Chris Lattner | 8383a7b | 2008-04-20 20:35:01 +0000 | [diff] [blame] | 1 | //===- JumpThreading.cpp - Thread control through conditional blocks ------===// |
| 2 | // |
| 3 | // The LLVM Compiler Infrastructure |
| 4 | // |
| 5 | // This file is distributed under the University of Illinois Open Source |
| 6 | // License. See LICENSE.TXT for details. |
| 7 | // |
| 8 | //===----------------------------------------------------------------------===// |
| 9 | // |
Chris Lattner | 177480b | 2008-04-20 21:13:06 +0000 | [diff] [blame] | 10 | // This file implements the Jump Threading pass. |
Chris Lattner | 8383a7b | 2008-04-20 20:35:01 +0000 | [diff] [blame] | 11 | // |
| 12 | //===----------------------------------------------------------------------===// |
| 13 | |
| 14 | #define DEBUG_TYPE "jump-threading" |
| 15 | #include "llvm/Transforms/Scalar.h" |
Chris Lattner | 177480b | 2008-04-20 21:13:06 +0000 | [diff] [blame] | 16 | #include "llvm/IntrinsicInst.h" |
Owen Anderson | 1ff50b3 | 2009-07-03 00:54:20 +0000 | [diff] [blame] | 17 | #include "llvm/LLVMContext.h" |
Chris Lattner | 8383a7b | 2008-04-20 20:35:01 +0000 | [diff] [blame] | 18 | #include "llvm/Pass.h" |
Chris Lattner | 9819ef7 | 2009-11-09 23:00:14 +0000 | [diff] [blame] | 19 | #include "llvm/Analysis/InstructionSimplify.h" |
Chris Lattner | cc4d3b2 | 2009-11-11 02:08:33 +0000 | [diff] [blame] | 20 | #include "llvm/Analysis/LazyValueInfo.h" |
Dan Gohman | dd9344f | 2010-05-28 16:19:17 +0000 | [diff] [blame] | 21 | #include "llvm/Analysis/Loads.h" |
Chris Lattner | 2cc6751 | 2008-04-21 02:57:57 +0000 | [diff] [blame] | 22 | #include "llvm/Transforms/Utils/BasicBlockUtils.h" |
Chris Lattner | bd3401f | 2008-04-20 22:39:42 +0000 | [diff] [blame] | 23 | #include "llvm/Transforms/Utils/Local.h" |
Chris Lattner | 433a0db | 2009-10-10 09:05:58 +0000 | [diff] [blame] | 24 | #include "llvm/Transforms/Utils/SSAUpdater.h" |
Chris Lattner | ef0c674 | 2008-12-01 04:48:07 +0000 | [diff] [blame] | 25 | #include "llvm/Target/TargetData.h" |
Mike Stump | fe095f3 | 2009-05-04 18:40:41 +0000 | [diff] [blame] | 26 | #include "llvm/ADT/DenseMap.h" |
| 27 | #include "llvm/ADT/Statistic.h" |
| 28 | #include "llvm/ADT/STLExtras.h" |
| 29 | #include "llvm/ADT/SmallPtrSet.h" |
| 30 | #include "llvm/ADT/SmallSet.h" |
Chris Lattner | 8383a7b | 2008-04-20 20:35:01 +0000 | [diff] [blame] | 31 | #include "llvm/Support/CommandLine.h" |
Chris Lattner | 177480b | 2008-04-20 21:13:06 +0000 | [diff] [blame] | 32 | #include "llvm/Support/Debug.h" |
Chris Lattner | 5660846 | 2009-12-28 08:20:46 +0000 | [diff] [blame] | 33 | #include "llvm/Support/ValueHandle.h" |
Daniel Dunbar | 93b67e4 | 2009-07-26 07:49:05 +0000 | [diff] [blame] | 34 | #include "llvm/Support/raw_ostream.h" |
Chris Lattner | 8383a7b | 2008-04-20 20:35:01 +0000 | [diff] [blame] | 35 | using namespace llvm; |
| 36 | |
Chris Lattner | bd3401f | 2008-04-20 22:39:42 +0000 | [diff] [blame] | 37 | STATISTIC(NumThreads, "Number of jumps threaded"); |
| 38 | STATISTIC(NumFolds, "Number of terminators folded"); |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 39 | STATISTIC(NumDupes, "Number of branch blocks duplicated to eliminate phi"); |
Chris Lattner | 8383a7b | 2008-04-20 20:35:01 +0000 | [diff] [blame] | 40 | |
Chris Lattner | 177480b | 2008-04-20 21:13:06 +0000 | [diff] [blame] | 41 | static cl::opt<unsigned> |
| 42 | Threshold("jump-threading-threshold", |
| 43 | cl::desc("Max block size to duplicate for jump threading"), |
| 44 | cl::init(6), cl::Hidden); |
| 45 | |
Chris Lattner | cc4d3b2 | 2009-11-11 02:08:33 +0000 | [diff] [blame] | 46 | // Turn on use of LazyValueInfo. |
| 47 | static cl::opt<bool> |
Owen Anderson | f35b08d | 2010-08-05 22:11:31 +0000 | [diff] [blame] | 48 | EnableLVI("enable-jump-threading-lvi", |
| 49 | cl::desc("Use LVI for jump threading"), |
| 50 | cl::init(false), |
| 51 | cl::ReallyHidden); |
Chris Lattner | cc4d3b2 | 2009-11-11 02:08:33 +0000 | [diff] [blame] | 52 | |
| 53 | |
| 54 | |
Chris Lattner | 8383a7b | 2008-04-20 20:35:01 +0000 | [diff] [blame] | 55 | namespace { |
Chris Lattner | 94019f8 | 2008-05-09 04:43:13 +0000 | [diff] [blame] | 56 | /// This pass performs 'jump threading', which looks at blocks that have |
| 57 | /// multiple predecessors and multiple successors. If one or more of the |
| 58 | /// predecessors of the block can be proven to always jump to one of the |
| 59 | /// successors, we forward the edge from the predecessor to the successor by |
| 60 | /// duplicating the contents of this block. |
| 61 | /// |
| 62 | /// An example of when this can occur is code like this: |
| 63 | /// |
| 64 | /// if () { ... |
| 65 | /// X = 4; |
| 66 | /// } |
| 67 | /// if (X < 3) { |
| 68 | /// |
| 69 | /// In this case, the unconditional branch at the end of the first if can be |
| 70 | /// revectored to the false side of the second if. |
| 71 | /// |
Chris Lattner | 3e8b663 | 2009-09-02 06:11:42 +0000 | [diff] [blame] | 72 | class JumpThreading : public FunctionPass { |
Chris Lattner | ef0c674 | 2008-12-01 04:48:07 +0000 | [diff] [blame] | 73 | TargetData *TD; |
Chris Lattner | cc4d3b2 | 2009-11-11 02:08:33 +0000 | [diff] [blame] | 74 | LazyValueInfo *LVI; |
Mike Stump | fe095f3 | 2009-05-04 18:40:41 +0000 | [diff] [blame] | 75 | #ifdef NDEBUG |
| 76 | SmallPtrSet<BasicBlock*, 16> LoopHeaders; |
| 77 | #else |
| 78 | SmallSet<AssertingVH<BasicBlock>, 16> LoopHeaders; |
| 79 | #endif |
Chris Lattner | 8383a7b | 2008-04-20 20:35:01 +0000 | [diff] [blame] | 80 | public: |
| 81 | static char ID; // Pass identification |
Owen Anderson | 90c579d | 2010-08-06 18:33:48 +0000 | [diff] [blame] | 82 | JumpThreading() : FunctionPass(ID) {} |
Chris Lattner | 8383a7b | 2008-04-20 20:35:01 +0000 | [diff] [blame] | 83 | |
| 84 | bool runOnFunction(Function &F); |
Mike Stump | fe095f3 | 2009-05-04 18:40:41 +0000 | [diff] [blame] | 85 | |
Chris Lattner | cc4d3b2 | 2009-11-11 02:08:33 +0000 | [diff] [blame] | 86 | virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| 87 | if (EnableLVI) |
| 88 | AU.addRequired<LazyValueInfo>(); |
| 89 | } |
| 90 | |
| 91 | void FindLoopHeaders(Function &F); |
Chris Lattner | c7bcbf6 | 2008-11-27 07:20:04 +0000 | [diff] [blame] | 92 | bool ProcessBlock(BasicBlock *BB); |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 93 | bool ThreadEdge(BasicBlock *BB, const SmallVectorImpl<BasicBlock*> &PredBBs, |
| 94 | BasicBlock *SuccBB); |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 95 | bool DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB, |
Chris Lattner | 2249a0b | 2010-01-12 02:07:17 +0000 | [diff] [blame] | 96 | const SmallVectorImpl<BasicBlock *> &PredBBs); |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 97 | |
| 98 | typedef SmallVectorImpl<std::pair<ConstantInt*, |
| 99 | BasicBlock*> > PredValueInfo; |
| 100 | |
| 101 | bool ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB, |
| 102 | PredValueInfo &Result); |
Chris Lattner | 1c96b41 | 2009-11-12 01:37:43 +0000 | [diff] [blame] | 103 | bool ProcessThreadableEdges(Value *Cond, BasicBlock *BB); |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 104 | |
| 105 | |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 106 | bool ProcessBranchOnDuplicateCond(BasicBlock *PredBB, BasicBlock *DestBB); |
Chris Lattner | 3cda3cd | 2008-12-04 06:31:07 +0000 | [diff] [blame] | 107 | bool ProcessSwitchOnDuplicateCond(BasicBlock *PredBB, BasicBlock *DestBB); |
Chris Lattner | 6bf7750 | 2008-04-22 07:05:46 +0000 | [diff] [blame] | 108 | |
Chris Lattner | 77beb47 | 2010-01-11 23:41:09 +0000 | [diff] [blame] | 109 | bool ProcessBranchOnPHI(PHINode *PN); |
Chris Lattner | 2249a0b | 2010-01-12 02:07:17 +0000 | [diff] [blame] | 110 | bool ProcessBranchOnXOR(BinaryOperator *BO); |
Chris Lattner | 69e067f | 2008-11-27 05:07:53 +0000 | [diff] [blame] | 111 | |
| 112 | bool SimplifyPartiallyRedundantLoad(LoadInst *LI); |
Chris Lattner | 8383a7b | 2008-04-20 20:35:01 +0000 | [diff] [blame] | 113 | }; |
Chris Lattner | 8383a7b | 2008-04-20 20:35:01 +0000 | [diff] [blame] | 114 | } |
| 115 | |
Dan Gohman | 844731a | 2008-05-13 00:00:25 +0000 | [diff] [blame] | 116 | char JumpThreading::ID = 0; |
Owen Anderson | d13db2c | 2010-07-21 22:09:45 +0000 | [diff] [blame] | 117 | INITIALIZE_PASS(JumpThreading, "jump-threading", |
| 118 | "Jump Threading", false, false); |
Dan Gohman | 844731a | 2008-05-13 00:00:25 +0000 | [diff] [blame] | 119 | |
Chris Lattner | 8383a7b | 2008-04-20 20:35:01 +0000 | [diff] [blame] | 120 | // Public interface to the Jump Threading pass |
| 121 | FunctionPass *llvm::createJumpThreadingPass() { return new JumpThreading(); } |
| 122 | |
| 123 | /// runOnFunction - Top level algorithm. |
| 124 | /// |
| 125 | bool JumpThreading::runOnFunction(Function &F) { |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 126 | DEBUG(dbgs() << "Jump threading on function '" << F.getName() << "'\n"); |
Dan Gohman | 02a436c | 2009-07-24 18:13:53 +0000 | [diff] [blame] | 127 | TD = getAnalysisIfAvailable<TargetData>(); |
Chris Lattner | cc4d3b2 | 2009-11-11 02:08:33 +0000 | [diff] [blame] | 128 | LVI = EnableLVI ? &getAnalysis<LazyValueInfo>() : 0; |
Chris Lattner | bd3401f | 2008-04-20 22:39:42 +0000 | [diff] [blame] | 129 | |
Mike Stump | fe095f3 | 2009-05-04 18:40:41 +0000 | [diff] [blame] | 130 | FindLoopHeaders(F); |
| 131 | |
Benjamin Kramer | 66b581e | 2010-01-07 13:50:07 +0000 | [diff] [blame] | 132 | bool Changed, EverChanged = false; |
| 133 | do { |
| 134 | Changed = false; |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 135 | for (Function::iterator I = F.begin(), E = F.end(); I != E;) { |
| 136 | BasicBlock *BB = I; |
Chris Lattner | f3183f6 | 2009-11-10 21:40:01 +0000 | [diff] [blame] | 137 | // Thread all of the branches we can over this block. |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 138 | while (ProcessBlock(BB)) |
Chris Lattner | bd3401f | 2008-04-20 22:39:42 +0000 | [diff] [blame] | 139 | Changed = true; |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 140 | |
| 141 | ++I; |
| 142 | |
| 143 | // If the block is trivially dead, zap it. This eliminates the successor |
| 144 | // edges which simplifies the CFG. |
| 145 | if (pred_begin(BB) == pred_end(BB) && |
Chris Lattner | 20fa76e | 2008-12-08 22:44:07 +0000 | [diff] [blame] | 146 | BB != &BB->getParent()->getEntryBlock()) { |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 147 | DEBUG(dbgs() << " JT: Deleting dead block '" << BB->getName() |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 148 | << "' with terminator: " << *BB->getTerminator() << '\n'); |
Mike Stump | fe095f3 | 2009-05-04 18:40:41 +0000 | [diff] [blame] | 149 | LoopHeaders.erase(BB); |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 150 | DeleteDeadBlock(BB); |
| 151 | Changed = true; |
Chris Lattner | f3183f6 | 2009-11-10 21:40:01 +0000 | [diff] [blame] | 152 | } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) { |
| 153 | // Can't thread an unconditional jump, but if the block is "almost |
| 154 | // empty", we can replace uses of it with uses of the successor and make |
| 155 | // this dead. |
| 156 | if (BI->isUnconditional() && |
| 157 | BB != &BB->getParent()->getEntryBlock()) { |
| 158 | BasicBlock::iterator BBI = BB->getFirstNonPHI(); |
| 159 | // Ignore dbg intrinsics. |
| 160 | while (isa<DbgInfoIntrinsic>(BBI)) |
| 161 | ++BBI; |
| 162 | // If the terminator is the only non-phi instruction, try to nuke it. |
| 163 | if (BBI->isTerminator()) { |
Chris Lattner | 6f84a5f | 2009-11-10 21:45:09 +0000 | [diff] [blame] | 164 | // Since TryToSimplifyUncondBranchFromEmptyBlock may delete the |
| 165 | // block, we have to make sure it isn't in the LoopHeaders set. We |
Chris Lattner | 46875c0 | 2009-12-01 06:04:43 +0000 | [diff] [blame] | 166 | // reinsert afterward if needed. |
Chris Lattner | 6f84a5f | 2009-11-10 21:45:09 +0000 | [diff] [blame] | 167 | bool ErasedFromLoopHeaders = LoopHeaders.erase(BB); |
Chris Lattner | 46875c0 | 2009-12-01 06:04:43 +0000 | [diff] [blame] | 168 | BasicBlock *Succ = BI->getSuccessor(0); |
