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Chris Lattnerb03832d2002-09-24 00:08:39 +00001//===- BreakCriticalEdges.cpp - Critical Edge Elimination Pass ------------===//
Misha Brukmanb1c93172005-04-21 23:48:37 +00002//
Chandler Carruth2946cd72019-01-19 08:50:56 +00003// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
Misha Brukmanb1c93172005-04-21 23:48:37 +00006//
John Criswell482202a2003-10-20 19:43:21 +00007//===----------------------------------------------------------------------===//
Chris Lattnerb03832d2002-09-24 00:08:39 +00008//
9// BreakCriticalEdges pass - Break all of the critical edges in the CFG by
10// inserting a dummy basic block. This pass may be "required" by passes that
11// cannot deal with critical edges. For this usage, the structure type is
12// forward declared. This pass obviously invalidates the CFG, but can update
Cameron Zwarichb7036542011-01-18 04:11:31 +000013// dominator trees.
Chris Lattnerb03832d2002-09-24 00:08:39 +000014//
15//===----------------------------------------------------------------------===//
16
Wei Mie04d0ef2016-07-22 18:04:25 +000017#include "llvm/Transforms/Utils/BreakCriticalEdges.h"
Hiroshi Yamauchi9364fa32017-12-04 20:36:01 +000018#include "llvm/ADT/SetVector.h"
Chandler Carruthed0881b2012-12-03 16:50:05 +000019#include "llvm/ADT/SmallVector.h"
20#include "llvm/ADT/Statistic.h"
Hiroshi Yamauchif3bda1d2017-12-12 19:07:43 +000021#include "llvm/Analysis/BlockFrequencyInfo.h"
22#include "llvm/Analysis/BranchProbabilityInfo.h"
Nick Lewycky0b682452013-07-27 01:24:00 +000023#include "llvm/Analysis/CFG.h"
Chris Lattner89c1dfc2005-08-13 01:38:43 +000024#include "llvm/Analysis/LoopInfo.h"
Alina Sbirleaab6f84f72018-08-21 23:32:03 +000025#include "llvm/Analysis/MemorySSAUpdater.h"
Matt Arsenault65b4ab92019-02-22 15:01:41 +000026#include "llvm/Analysis/PostDominators.h"
Chandler Carruth1305dc32014-03-04 11:45:46 +000027#include "llvm/IR/CFG.h"
Chandler Carruth5ad5f152014-01-13 09:26:24 +000028#include "llvm/IR/Dominators.h"
Chandler Carruth9fb823b2013-01-02 11:36:10 +000029#include "llvm/IR/Instructions.h"
30#include "llvm/IR/Type.h"
Reid Kleckner05da2fe2019-11-13 13:15:01 -080031#include "llvm/InitializePasses.h"
Torok Edwin56d06592009-07-11 20:10:48 +000032#include "llvm/Support/ErrorHandling.h"
David Blaikiea373d182018-03-28 17:44:36 +000033#include "llvm/Transforms/Utils.h"
Chandler Carruthed0881b2012-12-03 16:50:05 +000034#include "llvm/Transforms/Utils/BasicBlockUtils.h"
Hiroshi Yamauchi9364fa32017-12-04 20:36:01 +000035#include "llvm/Transforms/Utils/Cloning.h"
36#include "llvm/Transforms/Utils/ValueMapper.h"
Chris Lattnerdf3c3422004-01-09 06:12:26 +000037using namespace llvm;
Brian Gaeke960707c2003-11-11 22:41:34 +000038
Chandler Carruth964daaa2014-04-22 02:55:47 +000039#define DEBUG_TYPE "break-crit-edges"
40
Chris Lattner45f966d2006-12-19 22:17:40 +000041STATISTIC(NumBroken, "Number of blocks inserted");
Chris Lattnerb03832d2002-09-24 00:08:39 +000042
Chris Lattner45f966d2006-12-19 22:17:40 +000043namespace {
Nick Lewycky02d5f772009-10-25 06:33:48 +000044 struct BreakCriticalEdges : public FunctionPass {
Nick Lewyckye7da2d62007-05-06 13:37:16 +000045 static char ID; // Pass identification, replacement for typeid
Owen Anderson6c18d1a2010-10-19 17:21:58 +000046 BreakCriticalEdges() : FunctionPass(ID) {
47 initializeBreakCriticalEdgesPass(*PassRegistry::getPassRegistry());
48 }
