIter allSuccsEnd = allSuccs.end();
1259 for (AllSuccessorIter allSuccsIter = allSuccs.begin(); allSuccsIter != allSuccsEnd; ++allSuccsIter)
1261 BasicBlock* succ = (*allSuccsIter);
1262 // Walk the statements for phi nodes.
1263 for (GenTreePtr stmt = succ->bbTreeList; stmt != nullptr && stmt->IsPhiDefnStmt(); stmt = stmt->gtNext)
1265 GenTreePtr tree = stmt->gtStmt.gtStmtExpr;
1266 assert(tree->IsPhiDefn());
1268 // Get the phi node from GT_ASG.
1269 GenTreePtr phiNode = tree->gtOp.gtOp2;
1270 assert(phiNode->gtOp.gtOp1 == nullptr || phiNode->gtOp.gtOp1->OperGet() == GT_LIST);
1272 unsigned lclNum = tree->gtOp.gtOp1->gtLclVar.gtLclNum;
1273 unsigned ssaNum = pRenameState->CountForUse(lclNum);
1274 // Search the arglist for an existing definition for ssaNum.
1275 // (Can we assert that its the head of the list? This should only happen when we add
1276 // during renaming for a definition that occurs within a try, and then that's the last
1277 // value of the var within that basic block.)
1278 GenTreeArgList* argList = (phiNode->gtOp.gtOp1 == nullptr ? nullptr : phiNode->gtOp.gtOp1->AsArgList());
1280 while (argList != nullptr)
1282 if (argList->Current()->AsLclVarCommon()->GetSsaNum() == ssaNum)
1287 argList = argList->Rest();
1291 GenTreePtr newPhiArg =
1292 new (m_pCompiler, GT_PHI_ARG) GenTreePhiArg(tree->gtOp.gtOp1->TypeGet(), lclNum, ssaNum, block);
1293 argList = (phiNode->gtOp.gtOp1 == nullptr ? nullptr : phiNode->gtOp.gtOp1->AsArgList());
1294 phiNode->gtOp.gtOp1 = new (m_pCompiler, GT_LIST) GenTreeArgList(newPhiArg, argList);
1295 DBG_SSA_JITDUMP(" Added phi arg u:%d for V%02u from BB%02u in BB%02u.\n", ssaNum, lclNum, block->bbNum,
1299 m_pCompiler->gtSetStmtInfo(stmt);
1300 m_pCompiler->fgSetStmtSeq(stmt);
1304 if (succ->bbHeapSsaPhiFunc != nullptr)
1306 if (succ->bbHeapSsaPhiFunc == BasicBlock::EmptyHeapPhiDef)
1308 succ->bbHeapSsaPhiFunc = new (m_pCompiler) BasicBlock::HeapPhiArg(block);
1312 BasicBlock::HeapPhiArg* curArg = succ->bbHeapSsaPhiFunc;
1314 // This is a quadratic algorithm. We might need to consider some switch over to a hash table
1315 // representation for the arguments of a phi node, to make this linear.
1316 while (curArg != nullptr)
1318 if (curArg->m_predBB == block)
1323 curArg = curArg->m_nextArg;
1327 succ->bbHeapSsaPhiFunc = new (m_pCompiler) BasicBlock::HeapPhiArg(block, succ->bbHeapSsaPhiFunc);
1330 DBG_SSA_JITDUMP(" Added phi arg for Heap from BB%02u in BB%02u.\n", block->bbNum, succ->bbNum);
1333 // If "succ" is the first block of a try block (and "block" is not also in that try block)
1334 // then we must look at the vars that have phi defs in the corresponding handler;
1335 // the current SSA name for such vars must be included as an argument to that phi.
1336 if (m_pCompiler->bbIsTryBeg(succ))
1338 assert(succ->hasTryIndex());
1339 unsigned tryInd = succ->getTryIndex();
1341 while (tryInd != EHblkDsc::NO_ENCLOSING_INDEX)
1343 // Check if the predecessor "block" is within the same try block.
1344 if (block->hasTryIndex())
1346 for (unsigned blockTryInd = block->getTryIndex(); blockTryInd != EHblkDsc::NO_ENCLOSING_INDEX;
1347 blockTryInd = m_pCompiler->ehGetEnclosingTryIndex(blockTryInd))
1349 if (blockTryInd == tryInd)
1351 // It is; don't execute the loop below.
