1 //===- StackColoring.cpp --------------------------------------------------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This pass implements the stack-coloring optimization that looks for 10 // lifetime markers machine instructions (LIFESTART_BEGIN and LIFESTART_END), 11 // which represent the possible lifetime of stack slots. It attempts to 12 // merge disjoint stack slots and reduce the used stack space. 13 // NOTE: This pass is not StackSlotColoring, which optimizes spill slots. 14 // 15 // TODO: In the future we plan to improve stack coloring in the following ways: 16 // 1. Allow merging multiple small slots into a single larger slot at different 17 // offsets. 18 // 2. Merge this pass with StackSlotColoring and allow merging of allocas with 19 // spill slots. 20 // 21 //===----------------------------------------------------------------------===// 22 23 #include "llvm/ADT/BitVector.h" 24 #include "llvm/ADT/DenseMap.h" 25 #include "llvm/ADT/DepthFirstIterator.h" 26 #include "llvm/ADT/SmallPtrSet.h" 27 #include "llvm/ADT/SmallVector.h" 28 #include "llvm/ADT/Statistic.h" 29 #include "llvm/Analysis/ValueTracking.h" 30 #include "llvm/CodeGen/LiveInterval.h" 31 #include "llvm/CodeGen/MachineBasicBlock.h" 32 #include "llvm/CodeGen/MachineFrameInfo.h" 33 #include "llvm/CodeGen/MachineFunction.h" 34 #include "llvm/CodeGen/MachineFunctionPass.h" 35 #include "llvm/CodeGen/MachineInstr.h" 36 #include "llvm/CodeGen/MachineMemOperand.h" 37 #include "llvm/CodeGen/MachineOperand.h" 38 #include "llvm/CodeGen/Passes.h" 39 #include "llvm/CodeGen/SelectionDAGNodes.h" 40 #include "llvm/CodeGen/SlotIndexes.h" 41 #include "llvm/CodeGen/TargetOpcodes.h" 42 #include "llvm/CodeGen/WinEHFuncInfo.h" 43 #include "llvm/Config/llvm-config.h" 44 #include "llvm/IR/Constants.h" 45 #include "llvm/IR/DebugInfoMetadata.h" 46 #include "llvm/IR/Function.h" 47 #include "llvm/IR/Instructions.h" 48 #include "llvm/IR/Metadata.h" 49 #include "llvm/IR/Use.h" 50 #include "llvm/IR/Value.h" 51 #include "llvm/InitializePasses.h" 52 #include "llvm/Pass.h" 53 #include "llvm/Support/Casting.h" 54 #include "llvm/Support/CommandLine.h" 55 #include "llvm/Support/Compiler.h" 56 #include "llvm/Support/Debug.h" 57 #include "llvm/Support/raw_ostream.h" 58 #include <algorithm> 59 #include <cassert> 60 #include <limits> 61 #include <memory> 62 #include <utility> 63 64 using namespace llvm; 65 66 #define DEBUG_TYPE "stack-coloring" 67 68 static cl::opt<bool> 69 DisableColoring("no-stack-coloring", 70 cl::init(false), cl::Hidden, 71 cl::desc("Disable stack coloring")); 72 73 /// The user may write code that uses allocas outside of the declared lifetime 74 /// zone. This can happen when the user returns a reference to a local 75 /// data-structure. We can detect these cases and decide not to optimize the 76 /// code. If this flag is enabled, we try to save the user. This option 77 /// is treated as overriding LifetimeStartOnFirstUse below. 78 static cl::opt<bool> 79 ProtectFromEscapedAllocas("protect-from-escaped-allocas", 80 cl::init(false), cl::Hidden, 81 cl::desc("Do not optimize lifetime zones that " 82 "are broken")); 83 84 /// Enable enhanced dataflow scheme for lifetime analysis (treat first 85 /// use of stack slot as start of slot lifetime, as opposed to looking 86 /// for LIFETIME_START marker). See "Implementation notes" below for 87 /// more info. 88 static cl::opt<bool> 89 LifetimeStartOnFirstUse("stackcoloring-lifetime-start-on-first-use", 90 cl::init(true), cl::Hidden, 91 cl::desc("Treat stack lifetimes as starting on first use, not on START marker.")); 92 93 94 STATISTIC(NumMarkerSeen, "Number of lifetime markers found."); 95 STATISTIC(StackSpaceSaved, "Number of bytes saved due to merging slots."); 96 STATISTIC(StackSlotMerged, "Number of stack slot merged."); 97 STATISTIC(EscapedAllocas, "Number of allocas that escaped the lifetime region"); 98 99 //===----------------------------------------------------------------------===// 100 // StackColoring Pass 101 //===----------------------------------------------------------------------===// 102 // 103 // Stack Coloring reduces stack usage by merging stack slots when they 104 // can't be used together. For example, consider the following C program: 105 // 106 // void bar(char *, int); 107 // void foo(bool var) { 108 // A: { 109 // char z[4096]; 110 // bar(z, 0); 111 // } 112 // 113 // char *p; 114 // char x[4096]; 115 // char y[4096]; 116 // if (var) { 117 // p = x; 118 // } else { 119 // bar(y, 1); 120 // p = y + 1024; 121 // } 122 // B: 123 // bar(p, 2); 124 // } 125 // 126 // Naively-compiled, this program would use 12k of stack space. However, the 127 // stack slot corresponding to `z` is always destroyed before either of the 128 // stack slots for `x` or `y` are used, and then `x` is only used if `var` 129 // is true, while `y` is only used if `var` is false. So in no time are 2 130 // of the stack slots used together, and therefore we can merge them, 131 // compiling the function using only a single 4k alloca: 132 // 133 // void foo(bool var) { // equivalent 134 // char x[4096]; 135 // char *p; 136 // bar(x, 0); 137 // if (var) { 138 // p = x; 139 // } else { 140 // bar(x, 1); 141 // p = x + 1024; 142 // } 143 // bar(p, 2); 144 // } 145 // 146 // This is an important optimization if we want stack space to be under 147 // control in large functions, both open-coded ones and ones created by 148 // inlining. 