Devang Patel09f162c2007-05-01 21:15:47 +000049
Kostya Serebryanye5ea4242014-11-19 00:17:31 +000050 bool runOnFunction(Function &F) override {
Chandler Carruth37df2cf2015-01-19 12:09:11 +000051 auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>();
52 auto *DT = DTWP ? &DTWP->getDomTree() : nullptr;
Matt Arsenault65b4ab92019-02-22 15:01:41 +000053
54 auto *PDTWP = getAnalysisIfAvailable<PostDominatorTreeWrapperPass>();
55 auto *PDT = PDTWP ? &PDTWP->getPostDomTree() : nullptr;
56
Chandler Carruth37df2cf2015-01-19 12:09:11 +000057 auto *LIWP = getAnalysisIfAvailable<LoopInfoWrapperPass>();
58 auto *LI = LIWP ? &LIWP->getLoopInfo() : nullptr;
59 unsigned N =
Matt Arsenault65b4ab92019-02-22 15:01:41 +000060 SplitAllCriticalEdges(F, CriticalEdgeSplittingOptions(DT, LI, nullptr, PDT));
Kostya Serebryanye5ea4242014-11-19 00:17:31 +000061 NumBroken += N;
62 return N > 0;
63 }
Misha Brukmanb1c93172005-04-21 23:48:37 +000064
Craig Topper3e4c6972014-03-05 09:10:37 +000065 void getAnalysisUsage(AnalysisUsage &AU) const override {
Chandler Carruth73523022014-01-13 13:07:17 +000066 AU.addPreserved<DominatorTreeWrapperPass>();
Chandler Carruth4f8f3072015-01-17 14:16:18 +000067 AU.addPreserved<LoopInfoWrapperPass>();
Chris Lattner72272a72003-10-12 21:52:28 +000068
69 // No loop canonicalization guarantees are broken by this pass.
70 AU.addPreservedID(LoopSimplifyID);
Chris Lattner4bec6652002-09-24 15:43:12 +000071 }
72 };
Alexander Kornienkof00654e2015-06-23 09:49:53 +000073}
Chris Lattnerb03832d2002-09-24 00:08:39 +000074
Dan Gohmand78c4002008-05-13 00:00:25 +000075char BreakCriticalEdges::ID = 0;
Owen Andersond31d82d2010-08-23 17:52:01 +000076INITIALIZE_PASS(BreakCriticalEdges, "break-crit-edges",
Owen Andersondf7a4f22010-10-07 22:25:06 +000077 "Break critical edges in CFG", false, false)
Dan Gohmand78c4002008-05-13 00:00:25 +000078
Chris Lattner0ab5e2c2011-04-15 05:18:47 +000079// Publicly exposed interface to pass...
Owen Andersona7aed182010-08-06 18:33:48 +000080char &llvm::BreakCriticalEdgesID = BreakCriticalEdges::ID;
Chris Lattner7471b962004-07-31 10:01:58 +000081FunctionPass *llvm::createBreakCriticalEdgesPass() {
82 return new BreakCriticalEdges();
83}
Chris Lattnerb03832d2002-09-24 00:08:39 +000084
Wei Mie04d0ef2016-07-22 18:04:25 +000085PreservedAnalyses BreakCriticalEdgesPass::run(Function &F,
86 FunctionAnalysisManager &AM) {
87 auto *DT = AM.getCachedResult<DominatorTreeAnalysis>(F);
88 auto *LI = AM.getCachedResult<LoopAnalysis>(F);
89 unsigned N = SplitAllCriticalEdges(F, CriticalEdgeSplittingOptions(DT, LI));
90 NumBroken += N;
91 if (N == 0)
92 return PreservedAnalyses::all();
93 PreservedAnalyses PA;
94 PA.preserve<DominatorTreeAnalysis>();
95 PA.preserve<LoopAnalysis>();
96 return PA;
97}
98
Chris Lattner1e6d3052003-11-10 04:42:42 +000099//===----------------------------------------------------------------------===//
100// Implementation of the external critical edge manipulation functions
101//===----------------------------------------------------------------------===//
Chris Lattner75f80bd2002-09-24 15:51:56 +0000102
Sanjay Patel85ce0f12016-04-23 16:31:48 +0000103/// When a loop exit edge is split, LCSSA form may require new PHIs in the new
104/// exit block. This function inserts the new PHIs, as needed. Preds is a list
105/// of preds inside the loop, SplitBB is the new loop exit block, and DestBB is
106/// the old loop exit, now the successor of SplitBB.