1352 tryInd = EHblkDsc::NO_ENCLOSING_INDEX;
1357 // The loop just above found that the predecessor "block" is within the same
1358 // try block as "succ." So we don't need to process this try, or any
1359 // further outer try blocks here, since they would also contain both "succ"
1361 if (tryInd == EHblkDsc::NO_ENCLOSING_INDEX)
1367 EHblkDsc* succTry = m_pCompiler->ehGetDsc(tryInd);
1368 // This is necessarily true on the first iteration, but not
1369 // necessarily on the second and subsequent.
1370 if (succTry->ebdTryBeg != succ)
1375 // succ is the first block of this try. Look at phi defs in the handler.
1376 // For a filter, we consider the filter to be the "real" handler.
1377 BasicBlock* handlerStart = succTry->ExFlowBlock();
1379 for (GenTreePtr stmt = handlerStart->bbTreeList; stmt; stmt = stmt->gtNext)
1381 GenTreePtr tree = stmt->gtStmt.gtStmtExpr;
1383 // Check if the first n of the statements are phi nodes. If not, exit.
1384 if (tree->OperGet() != GT_ASG || tree->gtOp.gtOp2 == nullptr ||
1385 tree->gtOp.gtOp2->OperGet() != GT_PHI)
1390 // Get the phi node from GT_ASG.
1391 GenTreePtr lclVar = tree->gtOp.gtOp1;
1392 unsigned lclNum = lclVar->gtLclVar.gtLclNum;
1394 // If the variable is live-out of "blk", and is therefore live on entry to the try-block-start
1395 // "succ", then we make sure the current SSA name for the
1396 // var is one of the args of the phi node. If not, go on.
1397 LclVarDsc* lclVarDsc = &m_pCompiler->lvaTable[lclNum];
1398 if (!lclVarDsc->lvTracked ||
1399 !VarSetOps::IsMember(m_pCompiler, block->bbLiveOut, lclVarDsc->lvVarIndex))
1404 GenTreePtr phiNode = tree->gtOp.gtOp2;
1405 assert(phiNode->gtOp.gtOp1 == nullptr || phiNode->gtOp.gtOp1->OperGet() == GT_LIST);
1406 GenTreeArgList* argList = reinterpret_cast<GenTreeArgList*>(phiNode->gtOp.gtOp1);
1408 // What is the current SSAName from the predecessor for this local?
1409 unsigned ssaNum = pRenameState->CountForUse(lclNum);
1411 // See if this ssaNum is already an arg to the phi.
1412 bool alreadyArg = false;
1413 for (GenTreeArgList* curArgs = argList; curArgs != nullptr; curArgs = curArgs->Rest())
1415 if (curArgs->Current()->gtPhiArg.gtSsaNum == ssaNum)
1423 // Add the new argument.
1424 GenTreePtr newPhiArg =
1425 new (m_pCompiler, GT_PHI_ARG) GenTreePhiArg(lclVar->TypeGet(), lclNum, ssaNum, block);
1426 phiNode->gtOp.gtOp1 = new (m_pCompiler, GT_LIST) GenTreeArgList(newPhiArg, argList);
1428 DBG_SSA_JITDUMP(" Added phi arg u:%d for V%02u from BB%02u in BB%02u.\n", ssaNum, lclNum,
1429 block->bbNum, handlerStart->bbNum);
1431 m_pCompiler->gtSetStmtInfo(stmt);
1432 m_pCompiler->fgSetStmtSeq(stmt);
1437 if (handlerStart->bbHeapSsaPhiFunc != nullptr)
1439 if (handlerStart->bbHeapSsaPhiFunc == BasicBlock::EmptyHeapPhiDef)
1441 handlerStart->bbHeapSsaPhiFunc = new (m_pCompiler) BasicBlock::HeapPhiArg(block);
1446 BasicBlock::HeapPhiArg* curArg = handlerStart->bbHeapSsaPhiFunc;
1447 while (curArg != nullptr)
1449 assert(curArg->m_predBB != block);
1450 curArg = curArg->m_nextArg;
1453 handlerStart->bbHeapSsaPhiFunc =
1454 new (m_pCompiler) BasicBlock::HeapPhiArg(block, handlerStart->bbHeapSsaPhiFunc);
1456 DBG_SSA_JITDUMP(" Added phi arg for Heap from BB%02u in BB%02u.\n", block->bbNum,
1457 handlerStart->bbNum);
1460 tryInd = succTry->ebdEnclosingTryIndex;
1467 * Walk the block's tree in the evaluation order and reclaim rename stack for var definitions.