149 // 150 // Implementation Notes: 151 // --------------------- 152 // 153 // An important part of the above reasoning is that `z` can't be accessed 154 // while the latter 2 calls to `bar` are running. This is justified because 155 // `z`'s lifetime is over after we exit from block `A:`, so any further 156 // accesses to it would be UB. The way we represent this information 157 // in LLVM is by having frontends delimit blocks with `lifetime.start` 158 // and `lifetime.end` intrinsics. 159 // 160 // The effect of these intrinsics seems to be as follows (maybe I should 161 // specify this in the reference?): 162 // 163 // L1) at start, each stack-slot is marked as *out-of-scope*, unless no 164 // lifetime intrinsic refers to that stack slot, in which case 165 // it is marked as *in-scope*. 166 // L2) on a `lifetime.start`, a stack slot is marked as *in-scope* and 167 // the stack slot is overwritten with `undef`. 168 // L3) on a `lifetime.end`, a stack slot is marked as *out-of-scope*. 169 // L4) on function exit, all stack slots are marked as *out-of-scope*. 170 // L5) `lifetime.end` is a no-op when called on a slot that is already 171 // *out-of-scope*. 172 // L6) memory accesses to *out-of-scope* stack slots are UB. 173 // L7) when a stack-slot is marked as *out-of-scope*, all pointers to it 174 // are invalidated, unless the slot is "degenerate". This is used to 175 // justify not marking slots as in-use until the pointer to them is 176 // used, but feels a bit hacky in the presence of things like LICM. See 177 // the "Degenerate Slots" section for more details. 178 // 179 // Now, let's ground stack coloring on these rules. We'll define a slot 180 // as *in-use* at a (dynamic) point in execution if it either can be 181 // written to at that point, or if it has a live and non-undef content 182 // at that point. 183 // 184 // Obviously, slots that are never *in-use* together can be merged, and 185 // in our example `foo`, the slots for `x`, `y` and `z` are never 186 // in-use together (of course, sometimes slots that *are* in-use together 187 // might still be mergable, but we don't care about that here). 188 // 189 // In this implementation, we successively merge pairs of slots that are 190 // not *in-use* together. We could be smarter - for example, we could merge 191 // a single large slot with 2 small slots, or we could construct the 192 // interference graph and run a "smart" graph coloring algorithm, but with 193 // that aside, how do we find out whether a pair of slots might be *in-use* 194 // together? 195 // 196 // From our rules, we see that *out-of-scope* slots are never *in-use*, 197 // and from (L7) we see that "non-degenerate" slots remain non-*in-use* 198 // until their address is taken. Therefore, we can approximate slot activity 199 // using dataflow. 200 // 201 // A subtle point: naively, we might try to figure out which pairs of 202 // stack-slots interfere by propagating `S in-use` through the CFG for every 203 // stack-slot `S`, and having `S` and `T` interfere if there is a CFG point in 204 // which they are both *in-use*. 205 // 206 // That is sound, but overly conservative in some cases: in our (artificial) 207 // example `foo`, either `x` or `y` might be in use at the label `B:`, but 208 // as `x` is only in use if we came in from the `var` edge and `y` only 209 // if we came from the `!var` edge, they still can't be in use together. 210 // See PR32488 for an important real-life case. 211 // 212 // If we wanted to find all points of interference precisely, we could 213 // propagate `S in-use` and `S&T in-use` predicates through the CFG. That 214 // would be precise, but requires propagating `O(n^2)` dataflow facts. 