Bill Wendling325e6cd2012-04-30 10:25:51 +0000107static void createPHIsForSplitLoopExit(ArrayRef<BasicBlock *> Preds,
Dan Gohmanec4557f2009-09-09 18:18:18 +0000108 BasicBlock *SplitBB,
109 BasicBlock *DestBB) {
110 // SplitBB shouldn't have anything non-trivial in it yet.
Bill Wendlingbf4b9af2012-04-30 10:44:54 +0000111 assert((SplitBB->getFirstNonPHI() == SplitBB->getTerminator() ||
112 SplitBB->isLandingPad()) && "SplitBB has non-PHI nodes!");
Dan Gohmanec4557f2009-09-09 18:18:18 +0000113
Bill Wendlingbf4b9af2012-04-30 10:44:54 +0000114 // For each PHI in the destination block.
Benjamin Kramerc7fc81e2017-12-30 15:27:33 +0000115 for (PHINode &PN : DestBB->phis()) {
116 unsigned Idx = PN.getBasicBlockIndex(SplitBB);
117 Value *V = PN.getIncomingValue(Idx);
Bill Wendlingbf4b9af2012-04-30 10:44:54 +0000118
Dan Gohmanec4557f2009-09-09 18:18:18 +0000119 // If the input is a PHI which already satisfies LCSSA, don't create
120 // a new one.
121 if (const PHINode *VP = dyn_cast<PHINode>(V))
122 if (VP->getParent() == SplitBB)
123 continue;
Bill Wendlingbf4b9af2012-04-30 10:44:54 +0000124
Dan Gohmanec4557f2009-09-09 18:18:18 +0000125 // Otherwise a new PHI is needed. Create one and populate it.
Duncan P. N. Exon Smith5b4c8372015-10-13 02:39:05 +0000126 PHINode *NewPN = PHINode::Create(
Benjamin Kramerc7fc81e2017-12-30 15:27:33 +0000127 PN.getType(), Preds.size(), "split",
Duncan P. N. Exon Smith5b4c8372015-10-13 02:39:05 +0000128 SplitBB->isLandingPad() ? &SplitBB->front() : SplitBB->getTerminator());
Dan Gohmanec4557f2009-09-09 18:18:18 +0000129 for (unsigned i = 0, e = Preds.size(); i != e; ++i)
130 NewPN->addIncoming(V, Preds[i]);
Bill Wendlingbf4b9af2012-04-30 10:44:54 +0000131
Dan Gohmanec4557f2009-09-09 18:18:18 +0000132 // Update the original PHI.
Benjamin Kramerc7fc81e2017-12-30 15:27:33 +0000133 PN.setIncomingValue(Idx, NewPN);
Dan Gohmanec4557f2009-09-09 18:18:18 +0000134 }
135}
136
Sanjay Patel85ce0f12016-04-23 16:31:48 +0000137BasicBlock *
Chandler Carruthb99a24682018-10-15 09:17:09 +0000138llvm::SplitCriticalEdge(Instruction *TI, unsigned SuccNum,
Sanjay Patel85ce0f12016-04-23 16:31:48 +0000139 const CriticalEdgeSplittingOptions &Options) {
Chandler Carruth37df2cf2015-01-19 12:09:11 +0000140 if (!isCriticalEdge(TI, SuccNum, Options.MergeIdenticalEdges))
141 return nullptr;
Andrew Trick411842f2011-10-04 03:34:49 +0000142
Chris Lattnerba364b02009-10-31 21:51:10 +0000143 assert(!isa<IndirectBrInst>(TI) &&
144 "Cannot split critical edge from IndirectBrInst");
Andrew Trick411842f2011-10-04 03:34:49 +0000145
Chris Lattner75f80bd2002-09-24 15:51:56 +0000146 BasicBlock *TIBB = TI->getParent();
Chris Lattner12764c82002-10-31 02:44:36 +0000147 BasicBlock *DestBB = TI->getSuccessor(SuccNum);
Chris Lattner75f80bd2002-09-24 15:51:56 +0000148
David Majnemereb518bd2015-08-04 08:21:40 +0000149 // Splitting the critical edge to a pad block is non-trivial. Don't do
Bill Wendling2dfbcc42011-08-17 21:04:05 +0000150 // it in this generic function.