Chris Lattner | f3183f6 | 2009-11-10 21:40:01 +0000 | [diff] [blame] | 169 | |
Chris Lattner | 46875c0 | 2009-12-01 06:04:43 +0000 | [diff] [blame] | 170 | if (TryToSimplifyUncondBranchFromEmptyBlock(BB)) { |
Chris Lattner | f3183f6 | 2009-11-10 21:40:01 +0000 | [diff] [blame] | 171 | Changed = true; |
Chris Lattner | 46875c0 | 2009-12-01 06:04:43 +0000 | [diff] [blame] | 172 | // If we deleted BB and BB was the header of a loop, then the |
| 173 | // successor is now the header of the loop. |
| 174 | BB = Succ; |
| 175 | } |
| 176 | |
| 177 | if (ErasedFromLoopHeaders) |
Chris Lattner | f3183f6 | 2009-11-10 21:40:01 +0000 | [diff] [blame] | 178 | LoopHeaders.insert(BB); |
| 179 | } |
| 180 | } |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 181 | } |
| 182 | } |
Chris Lattner | bd3401f | 2008-04-20 22:39:42 +0000 | [diff] [blame] | 183 | EverChanged |= Changed; |
Benjamin Kramer | 66b581e | 2010-01-07 13:50:07 +0000 | [diff] [blame] | 184 | } while (Changed); |
Mike Stump | fe095f3 | 2009-05-04 18:40:41 +0000 | [diff] [blame] | 185 | |
| 186 | LoopHeaders.clear(); |
Chris Lattner | bd3401f | 2008-04-20 22:39:42 +0000 | [diff] [blame] | 187 | return EverChanged; |
Chris Lattner | 8383a7b | 2008-04-20 20:35:01 +0000 | [diff] [blame] | 188 | } |
Chris Lattner | 177480b | 2008-04-20 21:13:06 +0000 | [diff] [blame] | 189 | |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 190 | /// getJumpThreadDuplicationCost - Return the cost of duplicating this block to |
| 191 | /// thread across it. |
| 192 | static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB) { |
| 193 | /// Ignore PHI nodes, these will be flattened when duplication happens. |
| 194 | BasicBlock::const_iterator I = BB->getFirstNonPHI(); |
| 195 | |
Chris Lattner | b14b88a | 2009-11-11 00:21:58 +0000 | [diff] [blame] | 196 | // FIXME: THREADING will delete values that are just used to compute the |
| 197 | // branch, so they shouldn't count against the duplication cost. |
| 198 | |
| 199 | |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 200 | // Sum up the cost of each instruction until we get to the terminator. Don't |
| 201 | // include the terminator because the copy won't include it. |
| 202 | unsigned Size = 0; |
| 203 | for (; !isa<TerminatorInst>(I); ++I) { |
| 204 | // Debugger intrinsics don't incur code size. |
| 205 | if (isa<DbgInfoIntrinsic>(I)) continue; |
| 206 | |
| 207 | // If this is a pointer->pointer bitcast, it is free. |
Duncan Sands | 1df9859 | 2010-02-16 11:11:14 +0000 | [diff] [blame] | 208 | if (isa<BitCastInst>(I) && I->getType()->isPointerTy()) |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 209 | continue; |
| 210 | |
| 211 | // All other instructions count for at least one unit. |
| 212 | ++Size; |
| 213 | |
| 214 | // Calls are more expensive. If they are non-intrinsic calls, we model them |
| 215 | // as having cost of 4. If they are a non-vector intrinsic, we model them |
| 216 | // as having cost of 2 total, and if they are a vector intrinsic, we model |
| 217 | // them as having cost 1. |
| 218 | if (const CallInst *CI = dyn_cast<CallInst>(I)) { |
| 219 | if (!isa<IntrinsicInst>(CI)) |
| 220 | Size += 3; |
Duncan Sands | 1df9859 | 2010-02-16 11:11:14 +0000 | [diff] [blame] | 221 | else if (!CI->getType()->isVectorTy()) |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 222 | Size += 1; |
| 223 | } |
| 224 | } |
| 225 | |
| 226 | // Threading through a switch statement is particularly profitable. If this |
| 227 | // block ends in a switch, decrease its cost to make it more likely to happen. |
| 228 | if (isa<SwitchInst>(I)) |
| 229 | Size = Size > 6 ? Size-6 : 0; |
| 230 | |
| 231 | return Size; |
| 232 | } |
| 233 | |
Mike Stump | fe095f3 | 2009-05-04 18:40:41 +0000 | [diff] [blame] | 234 | /// FindLoopHeaders - We do not want jump threading to turn proper loop |
| 235 | /// structures into irreducible loops. Doing this breaks up the loop nesting |
| 236 | /// hierarchy and pessimizes later transformations. To prevent this from |
| 237 | /// happening, we first have to find the loop headers. Here we approximate this |
| 238 | /// by finding targets of backedges in the CFG. |
| 239 | /// |
| 240 | /// Note that there definitely are cases when we want to allow threading of |
| 241 | /// edges across a loop header. For example, threading a jump from outside the |
| 242 | /// loop (the preheader) to an exit block of the loop is definitely profitable. |
| 243 | /// It is also almost always profitable to thread backedges from within the loop |
| 244 | /// to exit blocks, and is often profitable to thread backedges to other blocks |
| 245 | /// within the loop (forming a nested loop). This simple analysis is not rich |
| 246 | /// enough to track all of these properties and keep it up-to-date as the CFG |
| 247 | /// mutates, so we don't allow any of these transformations. |
| 248 | /// |
| 249 | void JumpThreading::FindLoopHeaders(Function &F) { |
| 250 | SmallVector<std::pair<const BasicBlock*,const BasicBlock*>, 32> Edges; |
| 251 | FindFunctionBackedges(F, Edges); |
| 252 | |
| 253 | for (unsigned i = 0, e = Edges.size(); i != e; ++i) |
| 254 | LoopHeaders.insert(const_cast<BasicBlock*>(Edges[i].second)); |
| 255 | } |
| 256 | |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 257 | /// ComputeValueKnownInPredecessors - Given a basic block BB and a value V, see |
| 258 | /// if we can infer that the value is a known ConstantInt in any of our |
Chris Lattner | e7e63fe | 2009-11-09 00:41:49 +0000 | [diff] [blame] | 259 | /// predecessors. If so, return the known list of value and pred BB in the |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 260 | /// result vector. If a value is known to be undef, it is returned as null. |
| 261 | /// |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 262 | /// This returns true if there were any known values. |
| 263 | /// |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 264 | bool JumpThreading:: |
| 265 | ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,PredValueInfo &Result){ |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 266 | // If V is a constantint, then it is known in all predecessors. |
| 267 | if (isa<ConstantInt>(V) || isa<UndefValue>(V)) { |
| 268 | ConstantInt *CI = dyn_cast<ConstantInt>(V); |
Chris Lattner | cc4d3b2 | 2009-11-11 02:08:33 +0000 | [diff] [blame] | 269 | |
| 270 | for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) |
| 271 | Result.push_back(std::make_pair(CI, *PI)); |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 272 | return true; |
| 273 | } |
| 274 | |
| 275 | // If V is a non-instruction value, or an instruction in a different block, |
| 276 | // then it can't be derived from a PHI. |
| 277 | Instruction *I = dyn_cast<Instruction>(V); |
Chris Lattner | cc4d3b2 | 2009-11-11 02:08:33 +0000 | [diff] [blame] | 278 | if (I == 0 || I->getParent() != BB) { |
| 279 | |
| 280 | // Okay, if this is a live-in value, see if it has a known value at the end |
| 281 | // of any of our predecessors. |
| 282 | // |
| 283 | // FIXME: This should be an edge property, not a block end property. |
| 284 | /// TODO: Per PR2563, we could infer value range information about a |
| 285 | /// predecessor based on its terminator. |
| 286 | // |
| 287 | if (LVI) { |
Chris Lattner | f496e79 | 2009-11-12 04:57:13 +0000 | [diff] [blame] | 288 | // FIXME: change this to use the more-rich 'getPredicateOnEdge' method if |
| 289 | // "I" is a non-local compare-with-a-constant instruction. This would be |
| 290 | // able to handle value inequalities better, for example if the compare is |
| 291 | // "X < 4" and "X < 3" is known true but "X < 4" itself is not available. |
| 292 | // Perhaps getConstantOnEdge should be smart enough to do this? |
| 293 | |
Chris Lattner | cc4d3b2 | 2009-11-11 02:08:33 +0000 | [diff] [blame] | 294 | for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 295 | BasicBlock *P = *PI; |
Chris Lattner | cc4d3b2 | 2009-11-11 02:08:33 +0000 | [diff] [blame] | 296 | // If the value is known by LazyValueInfo to be a constant in a |
| 297 | // predecessor, use that information to try to thread this block. |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 298 | Constant *PredCst = LVI->getConstantOnEdge(V, P, BB); |
Chris Lattner | cc4d3b2 | 2009-11-11 02:08:33 +0000 | [diff] [blame] | 299 | if (PredCst == 0 || |
| 300 | (!isa<ConstantInt>(PredCst) && !isa<UndefValue>(PredCst))) |
| 301 | continue; |
| 302 | |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 303 | Result.push_back(std::make_pair(dyn_cast<ConstantInt>(PredCst), P)); |
Chris Lattner | cc4d3b2 | 2009-11-11 02:08:33 +0000 | [diff] [blame] | 304 | } |
| 305 | |
| 306 | return !Result.empty(); |
| 307 | } |
| 308 | |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 309 | return false; |
Chris Lattner | cc4d3b2 | 2009-11-11 02:08:33 +0000 | [diff] [blame] | 310 | } |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 311 | |
| 312 | /// If I is a PHI node, then we know the incoming values for any constants. |
| 313 | if (PHINode *PN = dyn_cast<PHINode>(I)) { |
| 314 | for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { |
| 315 | Value *InVal = PN->getIncomingValue(i); |
| 316 | if (isa<ConstantInt>(InVal) || isa<UndefValue>(InVal)) { |
| 317 | ConstantInt *CI = dyn_cast<ConstantInt>(InVal); |
| 318 | Result.push_back(std::make_pair(CI, PN->getIncomingBlock(i))); |
| 319 | } |
| 320 | } |
| 321 | return !Result.empty(); |
| 322 | } |
| 323 | |
| 324 | SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> LHSVals, RHSVals; |
| 325 | |
| 326 | // Handle some boolean conditions. |
| 327 | if (I->getType()->getPrimitiveSizeInBits() == 1) { |
| 328 | // X | true -> true |
| 329 | // X & false -> false |
| 330 | if (I->getOpcode() == Instruction::Or || |
| 331 | I->getOpcode() == Instruction::And) { |
| 332 | ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals); |
| 333 | ComputeValueKnownInPredecessors(I->getOperand(1), BB, RHSVals); |
| 334 | |
| 335 | if (LHSVals.empty() && RHSVals.empty()) |
| 336 | return false; |
| 337 | |
| 338 | ConstantInt *InterestingVal; |
| 339 | if (I->getOpcode() == Instruction::Or) |
| 340 | InterestingVal = ConstantInt::getTrue(I->getContext()); |
| 341 | else |
| 342 | InterestingVal = ConstantInt::getFalse(I->getContext()); |
| 343 | |
Chris Lattner | 2fa7b48e | 2010-08-18 03:14:36 +0000 | [diff] [blame^] | 344 | SmallPtrSet<BasicBlock*, 4> LHSKnownBBs; |
| 345 | |
Chris Lattner | 1e45265 | 2010-02-11 04:40:44 +0000 | [diff] [blame] | 346 | // Scan for the sentinel. If we find an undef, force it to the |
| 347 | // interesting value: x|undef -> true and x&undef -> false. |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 348 | for (unsigned i = 0, e = LHSVals.size(); i != e; ++i) |
Chris Lattner | 1e45265 | 2010-02-11 04:40:44 +0000 | [diff] [blame] | 349 | if (LHSVals[i].first == InterestingVal || LHSVals[i].first == 0) { |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 350 | Result.push_back(LHSVals[i]); |
Chris Lattner | 1e45265 | 2010-02-11 04:40:44 +0000 | [diff] [blame] | 351 | Result.back().first = InterestingVal; |
Chris Lattner | 2fa7b48e | 2010-08-18 03:14:36 +0000 | [diff] [blame^] | 352 | LHSKnownBBs.insert(LHSVals[i].second); |
Chris Lattner | 1e45265 | 2010-02-11 04:40:44 +0000 | [diff] [blame] | 353 | } |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 354 | for (unsigned i = 0, e = RHSVals.size(); i != e; ++i) |
Chris Lattner | 1e45265 | 2010-02-11 04:40:44 +0000 | [diff] [blame] | 355 | if (RHSVals[i].first == InterestingVal || RHSVals[i].first == 0) { |
Chris Lattner | 0a96144 | 2010-07-12 00:47:34 +0000 | [diff] [blame] | 356 | // If we already inferred a value for this block on the LHS, don't |
| 357 | // re-add it. |
Chris Lattner | 2fa7b48e | 2010-08-18 03:14:36 +0000 | [diff] [blame^] | 358 | if (!LHSKnownBBs.count(RHSVals[i].second)) { |