215 // 216 // However, we aren't interested in the *set* of points of interference 217 // between 2 stack slots, only *whether* there *is* such a point. So we 218 // can rely on a little trick: for `S` and `T` to be in-use together, 219 // one of them needs to become in-use while the other is in-use (or 220 // they might both become in use simultaneously). We can check this 221 // by also keeping track of the points at which a stack slot might *start* 222 // being in-use. 223 // 224 // Exact first use: 225 // ---------------- 226 // 227 // Consider the following motivating example: 228 // 229 // int foo() { 230 // char b1[1024], b2[1024]; 231 // if (...) { 232 // char b3[1024]; 233 // <uses of b1, b3>; 234 // return x; 235 // } else { 236 // char b4[1024], b5[1024]; 237 // <uses of b2, b4, b5>; 238 // return y; 239 // } 240 // } 241 // 242 // In the code above, "b3" and "b4" are declared in distinct lexical 243 // scopes, meaning that it is easy to prove that they can share the 244 // same stack slot. Variables "b1" and "b2" are declared in the same 245 // scope, meaning that from a lexical point of view, their lifetimes 246 // overlap. From a control flow pointer of view, however, the two 247 // variables are accessed in disjoint regions of the CFG, thus it 248 // should be possible for them to share the same stack slot. An ideal 249 // stack allocation for the function above would look like: 250 // 251 // slot 0: b1, b2 252 // slot 1: b3, b4 253 // slot 2: b5 254 // 255 // Achieving this allocation is tricky, however, due to the way 256 // lifetime markers are inserted. Here is a simplified view of the 257 // control flow graph for the code above: 258 // 259 // +------ block 0 -------+ 260 // 0| LIFETIME_START b1, b2 | 261 // 1| <test 'if' condition> | 262 // +-----------------------+ 263 // ./ \. 264 // +------ block 1 -------+ +------ block 2 -------+ 265 // 2| LIFETIME_START b3 | 5| LIFETIME_START b4, b5 | 266 // 3| <uses of b1, b3> | 6| <uses of b2, b4, b5> | 267 // 4| LIFETIME_END b3 | 7| LIFETIME_END b4, b5 | 268 // +-----------------------+ +-----------------------+ 269 // \. /. 270 // +------ block 3 -------+ 271 // 8| <cleanupcode> | 272 // 9| LIFETIME_END b1, b2 | 273 // 10| return | 274 // +-----------------------+ 275 // 276 // If we create live intervals for the variables above strictly based 277 // on the lifetime markers, we'll get the set of intervals on the 278 // left. If we ignore the lifetime start markers and instead treat a 279 // variable's lifetime as beginning with the first reference to the 280 // var, then we get the intervals on the right. 281 // 282 // LIFETIME_START First Use 283 // b1: [0,9] [3,4] [8,9] 284 // b2: [0,9] [6,9] 285 // b3: [2,4] [3,4] 286 // b4: [5,7] [6,7] 287 // b5: [5,7] [6,7] 288 // 289 // For the intervals on the left, the best we can do is overlap two 290 // variables (b3 and b4, for example); this gives us a stack size of 291 // 4*1024 bytes, not ideal. When treating first-use as the start of a 292 // lifetime, we can additionally overlap b1 and b5, giving us a 3*1024 293 // byte stack (better). 294 // 295 // Degenerate Slots: 296 // ----------------- 297 // 298 // Relying entirely on first-use of stack slots is problematic, 299 // however, due to the fact that optimizations can sometimes migrate 300 // uses of a variable outside of its lifetime start/end region. Here 301 // is an example: 302 // 303 // int bar() { 304 // char b1[1024], b2[1024]; 305 // if (...) { 306 // <uses of b2> 307 // return y; 308 // } else { 309 // <uses of b1> 310 // while (...) { 311 // char b3[1024]; 312 // <uses of b3> 313 // } 314 // } 315 // } 316 // 317 // Before optimization, the control flow graph for the code above 318 // might look like the following: 319 // 320 // +------ block 0 -------+ 321 // 0| LIFETIME_START b1, b2 | 322 // 1| <test 'if' condition> | 323 // +-----------------------+ 324 // ./ \. 325 // +------ block 1 -------+ +------- block 2 -------+ 326 // 2| <uses of b2> | 3| <uses of b1> | 327 // +-----------------------+ +-----------------------+ 328 // | | 329 // | +------- block 3 -------+ <-\. 330 // | 4| <while condition> | | 331 // | +-----------------------+ | 332 // | / | | 333 // | / +------- block 4 -------+ 334 // \ / 5| LIFETIME_START b3 | | 335 // \ / 6| <uses of b3> | | 336 // \ / 7| LIFETIME_END b3 | | 337 // \ | +------------------------+ | 338 // \ | \ / 339 // +------ block 5 -----+ \--------------- 340 // 8| <cleanupcode> | 341 // 9| LIFETIME_END b1, b2 | 342 // 10| return | 343 // +---------------------+ 344 // 345 // During optimization, however, it can happen that an instruction 346 // computing an address in "b3" (for example, a loop-invariant GEP) is 347 // hoisted up out of the loop from block 4 to block 2. [Note that 348 // this is not an actual load from the stack, only an instruction that 349 // computes the address to be loaded]. If this happens, there is now a 350 // path leading from the first use of b3 to the return instruction 351 // that does not encounter the b3 LIFETIME_END, hence b3's lifetime is 352 // now larger than if we were computing live intervals strictly based 353 // on lifetime markers. In the example above, this lengthened lifetime 354 // would mean that it would appear illegal to overlap b3 with b2. 