David Majnemereb518bd2015-08-04 08:21:40 +0000151 if (DestBB->isEHPad()) return nullptr;
Bill Wendling2dfbcc42011-08-17 21:04:05 +0000152
Craig Topper784929d2019-02-08 20:48:56 +0000153 // Don't split the non-fallthrough edge from a callbr.
154 if (isa<CallBrInst>(TI) && SuccNum > 0)
155 return nullptr;
156
Craig Topper03e93f52019-03-12 18:20:25 +0000157 if (Options.IgnoreUnreachableDests &&
158 isa<UnreachableInst>(DestBB->getFirstNonPHIOrDbgOrLifetime()))
159 return nullptr;
160
Chris Lattner75f80bd2002-09-24 15:51:56 +0000161 // Create a new basic block, linking it into the CFG.
Owen Anderson55f1c092009-08-13 21:58:54 +0000162 BasicBlock *NewBB = BasicBlock::Create(TI->getContext(),
163 TIBB->getName() + "." + DestBB->getName() + "_crit_edge");
Chris Lattner72c4dce2010-02-13 04:24:19 +0000164 // Create our unconditional branch.
Devang Patelc23bcbc2011-05-17 19:43:06 +0000165 BranchInst *NewBI = BranchInst::Create(DestBB, NewBB);
166 NewBI->setDebugLoc(TI->getDebugLoc());
Misha Brukmanb1c93172005-04-21 23:48:37 +0000167
Chris Lattner80ea2072006-10-28 06:44:56 +0000168 // Branch to the new block, breaking the edge.
Chris Lattner75f80bd2002-09-24 15:51:56 +0000169 TI->setSuccessor(SuccNum, NewBB);
170
171 // Insert the block into the function... right after the block TI lives in.
172 Function &F = *TIBB->getParent();
Duncan P. N. Exon Smith5b4c8372015-10-13 02:39:05 +0000173 Function::iterator FBBI = TIBB->getIterator();
Chris Lattner233f97a2007-04-17 18:09:47 +0000174 F.getBasicBlockList().insert(++FBBI, NewBB);
Andrew Trick411842f2011-10-04 03:34:49 +0000175
Chris Lattner75f80bd2002-09-24 15:51:56 +0000176 // If there are any PHI nodes in DestBB, we need to update them so that they
177 // merge incoming values from NewBB instead of from TIBB.
Jay Foad61ea0e42011-06-23 09:09:15 +0000178 {
179 unsigned BBIdx = 0;
180 for (BasicBlock::iterator I = DestBB->begin(); isa<PHINode>(I); ++I) {
181 // We no longer enter through TIBB, now we come in through NewBB.
182 // Revector exactly one entry in the PHI node that used to come from
183 // TIBB to come from NewBB.
184 PHINode *PN = cast<PHINode>(I);
185
186 // Reuse the previous value of BBIdx if it lines up. In cases where we
187 // have multiple phi nodes with *lots* of predecessors, this is a speed
188 // win because we don't have to scan the PHI looking for TIBB. This
189 // happens because the BB list of PHI nodes are usually in the same
190 // order.
191 if (PN->getIncomingBlock(BBIdx) != TIBB)
Andrew Trick411842f2011-10-04 03:34:49 +0000192 BBIdx = PN->getBasicBlockIndex(TIBB);
Jay Foad61ea0e42011-06-23 09:09:15 +0000193 PN->setIncomingBlock(BBIdx, NewBB);
Chris Lattner5e7f7052010-02-13 05:01:14 +0000194 }
Chris Lattner75f80bd2002-09-24 15:51:56 +0000195 }
Andrew Trick411842f2011-10-04 03:34:49 +0000196
Chris Lattner80ea2072006-10-28 06:44:56 +0000197 // If there are any other edges from TIBB to DestBB, update those to go
198 // through the split block, making those edges non-critical as well (and
199 // reducing the number of phi entries in the DestBB if relevant).
Chandler Carruth37df2cf2015-01-19 12:09:11 +0000200 if (Options.MergeIdenticalEdges) {
Chris Lattner80ea2072006-10-28 06:44:56 +0000201 for (unsigned i = SuccNum+1, e = TI->getNumSuccessors(); i != e; ++i) {
202 if (TI->getSuccessor(i) != DestBB) continue;
Andrew Trick411842f2011-10-04 03:34:49 +0000203
Chris Lattner80ea2072006-10-28 06:44:56 +0000204 // Remove an entry for TIBB from DestBB phi nodes.