1469 * @param block Block for which SSA variables have to be renamed.
1470 * @param pRenameState The incremental rename information stored during renaming process.
1473 void SsaBuilder::BlockPopStacks(BasicBlock* block, SsaRenameState* pRenameState)
1475 // Pop the names given to the non-phi nodes.
1476 pRenameState->PopBlockStacks(block);
1479 pRenameState->PopBlockHeapStack(block);
1483 * Perform variable renaming.
1485 * Walks the blocks and renames all var defs with ssa numbers and all uses with the
1486 * current count that is in the top of the stack. Assigns phi node rhs variables
1487 * (i.e., the arguments to the phi.) Then, calls the function recursively on child
1488 * nodes in the DOM tree to continue the renaming process.
1490 * @param block Block for which SSA variables have to be renamed.
1491 * @param pRenameState The incremental rename information stored during renaming process.
1493 * @remarks At the end of the method, m_uses and m_defs should be populated linking the
1496 * @see Briggs, Cooper, Harvey and Simpson "Practical Improvements to the Construction
1497 * and Destruction of Static Single Assignment Form."
1500 void SsaBuilder::RenameVariables(BlkToBlkSetMap* domTree, SsaRenameState* pRenameState)
1502 JITDUMP("*************** In SsaBuilder::RenameVariables()\n");
1504 // The first thing we do is treat parameters and must-init variables as if they have a
1505 // virtual definition before entry -- they start out at SSA name 1.
1506 for (unsigned i = 0; i < m_pCompiler->lvaCount; i++)
1508 LclVarDsc* varDsc = &m_pCompiler->lvaTable[i];
1511 varDsc->lvNumSsaNames = SsaConfig::UNINIT_SSA_NUM; // Start off fresh...
1514 if (varDsc->lvIsParam || m_pCompiler->info.compInitMem || varDsc->lvMustInit ||
1515 (varDsc->lvTracked &&
1516 VarSetOps::IsMember(m_pCompiler, m_pCompiler->fgFirstBB->bbLiveIn, varDsc->lvVarIndex)))
1518 unsigned count = pRenameState->CountForDef(i);
1520 // In ValueNum we'd assume un-inited variables get FIRST_SSA_NUM.
1521 assert(count == SsaConfig::FIRST_SSA_NUM);
1523 varDsc->lvNumSsaNames++;
1525 pRenameState->Push(nullptr, i, count);
1528 // In ValueNum we'd assume un-inited heap gets FIRST_SSA_NUM.
1529 // The heap is a parameter. Use FIRST_SSA_NUM as first SSA name.
1530 unsigned initHeapCount = pRenameState->CountForHeapDef();
1531 assert(initHeapCount == SsaConfig::FIRST_SSA_NUM);
1532 pRenameState->PushHeap(m_pCompiler->fgFirstBB, initHeapCount);
1534 // Initialize the heap ssa numbers for unreachable blocks. ValueNum expects
1535 // heap ssa numbers to have some intitial value.
1536 for (BasicBlock* block = m_pCompiler->fgFirstBB; block; block = block->bbNext)
1538 if (block->bbIDom == nullptr)
1540 block->bbHeapSsaNumIn = initHeapCount;
1541 block->bbHeapSsaNumOut = initHeapCount;
1548 bool m_processed; // Whether the this block have already been processed: its var renamed, and children
1550 // If so, awaiting only BlockPopStacks.
1551 BlockWork(BasicBlock* blk, bool processed = false) : m_blk(blk), m_processed(processed)
1555 typedef jitstd::vector<BlockWork> BlockWorkStack;
1556 BlockWorkStack* blocksToDo =
1557 new (jitstd::utility::allocate<BlockWorkStack>(m_allocator), jitstd::placement_t()) BlockWorkStack(m_allocator);
1559 blocksToDo->push_back(BlockWork(m_pCompiler->fgFirstBB)); // Probably have to include other roots of dom tree.