355 // 356 // To deal with this such cases, the code in ::collectMarkers() below 357 // tries to identify "degenerate" slots -- those slots where on a single 358 // forward pass through the CFG we encounter a first reference to slot 359 // K before we hit the slot K lifetime start marker. For such slots, 360 // we fall back on using the lifetime start marker as the beginning of 361 // the variable's lifetime. NB: with this implementation, slots can 362 // appear degenerate in cases where there is unstructured control flow: 363 // 364 // if (q) goto mid; 365 // if (x > 9) { 366 // int b[100]; 367 // memcpy(&b[0], ...); 368 // mid: b[k] = ...; 369 // abc(&b); 370 // } 371 // 372 // If in RPO ordering chosen to walk the CFG we happen to visit the b[k] 373 // before visiting the memcpy block (which will contain the lifetime start 374 // for "b" then it will appear that 'b' has a degenerate lifetime. 375 // 376 377 namespace { 378 379 /// StackColoring - A machine pass for merging disjoint stack allocations, 380 /// marked by the LIFETIME_START and LIFETIME_END pseudo instructions. 381 class StackColoring : public MachineFunctionPass { 382 MachineFrameInfo *MFI; 383 MachineFunction *MF; 384 385 /// A class representing liveness information for a single basic block. 386 /// Each bit in the BitVector represents the liveness property 387 /// for a different stack slot. 388 struct BlockLifetimeInfo { 389 /// Which slots BEGINs in each basic block. 390 BitVector Begin; 391 392 /// Which slots ENDs in each basic block. 393 BitVector End; 394 395 /// Which slots are marked as LIVE_IN, coming into each basic block. 396 BitVector LiveIn; 397 398 /// Which slots are marked as LIVE_OUT, coming out of each basic block. 399 BitVector LiveOut; 400 }; 401 402 /// Maps active slots (per bit) for each basic block. 403 using LivenessMap = DenseMap<const MachineBasicBlock *, BlockLifetimeInfo>; 404 LivenessMap BlockLiveness; 405 406 /// Maps serial numbers to basic blocks. 407 DenseMap<const MachineBasicBlock *, int> BasicBlocks; 408 409 /// Maps basic blocks to a serial number. 410 SmallVector<const MachineBasicBlock *, 8> BasicBlockNumbering; 411 412 /// Maps slots to their use interval. Outside of this interval, slots 413 /// values are either dead or `undef` and they will not be written to. 414 SmallVector<std::unique_ptr<LiveInterval>, 16> Intervals; 415 416 /// Maps slots to the points where they can become in-use. 417 SmallVector<SmallVector<SlotIndex, 4>, 16> LiveStarts; 418 419 /// VNInfo is used for the construction of LiveIntervals. 420 VNInfo::Allocator VNInfoAllocator; 421 422 /// SlotIndex analysis object. 423 SlotIndexes *Indexes; 424 425 /// The list of lifetime markers found. These markers are to be removed 426 /// once the coloring is done. 427 SmallVector<MachineInstr*, 8> Markers; 428 429 /// Record the FI slots for which we have seen some sort of 430 /// lifetime marker (either start or end). 431 BitVector InterestingSlots; 432 433 /// FI slots that need to be handled conservatively (for these 434 /// slots lifetime-start-on-first-use is disabled). 435 BitVector ConservativeSlots; 436 437 /// Number of iterations taken during data flow analysis. 438 unsigned NumIterations; 439 440 public: 441 static char ID; 442 443 StackColoring() : MachineFunctionPass(ID) { 444 initializeStackColoringPass(*PassRegistry::getPassRegistry()); 445 } 446 447 void getAnalysisUsage(AnalysisUsage &AU) const override; 448 bool runOnMachineFunction(MachineFunction &Func) override; 449 450 private: 451 /// Used in collectMarkers 452 using BlockBitVecMap = DenseMap<const MachineBasicBlock *, BitVector>; 453 454 /// Debug. 455 void dump() const; 456 void dumpIntervals() const; 457 void dumpBB(MachineBasicBlock *MBB) const; 458 void dumpBV(const char *tag, const BitVector &BV) const; 459 460 /// Removes all of the lifetime marker instructions from the function. 461 /// \returns true if any markers were removed. 462 bool removeAllMarkers(); 463 464 /// Scan the machine function and find all of the lifetime markers. 465 /// Record the findings in the BEGIN and END vectors. 466 /// \returns the number of markers found. 467 unsigned collectMarkers(unsigned NumSlot); 468 469 /// Perform the dataflow calculation and calculate the lifetime for each of 470 /// the slots, based on the BEGIN/END vectors. Set the LifetimeLIVE_IN and 471 /// LifetimeLIVE_OUT maps that represent which stack slots are live coming 472 /// in and out blocks. 473 void calculateLocalLiveness(); 474 475 /// Returns TRUE if we're using the first-use-begins-lifetime method for 476 /// this slot (if FALSE, then the start marker is treated as start of lifetime). 477 bool applyFirstUse(int Slot) { 478 if (!LifetimeStartOnFirstUse || ProtectFromEscapedAllocas) 479 return false; 480 if (ConservativeSlots.test(Slot)) 481 return false; 482 return true; 483 } 484 485 /// Examines the specified instruction and returns TRUE if the instruction 486 /// represents the start or end of an interesting lifetime. The slot or slots 487 /// starting or ending are added to the vector "slots" and "isStart" is set 488 /// accordingly. 