Max Kazantsev20b91892019-02-12 07:09:29 +0000205 DestBB->removePredecessor(TIBB, Options.KeepOneInputPHIs);
Andrew Trick411842f2011-10-04 03:34:49 +0000206
Chris Lattner80ea2072006-10-28 06:44:56 +0000207 // We found another edge to DestBB, go to NewBB instead.
208 TI->setSuccessor(i, NewBB);
209 }
210 }
Andrew Trick411842f2011-10-04 03:34:49 +0000211
Chris Lattner5e7f7052010-02-13 05:01:14 +0000212 // If we have nothing to update, just return.
Chandler Carruth37df2cf2015-01-19 12:09:11 +0000213 auto *DT = Options.DT;
Matt Arsenault65b4ab92019-02-22 15:01:41 +0000214 auto *PDT = Options.PDT;
Chandler Carruth37df2cf2015-01-19 12:09:11 +0000215 auto *LI = Options.LI;
Alina Sbirleaab6f84f72018-08-21 23:32:03 +0000216 auto *MSSAU = Options.MSSAU;
217 if (MSSAU)
Alina Sbirleaf98c2c52018-09-07 21:14:48 +0000218 MSSAU->wireOldPredecessorsToNewImmediatePredecessor(
219 DestBB, NewBB, {TIBB}, Options.MergeIdenticalEdges);
Alina Sbirleaab6f84f72018-08-21 23:32:03 +0000220
Matt Arsenault65b4ab92019-02-22 15:01:41 +0000221 if (!DT && !PDT && !LI)
Chris Lattner5e7f7052010-02-13 05:01:14 +0000222 return NewBB;
Chris Lattner5ac72de2002-10-08 21:06:27 +0000223
Matt Arsenault65b4ab92019-02-22 15:01:41 +0000224 if (DT || PDT) {
Jakub Kuderskie35a4492017-08-17 16:45:35 +0000225 // Update the DominatorTree.
226 // ---> NewBB -----\
227 // / V
228 // TIBB -------\\------> DestBB
Chris Lattnerbedbd6b2002-09-26 16:18:51 +0000229 //
Jakub Kuderskie35a4492017-08-17 16:45:35 +0000230 // First, inform the DT about the new path from TIBB to DestBB via NewBB,
231 // then delete the old edge from TIBB to DestBB. By doing this in that order
232 // DestBB stays reachable in the DT the whole time and its subtree doesn't
233 // get disconnected.
234 SmallVector<DominatorTree::UpdateType, 3> Updates;
235 Updates.push_back({DominatorTree::Insert, TIBB, NewBB});
236 Updates.push_back({DominatorTree::Insert, NewBB, DestBB});
237 if (llvm::find(successors(TIBB), DestBB) == succ_end(TIBB))
238 Updates.push_back({DominatorTree::Delete, TIBB, DestBB});
Andrew Trick411842f2011-10-04 03:34:49 +0000239
Matt Arsenault65b4ab92019-02-22 15:01:41 +0000240 if (DT)
241 DT->applyUpdates(Updates);
242 if (PDT)
243 PDT->applyUpdates(Updates);
Chris Lattner75f80bd2002-09-24 15:51:56 +0000244 }
Chris Lattner12764c82002-10-31 02:44:36 +0000245
Chris Lattner89c1dfc2005-08-13 01:38:43 +0000246 // Update LoopInfo if it is around.
Chris Lattner5e7f7052010-02-13 05:01:14 +0000247 if (LI) {
Dan Gohman3ddbc242009-09-08 15:45:00 +0000248 if (Loop *TIL = LI->getLoopFor(TIBB)) {
249 // If one or the other blocks were not in a loop, the new block is not
250 // either, and thus LI doesn't need to be updated.
Chris Lattner89c1dfc2005-08-13 01:38:43 +0000251 if (Loop *DestLoop = LI->getLoopFor(DestBB)) {
252 if (TIL == DestLoop) {
253 // Both in the same loop, the NewBB joins loop.
Chandler Carruth691addc2015-01-18 01:25:51 +0000254 DestLoop->addBasicBlockToLoop(NewBB, *LI);
Dan Gohman18fa5682009-12-18 01:24:09 +0000255 } else if (TIL->contains(DestLoop)) {
Chris Lattner8aca0ee2006-10-03 07:02:02 +0000256 // Edge from an outer loop to an inner loop. Add to the outer loop.