1561 while (blocksToDo->size() != 0)
1563 BlockWork blockWrk = blocksToDo->back();
1564 blocksToDo->pop_back();
1565 BasicBlock* block = blockWrk.m_blk;
1567 DBG_SSA_JITDUMP("[SsaBuilder::RenameVariables](BB%02u, processed = %d)\n", block->bbNum, blockWrk.m_processed);
1569 if (!blockWrk.m_processed)
1571 // Push the block back on the stack with "m_processed" true, to record the fact that when its children have
1572 // been (recursively) processed, we still need to call BlockPopStacks on it.
1573 blocksToDo->push_back(BlockWork(block, true));
1575 // Walk the block give counts to DEFs and give top of stack count for USEs.
1576 BlockRenameVariables(block, pRenameState);
1578 // Assign arguments to the phi node of successors, corresponding to the block's index.
1579 AssignPhiNodeRhsVariables(block, pRenameState);
1581 // Recurse with the block's DOM children.
1583 if (domTree->Lookup(block, &pBlkSet))
1585 for (BlkSet::KeyIterator child = pBlkSet->Begin(); !child.Equal(pBlkSet->End()); ++child)
1587 DBG_SSA_JITDUMP("[SsaBuilder::RenameVariables](pushing dom child BB%02u)\n", child.Get()->bbNum);
1588 blocksToDo->push_back(BlockWork(child.Get()));
1594 // Done, pop all the stack count, if there is one for this block.
1595 BlockPopStacks(block, pRenameState);
1596 DBG_SSA_JITDUMP("[SsaBuilder::RenameVariables] done with BB%02u\n", block->bbNum);
1600 // Remember the number of Heap SSA names.
1601 m_pCompiler->lvHeapNumSsaNames = pRenameState->HeapCount();
1606 * Print the blocks, the phi nodes get printed as well.
1609 * [0027CC0C] ----------- stmtExpr void (IL 0x019...0x01B)
1610 * N001 ( 1, 1) [0027CB70] ----------- const int 23
1611 * N003 ( 3, 3) [0027CBD8] -A------R-- = int
1612 * N002 ( 1, 1) [0027CBA4] D------N--- lclVar int V01 arg1 d:5
1615 * [0027D530] ----------- stmtExpr void (IL ???... ???)
1616 * N002 ( 0, 0) [0027D4C8] ----------- phi int
1617 * [0027D8CC] ----------- lclVar int V01 arg1 u:5
1618 * [0027D844] ----------- lclVar int V01 arg1 u:4
1619 * N004 ( 2, 2) [0027D4FC] -A------R-- = int
1620 * N003 ( 1, 1) [0027D460] D------N--- lclVar int V01 arg1 d:3
1622 void SsaBuilder::Print(BasicBlock** postOrder, int count)
1624 for (int i = count - 1; i >= 0; --i)
1626 printf("After SSA BB%02u:\n", postOrder[i]->bbNum);
1627 m_pCompiler->gtDispTreeList(postOrder[i]->bbTreeList);
1635 * Sorts the graph topologically.
1636 * - Collects them in postOrder array.
1638 * Identifies each block's immediate dominator.
1639 * - Computes this in bbIDom of each BasicBlock.
1641 * Computes DOM tree relation.
1642 * - Computes domTree as block -> set of blocks.
1643 * - Computes pre/post order traversal of the DOM tree.
1645 * Inserts phi nodes.
1646 * - Computes dominance frontier as block -> set of blocks.
1647 * - Allocates block use/def/livein/liveout and computes it.
1648 * - Inserts phi nodes with only rhs at the beginning of the blocks.
1650 * Renames variables.
1651 * - Walks blocks in evaluation order and gives uses and defs names.
1652 * - Gives empty phi nodes their rhs arguments as they become known while renaming.
1654 * @return true if successful, for now, this must always be true.
1656 * @see "A simple, fast dominance algorithm" by Keith D. Cooper, Timothy J. Harvey, Ken Kennedy.
1657 * @see Briggs, Cooper, Harvey and Simpson "Practical Improvements to the Construction
1658 * and Destruction of Static Single Assignment Form."