489 /// \returns True if inst contains a lifetime start or end 490 bool isLifetimeStartOrEnd(const MachineInstr &MI, 491 SmallVector<int, 4> &slots, 492 bool &isStart); 493 494 /// Construct the LiveIntervals for the slots. 495 void calculateLiveIntervals(unsigned NumSlots); 496 497 /// Go over the machine function and change instructions which use stack 498 /// slots to use the joint slots. 499 void remapInstructions(DenseMap<int, int> &SlotRemap); 500 501 /// The input program may contain instructions which are not inside lifetime 502 /// markers. This can happen due to a bug in the compiler or due to a bug in 503 /// user code (for example, returning a reference to a local variable). 504 /// This procedure checks all of the instructions in the function and 505 /// invalidates lifetime ranges which do not contain all of the instructions 506 /// which access that frame slot. 507 void removeInvalidSlotRanges(); 508 509 /// Map entries which point to other entries to their destination. 510 /// A->B->C becomes A->C. 511 void expungeSlotMap(DenseMap<int, int> &SlotRemap, unsigned NumSlots); 512 }; 513 514 } // end anonymous namespace 515 516 char StackColoring::ID = 0; 517 518 char &llvm::StackColoringID = StackColoring::ID; 519 520 INITIALIZE_PASS_BEGIN(StackColoring, DEBUG_TYPE, 521 "Merge disjoint stack slots", false, false) 522 INITIALIZE_PASS_DEPENDENCY(SlotIndexes) 523 INITIALIZE_PASS_END(StackColoring, DEBUG_TYPE, 524 "Merge disjoint stack slots", false, false) 525 526 void StackColoring::getAnalysisUsage(AnalysisUsage &AU) const { 527 AU.addRequired<SlotIndexes>(); 528 MachineFunctionPass::getAnalysisUsage(AU); 529 } 530 531 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) 532 LLVM_DUMP_METHOD void StackColoring::dumpBV(const char *tag, 533 const BitVector &BV) const { 534 dbgs() << tag << " : { "; 535 for (unsigned I = 0, E = BV.size(); I != E; ++I) 536 dbgs() << BV.test(I) << " "; 537 dbgs() << "}\n"; 538 } 539 540 LLVM_DUMP_METHOD void StackColoring::dumpBB(MachineBasicBlock *MBB) const { 541 LivenessMap::const_iterator BI = BlockLiveness.find(MBB); 542 assert(BI != BlockLiveness.end() && "Block not found"); 543 const BlockLifetimeInfo &BlockInfo = BI->second; 544 545 dumpBV("BEGIN", BlockInfo.Begin); 546 dumpBV("END", BlockInfo.End); 547 dumpBV("LIVE_IN", BlockInfo.LiveIn); 548 dumpBV("LIVE_OUT", BlockInfo.LiveOut); 549 } 550 551 LLVM_DUMP_METHOD void StackColoring::dump() const { 552 for (MachineBasicBlock *MBB : depth_first(MF)) { 553 dbgs() << "Inspecting block #" << MBB->getNumber() << " [" 554 << MBB->getName() << "]\n"; 555 dumpBB(MBB); 556 } 557 } 558 559 LLVM_DUMP_METHOD void StackColoring::dumpIntervals() const { 560 for (unsigned I = 0, E = Intervals.size(); I != E; ++I) { 561 dbgs() << "Interval[" << I << "]:\n"; 562 Intervals[I]->dump(); 563 } 564 } 565 #endif 566 567 static inline int getStartOrEndSlot(const MachineInstr &MI) 568 { 569 assert((MI.getOpcode() == TargetOpcode::LIFETIME_START || 570 MI.getOpcode() == TargetOpcode::LIFETIME_END) && 571 "Expected LIFETIME_START or LIFETIME_END op"); 572 const MachineOperand &MO = MI.getOperand(0); 573 int Slot = MO.getIndex(); 574 if (Slot >= 0) 575 return Slot; 576 return -1; 577 } 578 579 // At the moment the only way to end a variable lifetime is with 580 // a VARIABLE_LIFETIME op (which can't contain a start). If things 581 // change and the IR allows for a single inst that both begins 582 // and ends lifetime(s), this interface will need to be reworked. 583 bool StackColoring::isLifetimeStartOrEnd(const MachineInstr &MI, 584 SmallVector<int, 4> &slots, 585 bool &isStart) { 586 if (MI.getOpcode() == TargetOpcode::LIFETIME_START || 587 MI.getOpcode() == TargetOpcode::LIFETIME_END) { 588 int Slot = getStartOrEndSlot(MI); 589 if (Slot < 0) 590 return false; 591 if (!InterestingSlots.test(Slot)) 592 return false; 593 slots.push_back(Slot); 594 if (MI.getOpcode() == TargetOpcode::LIFETIME_END) { 595 isStart = false; 596 return true; 597 } 598 if (!applyFirstUse(Slot)) { 599 isStart = true; 600 return true; 601 } 602 } else if (LifetimeStartOnFirstUse && !ProtectFromEscapedAllocas) { 603 if (!MI.isDebugInstr()) { 604 bool found = false; 605 for (const MachineOperand &MO : MI.operands()) { 606 if (!MO.isFI()) 607 continue; 608 int Slot = MO.getIndex(); 609 if (Slot<0) 610 continue; 611 if (InterestingSlots.test(Slot) && applyFirstUse(Slot)) { 612 slots.push_back(Slot); 613 found = true; 614 } 615 } 616 if (found) { 617 isStart = true; 618 return true; 619 } 620 } 621 } 622 return false; 623 } 624 625 unsigned StackColoring::collectMarkers(unsigned NumSlot) { 626 unsigned MarkersFound = 0; 627 BlockBitVecMap SeenStartMap; 628 InterestingSlots.clear(); 629 InterestingSlots.resize(NumSlot); 630 ConservativeSlots.clear(); 631 ConservativeSlots.resize(NumSlot); 632 633 // number of start and end lifetime ops for each slot 634 SmallVector<int, 8> NumStartLifetimes(NumSlot, 0); 635 SmallVector<int, 8> NumEndLifetimes(NumSlot, 0); 636 637 // Step 1: collect markers and populate the "InterestingSlots" 638 // and "ConservativeSlots" sets. 639 for (MachineBasicBlock *MBB : depth_first(MF)) { 640 // Compute the set of slots for which we've seen a START marker but have 641 // not yet seen an END marker at this point in the walk (e.g. on entry 642 // to this bb). 