Chandler Carruth691addc2015-01-18 01:25:51 +0000257 TIL->addBasicBlockToLoop(NewBB, *LI);
Dan Gohman18fa5682009-12-18 01:24:09 +0000258 } else if (DestLoop->contains(TIL)) {
Chris Lattner8aca0ee2006-10-03 07:02:02 +0000259 // Edge from an inner loop to an outer loop. Add to the outer loop.
Chandler Carruth691addc2015-01-18 01:25:51 +0000260 DestLoop->addBasicBlockToLoop(NewBB, *LI);
Chris Lattner89c1dfc2005-08-13 01:38:43 +0000261 } else {
262 // Edge from two loops with no containment relation. Because these
263 // are natural loops, we know that the destination block must be the
264 // header of its loop (adding a branch into a loop elsewhere would
265 // create an irreducible loop).
266 assert(DestLoop->getHeader() == DestBB &&
267 "Should not create irreducible loops!");
268 if (Loop *P = DestLoop->getParentLoop())
Chandler Carruth691addc2015-01-18 01:25:51 +0000269 P->addBasicBlockToLoop(NewBB, *LI);
Chris Lattner89c1dfc2005-08-13 01:38:43 +0000270 }
271 }
Chandler Carruthad34d912015-01-19 10:23:00 +0000272
Chandler Carruthd4be9dc2014-01-29 13:16:53 +0000273 // If TIBB is in a loop and DestBB is outside of that loop, we may need
274 // to update LoopSimplify form and LCSSA form.
Chandler Carruthad34d912015-01-19 10:23:00 +0000275 if (!TIL->contains(DestBB)) {
Dan Gohmanec4557f2009-09-09 18:18:18 +0000276 assert(!TIL->contains(NewBB) &&
277 "Split point for loop exit is contained in loop!");
278
279 // Update LCSSA form in the newly created exit block.
Chandler Carruth37df2cf2015-01-19 12:09:11 +0000280 if (Options.PreserveLCSSA) {
Bill Wendling325e6cd2012-04-30 10:25:51 +0000281 createPHIsForSplitLoopExit(TIBB, NewBB, DestBB);
Chandler Carruthad34d912015-01-19 10:23:00 +0000282 }
Dan Gohmanec4557f2009-09-09 18:18:18 +0000283
Chandler Carruthd4be9dc2014-01-29 13:16:53 +0000284 // The only that we can break LoopSimplify form by splitting a critical
285 // edge is if after the split there exists some edge from TIL to DestBB
286 // *and* the only edge into DestBB from outside of TIL is that of
287 // NewBB. If the first isn't true, then LoopSimplify still holds, NewBB
288 // is the new exit block and it has no non-loop predecessors. If the
289 // second isn't true, then DestBB was not in LoopSimplify form prior to
290 // the split as it had a non-loop predecessor. In both of these cases,
291 // the predecessor must be directly in TIL, not in a subloop, or again
292 // LoopSimplify doesn't hold.
293 SmallVector<BasicBlock *, 4> LoopPreds;
Duncan P. N. Exon Smith6c990152014-07-21 17:06:51 +0000294 for (pred_iterator I = pred_begin(DestBB), E = pred_end(DestBB); I != E;
295 ++I) {
296 BasicBlock *P = *I;
Chandler Carruthd4be9dc2014-01-29 13:16:53 +0000297 if (P == NewBB)
298 continue; // The new block is known.
299 if (LI->getLoopFor(P) != TIL) {
300 // No need to re-simplify, it wasn't to start with.
301 LoopPreds.clear();
302 break;
Gabor Greiffd8e7d42010-07-09 16:31:08 +0000303 }
Chandler Carruthd4be9dc2014-01-29 13:16:53 +0000304 LoopPreds.push_back(P);
305 }
306 if (!LoopPreds.empty()) {
David Majnemereb518bd2015-08-04 08:21:40 +0000307 assert(!DestBB->isEHPad() && "We don't split edges to EH pads!");
Chandler Carruthb5797b62015-01-18 09:21:15 +0000308 BasicBlock *NewExitBB = SplitBlockPredecessors(
Alina Sbirleaab6f84f72018-08-21 23:32:03 +0000309 DestBB, LoopPreds, "split", DT, LI, MSSAU, Options.PreserveLCSSA);
Chandler Carruth37df2cf2015-01-19 12:09:11 +0000310 if (Options.PreserveLCSSA)
Chandler Carruthd4be9dc2014-01-29 13:16:53 +0000311 createPHIsForSplitLoopExit(LoopPreds, NewExitBB, DestBB);
Dan Gohman3ddbc242009-09-08 15:45:00 +0000312 }
313 }
Dan Gohman3ddbc242009-09-08 15:45:00 +0000314 }
Chris Lattner89c1dfc2005-08-13 01:38:43 +0000315 }
Dan Gohman3ddbc242009-09-08 15:45:00 +0000316
317 return NewBB;
Chris Lattner75f80bd2002-09-24 15:51:56 +0000318}
Hiroshi Yamauchi9364fa32017-12-04 20:36:01 +0000319
320// Return the unique indirectbr predecessor of a block. This may return null
321// even if such a predecessor exists, if it's not useful for splitting.