Chris Lattner | 0a96144 | 2010-07-12 00:47:34 +0000 | [diff] [blame] | 359 | Result.push_back(RHSVals[i]); |
| 360 | Result.back().first = InterestingVal; |
| 361 | } |
Chris Lattner | 1e45265 | 2010-02-11 04:40:44 +0000 | [diff] [blame] | 362 | } |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 363 | return !Result.empty(); |
| 364 | } |
| 365 | |
Chris Lattner | 055d046 | 2009-11-10 22:39:16 +0000 | [diff] [blame] | 366 | // Handle the NOT form of XOR. |
| 367 | if (I->getOpcode() == Instruction::Xor && |
| 368 | isa<ConstantInt>(I->getOperand(1)) && |
| 369 | cast<ConstantInt>(I->getOperand(1))->isOne()) { |
| 370 | ComputeValueKnownInPredecessors(I->getOperand(0), BB, Result); |
| 371 | if (Result.empty()) |
| 372 | return false; |
| 373 | |
| 374 | // Invert the known values. |
| 375 | for (unsigned i = 0, e = Result.size(); i != e; ++i) |
Chris Lattner | 1fb5630 | 2009-11-15 19:57:43 +0000 | [diff] [blame] | 376 | if (Result[i].first) |
| 377 | Result[i].first = |
| 378 | cast<ConstantInt>(ConstantExpr::getNot(Result[i].first)); |
Chris Lattner | 055d046 | 2009-11-10 22:39:16 +0000 | [diff] [blame] | 379 | return true; |
| 380 | } |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 381 | } |
| 382 | |
| 383 | // Handle compare with phi operand, where the PHI is defined in this block. |
| 384 | if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) { |
| 385 | PHINode *PN = dyn_cast<PHINode>(Cmp->getOperand(0)); |
| 386 | if (PN && PN->getParent() == BB) { |
| 387 | // We can do this simplification if any comparisons fold to true or false. |
| 388 | // See if any do. |
| 389 | for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { |
| 390 | BasicBlock *PredBB = PN->getIncomingBlock(i); |
| 391 | Value *LHS = PN->getIncomingValue(i); |
| 392 | Value *RHS = Cmp->getOperand(1)->DoPHITranslation(BB, PredBB); |
| 393 | |
Chris Lattner | 2ad00bf | 2009-11-11 22:31:38 +0000 | [diff] [blame] | 394 | Value *Res = SimplifyCmpInst(Cmp->getPredicate(), LHS, RHS, TD); |
Chris Lattner | 66c04c4 | 2009-11-12 05:24:05 +0000 | [diff] [blame] | 395 | if (Res == 0) { |
| 396 | if (!LVI || !isa<Constant>(RHS)) |
| 397 | continue; |
| 398 | |
| 399 | LazyValueInfo::Tristate |
| 400 | ResT = LVI->getPredicateOnEdge(Cmp->getPredicate(), LHS, |
| 401 | cast<Constant>(RHS), PredBB, BB); |
| 402 | if (ResT == LazyValueInfo::Unknown) |
| 403 | continue; |
| 404 | Res = ConstantInt::get(Type::getInt1Ty(LHS->getContext()), ResT); |
| 405 | } |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 406 | |
| 407 | if (isa<UndefValue>(Res)) |
| 408 | Result.push_back(std::make_pair((ConstantInt*)0, PredBB)); |
| 409 | else if (ConstantInt *CI = dyn_cast<ConstantInt>(Res)) |
| 410 | Result.push_back(std::make_pair(CI, PredBB)); |
| 411 | } |
| 412 | |
| 413 | return !Result.empty(); |
| 414 | } |
| 415 | |
Chris Lattner | 2ad00bf | 2009-11-11 22:31:38 +0000 | [diff] [blame] | 416 | |
| 417 | // If comparing a live-in value against a constant, see if we know the |
| 418 | // live-in value on any predecessors. |
| 419 | if (LVI && isa<Constant>(Cmp->getOperand(1)) && |
Duncan Sands | b0bc6c3 | 2010-02-15 16:12:20 +0000 | [diff] [blame] | 420 | Cmp->getType()->isIntegerTy() && // Not vector compare. |
Chris Lattner | 2ad00bf | 2009-11-11 22:31:38 +0000 | [diff] [blame] | 421 | (!isa<Instruction>(Cmp->getOperand(0)) || |
| 422 | cast<Instruction>(Cmp->getOperand(0))->getParent() != BB)) { |
| 423 | Constant *RHSCst = cast<Constant>(Cmp->getOperand(1)); |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 424 | |
Chris Lattner | 2ad00bf | 2009-11-11 22:31:38 +0000 | [diff] [blame] | 425 | for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 426 | BasicBlock *P = *PI; |
Chris Lattner | 2ad00bf | 2009-11-11 22:31:38 +0000 | [diff] [blame] | 427 | // If the value is known by LazyValueInfo to be a constant in a |
| 428 | // predecessor, use that information to try to thread this block. |
Chris Lattner | 0e0ff29 | 2009-11-12 04:37:50 +0000 | [diff] [blame] | 429 | LazyValueInfo::Tristate |
| 430 | Res = LVI->getPredicateOnEdge(Cmp->getPredicate(), Cmp->getOperand(0), |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 431 | RHSCst, P, BB); |
Chris Lattner | 0e0ff29 | 2009-11-12 04:37:50 +0000 | [diff] [blame] | 432 | if (Res == LazyValueInfo::Unknown) |
Chris Lattner | 2ad00bf | 2009-11-11 22:31:38 +0000 | [diff] [blame] | 433 | continue; |
Chris Lattner | 0e0ff29 | 2009-11-12 04:37:50 +0000 | [diff] [blame] | 434 | |
| 435 | Constant *ResC = ConstantInt::get(Cmp->getType(), Res); |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 436 | Result.push_back(std::make_pair(cast<ConstantInt>(ResC), P)); |
Chris Lattner | 2ad00bf | 2009-11-11 22:31:38 +0000 | [diff] [blame] | 437 | } |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 438 | |
Chris Lattner | 2ad00bf | 2009-11-11 22:31:38 +0000 | [diff] [blame] | 439 | return !Result.empty(); |
| 440 | } |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 441 | } |
| 442 | return false; |
| 443 | } |
| 444 | |
| 445 | |
Chris Lattner | 6bf7750 | 2008-04-22 07:05:46 +0000 | [diff] [blame] | 446 | |
Chris Lattner | e33583b | 2009-10-11 04:18:15 +0000 | [diff] [blame] | 447 | /// GetBestDestForBranchOnUndef - If we determine that the specified block ends |
| 448 | /// in an undefined jump, decide which block is best to revector to. |
| 449 | /// |
| 450 | /// Since we can pick an arbitrary destination, we pick the successor with the |
| 451 | /// fewest predecessors. This should reduce the in-degree of the others. |
| 452 | /// |
| 453 | static unsigned GetBestDestForJumpOnUndef(BasicBlock *BB) { |
| 454 | TerminatorInst *BBTerm = BB->getTerminator(); |
| 455 | unsigned MinSucc = 0; |
| 456 | BasicBlock *TestBB = BBTerm->getSuccessor(MinSucc); |
| 457 | // Compute the successor with the minimum number of predecessors. |
| 458 | unsigned MinNumPreds = std::distance(pred_begin(TestBB), pred_end(TestBB)); |
| 459 | for (unsigned i = 1, e = BBTerm->getNumSuccessors(); i != e; ++i) { |
| 460 | TestBB = BBTerm->getSuccessor(i); |
| 461 | unsigned NumPreds = std::distance(pred_begin(TestBB), pred_end(TestBB)); |
| 462 | if (NumPreds < MinNumPreds) |
| 463 | MinSucc = i; |
| 464 | } |
| 465 | |
| 466 | return MinSucc; |
| 467 | } |
| 468 | |
Chris Lattner | c7bcbf6 | 2008-11-27 07:20:04 +0000 | [diff] [blame] | 469 | /// ProcessBlock - If there are any predecessors whose control can be threaded |
Chris Lattner | 177480b | 2008-04-20 21:13:06 +0000 | [diff] [blame] | 470 | /// through to a successor, transform them now. |
Chris Lattner | c7bcbf6 | 2008-11-27 07:20:04 +0000 | [diff] [blame] | 471 | bool JumpThreading::ProcessBlock(BasicBlock *BB) { |
Chris Lattner | 8231fd1 | 2010-01-23 18:56:07 +0000 | [diff] [blame] | 472 | // If the block is trivially dead, just return and let the caller nuke it. |
| 473 | // This simplifies other transformations. |
| 474 | if (pred_begin(BB) == pred_end(BB) && |
| 475 | BB != &BB->getParent()->getEntryBlock()) |
| 476 | return false; |
| 477 | |
Chris Lattner | 69e067f | 2008-11-27 05:07:53 +0000 | [diff] [blame] | 478 | // If this block has a single predecessor, and if that pred has a single |
| 479 | // successor, merge the blocks. This encourages recursive jump threading |
| 480 | // because now the condition in this block can be threaded through |
| 481 | // predecessors of our predecessor block. |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 482 | if (BasicBlock *SinglePred = BB->getSinglePredecessor()) { |
Chris Lattner | f5102a0 | 2008-11-28 19:54:49 +0000 | [diff] [blame] | 483 | if (SinglePred->getTerminator()->getNumSuccessors() == 1 && |
| 484 | SinglePred != BB) { |
Mike Stump | fe095f3 | 2009-05-04 18:40:41 +0000 | [diff] [blame] | 485 | // If SinglePred was a loop header, BB becomes one. |
| 486 | if (LoopHeaders.erase(SinglePred)) |
| 487 | LoopHeaders.insert(BB); |
| 488 | |
Chris Lattner | 3d86d24 | 2008-11-27 19:25:19 +0000 | [diff] [blame] | 489 | // Remember if SinglePred was the entry block of the function. If so, we |
| 490 | // will need to move BB back to the entry position. |
| 491 | bool isEntry = SinglePred == &SinglePred->getParent()->getEntryBlock(); |
Chris Lattner | 69e067f | 2008-11-27 05:07:53 +0000 | [diff] [blame] | 492 | MergeBasicBlockIntoOnlyPred(BB); |
Chris Lattner | 3d86d24 | 2008-11-27 19:25:19 +0000 | [diff] [blame] | 493 | |
| 494 | if (isEntry && BB != &BB->getParent()->getEntryBlock()) |
| 495 | BB->moveBefore(&BB->getParent()->getEntryBlock()); |
Chris Lattner | 69e067f | 2008-11-27 05:07:53 +0000 | [diff] [blame] | 496 | return true; |
| 497 | } |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 498 | } |
| 499 | |
| 500 | // Look to see if the terminator is a branch of switch, if not we can't thread |
| 501 | // it. |
Chris Lattner | 177480b | 2008-04-20 21:13:06 +0000 | [diff] [blame] | 502 | Value *Condition; |
Chris Lattner | bd3401f | 2008-04-20 22:39:42 +0000 | [diff] [blame] | 503 | if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) { |
| 504 | // Can't thread an unconditional jump. |
| 505 | if (BI->isUnconditional()) return false; |
Chris Lattner | 177480b | 2008-04-20 21:13:06 +0000 | [diff] [blame] | 506 | Condition = BI->getCondition(); |
Chris Lattner | bd3401f | 2008-04-20 22:39:42 +0000 | [diff] [blame] | 507 | } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) |
Chris Lattner | 177480b | 2008-04-20 21:13:06 +0000 | [diff] [blame] | 508 | Condition = SI->getCondition(); |
| 509 | else |
| 510 | return false; // Must be an invoke. |
Chris Lattner | bd3401f | 2008-04-20 22:39:42 +0000 | [diff] [blame] | 511 | |
| 512 | // If the terminator of this block is branching on a constant, simplify the |
Chris Lattner | 037c781 | 2008-04-21 18:25:01 +0000 | [diff] [blame] | 513 | // terminator to an unconditional branch. This can occur due to threading in |
Chris Lattner | bd3401f | 2008-04-20 22:39:42 +0000 | [diff] [blame] | 514 | // other blocks. |
| 515 | if (isa<ConstantInt>(Condition)) { |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 516 | DEBUG(dbgs() << " In block '" << BB->getName() |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 517 | << "' folding terminator: " << *BB->getTerminator() << '\n'); |
Chris Lattner | bd3401f | 2008-04-20 22:39:42 +0000 | [diff] [blame] | 518 | ++NumFolds; |
| 519 | ConstantFoldTerminator(BB); |
| 520 | return true; |
| 521 | } |
| 522 | |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 523 | // If the terminator is branching on an undef, we can pick any of the |
Chris Lattner | e33583b | 2009-10-11 04:18:15 +0000 | [diff] [blame] | 524 | // successors to branch to. Let GetBestDestForJumpOnUndef decide. |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 525 | if (isa<UndefValue>(Condition)) { |
Chris Lattner | e33583b | 2009-10-11 04:18:15 +0000 | [diff] [blame] | 526 | unsigned BestSucc = GetBestDestForJumpOnUndef(BB); |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 527 | |
| 528 | // Fold the branch/switch. |
Chris Lattner | e33583b | 2009-10-11 04:18:15 +0000 | [diff] [blame] | 529 | TerminatorInst *BBTerm = BB->getTerminator(); |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 530 | for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i) { |
Chris Lattner | e33583b | 2009-10-11 04:18:15 +0000 | [diff] [blame] | 531 | if (i == BestSucc) continue; |
Chris Lattner | c2c23d0 | 2009-11-09 22:32:36 +0000 | [diff] [blame] | 532 | RemovePredecessorAndSimplify(BBTerm->getSuccessor(i), BB, TD); |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 533 | } |
| 534 | |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 535 | DEBUG(dbgs() << " In block '" << BB->getName() |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 536 | << "' folding undef terminator: " << *BBTerm << '\n'); |
Chris Lattner | e33583b | 2009-10-11 04:18:15 +0000 | [diff] [blame] | 537 | BranchInst::Create(BBTerm->getSuccessor(BestSucc), BBTerm); |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 538 | BBTerm->eraseFromParent(); |