1660 void SsaBuilder::Build()
1663 if (m_pCompiler->verbose)
1665 printf("*************** In SsaBuilder::Build()\n");
1669 // Ensure that there's a first block outside a try, so that the dominator tree has a unique root.
1672 // Just to keep block no. & index same add 1.
1673 int blockCount = m_pCompiler->fgBBNumMax + 1;
1675 JITDUMP("[SsaBuilder] Max block count is %d.\n", blockCount);
1677 // Allocate the postOrder array for the graph.
1679 BasicBlock** postOrder;
1681 if (blockCount > DEFAULT_MIN_OPTS_BB_COUNT)
1683 postOrder = new (m_pCompiler->getAllocator()) BasicBlock*[blockCount];
1687 postOrder = (BasicBlock**)alloca(blockCount * sizeof(BasicBlock*));
1690 // Topologically sort the graph.
1691 int count = TopologicalSort(postOrder, blockCount);
1692 JITDUMP("[SsaBuilder] Topologically sorted the graph.\n");
1693 EndPhase(PHASE_BUILD_SSA_TOPOSORT);
1696 ComputeImmediateDom(postOrder, count);
1698 // Compute the dominator tree.
1699 BlkToBlkSetMap* domTree = new (m_pCompiler->getAllocator()) BlkToBlkSetMap(m_pCompiler->getAllocator());
1700 ComputeDominators(postOrder, count, domTree);
1701 EndPhase(PHASE_BUILD_SSA_DOMS);
1703 // Insert phi functions.
1704 InsertPhiFunctions(postOrder, count);
1706 // Rename local variables and collect UD information for each ssa var.
1707 SsaRenameState* pRenameState = new (jitstd::utility::allocate<SsaRenameState>(m_allocator), jitstd::placement_t())
1708 SsaRenameState(m_allocator, m_pCompiler->lvaCount);
1709 RenameVariables(domTree, pRenameState);
1710 EndPhase(PHASE_BUILD_SSA_RENAME);
1713 // At this point we are in SSA form. Print the SSA form.
1714 if (m_pCompiler->verboseSsa)
1716 Print(postOrder, count);
1721 void SsaBuilder::SetupBBRoot()
1723 // Allocate a bbroot, if necessary.
1724 // We need a unique block to be the root of the dominator tree.
1725 // This can be violated if the first block is in a try, or if it is the first block of
1726 // a loop (which would necessarily be an infinite loop) -- i.e., it has a predecessor.
1728 // If neither condition holds, no reason to make a new block.
1729 if (!m_pCompiler->fgFirstBB->hasTryIndex() && m_pCompiler->fgFirstBB->bbPreds == nullptr)
1734 BasicBlock* bbRoot = m_pCompiler->bbNewBasicBlock(BBJ_NONE);
1735 bbRoot->bbFlags |= BBF_INTERNAL;
1737 // May need to fix up preds list, so remember the old first block.
1738 BasicBlock* oldFirst = m_pCompiler->fgFirstBB;
1740 // Copy the liveness information from the first basic block.
1741 if (m_pCompiler->fgLocalVarLivenessDone)
1743 VarSetOps::Assign(m_pCompiler, bbRoot->bbLiveIn, oldFirst->bbLiveIn);
1744 VarSetOps::Assign(m_pCompiler, bbRoot->bbLiveOut, oldFirst->bbLiveIn);
1747 // Copy the bbWeight. (This is technically wrong, if the first block is a loop head, but
1748 // it shouldn't matter...)
1749 bbRoot->inheritWeight(oldFirst);
1751 // There's an artifical incoming reference count for the first BB. We're about to make it no longer
1752 // the first BB, so decrement that.
1753 assert(oldFirst->bbRefs > 0);
1756 m_pCompiler->fgInsertBBbefore(m_pCompiler->fgFirstBB, bbRoot);
1758 assert(m_pCompiler->fgFirstBB == bbRoot);
1759 if (m_pCompiler->fgComputePredsDone)
1761 m_pCompiler->fgAddRefPred(oldFirst, bbRoot);
1766 // This method asserts that SSA name constraints specified are satisfied.