643 BitVector BetweenStartEnd; 644 BetweenStartEnd.resize(NumSlot); 645 for (MachineBasicBlock::const_pred_iterator PI = MBB->pred_begin(), 646 PE = MBB->pred_end(); PI != PE; ++PI) { 647 BlockBitVecMap::const_iterator I = SeenStartMap.find(*PI); 648 if (I != SeenStartMap.end()) { 649 BetweenStartEnd |= I->second; 650 } 651 } 652 653 // Walk the instructions in the block to look for start/end ops. 654 for (MachineInstr &MI : *MBB) { 655 if (MI.getOpcode() == TargetOpcode::LIFETIME_START || 656 MI.getOpcode() == TargetOpcode::LIFETIME_END) { 657 int Slot = getStartOrEndSlot(MI); 658 if (Slot < 0) 659 continue; 660 InterestingSlots.set(Slot); 661 if (MI.getOpcode() == TargetOpcode::LIFETIME_START) { 662 BetweenStartEnd.set(Slot); 663 NumStartLifetimes[Slot] += 1; 664 } else { 665 BetweenStartEnd.reset(Slot); 666 NumEndLifetimes[Slot] += 1; 667 } 668 const AllocaInst *Allocation = MFI->getObjectAllocation(Slot); 669 if (Allocation) { 670 LLVM_DEBUG(dbgs() << "Found a lifetime "); 671 LLVM_DEBUG(dbgs() << (MI.getOpcode() == TargetOpcode::LIFETIME_START 672 ? "start" 673 : "end")); 674 LLVM_DEBUG(dbgs() << " marker for slot #" << Slot); 675 LLVM_DEBUG(dbgs() 676 << " with allocation: " << Allocation->getName() << "\n"); 677 } 678 Markers.push_back(&MI); 679 MarkersFound += 1; 680 } else { 681 for (const MachineOperand &MO : MI.operands()) { 682 if (!MO.isFI()) 683 continue; 684 int Slot = MO.getIndex(); 685 if (Slot < 0) 686 continue; 687 if (! BetweenStartEnd.test(Slot)) { 688 ConservativeSlots.set(Slot); 689 } 690 } 691 } 692 } 693 BitVector &SeenStart = SeenStartMap[MBB]; 694 SeenStart |= BetweenStartEnd; 695 } 696 if (!MarkersFound) { 697 return 0; 698 } 699 700 // PR27903: slots with multiple start or end lifetime ops are not 701 // safe to enable for "lifetime-start-on-first-use". 702 for (unsigned slot = 0; slot < NumSlot; ++slot) 703 if (NumStartLifetimes[slot] > 1 || NumEndLifetimes[slot] > 1) 704 ConservativeSlots.set(slot); 705 LLVM_DEBUG(dumpBV("Conservative slots", ConservativeSlots)); 706 707 // Step 2: compute begin/end sets for each block 708 709 // NOTE: We use a depth-first iteration to ensure that we obtain a 710 // deterministic numbering. 711 for (MachineBasicBlock *MBB : depth_first(MF)) { 712 // Assign a serial number to this basic block. 713 BasicBlocks[MBB] = BasicBlockNumbering.size(); 714 BasicBlockNumbering.push_back(MBB); 715 716 // Keep a reference to avoid repeated lookups. 717 BlockLifetimeInfo &BlockInfo = BlockLiveness[MBB]; 718 719 BlockInfo.Begin.resize(NumSlot); 720 BlockInfo.End.resize(NumSlot); 721 722 SmallVector<int, 4> slots; 723 for (MachineInstr &MI : *MBB) { 724 bool isStart = false; 725 slots.clear(); 726 if (isLifetimeStartOrEnd(MI, slots, isStart)) { 727 if (!isStart) { 728 assert(slots.size() == 1 && "unexpected: MI ends multiple slots"); 729 int Slot = slots[0]; 730 if (BlockInfo.Begin.test(Slot)) { 731 BlockInfo.Begin.reset(Slot); 732 } 733 BlockInfo.End.set(Slot); 734 } else { 735 for (auto Slot : slots) { 736 LLVM_DEBUG(dbgs() << "Found a use of slot #" << Slot); 737 LLVM_DEBUG(dbgs() 738 << " at " << printMBBReference(*MBB) << " index "); 739 LLVM_DEBUG(Indexes->getInstructionIndex(MI).print(dbgs())); 740 const AllocaInst *Allocation = MFI->getObjectAllocation(Slot); 741 if (Allocation) { 742 LLVM_DEBUG(dbgs() 743 << " with allocation: " << Allocation->getName()); 744 } 745 LLVM_DEBUG(dbgs() << "\n"); 746 if (BlockInfo.End.test(Slot)) { 747 BlockInfo.End.reset(Slot); 748 } 749 BlockInfo.Begin.set(Slot); 750 } 751 } 752 } 753 } 754 } 755 756 // Update statistics. 757 NumMarkerSeen += MarkersFound; 758 return MarkersFound; 759 } 760 761 void StackColoring::calculateLocalLiveness() { 762 unsigned NumIters = 0; 763 bool changed = true; 764 while (changed) { 765 changed = false; 766 ++NumIters; 767 768 for (const MachineBasicBlock *BB : BasicBlockNumbering) { 769 // Use an iterator to avoid repeated lookups. 770 LivenessMap::iterator BI = BlockLiveness.find(BB); 771 assert(BI != BlockLiveness.end() && "Block not found"); 772 BlockLifetimeInfo &BlockInfo = BI->second; 773 774 // Compute LiveIn by unioning together the LiveOut sets of all preds. 