| 539 | return true; |
| 540 | } |
| 541 | |
| 542 | Instruction *CondInst = dyn_cast<Instruction>(Condition); |
| 543 | |
| 544 | // If the condition is an instruction defined in another block, see if a |
| 545 | // predecessor has the same condition: |
| 546 | // br COND, BBX, BBY |
| 547 | // BBX: |
| 548 | // br COND, BBZ, BBW |
Chris Lattner | 0e0ff29 | 2009-11-12 04:37:50 +0000 | [diff] [blame] | 549 | if (!LVI && |
| 550 | !Condition->hasOneUse() && // Multiple uses. |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 551 | (CondInst == 0 || CondInst->getParent() != BB)) { // Non-local definition. |
| 552 | pred_iterator PI = pred_begin(BB), E = pred_end(BB); |
| 553 | if (isa<BranchInst>(BB->getTerminator())) { |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 554 | for (; PI != E; ++PI) { |
| 555 | BasicBlock *P = *PI; |
| 556 | if (BranchInst *PBI = dyn_cast<BranchInst>(P->getTerminator())) |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 557 | if (PBI->isConditional() && PBI->getCondition() == Condition && |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 558 | ProcessBranchOnDuplicateCond(P, BB)) |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 559 | return true; |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 560 | } |
Chris Lattner | 3cda3cd | 2008-12-04 06:31:07 +0000 | [diff] [blame] | 561 | } else { |
| 562 | assert(isa<SwitchInst>(BB->getTerminator()) && "Unknown jump terminator"); |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 563 | for (; PI != E; ++PI) { |
| 564 | BasicBlock *P = *PI; |
| 565 | if (SwitchInst *PSI = dyn_cast<SwitchInst>(P->getTerminator())) |
Chris Lattner | 3cda3cd | 2008-12-04 06:31:07 +0000 | [diff] [blame] | 566 | if (PSI->getCondition() == Condition && |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 567 | ProcessSwitchOnDuplicateCond(P, BB)) |
Chris Lattner | 3cda3cd | 2008-12-04 06:31:07 +0000 | [diff] [blame] | 568 | return true; |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 569 | } |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 570 | } |
| 571 | } |
| 572 | |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 573 | // All the rest of our checks depend on the condition being an instruction. |
Chris Lattner | 87e9f59 | 2009-11-12 01:41:34 +0000 | [diff] [blame] | 574 | if (CondInst == 0) { |
| 575 | // FIXME: Unify this with code below. |
| 576 | if (LVI && ProcessThreadableEdges(Condition, BB)) |
| 577 | return true; |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 578 | return false; |
Chris Lattner | 87e9f59 | 2009-11-12 01:41:34 +0000 | [diff] [blame] | 579 | } |
| 580 | |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 581 | |
Nick Lewycky | 9683f18 | 2009-06-19 04:56:29 +0000 | [diff] [blame] | 582 | if (CmpInst *CondCmp = dyn_cast<CmpInst>(CondInst)) { |
Chris Lattner | 0e0ff29 | 2009-11-12 04:37:50 +0000 | [diff] [blame] | 583 | if (!LVI && |
| 584 | (!isa<PHINode>(CondCmp->getOperand(0)) || |
| 585 | cast<PHINode>(CondCmp->getOperand(0))->getParent() != BB)) { |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 586 | // If we have a comparison, loop over the predecessors to see if there is |
| 587 | // a condition with a lexically identical value. |
| 588 | pred_iterator PI = pred_begin(BB), E = pred_end(BB); |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 589 | for (; PI != E; ++PI) { |
| 590 | BasicBlock *P = *PI; |
| 591 | if (BranchInst *PBI = dyn_cast<BranchInst>(P->getTerminator())) |
| 592 | if (PBI->isConditional() && P != BB) { |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 593 | if (CmpInst *CI = dyn_cast<CmpInst>(PBI->getCondition())) { |
| 594 | if (CI->getOperand(0) == CondCmp->getOperand(0) && |
| 595 | CI->getOperand(1) == CondCmp->getOperand(1) && |
| 596 | CI->getPredicate() == CondCmp->getPredicate()) { |
| 597 | // TODO: Could handle things like (x != 4) --> (x == 17) |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 598 | if (ProcessBranchOnDuplicateCond(P, BB)) |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 599 | return true; |
| 600 | } |
Chris Lattner | 79c740f | 2009-06-19 16:27:56 +0000 | [diff] [blame] | 601 | } |
| 602 | } |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 603 | } |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 604 | } |
Nick Lewycky | 9683f18 | 2009-06-19 04:56:29 +0000 | [diff] [blame] | 605 | } |
Chris Lattner | 69e067f | 2008-11-27 05:07:53 +0000 | [diff] [blame] | 606 | |
| 607 | // Check for some cases that are worth simplifying. Right now we want to look |
| 608 | // for loads that are used by a switch or by the condition for the branch. If |
| 609 | // we see one, check to see if it's partially redundant. If so, insert a PHI |
| 610 | // which can then be used to thread the values. |
| 611 | // |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 612 | Value *SimplifyValue = CondInst; |
Chris Lattner | 69e067f | 2008-11-27 05:07:53 +0000 | [diff] [blame] | 613 | if (CmpInst *CondCmp = dyn_cast<CmpInst>(SimplifyValue)) |
| 614 | if (isa<Constant>(CondCmp->getOperand(1))) |
| 615 | SimplifyValue = CondCmp->getOperand(0); |
| 616 | |
Chris Lattner | 4e447eb | 2009-11-15 19:58:31 +0000 | [diff] [blame] | 617 | // TODO: There are other places where load PRE would be profitable, such as |
| 618 | // more complex comparisons. |
Chris Lattner | 69e067f | 2008-11-27 05:07:53 +0000 | [diff] [blame] | 619 | if (LoadInst *LI = dyn_cast<LoadInst>(SimplifyValue)) |
| 620 | if (SimplifyPartiallyRedundantLoad(LI)) |
| 621 | return true; |
| 622 | |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 623 | |
| 624 | // Handle a variety of cases where we are branching on something derived from |
| 625 | // a PHI node in the current block. If we can prove that any predecessors |
| 626 | // compute a predictable value based on a PHI node, thread those predecessors. |
| 627 | // |
Chris Lattner | cc4d3b2 | 2009-11-11 02:08:33 +0000 | [diff] [blame] | 628 | if (ProcessThreadableEdges(CondInst, BB)) |
| 629 | return true; |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 630 | |
Chris Lattner | 77beb47 | 2010-01-11 23:41:09 +0000 | [diff] [blame] | 631 | // If this is an otherwise-unfoldable branch on a phi node in the current |
| 632 | // block, see if we can simplify. |
| 633 | if (PHINode *PN = dyn_cast<PHINode>(CondInst)) |
| 634 | if (PN->getParent() == BB && isa<BranchInst>(BB->getTerminator())) |
| 635 | return ProcessBranchOnPHI(PN); |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 636 | |
Chris Lattner | 2249a0b | 2010-01-12 02:07:17 +0000 | [diff] [blame] | 637 | |
| 638 | // If this is an otherwise-unfoldable branch on a XOR, see if we can simplify. |
| 639 | if (CondInst->getOpcode() == Instruction::Xor && |
| 640 | CondInst->getParent() == BB && isa<BranchInst>(BB->getTerminator())) |
| 641 | return ProcessBranchOnXOR(cast<BinaryOperator>(CondInst)); |
| 642 | |
| 643 | |
Chris Lattner | 69e067f | 2008-11-27 05:07:53 +0000 | [diff] [blame] | 644 | // TODO: If we have: "br (X > 0)" and we have a predecessor where we know |
Chris Lattner | 77beb47 | 2010-01-11 23:41:09 +0000 | [diff] [blame] | 645 | // "(X == 4)", thread through this block. |
Chris Lattner | a5ddb59 | 2008-04-22 21:40:39 +0000 | [diff] [blame] | 646 | |
Chris Lattner | d38c14e | 2008-04-22 06:36:15 +0000 | [diff] [blame] | 647 | return false; |
| 648 | } |
| 649 | |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 650 | /// ProcessBranchOnDuplicateCond - We found a block and a predecessor of that |
| 651 | /// block that jump on exactly the same condition. This means that we almost |
| 652 | /// always know the direction of the edge in the DESTBB: |
| 653 | /// PREDBB: |
| 654 | /// br COND, DESTBB, BBY |
| 655 | /// DESTBB: |
| 656 | /// br COND, BBZ, BBW |
| 657 | /// |
| 658 | /// If DESTBB has multiple predecessors, we can't just constant fold the branch |
| 659 | /// in DESTBB, we have to thread over it. |
| 660 | bool JumpThreading::ProcessBranchOnDuplicateCond(BasicBlock *PredBB, |
| 661 | BasicBlock *BB) { |
| 662 | BranchInst *PredBI = cast<BranchInst>(PredBB->getTerminator()); |
| 663 | |
| 664 | // If both successors of PredBB go to DESTBB, we don't know anything. We can |
| 665 | // fold the branch to an unconditional one, which allows other recursive |
| 666 | // simplifications. |
| 667 | bool BranchDir; |
| 668 | if (PredBI->getSuccessor(1) != BB) |
| 669 | BranchDir = true; |
| 670 | else if (PredBI->getSuccessor(0) != BB) |
| 671 | BranchDir = false; |
| 672 | else { |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 673 | DEBUG(dbgs() << " In block '" << PredBB->getName() |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 674 | << "' folding terminator: " << *PredBB->getTerminator() << '\n'); |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 675 | ++NumFolds; |
| 676 | ConstantFoldTerminator(PredBB); |
| 677 | return true; |
| 678 | } |
| 679 | |
| 680 | BranchInst *DestBI = cast<BranchInst>(BB->getTerminator()); |
| 681 | |
| 682 | // If the dest block has one predecessor, just fix the branch condition to a |
| 683 | // constant and fold it. |
| 684 | if (BB->getSinglePredecessor()) { |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 685 | DEBUG(dbgs() << " In block '" << BB->getName() |
Daniel Dunbar | 93b67e4 | 2009-07-26 07:49:05 +0000 | [diff] [blame] | 686 | << "' folding condition to '" << BranchDir << "': " |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 687 | << *BB->getTerminator() << '\n'); |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 688 | ++NumFolds; |
Chris Lattner | 5a06cf6 | 2009-10-11 18:39:58 +0000 | [diff] [blame] | 689 | Value *OldCond = DestBI->getCondition(); |
Owen Anderson | 1d0be15 | 2009-08-13 21:58:54 +0000 | [diff] [blame] | 690 | DestBI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()), |
| 691 | BranchDir)); |
Chris Lattner | 6f285d2 | 2010-04-10 18:26:57 +0000 | [diff] [blame] | 692 | // Delete dead instructions before we fold the branch. Folding the branch |
| 693 | // can eliminate edges from the CFG which can end up deleting OldCond. |
Chris Lattner | 5a06cf6 | 2009-10-11 18:39:58 +0000 | [diff] [blame] | 694 | RecursivelyDeleteTriviallyDeadInstructions(OldCond); |
Chris Lattner | 6f285d2 | 2010-04-10 18:26:57 +0000 | [diff] [blame] | 695 | ConstantFoldTerminator(BB); |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 696 | return true; |
| 697 | } |
Chris Lattner | bdbf1a1 | 2009-10-11 04:33:43 +0000 | [diff] [blame] | 698 | |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 699 | |
| 700 | // Next, figure out which successor we are threading to. |
| 701 | BasicBlock *SuccBB = DestBI->getSuccessor(!BranchDir); |
| 702 | |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 703 | SmallVector<BasicBlock*, 2> Preds; |
| 704 | Preds.push_back(PredBB); |
| 705 | |
Mike Stump | fe095f3 | 2009-05-04 18:40:41 +0000 | [diff] [blame] | 706 | // Ok, try to thread it! |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 707 | return ThreadEdge(BB, Preds, SuccBB); |
Chris Lattner | 421fa9e | 2008-12-03 07:48:08 +0000 | [diff] [blame] | 708 | } |
| 709 | |
Chris Lattner | 3cda3cd | 2008-12-04 06:31:07 +0000 | [diff] [blame] | 710 | /// ProcessSwitchOnDuplicateCond - We found a block and a predecessor of that |
| 711 | /// block that switch on exactly the same condition. This means that we almost |
| 712 | /// always know the direction of the edge in the DESTBB: |
| 713 | /// PREDBB: |
| 714 | /// switch COND [... DESTBB, BBY ... ] |
| 715 | /// DESTBB: |
| 716 | /// switch COND [... BBZ, BBW ] |
| 717 | /// |
| 718 | /// Optimizing switches like this is very important, because simplifycfg builds |
| 719 | /// switches out of repeated 'if' conditions. |
| 720 | bool JumpThreading::ProcessSwitchOnDuplicateCond(BasicBlock *PredBB, |
| 721 | BasicBlock *DestBB) { |
Chris Lattner | 2c7ed11 | 2009-01-19 21:20:34 +0000 | [diff] [blame] | 722 | // Can't thread edge to self. |
| 723 | if (PredBB == DestBB) |