322// If a predecessor is found, OtherPreds will contain all other (non-indirectbr)
323// predecessors of BB.
324static BasicBlock *
325findIBRPredecessor(BasicBlock *BB, SmallVectorImpl<BasicBlock *> &OtherPreds) {
326 // If the block doesn't have any PHIs, we don't care about it, since there's
327 // no point in splitting it.
328 PHINode *PN = dyn_cast<PHINode>(BB->begin());
329 if (!PN)
330 return nullptr;
331
332 // Verify we have exactly one IBR predecessor.
333 // Conservatively bail out if one of the other predecessors is not a "regular"
334 // terminator (that is, not a switch or a br).
335 BasicBlock *IBB = nullptr;
336 for (unsigned Pred = 0, E = PN->getNumIncomingValues(); Pred != E; ++Pred) {
337 BasicBlock *PredBB = PN->getIncomingBlock(Pred);
Chandler Carruthedb12a82018-10-15 10:04:59 +0000338 Instruction *PredTerm = PredBB->getTerminator();
Hiroshi Yamauchi9364fa32017-12-04 20:36:01 +0000339 switch (PredTerm->getOpcode()) {
340 case Instruction::IndirectBr:
341 if (IBB)
342 return nullptr;
343 IBB = PredBB;
344 break;
345 case Instruction::Br:
346 case Instruction::Switch:
347 OtherPreds.push_back(PredBB);
348 continue;
349 default:
350 return nullptr;
351 }
352 }
353
354 return IBB;
355}
356
Hiroshi Yamauchif3bda1d2017-12-12 19:07:43 +0000357bool llvm::SplitIndirectBrCriticalEdges(Function &F,
358 BranchProbabilityInfo *BPI,
359 BlockFrequencyInfo *BFI) {
Hiroshi Yamauchi9364fa32017-12-04 20:36:01 +0000360 // Check whether the function has any indirectbrs, and collect which blocks
361 // they may jump to. Since most functions don't have indirect branches,
362 // this lowers the common case's overhead to O(Blocks) instead of O(Edges).
363 SmallSetVector<BasicBlock *, 16> Targets;
364 for (auto &BB : F) {
365 auto *IBI = dyn_cast<IndirectBrInst>(BB.getTerminator());
366 if (!IBI)
367 continue;
368
369 for (unsigned Succ = 0, E = IBI->getNumSuccessors(); Succ != E; ++Succ)
370 Targets.insert(IBI->getSuccessor(Succ));
371 }
372
373 if (Targets.empty())
374 return false;
375
Hiroshi Yamauchif3bda1d2017-12-12 19:07:43 +0000376 bool ShouldUpdateAnalysis = BPI && BFI;
Hiroshi Yamauchi9364fa32017-12-04 20:36:01 +0000377 bool Changed = false;
378 for (BasicBlock *Target : Targets) {
379 SmallVector<BasicBlock *, 16> OtherPreds;
380 BasicBlock *IBRPred = findIBRPredecessor(Target, OtherPreds);
381 // If we did not found an indirectbr, or the indirectbr is the only
382 // incoming edge, this isn't the kind of edge we're looking for.
383 if (!IBRPred || OtherPreds.empty())
384 continue;
385
386 // Don't even think about ehpads/landingpads.
387 Instruction *FirstNonPHI = Target->getFirstNonPHI();
388 if (FirstNonPHI->isEHPad() || Target->isLandingPad())
389 continue;
390
391 BasicBlock *BodyBlock = Target->splitBasicBlock(FirstNonPHI, ".split");
Hiroshi Yamauchif3bda1d2017-12-12 19:07:43 +0000392 if (ShouldUpdateAnalysis) {
393 // Copy the BFI/BPI from Target to BodyBlock.