775 BitVector LocalLiveIn; 776 for (MachineBasicBlock::const_pred_iterator PI = BB->pred_begin(), 777 PE = BB->pred_end(); PI != PE; ++PI) { 778 LivenessMap::const_iterator I = BlockLiveness.find(*PI); 779 // PR37130: transformations prior to stack coloring can 780 // sometimes leave behind statically unreachable blocks; these 781 // can be safely skipped here. 782 if (I != BlockLiveness.end()) 783 LocalLiveIn |= I->second.LiveOut; 784 } 785 786 // Compute LiveOut by subtracting out lifetimes that end in this 787 // block, then adding in lifetimes that begin in this block. If 788 // we have both BEGIN and END markers in the same basic block 789 // then we know that the BEGIN marker comes after the END, 790 // because we already handle the case where the BEGIN comes 791 // before the END when collecting the markers (and building the 792 // BEGIN/END vectors). 793 BitVector LocalLiveOut = LocalLiveIn; 794 LocalLiveOut.reset(BlockInfo.End); 795 LocalLiveOut |= BlockInfo.Begin; 796 797 // Update block LiveIn set, noting whether it has changed. 798 if (LocalLiveIn.test(BlockInfo.LiveIn)) { 799 changed = true; 800 BlockInfo.LiveIn |= LocalLiveIn; 801 } 802 803 // Update block LiveOut set, noting whether it has changed. 804 if (LocalLiveOut.test(BlockInfo.LiveOut)) { 805 changed = true; 806 BlockInfo.LiveOut |= LocalLiveOut; 807 } 808 } 809 } // while changed. 810 811 NumIterations = NumIters; 812 } 813 814 void StackColoring::calculateLiveIntervals(unsigned NumSlots) { 815 SmallVector<SlotIndex, 16> Starts; 816 SmallVector<bool, 16> DefinitelyInUse; 817 818 // For each block, find which slots are active within this block 819 // and update the live intervals. 820 for (const MachineBasicBlock &MBB : *MF) { 821 Starts.clear(); 822 Starts.resize(NumSlots); 823 DefinitelyInUse.clear(); 824 DefinitelyInUse.resize(NumSlots); 825 826 // Start the interval of the slots that we previously found to be 'in-use'. 827 BlockLifetimeInfo &MBBLiveness = BlockLiveness[&MBB]; 828 for (int pos = MBBLiveness.LiveIn.find_first(); pos != -1; 829 pos = MBBLiveness.LiveIn.find_next(pos)) { 830 Starts[pos] = Indexes->getMBBStartIdx(&MBB); 831 } 832 833 // Create the interval for the basic blocks containing lifetime begin/end. 834 for (const MachineInstr &MI : MBB) { 835 SmallVector<int, 4> slots; 836 bool IsStart = false; 837 if (!isLifetimeStartOrEnd(MI, slots, IsStart)) 838 continue; 839 SlotIndex ThisIndex = Indexes->getInstructionIndex(MI); 840 for (auto Slot : slots) { 841 if (IsStart) { 842 // If a slot is already definitely in use, we don't have to emit 843 // a new start marker because there is already a pre-existing 844 // one. 845 if (!DefinitelyInUse[Slot]) { 846 LiveStarts[Slot].push_back(ThisIndex); 847 DefinitelyInUse[Slot] = true; 848 } 849 if (!Starts[Slot].isValid()) 850 Starts[Slot] = ThisIndex; 851 } else { 852 if (Starts[Slot].isValid()) { 853 VNInfo *VNI = Intervals[Slot]->getValNumInfo(0); 854 Intervals[Slot]->addSegment( 855 LiveInterval::Segment(Starts[Slot], ThisIndex, VNI)); 856 Starts[Slot] = SlotIndex(); // Invalidate the start index 857 DefinitelyInUse[Slot] = false; 858 } 859 } 860 } 861 } 862 863 // Finish up started segments 864 for (unsigned i = 0; i < NumSlots; ++i) { 865 if (!Starts[i].isValid()) 866 continue; 867 868 SlotIndex EndIdx = Indexes->getMBBEndIdx(&MBB); 869 VNInfo *VNI = Intervals[i]->getValNumInfo(0); 870 Intervals[i]->addSegment(LiveInterval::Segment(Starts[i], EndIdx, VNI)); 871 } 872 } 873 } 874 875 bool StackColoring::removeAllMarkers() { 876 unsigned Count = 0; 877 for (MachineInstr *MI : Markers) { 878 MI->eraseFromParent(); 879 Count++; 880 } 881 Markers.clear(); 882 883 LLVM_DEBUG(dbgs() << "Removed " << Count << " markers.\n"); 884 return Count; 885 } 886 887 void StackColoring::remapInstructions(DenseMap<int, int> &SlotRemap) { 888 unsigned FixedInstr = 0; 889 unsigned FixedMemOp = 0; 890 unsigned FixedDbg = 0; 891 892 // Remap debug information that refers to stack slots. 893 for (auto &VI : MF->getVariableDbgInfo()) { 894 if (!VI.Var) 895 continue; 896 if (SlotRemap.count(VI.Slot)) { 897 LLVM_DEBUG(dbgs() << "Remapping debug info for [" 898 << cast<DILocalVariable>(VI.Var)->getName() << "].\n"); 899 VI.Slot = SlotRemap[VI.Slot]; 900 FixedDbg++; 901 } 902 } 903 904 // Keep a list of *allocas* which need to be remapped. 905 DenseMap<const AllocaInst*, const AllocaInst*> Allocas; 906 907 // Keep a list of allocas which has been affected by the remap. 908 SmallPtrSet<const AllocaInst*, 32> MergedAllocas; 909 910 for (const std::pair<int, int> &SI : SlotRemap) { 911 const AllocaInst *From = MFI->getObjectAllocation(SI.first); 912 const AllocaInst *To = MFI->getObjectAllocation(SI.second); 913 assert(To && From && "Invalid allocation object"); 914 Allocas[From] = To; 915 916 // AA might be used later for instruction scheduling, and we need it to be 917 // able to deduce the correct aliasing releationships between pointers 918 // derived from the alloca being remapped and the target of that remapping. 