| 724 | return false; |
| 725 | |
Chris Lattner | 3cda3cd | 2008-12-04 06:31:07 +0000 | [diff] [blame] | 726 | SwitchInst *PredSI = cast<SwitchInst>(PredBB->getTerminator()); |
| 727 | SwitchInst *DestSI = cast<SwitchInst>(DestBB->getTerminator()); |
| 728 | |
| 729 | // There are a variety of optimizations that we can potentially do on these |
| 730 | // blocks: we order them from most to least preferable. |
| 731 | |
| 732 | // If DESTBB *just* contains the switch, then we can forward edges from PREDBB |
| 733 | // directly to their destination. This does not introduce *any* code size |
Dale Johannesen | 6b23339 | 2009-03-17 00:38:24 +0000 | [diff] [blame] | 734 | // growth. Skip debug info first. |
| 735 | BasicBlock::iterator BBI = DestBB->begin(); |
| 736 | while (isa<DbgInfoIntrinsic>(BBI)) |
| 737 | BBI++; |
Chris Lattner | 3cda3cd | 2008-12-04 06:31:07 +0000 | [diff] [blame] | 738 | |
| 739 | // FIXME: Thread if it just contains a PHI. |
Dale Johannesen | 6b23339 | 2009-03-17 00:38:24 +0000 | [diff] [blame] | 740 | if (isa<SwitchInst>(BBI)) { |
Chris Lattner | 3cda3cd | 2008-12-04 06:31:07 +0000 | [diff] [blame] | 741 | bool MadeChange = false; |
| 742 | // Ignore the default edge for now. |
| 743 | for (unsigned i = 1, e = DestSI->getNumSuccessors(); i != e; ++i) { |
| 744 | ConstantInt *DestVal = DestSI->getCaseValue(i); |
| 745 | BasicBlock *DestSucc = DestSI->getSuccessor(i); |
| 746 | |
| 747 | // Okay, DestSI has a case for 'DestVal' that goes to 'DestSucc'. See if |
| 748 | // PredSI has an explicit case for it. If so, forward. If it is covered |
| 749 | // by the default case, we can't update PredSI. |
| 750 | unsigned PredCase = PredSI->findCaseValue(DestVal); |
| 751 | if (PredCase == 0) continue; |
| 752 | |
| 753 | // If PredSI doesn't go to DestBB on this value, then it won't reach the |
| 754 | // case on this condition. |
| 755 | if (PredSI->getSuccessor(PredCase) != DestBB && |
| 756 | DestSI->getSuccessor(i) != DestBB) |
| 757 | continue; |
Chris Lattner | 08bc270 | 2009-12-06 17:17:23 +0000 | [diff] [blame] | 758 | |
| 759 | // Do not forward this if it already goes to this destination, this would |
| 760 | // be an infinite loop. |
| 761 | if (PredSI->getSuccessor(PredCase) == DestSucc) |
| 762 | continue; |
Chris Lattner | 3cda3cd | 2008-12-04 06:31:07 +0000 | [diff] [blame] | 763 | |
| 764 | // Otherwise, we're safe to make the change. Make sure that the edge from |
| 765 | // DestSI to DestSucc is not critical and has no PHI nodes. |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 766 | DEBUG(dbgs() << "FORWARDING EDGE " << *DestVal << " FROM: " << *PredSI); |
| 767 | DEBUG(dbgs() << "THROUGH: " << *DestSI); |
Chris Lattner | 3cda3cd | 2008-12-04 06:31:07 +0000 | [diff] [blame] | 768 | |
| 769 | // If the destination has PHI nodes, just split the edge for updating |
| 770 | // simplicity. |
| 771 | if (isa<PHINode>(DestSucc->begin()) && !DestSucc->getSinglePredecessor()){ |
| 772 | SplitCriticalEdge(DestSI, i, this); |
| 773 | DestSucc = DestSI->getSuccessor(i); |
| 774 | } |
| 775 | FoldSingleEntryPHINodes(DestSucc); |
| 776 | PredSI->setSuccessor(PredCase, DestSucc); |
| 777 | MadeChange = true; |
| 778 | } |
| 779 | |
| 780 | if (MadeChange) |
| 781 | return true; |
| 782 | } |
| 783 | |
| 784 | return false; |
| 785 | } |
| 786 | |
| 787 | |
Chris Lattner | 69e067f | 2008-11-27 05:07:53 +0000 | [diff] [blame] | 788 | /// SimplifyPartiallyRedundantLoad - If LI is an obviously partially redundant |
| 789 | /// load instruction, eliminate it by replacing it with a PHI node. This is an |
| 790 | /// important optimization that encourages jump threading, and needs to be run |
| 791 | /// interlaced with other jump threading tasks. |
| 792 | bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) { |
| 793 | // Don't hack volatile loads. |
| 794 | if (LI->isVolatile()) return false; |
| 795 | |
| 796 | // If the load is defined in a block with exactly one predecessor, it can't be |
| 797 | // partially redundant. |
| 798 | BasicBlock *LoadBB = LI->getParent(); |
| 799 | if (LoadBB->getSinglePredecessor()) |
| 800 | return false; |
| 801 | |
| 802 | Value *LoadedPtr = LI->getOperand(0); |
| 803 | |
| 804 | // If the loaded operand is defined in the LoadBB, it can't be available. |
Chris Lattner | 4e447eb | 2009-11-15 19:58:31 +0000 | [diff] [blame] | 805 | // TODO: Could do simple PHI translation, that would be fun :) |
Chris Lattner | 69e067f | 2008-11-27 05:07:53 +0000 | [diff] [blame] | 806 | if (Instruction *PtrOp = dyn_cast<Instruction>(LoadedPtr)) |
| 807 | if (PtrOp->getParent() == LoadBB) |
| 808 | return false; |
| 809 | |
| 810 | // Scan a few instructions up from the load, to see if it is obviously live at |
| 811 | // the entry to its block. |
| 812 | BasicBlock::iterator BBIt = LI; |
| 813 | |
Chris Lattner | 4e447eb | 2009-11-15 19:58:31 +0000 | [diff] [blame] | 814 | if (Value *AvailableVal = |
| 815 | FindAvailableLoadedValue(LoadedPtr, LoadBB, BBIt, 6)) { |
Chris Lattner | 69e067f | 2008-11-27 05:07:53 +0000 | [diff] [blame] | 816 | // If the value if the load is locally available within the block, just use |
| 817 | // it. This frequently occurs for reg2mem'd allocas. |
| 818 | //cerr << "LOAD ELIMINATED:\n" << *BBIt << *LI << "\n"; |
Chris Lattner | 2a99b48 | 2009-01-09 06:08:12 +0000 | [diff] [blame] | 819 | |
| 820 | // If the returned value is the load itself, replace with an undef. This can |
| 821 | // only happen in dead loops. |
Owen Anderson | 9e9a0d5 | 2009-07-30 23:03:37 +0000 | [diff] [blame] | 822 | if (AvailableVal == LI) AvailableVal = UndefValue::get(LI->getType()); |
Chris Lattner | 69e067f | 2008-11-27 05:07:53 +0000 | [diff] [blame] | 823 | LI->replaceAllUsesWith(AvailableVal); |
| 824 | LI->eraseFromParent(); |
| 825 | return true; |
| 826 | } |
| 827 | |
| 828 | // Otherwise, if we scanned the whole block and got to the top of the block, |
| 829 | // we know the block is locally transparent to the load. If not, something |
| 830 | // might clobber its value. |
| 831 | if (BBIt != LoadBB->begin()) |
| 832 | return false; |
| 833 | |
| 834 | |
| 835 | SmallPtrSet<BasicBlock*, 8> PredsScanned; |
| 836 | typedef SmallVector<std::pair<BasicBlock*, Value*>, 8> AvailablePredsTy; |
| 837 | AvailablePredsTy AvailablePreds; |
| 838 | BasicBlock *OneUnavailablePred = 0; |
| 839 | |
| 840 | // If we got here, the loaded value is transparent through to the start of the |
| 841 | // block. Check to see if it is available in any of the predecessor blocks. |
| 842 | for (pred_iterator PI = pred_begin(LoadBB), PE = pred_end(LoadBB); |
| 843 | PI != PE; ++PI) { |
| 844 | BasicBlock *PredBB = *PI; |
| 845 | |
| 846 | // If we already scanned this predecessor, skip it. |
| 847 | if (!PredsScanned.insert(PredBB)) |
| 848 | continue; |
| 849 | |
| 850 | // Scan the predecessor to see if the value is available in the pred. |
| 851 | BBIt = PredBB->end(); |
Chris Lattner | 52c9585 | 2008-11-27 08:10:05 +0000 | [diff] [blame] | 852 | Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt, 6); |
Chris Lattner | 69e067f | 2008-11-27 05:07:53 +0000 | [diff] [blame] | 853 | if (!PredAvailable) { |
| 854 | OneUnavailablePred = PredBB; |
| 855 | continue; |
| 856 | } |
| 857 | |
| 858 | // If so, this load is partially redundant. Remember this info so that we |
| 859 | // can create a PHI node. |
| 860 | AvailablePreds.push_back(std::make_pair(PredBB, PredAvailable)); |
| 861 | } |
| 862 | |
| 863 | // If the loaded value isn't available in any predecessor, it isn't partially |
| 864 | // redundant. |
| 865 | if (AvailablePreds.empty()) return false; |
| 866 | |
| 867 | // Okay, the loaded value is available in at least one (and maybe all!) |
| 868 | // predecessors. If the value is unavailable in more than one unique |
| 869 | // predecessor, we want to insert a merge block for those common predecessors. |
| 870 | // This ensures that we only have to insert one reload, thus not increasing |
| 871 | // code size. |
| 872 | BasicBlock *UnavailablePred = 0; |
| 873 | |
| 874 | // If there is exactly one predecessor where the value is unavailable, the |
| 875 | // already computed 'OneUnavailablePred' block is it. If it ends in an |
| 876 | // unconditional branch, we know that it isn't a critical edge. |
| 877 | if (PredsScanned.size() == AvailablePreds.size()+1 && |
| 878 | OneUnavailablePred->getTerminator()->getNumSuccessors() == 1) { |
| 879 | UnavailablePred = OneUnavailablePred; |
| 880 | } else if (PredsScanned.size() != AvailablePreds.size()) { |
| 881 | // Otherwise, we had multiple unavailable predecessors or we had a critical |
| 882 | // edge from the one. |
| 883 | SmallVector<BasicBlock*, 8> PredsToSplit; |
| 884 | SmallPtrSet<BasicBlock*, 8> AvailablePredSet; |
| 885 | |
| 886 | for (unsigned i = 0, e = AvailablePreds.size(); i != e; ++i) |
| 887 | AvailablePredSet.insert(AvailablePreds[i].first); |
| 888 | |
| 889 | // Add all the unavailable predecessors to the PredsToSplit list. |
| 890 | for (pred_iterator PI = pred_begin(LoadBB), PE = pred_end(LoadBB); |
Chris Lattner | e58867e | 2010-06-14 19:45:43 +0000 | [diff] [blame] | 891 | PI != PE; ++PI) { |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 892 | BasicBlock *P = *PI; |
Chris Lattner | e58867e | 2010-06-14 19:45:43 +0000 | [diff] [blame] | 893 | // If the predecessor is an indirect goto, we can't split the edge. |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 894 | if (isa<IndirectBrInst>(P->getTerminator())) |
Chris Lattner | e58867e | 2010-06-14 19:45:43 +0000 | [diff] [blame] | 895 | return false; |
| 896 | |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 897 | if (!AvailablePredSet.count(P)) |
| 898 | PredsToSplit.push_back(P); |
Chris Lattner | e58867e | 2010-06-14 19:45:43 +0000 | [diff] [blame] | 899 | } |
Chris Lattner | 69e067f | 2008-11-27 05:07:53 +0000 | [diff] [blame] | 900 | |
| 901 | // Split them out to their own block. |
| 902 | UnavailablePred = |
| 903 | SplitBlockPredecessors(LoadBB, &PredsToSplit[0], PredsToSplit.size(), |
Chris Lattner | 4e447eb | 2009-11-15 19:58:31 +0000 | [diff] [blame] | 904 | "thread-pre-split", this); |
Chris Lattner | 69e067f | 2008-11-27 05:07:53 +0000 | [diff] [blame] | 905 | } |
| 906 | |
| 907 | // If the value isn't available in all predecessors, then there will be |
| 908 | // exactly one where it isn't available. Insert a load on that edge and add |
| 909 | // it to the AvailablePreds list. |
| 910 | if (UnavailablePred) { |
| 911 | assert(UnavailablePred->getTerminator()->getNumSuccessors() == 1 && |
| 912 | "Can't handle critical edge here!"); |
Chris Lattner | 4e447eb | 2009-11-15 19:58:31 +0000 | [diff] [blame] | 913 | Value *NewVal = new LoadInst(LoadedPtr, LI->getName()+".pr", false, |
| 914 | LI->getAlignment(), |
Chris Lattner | 69e067f | 2008-11-27 05:07:53 +0000 | [diff] [blame] | 915 | UnavailablePred->getTerminator()); |
| 916 | AvailablePreds.push_back(std::make_pair(UnavailablePred, NewVal)); |
| 917 | } |
| 918 | |
| 919 | // Now we know that each predecessor of this block has a value in |
| 920 | // AvailablePreds, sort them for efficient access as we're walking the preds. |
Chris Lattner | a352200 | 2008-12-01 06:52:57 +0000 | [diff] [blame] | 921 | array_pod_sort(AvailablePreds.begin(), AvailablePreds.end()); |
Chris Lattner | 69e067f | 2008-11-27 05:07:53 +0000 | [diff] [blame] | 922 | |
| 923 | // Create a PHI node at the start of the block for the PRE'd load value. |
| 924 | PHINode *PN = PHINode::Create(LI->getType(), "", LoadBB->begin()); |
| 925 | PN->takeName(LI); |
| 926 | |
| 927 | // Insert new entries into the PHI for each predecessor. A single block may |
| 928 | // have multiple entries here. |
| 929 | for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); PI != E; |
| 930 | ++PI) { |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 931 | BasicBlock *P = *PI; |
Chris Lattner | 69e067f | 2008-11-27 05:07:53 +0000 | [diff] [blame] | 932 | AvailablePredsTy::iterator I = |