394 for (unsigned I = 0, E = BodyBlock->getTerminator()->getNumSuccessors();
395 I < E; ++I)
396 BPI->setEdgeProbability(BodyBlock, I,
397 BPI->getEdgeProbability(Target, I));
398 BFI->setBlockFreq(BodyBlock, BFI->getBlockFreq(Target).getFrequency());
399 }
Hiroshi Yamauchi9364fa32017-12-04 20:36:01 +0000400 // It's possible Target was its own successor through an indirectbr.
401 // In this case, the indirectbr now comes from BodyBlock.
402 if (IBRPred == Target)
403 IBRPred = BodyBlock;
404
405 // At this point Target only has PHIs, and BodyBlock has the rest of the
406 // block's body. Create a copy of Target that will be used by the "direct"
407 // preds.
408 ValueToValueMapTy VMap;
409 BasicBlock *DirectSucc = CloneBasicBlock(Target, VMap, ".clone", &F);
410
Hiroshi Yamauchif3bda1d2017-12-12 19:07:43 +0000411 BlockFrequency BlockFreqForDirectSucc;
Hiroshi Yamauchi9364fa32017-12-04 20:36:01 +0000412 for (BasicBlock *Pred : OtherPreds) {
413 // If the target is a loop to itself, then the terminator of the split
Hiroshi Yamauchif3bda1d2017-12-12 19:07:43 +0000414 // block (BodyBlock) needs to be updated.
415 BasicBlock *Src = Pred != Target ? Pred : BodyBlock;
416 Src->getTerminator()->replaceUsesOfWith(Target, DirectSucc);
417 if (ShouldUpdateAnalysis)
418 BlockFreqForDirectSucc += BFI->getBlockFreq(Src) *
419 BPI->getEdgeProbability(Src, DirectSucc);
420 }
421 if (ShouldUpdateAnalysis) {
422 BFI->setBlockFreq(DirectSucc, BlockFreqForDirectSucc.getFrequency());
423 BlockFrequency NewBlockFreqForTarget =
424 BFI->getBlockFreq(Target) - BlockFreqForDirectSucc;
425 BFI->setBlockFreq(Target, NewBlockFreqForTarget.getFrequency());
426 BPI->eraseBlock(Target);
Hiroshi Yamauchi9364fa32017-12-04 20:36:01 +0000427 }
428
429 // Ok, now fix up the PHIs. We know the two blocks only have PHIs, and that
430 // they are clones, so the number of PHIs are the same.
431 // (a) Remove the edge coming from IBRPred from the "Direct" PHI
432 // (b) Leave that as the only edge in the "Indirect" PHI.
433 // (c) Merge the two in the body block.
434 BasicBlock::iterator Indirect = Target->begin(),
435 End = Target->getFirstNonPHI()->getIterator();
436 BasicBlock::iterator Direct = DirectSucc->begin();
437 BasicBlock::iterator MergeInsert = BodyBlock->getFirstInsertionPt();
438
439 assert(&*End == Target->getTerminator() &&
440 "Block was expected to only contain PHIs");
441
442 while (Indirect != End) {
443 PHINode *DirPHI = cast<PHINode>(Direct);
444 PHINode *IndPHI = cast<PHINode>(Indirect);
445
446 // Now, clean up - the direct block shouldn't get the indirect value,
447 // and vice versa.
448 DirPHI->removeIncomingValue(IBRPred);
449 Direct++;
450
451 // Advance the pointer here, to avoid invalidation issues when the old
452 // PHI is erased.
453 Indirect++;
454
455 PHINode *NewIndPHI = PHINode::Create(IndPHI->getType(), 1, "ind", IndPHI);
456 NewIndPHI->addIncoming(IndPHI->getIncomingValueForBlock(IBRPred),
457 IBRPred);
458
459 // Create a PHI in the body block, to merge the direct and indirect
460 // predecessors.
461 PHINode *MergePHI =
462 PHINode::Create(IndPHI->getType(), 2, "merge", &*MergeInsert);
463 MergePHI->addIncoming(NewIndPHI, Target);
464 MergePHI->addIncoming(DirPHI, DirectSucc);
465
466 IndPHI->replaceAllUsesWith(MergePHI);
467 IndPHI->eraseFromParent();
468 }
469
470 Changed = true;
471 }
472
473 return Changed;
474}