1767 void Compiler::JitTestCheckSSA()
1774 static unsigned GetHashCode(SSAName ssaNm)
1776 return ssaNm.m_lvNum << 16 | ssaNm.m_ssaNum;
1779 static bool Equals(SSAName ssaNm1, SSAName ssaNm2)
1781 return ssaNm1.m_lvNum == ssaNm2.m_lvNum && ssaNm1.m_ssaNum == ssaNm2.m_ssaNum;
1785 typedef SimplerHashTable<ssize_t, SmallPrimitiveKeyFuncs<ssize_t>, SSAName, JitSimplerHashBehavior>
1787 typedef SimplerHashTable<SSAName, SSAName, ssize_t, JitSimplerHashBehavior> SSANameToLabelMap;
1789 // If we have no test data, early out.
1790 if (m_nodeTestData == nullptr)
1795 NodeToTestDataMap* testData = GetNodeTestData();
1797 // First we have to know which nodes in the tree are reachable.
1798 NodeToIntMap* reachable = FindReachableNodesInNodeTestData();
1800 LabelToSSANameMap* labelToSSA = new (getAllocatorDebugOnly()) LabelToSSANameMap(getAllocatorDebugOnly());
1801 SSANameToLabelMap* ssaToLabel = new (getAllocatorDebugOnly()) SSANameToLabelMap(getAllocatorDebugOnly());
1805 printf("\nJit Testing: SSA names.\n");
1807 for (NodeToTestDataMap::KeyIterator ki = testData->Begin(); !ki.Equal(testData->End()); ++ki)
1809 TestLabelAndNum tlAndN;
1810 GenTreePtr node = ki.Get();
1811 bool b = testData->Lookup(node, &tlAndN);
1813 if (tlAndN.m_tl == TL_SsaName)
1815 if (node->OperGet() != GT_LCL_VAR)
1817 printf("SSAName constraint put on non-lcl-var expression ");
1819 printf(" (of type %s).\n", varTypeName(node->TypeGet()));
1822 GenTreeLclVarCommon* lcl = node->AsLclVarCommon();
1825 if (!reachable->Lookup(lcl, &dummy))
1829 printf(" had a test constraint declared, but has become unreachable at the time the constraint is "
1831 "(This is probably as a result of some optimization -- \n"
1832 "you may need to modify the test case to defeat this opt.)\n");
1840 printf(", SSA name = <%d, %d> -- SSA name class %d.\n", lcl->gtLclNum, lcl->gtSsaNum, tlAndN.m_num);
1843 if (labelToSSA->Lookup(tlAndN.m_num, &ssaNm))
1847 printf(" Already in hash tables.\n");
1849 // The mapping(s) must be one-to-one: if the label has a mapping, then the ssaNm must, as well.
1851 bool b = ssaToLabel->Lookup(ssaNm, &num2);
1852 // And the mappings must be the same.
1853 if (tlAndN.m_num != num2)
1857 printf(", SSA name = <%d, %d> was declared in SSA name class %d,\n", lcl->gtLclNum, lcl->gtSsaNum,
1860 "but this SSA name <%d,%d> has already been associated with a different SSA name class: %d.\n",
1861 ssaNm.m_lvNum, ssaNm.m_ssaNum, num2);
1864 // And the current node must be of the specified SSA family.
1865 if (!(lcl->gtLclNum == ssaNm.m_lvNum && lcl->gtSsaNum == ssaNm.m_ssaNum))
1869 printf(", SSA name = <%d, %d> was declared in SSA name class %d,\n", lcl->gtLclNum, lcl->gtSsaNum,
1871 printf("but that name class was previously bound to a different SSA name: <%d,%d>.\n",
1872 ssaNm.m_lvNum, ssaNm.m_ssaNum);
1878 ssaNm.m_lvNum = lcl->gtLclNum;
1879 ssaNm.m_ssaNum = lcl->gtSsaNum;
1881 // The mapping(s) must be one-to-one: if the label has no mapping, then the ssaNm may not, either.
1882 if (ssaToLabel->Lookup(ssaNm, &num))
1886 printf(", SSA name = <%d, %d> was declared in SSA name class %d,\n", lcl->gtLclNum, lcl->gtSsaNum,
1888 printf("but this SSA name has already been associated with a different name class: %d.\n", num);
1891 // Add to both mappings.
1892 labelToSSA->Set(tlAndN.m_num, ssaNm);
1893 ssaToLabel->Set(ssaNm, tlAndN.m_num);
1896 printf(" added to hash tables.\n");