| 933 | std::lower_bound(AvailablePreds.begin(), AvailablePreds.end(), |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 934 | std::make_pair(P, (Value*)0)); |
Chris Lattner | 69e067f | 2008-11-27 05:07:53 +0000 | [diff] [blame] | 935 | |
Gabor Greif | ee1f44f | 2010-07-12 14:10:24 +0000 | [diff] [blame] | 936 | assert(I != AvailablePreds.end() && I->first == P && |
Chris Lattner | 69e067f | 2008-11-27 05:07:53 +0000 | [diff] [blame] | 937 | "Didn't find entry for predecessor!"); |
| 938 | |
| 939 | PN->addIncoming(I->second, I->first); |
| 940 | } |
| 941 | |
| 942 | //cerr << "PRE: " << *LI << *PN << "\n"; |
| 943 | |
| 944 | LI->replaceAllUsesWith(PN); |
| 945 | LI->eraseFromParent(); |
| 946 | |
| 947 | return true; |
| 948 | } |
| 949 | |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 950 | /// FindMostPopularDest - The specified list contains multiple possible |
| 951 | /// threadable destinations. Pick the one that occurs the most frequently in |
| 952 | /// the list. |
| 953 | static BasicBlock * |
| 954 | FindMostPopularDest(BasicBlock *BB, |
| 955 | const SmallVectorImpl<std::pair<BasicBlock*, |
| 956 | BasicBlock*> > &PredToDestList) { |
| 957 | assert(!PredToDestList.empty()); |
| 958 | |
| 959 | // Determine popularity. If there are multiple possible destinations, we |
| 960 | // explicitly choose to ignore 'undef' destinations. We prefer to thread |
| 961 | // blocks with known and real destinations to threading undef. We'll handle |
| 962 | // them later if interesting. |
| 963 | DenseMap<BasicBlock*, unsigned> DestPopularity; |
| 964 | for (unsigned i = 0, e = PredToDestList.size(); i != e; ++i) |
| 965 | if (PredToDestList[i].second) |
| 966 | DestPopularity[PredToDestList[i].second]++; |
| 967 | |
| 968 | // Find the most popular dest. |
| 969 | DenseMap<BasicBlock*, unsigned>::iterator DPI = DestPopularity.begin(); |
| 970 | BasicBlock *MostPopularDest = DPI->first; |
| 971 | unsigned Popularity = DPI->second; |
| 972 | SmallVector<BasicBlock*, 4> SamePopularity; |
| 973 | |
| 974 | for (++DPI; DPI != DestPopularity.end(); ++DPI) { |
| 975 | // If the popularity of this entry isn't higher than the popularity we've |
| 976 | // seen so far, ignore it. |
| 977 | if (DPI->second < Popularity) |
| 978 | ; // ignore. |
| 979 | else if (DPI->second == Popularity) { |
| 980 | // If it is the same as what we've seen so far, keep track of it. |
| 981 | SamePopularity.push_back(DPI->first); |
| 982 | } else { |
| 983 | // If it is more popular, remember it. |
| 984 | SamePopularity.clear(); |
| 985 | MostPopularDest = DPI->first; |
| 986 | Popularity = DPI->second; |
| 987 | } |
| 988 | } |
| 989 | |
| 990 | // Okay, now we know the most popular destination. If there is more than |
| 991 | // destination, we need to determine one. This is arbitrary, but we need |
| 992 | // to make a deterministic decision. Pick the first one that appears in the |
| 993 | // successor list. |
| 994 | if (!SamePopularity.empty()) { |
| 995 | SamePopularity.push_back(MostPopularDest); |
| 996 | TerminatorInst *TI = BB->getTerminator(); |
| 997 | for (unsigned i = 0; ; ++i) { |
| 998 | assert(i != TI->getNumSuccessors() && "Didn't find any successor!"); |
| 999 | |
| 1000 | if (std::find(SamePopularity.begin(), SamePopularity.end(), |
| 1001 | TI->getSuccessor(i)) == SamePopularity.end()) |
| 1002 | continue; |
| 1003 | |
| 1004 | MostPopularDest = TI->getSuccessor(i); |
| 1005 | break; |
| 1006 | } |
| 1007 | } |
| 1008 | |
| 1009 | // Okay, we have finally picked the most popular destination. |
| 1010 | return MostPopularDest; |
| 1011 | } |
| 1012 | |
Chris Lattner | 1c96b41 | 2009-11-12 01:37:43 +0000 | [diff] [blame] | 1013 | bool JumpThreading::ProcessThreadableEdges(Value *Cond, BasicBlock *BB) { |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 1014 | // If threading this would thread across a loop header, don't even try to |
| 1015 | // thread the edge. |
| 1016 | if (LoopHeaders.count(BB)) |
| 1017 | return false; |
| 1018 | |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 1019 | SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> PredValues; |
Chris Lattner | 1c96b41 | 2009-11-12 01:37:43 +0000 | [diff] [blame] | 1020 | if (!ComputeValueKnownInPredecessors(Cond, BB, PredValues)) |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 1021 | return false; |
| 1022 | assert(!PredValues.empty() && |
| 1023 | "ComputeValueKnownInPredecessors returned true with no values"); |
| 1024 | |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 1025 | DEBUG(dbgs() << "IN BB: " << *BB; |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 1026 | for (unsigned i = 0, e = PredValues.size(); i != e; ++i) { |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 1027 | dbgs() << " BB '" << BB->getName() << "': FOUND condition = "; |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 1028 | if (PredValues[i].first) |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 1029 | dbgs() << *PredValues[i].first; |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 1030 | else |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 1031 | dbgs() << "UNDEF"; |
| 1032 | dbgs() << " for pred '" << PredValues[i].second->getName() |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 1033 | << "'.\n"; |
| 1034 | }); |
| 1035 | |
| 1036 | // Decide what we want to thread through. Convert our list of known values to |
| 1037 | // a list of known destinations for each pred. This also discards duplicate |
| 1038 | // predecessors and keeps track of the undefined inputs (which are represented |
Chris Lattner | e7e63fe | 2009-11-09 00:41:49 +0000 | [diff] [blame] | 1039 | // as a null dest in the PredToDestList). |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 1040 | SmallPtrSet<BasicBlock*, 16> SeenPreds; |
| 1041 | SmallVector<std::pair<BasicBlock*, BasicBlock*>, 16> PredToDestList; |
| 1042 | |
| 1043 | BasicBlock *OnlyDest = 0; |
| 1044 | BasicBlock *MultipleDestSentinel = (BasicBlock*)(intptr_t)~0ULL; |
| 1045 | |
| 1046 | for (unsigned i = 0, e = PredValues.size(); i != e; ++i) { |
| 1047 | BasicBlock *Pred = PredValues[i].second; |
| 1048 | if (!SeenPreds.insert(Pred)) |
| 1049 | continue; // Duplicate predecessor entry. |
| 1050 | |
| 1051 | // If the predecessor ends with an indirect goto, we can't change its |
| 1052 | // destination. |
| 1053 | if (isa<IndirectBrInst>(Pred->getTerminator())) |
| 1054 | continue; |
| 1055 | |
| 1056 | ConstantInt *Val = PredValues[i].first; |
| 1057 | |
| 1058 | BasicBlock *DestBB; |
| 1059 | if (Val == 0) // Undef. |
| 1060 | DestBB = 0; |
| 1061 | else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) |
| 1062 | DestBB = BI->getSuccessor(Val->isZero()); |
| 1063 | else { |
| 1064 | SwitchInst *SI = cast<SwitchInst>(BB->getTerminator()); |
| 1065 | DestBB = SI->getSuccessor(SI->findCaseValue(Val)); |
| 1066 | } |
| 1067 | |
| 1068 | // If we have exactly one destination, remember it for efficiency below. |
| 1069 | if (i == 0) |
| 1070 | OnlyDest = DestBB; |
| 1071 | else if (OnlyDest != DestBB) |
| 1072 | OnlyDest = MultipleDestSentinel; |
| 1073 | |
| 1074 | PredToDestList.push_back(std::make_pair(Pred, DestBB)); |
| 1075 | } |
| 1076 | |
| 1077 | // If all edges were unthreadable, we fail. |
| 1078 | if (PredToDestList.empty()) |
| 1079 | return false; |
| 1080 | |
| 1081 | // Determine which is the most common successor. If we have many inputs and |
| 1082 | // this block is a switch, we want to start by threading the batch that goes |
| 1083 | // to the most popular destination first. If we only know about one |
| 1084 | // threadable destination (the common case) we can avoid this. |
| 1085 | BasicBlock *MostPopularDest = OnlyDest; |
| 1086 | |
| 1087 | if (MostPopularDest == MultipleDestSentinel) |
| 1088 | MostPopularDest = FindMostPopularDest(BB, PredToDestList); |
| 1089 | |
| 1090 | // Now that we know what the most popular destination is, factor all |
| 1091 | // predecessors that will jump to it into a single predecessor. |
| 1092 | SmallVector<BasicBlock*, 16> PredsToFactor; |
| 1093 | for (unsigned i = 0, e = PredToDestList.size(); i != e; ++i) |
| 1094 | if (PredToDestList[i].second == MostPopularDest) { |
| 1095 | BasicBlock *Pred = PredToDestList[i].first; |
| 1096 | |
| 1097 | // This predecessor may be a switch or something else that has multiple |
| 1098 | // edges to the block. Factor each of these edges by listing them |
| 1099 | // according to # occurrences in PredsToFactor. |
| 1100 | TerminatorInst *PredTI = Pred->getTerminator(); |
| 1101 | for (unsigned i = 0, e = PredTI->getNumSuccessors(); i != e; ++i) |
| 1102 | if (PredTI->getSuccessor(i) == BB) |
| 1103 | PredsToFactor.push_back(Pred); |
| 1104 | } |
| 1105 | |
| 1106 | // If the threadable edges are branching on an undefined value, we get to pick |
| 1107 | // the destination that these predecessors should get to. |
| 1108 | if (MostPopularDest == 0) |
| 1109 | MostPopularDest = BB->getTerminator()-> |
| 1110 | getSuccessor(GetBestDestForJumpOnUndef(BB)); |
| 1111 | |
| 1112 | // Ok, try to thread it! |
| 1113 | return ThreadEdge(BB, PredsToFactor, MostPopularDest); |
| 1114 | } |
Chris Lattner | 69e067f | 2008-11-27 05:07:53 +0000 | [diff] [blame] | 1115 | |
Chris Lattner | 77beb47 | 2010-01-11 23:41:09 +0000 | [diff] [blame] | 1116 | /// ProcessBranchOnPHI - We have an otherwise unthreadable conditional branch on |
| 1117 | /// a PHI node in the current block. See if there are any simplifications we |
| 1118 | /// can do based on inputs to the phi node. |
Chris Lattner | d38c14e | 2008-04-22 06:36:15 +0000 | [diff] [blame] | 1119 | /// |
Chris Lattner | 77beb47 | 2010-01-11 23:41:09 +0000 | [diff] [blame] | 1120 | bool JumpThreading::ProcessBranchOnPHI(PHINode *PN) { |
Chris Lattner | 6b65f47 | 2009-10-11 04:40:21 +0000 | [diff] [blame] | 1121 | BasicBlock *BB = PN->getParent(); |
| 1122 | |
Chris Lattner | 2249a0b | 2010-01-12 02:07:17 +0000 | [diff] [blame] | 1123 | // TODO: We could make use of this to do it once for blocks with common PHI |
| 1124 | // values. |
| 1125 | SmallVector<BasicBlock*, 1> PredBBs; |
| 1126 | PredBBs.resize(1); |
| 1127 | |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 1128 | // If any of the predecessor blocks end in an unconditional branch, we can |
Chris Lattner | 77beb47 | 2010-01-11 23:41:09 +0000 | [diff] [blame] | 1129 | // *duplicate* the conditional branch into that block in order to further |
| 1130 | // encourage jump threading and to eliminate cases where we have branch on a |
| 1131 | // phi of an icmp (branch on icmp is much better). |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 1132 | for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { |
| 1133 | BasicBlock *PredBB = PN->getIncomingBlock(i); |
| 1134 | if (BranchInst *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator())) |
Chris Lattner | 2249a0b | 2010-01-12 02:07:17 +0000 | [diff] [blame] | 1135 | if (PredBr->isUnconditional()) { |
| 1136 | PredBBs[0] = PredBB; |
| 1137 | // Try to duplicate BB into PredBB. |
| 1138 | if (DuplicateCondBranchOnPHIIntoPred(BB, PredBBs)) |
| 1139 | return true; |
| 1140 | } |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 1141 | } |
| 1142 | |
Chris Lattner | 6b65f47 | 2009-10-11 04:40:21 +0000 | [diff] [blame] | 1143 | return false; |
Chris Lattner | bd3401f | 2008-04-20 22:39:42 +0000 | [diff] [blame] | 1144 | } |
| 1145 | |
Chris Lattner | 2249a0b | 2010-01-12 02:07:17 +0000 | [diff] [blame] | 1146 | /// ProcessBranchOnXOR - We have an otherwise unthreadable conditional branch on |
| 1147 | /// a xor instruction in the current block. See if there are any |
| 1148 | /// simplifications we can do based on inputs to the xor. |
| 1149 | /// |
| 1150 | bool JumpThreading::ProcessBranchOnXOR(BinaryOperator *BO) { |
| 1151 | BasicBlock *BB = BO->getParent(); |
| 1152 | |
| 1153 | // If either the LHS or RHS of the xor is a constant, don't do this |
| 1154 | // optimization. |
| 1155 | if (isa<ConstantInt>(BO->getOperand(0)) || |
| 1156 | isa<ConstantInt>(BO->getOperand(1))) |
| 1157 | return false; |
| 1158 | |
Chris Lattner | 2dd7657 | 2010-01-23 19:16:25 +0000 | [diff] [blame] | 1159 | // If the first instruction in BB isn't a phi, we won't be able to infer |
| 1160 | // anything special about any particular predecessor. |
| 1161 | if (!isa<PHINode>(BB->front())) |
| 1162 | return false; |
| 1163 | |
Chris Lattner | 2249a0b | 2010-01-12 02:07:17 +0000 | [diff] [blame] | 1164 | // If we have a xor as the branch input to this block, and we know that the |
| 1165 | // LHS or RHS of the xor in any predecessor is true/false, then we can clone |
| 1166 | // the condition into the predecessor and fix that value to true, saving some |
| 1167 | // logical ops on that path and encouraging other paths to simplify. |
| 1168 | // |
| 1169 | // This copies something like this: |
| 1170 | // |
| 1171 | // BB: |
| 1172 | // %X = phi i1 [1], [%X'] |
| 1173 | // %Y = icmp eq i32 %A, %B |
| 1174 | // %Z = xor i1 %X, %Y |
| 1175 | // br i1 %Z, ... |
| 1176 | // |
| 1177 | // Into: |
| 1178 | // BB': |
| 1179 | // %Y = icmp ne i32 %A, %B |
| 1180 | // br i1 %Z, ... |
| 1181 | |
| 1182 | SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> XorOpValues; |
| 1183 | bool isLHS = true; |
| 1184 | if (!ComputeValueKnownInPredecessors(BO->getOperand(0), BB, XorOpValues)) { |
| 1185 | assert(XorOpValues.empty()); |
| 1186 | if (!ComputeValueKnownInPredecessors(BO->getOperand(1), BB, XorOpValues)) |
| 1187 | return false; |
| 1188 | isLHS = false; |
| 1189 | } |
| 1190 | |
| 1191 | assert(!XorOpValues.empty() && |
| 1192 | "ComputeValueKnownInPredecessors returned true with no values"); |
| 1193 | |
| 1194 | // Scan the information to see which is most popular: true or false. The |
| 1195 | // predecessors can be of the set true, false, or undef. |
| 1196 | unsigned NumTrue = 0, NumFalse = 0; |
| 1197 | for (unsigned i = 0, e = XorOpValues.size(); i != e; ++i) { |
| 1198 | if (!XorOpValues[i].first) continue; // Ignore undefs for the count. |
| 1199 | if (XorOpValues[i].first->isZero()) |
| 1200 | ++NumFalse; |
| 1201 | else |
| 1202 | ++NumTrue; |
| 1203 | } |
| 1204 | |
| 1205 | // Determine which value to split on, true, false, or undef if neither. |
| 1206 | ConstantInt *SplitVal = 0; |
| 1207 | if (NumTrue > NumFalse) |
| 1208 | SplitVal = ConstantInt::getTrue(BB->getContext()); |
| 1209 | else if (NumTrue != 0 || NumFalse != 0) |
| 1210 | SplitVal = ConstantInt::getFalse(BB->getContext()); |
| 1211 | |
| 1212 | // Collect all of the blocks that this can be folded into so that we can |
| 1213 | // factor this once and clone it once. |
| 1214 | SmallVector<BasicBlock*, 8> BlocksToFoldInto; |
| 1215 | for (unsigned i = 0, e = XorOpValues.size(); i != e; ++i) { |
| 1216 | if (XorOpValues[i].first != SplitVal && XorOpValues[i].first != 0) continue; |
| 1217 | |
| 1218 | BlocksToFoldInto.push_back(XorOpValues[i].second); |
| 1219 | } |
| 1220 | |
Chris Lattner | 2dd7657 | 2010-01-23 19:16:25 +0000 | [diff] [blame] | 1221 | // If we inferred a value for all of the predecessors, then duplication won't |
| 1222 | // help us. However, we can just replace the LHS or RHS with the constant. |
| 1223 | if (BlocksToFoldInto.size() == |
| 1224 | cast<PHINode>(BB->front()).getNumIncomingValues()) { |
| 1225 | if (SplitVal == 0) { |
| 1226 | // If all preds provide undef, just nuke the xor, because it is undef too. |
| 1227 | BO->replaceAllUsesWith(UndefValue::get(BO->getType())); |
| 1228 | BO->eraseFromParent(); |
| 1229 | } else if (SplitVal->isZero()) { |
| 1230 | // If all preds provide 0, replace the xor with the other input. |
| 1231 | BO->replaceAllUsesWith(BO->getOperand(isLHS)); |
| 1232 | BO->eraseFromParent(); |
| 1233 | } else { |
| 1234 | // If all preds provide 1, set the computed value to 1. |
| 1235 | BO->setOperand(!isLHS, SplitVal); |
| 1236 | } |
| 1237 | |
| 1238 | return true; |
| 1239 | } |
| 1240 | |
Chris Lattner | 2249a0b | 2010-01-12 02:07:17 +0000 | [diff] [blame] | 1241 | // Try to duplicate BB into PredBB. |
Chris Lattner | 797c440 | 2010-01-12 02:07:50 +0000 | [diff] [blame] | 1242 | return DuplicateCondBranchOnPHIIntoPred(BB, BlocksToFoldInto); |
Chris Lattner | 2249a0b | 2010-01-12 02:07:17 +0000 | [diff] [blame] | 1243 | } |
| 1244 | |
| 1245 | |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 1246 | /// AddPHINodeEntriesForMappedBlock - We're adding 'NewPred' as a new |
| 1247 | /// predecessor to the PHIBB block. If it has PHI nodes, add entries for |
| 1248 | /// NewPred using the entries from OldPred (suitably mapped). |
| 1249 | static void AddPHINodeEntriesForMappedBlock(BasicBlock *PHIBB, |
| 1250 | BasicBlock *OldPred, |
| 1251 | BasicBlock *NewPred, |
| 1252 | DenseMap<Instruction*, Value*> &ValueMap) { |
| 1253 | for (BasicBlock::iterator PNI = PHIBB->begin(); |
| 1254 | PHINode *PN = dyn_cast<PHINode>(PNI); ++PNI) { |
| 1255 | // Ok, we have a PHI node. Figure out what the incoming value was for the |
| 1256 | // DestBlock. |
| 1257 | Value *IV = PN->getIncomingValueForBlock(OldPred); |
| 1258 | |
| 1259 | // Remap the value if necessary. |
| 1260 | if (Instruction *Inst = dyn_cast<Instruction>(IV)) { |
| 1261 | DenseMap<Instruction*, Value*>::iterator I = ValueMap.find(Inst); |
| 1262 | if (I != ValueMap.end()) |
| 1263 | IV = I->second; |
| 1264 | } |
| 1265 | |
| 1266 | PN->addIncoming(IV, NewPred); |
| 1267 | } |
| 1268 | } |
Chris Lattner | 6bf7750 | 2008-04-22 07:05:46 +0000 | [diff] [blame] | 1269 | |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 1270 | /// ThreadEdge - We have decided that it is safe and profitable to factor the |
| 1271 | /// blocks in PredBBs to one predecessor, then thread an edge from it to SuccBB |
| 1272 | /// across BB. Transform the IR to reflect this change. |
| 1273 | bool JumpThreading::ThreadEdge(BasicBlock *BB, |
| 1274 | const SmallVectorImpl<BasicBlock*> &PredBBs, |
Chris Lattner | bdbf1a1 | 2009-10-11 04:33:43 +0000 | [diff] [blame] | 1275 | BasicBlock *SuccBB) { |
Mike Stump | fe095f3 | 2009-05-04 18:40:41 +0000 | [diff] [blame] | 1276 | // If threading to the same block as we come from, we would infinite loop. |
| 1277 | if (SuccBB == BB) { |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 1278 | DEBUG(dbgs() << " Not threading across BB '" << BB->getName() |
Daniel Dunbar | 93b67e4 | 2009-07-26 07:49:05 +0000 | [diff] [blame] | 1279 | << "' - would thread to self!\n"); |
Mike Stump | fe095f3 | 2009-05-04 18:40:41 +0000 | [diff] [blame] | 1280 | return false; |
| 1281 | } |
| 1282 | |
| 1283 | // If threading this would thread across a loop header, don't thread the edge. |
| 1284 | // See the comments above FindLoopHeaders for justifications and caveats. |
| 1285 | if (LoopHeaders.count(BB)) { |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 1286 | DEBUG(dbgs() << " Not threading across loop header BB '" << BB->getName() |
Daniel Dunbar | 93b67e4 | 2009-07-26 07:49:05 +0000 | [diff] [blame] | 1287 | << "' to dest BB '" << SuccBB->getName() |
| 1288 | << "' - it might create an irreducible loop!\n"); |
Mike Stump | fe095f3 | 2009-05-04 18:40:41 +0000 | [diff] [blame] | 1289 | return false; |
| 1290 | } |
| 1291 | |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 1292 | unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB); |
| 1293 | if (JumpThreadCost > Threshold) { |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 1294 | DEBUG(dbgs() << " Not threading BB '" << BB->getName() |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 1295 | << "' - Cost is too high: " << JumpThreadCost << "\n"); |
| 1296 | return false; |
| 1297 | } |
| 1298 | |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 1299 | // And finally, do it! Start by factoring the predecessors is needed. |
| 1300 | BasicBlock *PredBB; |
| 1301 | if (PredBBs.size() == 1) |
| 1302 | PredBB = PredBBs[0]; |
| 1303 | else { |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 1304 | DEBUG(dbgs() << " Factoring out " << PredBBs.size() |
Chris Lattner | 5729d38 | 2009-11-07 08:05:03 +0000 | [diff] [blame] | 1305 | << " common predecessors.\n"); |
| 1306 | PredBB = SplitBlockPredecessors(BB, &PredBBs[0], PredBBs.size(), |
| 1307 | ".thr_comm", this); |
| 1308 | } |
| 1309 | |
Mike Stump | fe095f3 | 2009-05-04 18:40:41 +0000 | [diff] [blame] | 1310 | // And finally, do it! |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 1311 | DEBUG(dbgs() << " Threading edge from '" << PredBB->getName() << "' to '" |
Daniel Dunbar | 460f656 | 2009-07-26 09:48:23 +0000 | [diff] [blame] | 1312 | << SuccBB->getName() << "' with cost: " << JumpThreadCost |
Daniel Dunbar | 93b67e4 | 2009-07-26 07:49:05 +0000 | [diff] [blame] | 1313 | << ", across block:\n " |
| 1314 | << *BB << "\n"); |
Mike Stump | fe095f3 | 2009-05-04 18:40:41 +0000 | [diff] [blame] | 1315 | |
Owen Anderson | cfa7fb6 | 2010-07-26 18:48:03 +0000 | [diff] [blame] | 1316 | if (LVI) |
| 1317 | LVI->threadEdge(PredBB, BB, SuccBB); |
| 1318 | |
Chris Lattner | bd3401f | 2008-04-20 22:39:42 +0000 | [diff] [blame] | 1319 | // We are going to have to map operands from the original BB block to the new |
| 1320 | // copy of the block 'NewBB'. If there are PHI nodes in BB, evaluate them to |
| 1321 | // account for entry from PredBB. |
| 1322 | DenseMap<Instruction*, Value*> ValueMapping; |
| 1323 | |
Owen Anderson | 1d0be15 | 2009-08-13 21:58:54 +0000 | [diff] [blame] | 1324 | BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), |
| 1325 | BB->getName()+".thread", |
| 1326 | BB->getParent(), BB); |
Chris Lattner | bd3401f | 2008-04-20 22:39:42 +0000 | [diff] [blame] | 1327 | NewBB->moveAfter(PredBB); |
| 1328 | |
| 1329 | BasicBlock::iterator BI = BB->begin(); |
| 1330 | for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI) |
| 1331 | ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB); |
| 1332 | |
| 1333 | // Clone the non-phi instructions of BB into NewBB, keeping track of the |
| 1334 | // mapping and using it to remap operands in the cloned instructions. |
| 1335 | for (; !isa<TerminatorInst>(BI); ++BI) { |
Nick Lewycky | 6776064 | 2009-09-27 07:38:41 +0000 | [diff] [blame] | 1336 | Instruction *New = BI->clone(); |
Daniel Dunbar | 460f656 | 2009-07-26 09:48:23 +0000 | [diff] [blame] | 1337 | New->setName(BI->getName()); |
Chris Lattner | bd3401f | 2008-04-20 22:39:42 +0000 | [diff] [blame] | 1338 | NewBB->getInstList().push_back(New); |
| 1339 | ValueMapping[BI] = New; |
| 1340 | |
| 1341 | // Remap operands to patch up intra-block references. |
| 1342 | for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i) |
Dan Gohman | f530c92 | 2009-07-02 00:17:47 +0000 | [diff] [blame] | 1343 | if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) { |
| 1344 | DenseMap<Instruction*, Value*>::iterator I = ValueMapping.find(Inst); |
| 1345 | if (I != ValueMapping.end()) |
| 1346 | New->setOperand(i, I->second); |
| 1347 | } |
Chris Lattner | bd3401f | 2008-04-20 22:39:42 +0000 | [diff] [blame] | 1348 | } |
| 1349 | |
| 1350 | // We didn't copy the terminator from BB over to NewBB, because there is now |
| 1351 | // an unconditional jump to SuccBB. Insert the unconditional jump. |
| 1352 | BranchInst::Create(SuccBB, NewBB); |
| 1353 | |
| 1354 | // Check to see if SuccBB has PHI nodes. If so, we need to add entries to the |
| 1355 | // PHI nodes for NewBB now. |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 1356 | AddPHINodeEntriesForMappedBlock(SuccBB, BB, NewBB, ValueMapping); |
Chris Lattner | bd3401f | 2008-04-20 22:39:42 +0000 | [diff] [blame] | 1357 | |
Chris Lattner | 433a0db | 2009-10-10 09:05:58 +0000 | [diff] [blame] | 1358 | // If there were values defined in BB that are used outside the block, then we |
| 1359 | // now have to update all uses of the value to use either the original value, |
| 1360 | // the cloned value, or some PHI derived value. This can require arbitrary |
| 1361 | // PHI insertion, of which we are prepared to do, clean these up now. |
| 1362 | SSAUpdater SSAUpdate; |
| 1363 | SmallVector<Use*, 16> UsesToRename; |
| 1364 | for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) { |
| 1365 | // Scan all uses of this instruction to see if it is used outside of its |
| 1366 | // block, and if so, record them in UsesToRename. |
| 1367 | for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E; |
| 1368 | ++UI) { |
| 1369 | Instruction *User = cast<Instruction>(*UI); |
| 1370 | if (PHINode *UserPN = dyn_cast<PHINode>(User)) { |
| 1371 | if (UserPN->getIncomingBlock(UI) == BB) |
| 1372 | continue; |
| 1373 | } else if (User->getParent() == BB) |
| 1374 | continue; |
| 1375 | |
| 1376 | UsesToRename.push_back(&UI.getUse()); |
| 1377 | } |
| 1378 | |
| 1379 | // If there are no uses outside the block, we're done with this instruction. |
| 1380 | if (UsesToRename.empty()) |
| 1381 | continue; |
| 1382 | |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 1383 | DEBUG(dbgs() << "JT: Renaming non-local uses of: " << *I << "\n"); |
Chris Lattner | 433a0db | 2009-10-10 09:05:58 +0000 | [diff] [blame] | 1384 | |
| 1385 | // We found a use of I outside of BB. Rename all uses of I that are outside |
| 1386 | // its block to be uses of the appropriate PHI node etc. See ValuesInBlocks |
| 1387 | // with the two values we know. |
| 1388 | SSAUpdate.Initialize(I); |
| 1389 | SSAUpdate.AddAvailableValue(BB, I); |
| 1390 | SSAUpdate.AddAvailableValue(NewBB, ValueMapping[I]); |
| 1391 | |
| 1392 | while (!UsesToRename.empty()) |
| 1393 | SSAUpdate.RewriteUse(*UsesToRename.pop_back_val()); |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 1394 | DEBUG(dbgs() << "\n"); |
Chris Lattner | 433a0db | 2009-10-10 09:05:58 +0000 | [diff] [blame] | 1395 | } |
| 1396 | |
| 1397 | |
Chris Lattner | ef0c674 | 2008-12-01 04:48:07 +0000 | [diff] [blame] | 1398 | // Ok, NewBB is good to go. Update the terminator of PredBB to jump to |
Chris Lattner | bd3401f | 2008-04-20 22:39:42 +0000 | [diff] [blame] | 1399 | // NewBB instead of BB. This eliminates predecessors from BB, which requires |
| 1400 | // us to simplify any PHI nodes in BB. |
| 1401 | TerminatorInst *PredTerm = PredBB->getTerminator(); |
| 1402 | for (unsigned i = 0, e = PredTerm->getNumSuccessors(); i != e; ++i) |
| 1403 | if (PredTerm->getSuccessor(i) == BB) { |
Chris Lattner | c2c23d0 | 2009-11-09 22:32:36 +0000 | [diff] [blame] | 1404 | RemovePredecessorAndSimplify(BB, PredBB, TD); |
Chris Lattner | bd3401f | 2008-04-20 22:39:42 +0000 | [diff] [blame] | 1405 | PredTerm->setSuccessor(i, NewBB); |
| 1406 | } |
Chris Lattner | ef0c674 | 2008-12-01 04:48:07 +0000 | [diff] [blame] | 1407 | |
| 1408 | // At this point, the IR is fully up to date and consistent. Do a quick scan |
| 1409 | // over the new instructions and zap any that are constants or dead. This |
| 1410 | // frequently happens because of phi translation. |
Chris Lattner | 972a46c | 2010-01-12 20:41:47 +0000 | [diff] [blame] | 1411 | SimplifyInstructionsInBlock(NewBB, TD); |
Mike Stump | fe095f3 | 2009-05-04 18:40:41 +0000 | [diff] [blame] | 1412 | |
| 1413 | // Threaded an edge! |
| 1414 | ++NumThreads; |
| 1415 | return true; |
Chris Lattner | 177480b | 2008-04-20 21:13:06 +0000 | [diff] [blame] | 1416 | } |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 1417 | |
| 1418 | /// DuplicateCondBranchOnPHIIntoPred - PredBB contains an unconditional branch |
| 1419 | /// to BB which contains an i1 PHI node and a conditional branch on that PHI. |
| 1420 | /// If we can duplicate the contents of BB up into PredBB do so now, this |
| 1421 | /// improves the odds that the branch will be on an analyzable instruction like |
| 1422 | /// a compare. |
| 1423 | bool JumpThreading::DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB, |
Chris Lattner | 2249a0b | 2010-01-12 02:07:17 +0000 | [diff] [blame] | 1424 | const SmallVectorImpl<BasicBlock *> &PredBBs) { |
| 1425 | assert(!PredBBs.empty() && "Can't handle an empty set"); |
| 1426 | |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 1427 | // If BB is a loop header, then duplicating this block outside the loop would |
| 1428 | // cause us to transform this into an irreducible loop, don't do this. |
| 1429 | // See the comments above FindLoopHeaders for justifications and caveats. |
| 1430 | if (LoopHeaders.count(BB)) { |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 1431 | DEBUG(dbgs() << " Not duplicating loop header '" << BB->getName() |
Chris Lattner | 2249a0b | 2010-01-12 02:07:17 +0000 | [diff] [blame] | 1432 | << "' into predecessor block '" << PredBBs[0]->getName() |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 1433 | << "' - it might create an irreducible loop!\n"); |
| 1434 | return false; |
| 1435 | } |
| 1436 | |
| 1437 | unsigned DuplicationCost = getJumpThreadDuplicationCost(BB); |
| 1438 | if (DuplicationCost > Threshold) { |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 1439 | DEBUG(dbgs() << " Not duplicating BB '" << BB->getName() |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 1440 | << "' - Cost is too high: " << DuplicationCost << "\n"); |
| 1441 | return false; |
| 1442 | } |
| 1443 | |
Chris Lattner | 2249a0b | 2010-01-12 02:07:17 +0000 | [diff] [blame] | 1444 | // And finally, do it! Start by factoring the predecessors is needed. |
| 1445 | BasicBlock *PredBB; |
| 1446 | if (PredBBs.size() == 1) |
| 1447 | PredBB = PredBBs[0]; |
| 1448 | else { |
| 1449 | DEBUG(dbgs() << " Factoring out " << PredBBs.size() |
| 1450 | << " common predecessors.\n"); |
| 1451 | PredBB = SplitBlockPredecessors(BB, &PredBBs[0], PredBBs.size(), |
| 1452 | ".thr_comm", this); |
| 1453 | } |
| 1454 | |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 1455 | // Okay, we decided to do this! Clone all the instructions in BB onto the end |
| 1456 | // of PredBB. |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 1457 | DEBUG(dbgs() << " Duplicating block '" << BB->getName() << "' into end of '" |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 1458 | << PredBB->getName() << "' to eliminate branch on phi. Cost: " |
| 1459 | << DuplicationCost << " block is:" << *BB << "\n"); |
| 1460 | |
Chris Lattner | 2249a0b | 2010-01-12 02:07:17 +0000 | [diff] [blame] | 1461 | // Unless PredBB ends with an unconditional branch, split the edge so that we |
| 1462 | // can just clone the bits from BB into the end of the new PredBB. |
Chris Lattner | d668839 | 2010-01-23 19:21:31 +0000 | [diff] [blame] | 1463 | BranchInst *OldPredBranch = dyn_cast<BranchInst>(PredBB->getTerminator()); |
Chris Lattner | 2249a0b | 2010-01-12 02:07:17 +0000 | [diff] [blame] | 1464 | |
Chris Lattner | d668839 | 2010-01-23 19:21:31 +0000 | [diff] [blame] | 1465 | if (OldPredBranch == 0 || !OldPredBranch->isUnconditional()) { |
Chris Lattner | 2249a0b | 2010-01-12 02:07:17 +0000 | [diff] [blame] | 1466 | PredBB = SplitEdge(PredBB, BB, this); |
| 1467 | OldPredBranch = cast<BranchInst>(PredBB->getTerminator()); |
| 1468 | } |
| 1469 | |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 1470 | // We are going to have to map operands from the original BB block into the |
| 1471 | // PredBB block. Evaluate PHI nodes in BB. |
| 1472 | DenseMap<Instruction*, Value*> ValueMapping; |
| 1473 | |
| 1474 | BasicBlock::iterator BI = BB->begin(); |
| 1475 | for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI) |
| 1476 | ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB); |
| 1477 | |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 1478 | // Clone the non-phi instructions of BB into PredBB, keeping track of the |
| 1479 | // mapping and using it to remap operands in the cloned instructions. |
| 1480 | for (; BI != BB->end(); ++BI) { |
| 1481 | Instruction *New = BI->clone(); |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 1482 | |
| 1483 | // Remap operands to patch up intra-block references. |
| 1484 | for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i) |
| 1485 | if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) { |
| 1486 | DenseMap<Instruction*, Value*>::iterator I = ValueMapping.find(Inst); |
| 1487 | if (I != ValueMapping.end()) |
| 1488 | New->setOperand(i, I->second); |
| 1489 | } |
Chris Lattner | 972a46c | 2010-01-12 20:41:47 +0000 | [diff] [blame] | 1490 | |
| 1491 | // If this instruction can be simplified after the operands are updated, |
| 1492 | // just use the simplified value instead. This frequently happens due to |
| 1493 | // phi translation. |
| 1494 | if (Value *IV = SimplifyInstruction(New, TD)) { |
| 1495 | delete New; |
| 1496 | ValueMapping[BI] = IV; |
| 1497 | } else { |
| 1498 | // Otherwise, insert the new instruction into the block. |
| 1499 | New->setName(BI->getName()); |
| 1500 | PredBB->getInstList().insert(OldPredBranch, New); |
| 1501 | ValueMapping[BI] = New; |
| 1502 | } |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 1503 | } |
| 1504 | |
| 1505 | // Check to see if the targets of the branch had PHI nodes. If so, we need to |
| 1506 | // add entries to the PHI nodes for branch from PredBB now. |
| 1507 | BranchInst *BBBranch = cast<BranchInst>(BB->getTerminator()); |
| 1508 | AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(0), BB, PredBB, |
| 1509 | ValueMapping); |
| 1510 | AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(1), BB, PredBB, |
| 1511 | ValueMapping); |
| 1512 | |
| 1513 | // If there were values defined in BB that are used outside the block, then we |
| 1514 | // now have to update all uses of the value to use either the original value, |
| 1515 | // the cloned value, or some PHI derived value. This can require arbitrary |
| 1516 | // PHI insertion, of which we are prepared to do, clean these up now. |
| 1517 | SSAUpdater SSAUpdate; |
| 1518 | SmallVector<Use*, 16> UsesToRename; |
| 1519 | for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) { |
| 1520 | // Scan all uses of this instruction to see if it is used outside of its |
| 1521 | // block, and if so, record them in UsesToRename. |
| 1522 | for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E; |
| 1523 | ++UI) { |
| 1524 | Instruction *User = cast<Instruction>(*UI); |
| 1525 | if (PHINode *UserPN = dyn_cast<PHINode>(User)) { |
| 1526 | if (UserPN->getIncomingBlock(UI) == BB) |
| 1527 | continue; |
| 1528 | } else if (User->getParent() == BB) |
| 1529 | continue; |
| 1530 | |
| 1531 | UsesToRename.push_back(&UI.getUse()); |
| 1532 | } |
| 1533 | |
| 1534 | // If there are no uses outside the block, we're done with this instruction. |
| 1535 | if (UsesToRename.empty()) |
| 1536 | continue; |
| 1537 | |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 1538 | DEBUG(dbgs() << "JT: Renaming non-local uses of: " << *I << "\n"); |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 1539 | |
| 1540 | // We found a use of I outside of BB. Rename all uses of I that are outside |
| 1541 | // its block to be uses of the appropriate PHI node etc. See ValuesInBlocks |
| 1542 | // with the two values we know. |
| 1543 | SSAUpdate.Initialize(I); |
| 1544 | SSAUpdate.AddAvailableValue(BB, I); |
| 1545 | SSAUpdate.AddAvailableValue(PredBB, ValueMapping[I]); |
| 1546 | |
| 1547 | while (!UsesToRename.empty()) |
| 1548 | SSAUpdate.RewriteUse(*UsesToRename.pop_back_val()); |
David Greene | fe7fe66 | 2010-01-05 01:27:19 +0000 | [diff] [blame] | 1549 | DEBUG(dbgs() << "\n"); |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 1550 | } |
| 1551 | |
| 1552 | // PredBB no longer jumps to BB, remove entries in the PHI node for the edge |
| 1553 | // that we nuked. |
Chris Lattner | c2c23d0 | 2009-11-09 22:32:36 +0000 | [diff] [blame] | 1554 | RemovePredecessorAndSimplify(BB, PredBB, TD); |
Chris Lattner | 78c552e | 2009-10-11 07:24:57 +0000 | [diff] [blame] | 1555 | |
| 1556 | // Remove the unconditional branch at the end of the PredBB block. |
| 1557 | OldPredBranch->eraseFromParent(); |
| 1558 | |
| 1559 | ++NumDupes; |
| 1560 | return true; |
| 1561 | } |
| 1562 | |
| 1563 | |