919 // The only safe way, without directly informing AA about the remapping 920 // somehow, is to directly update the IR to reflect the change being made 921 // here. 922 Instruction *Inst = const_cast<AllocaInst *>(To); 923 if (From->getType() != To->getType()) { 924 BitCastInst *Cast = new BitCastInst(Inst, From->getType()); 925 Cast->insertAfter(Inst); 926 Inst = Cast; 927 } 928 929 // We keep both slots to maintain AliasAnalysis metadata later. 930 MergedAllocas.insert(From); 931 MergedAllocas.insert(To); 932 933 // Transfer the stack protector layout tag, but make sure that SSPLK_AddrOf 934 // does not overwrite SSPLK_SmallArray or SSPLK_LargeArray, and make sure 935 // that SSPLK_SmallArray does not overwrite SSPLK_LargeArray. 936 MachineFrameInfo::SSPLayoutKind FromKind 937 = MFI->getObjectSSPLayout(SI.first); 938 MachineFrameInfo::SSPLayoutKind ToKind = MFI->getObjectSSPLayout(SI.second); 939 if (FromKind != MachineFrameInfo::SSPLK_None && 940 (ToKind == MachineFrameInfo::SSPLK_None || 941 (ToKind != MachineFrameInfo::SSPLK_LargeArray && 942 FromKind != MachineFrameInfo::SSPLK_AddrOf))) 943 MFI->setObjectSSPLayout(SI.second, FromKind); 944 945 // The new alloca might not be valid in a llvm.dbg.declare for this 946 // variable, so undef out the use to make the verifier happy. 947 AllocaInst *FromAI = const_cast<AllocaInst *>(From); 948 if (FromAI->isUsedByMetadata()) 949 ValueAsMetadata::handleRAUW(FromAI, UndefValue::get(FromAI->getType())); 950 for (auto &Use : FromAI->uses()) { 951 if (BitCastInst *BCI = dyn_cast<BitCastInst>(Use.get())) 952 if (BCI->isUsedByMetadata()) 953 ValueAsMetadata::handleRAUW(BCI, UndefValue::get(BCI->getType())); 954 } 955 956 // Note that this will not replace uses in MMOs (which we'll update below), 957 // or anywhere else (which is why we won't delete the original 958 // instruction). 959 FromAI->replaceAllUsesWith(Inst); 960 } 961 962 // Remap all instructions to the new stack slots. 963 std::vector<std::vector<MachineMemOperand *>> SSRefs( 964 MFI->getObjectIndexEnd()); 965 for (MachineBasicBlock &BB : *MF) 966 for (MachineInstr &I : BB) { 967 // Skip lifetime markers. We'll remove them soon. 968 if (I.getOpcode() == TargetOpcode::LIFETIME_START || 969 I.getOpcode() == TargetOpcode::LIFETIME_END) 970 continue; 971 972 // Update the MachineMemOperand to use the new alloca. 973 for (MachineMemOperand *MMO : I.memoperands()) { 974 // We've replaced IR-level uses of the remapped allocas, so we only 975 // need to replace direct uses here. 976 const AllocaInst *AI = dyn_cast_or_null<AllocaInst>(MMO->getValue()); 977 if (!AI) 978 continue; 979 980 if (!Allocas.count(AI)) 981 continue; 982 983 MMO->setValue(Allocas[AI]); 984 FixedMemOp++; 985 } 986 987 // Update all of the machine instruction operands. 988 for (MachineOperand &MO : I.operands()) { 989 if (!MO.isFI()) 990 continue; 991 int FromSlot = MO.getIndex(); 992 993 // Don't touch arguments. 994 if (FromSlot<0) 995 continue; 996 997 // Only look at mapped slots. 998 if (!SlotRemap.count(FromSlot)) 999 continue; 1000 1001 // In a debug build, check that the instruction that we are modifying is 1002 // inside the expected live range. If the instruction is not inside 1003 // the calculated range then it means that the alloca usage moved 1004 // outside of the lifetime markers, or that the user has a bug. 1005 // NOTE: Alloca address calculations which happen outside the lifetime 1006 // zone are okay, despite the fact that we don't have a good way 1007 // for validating all of the usages of the calculation. 1008 #ifndef NDEBUG 1009 bool TouchesMemory = I.mayLoadOrStore(); 1010 // If we *don't* protect the user from escaped allocas, don't bother 1011 // validating the instructions. 1012 if (!I.isDebugInstr() && TouchesMemory && ProtectFromEscapedAllocas) { 1013 SlotIndex Index = Indexes->getInstructionIndex(I); 1014 const LiveInterval *Interval = &*Intervals[FromSlot]; 1015 assert(Interval->find(Index) != Interval->end() && 1016 "Found instruction usage outside of live range."); 1017 } 1018 #endif 1019 1020 // Fix the machine instructions. 1021 int ToSlot = SlotRemap[FromSlot]; 1022 MO.setIndex(ToSlot); 1023 FixedInstr++; 1024 } 1025 1026 // We adjust AliasAnalysis information for merged stack slots. 1027 SmallVector<MachineMemOperand *, 2> NewMMOs; 1028 bool ReplaceMemOps = false; 1029 for (MachineMemOperand *MMO : I.memoperands()) { 1030 // Collect MachineMemOperands which reference 1031 // FixedStackPseudoSourceValues with old frame indices. 1032 if (const auto *FSV = dyn_cast_or_null<FixedStackPseudoSourceValue>( 1033 MMO->getPseudoValue())) { 1034 int FI = FSV->getFrameIndex(); 1035 auto To = SlotRemap.find(FI); 1036 if (To != SlotRemap.end()) 1037 SSRefs[FI].push_back(MMO); 1038 } 1039 1040 // If this memory location can be a slot remapped here, 1041 // we remove AA information. 1042 bool MayHaveConflictingAAMD = false; 1043 if (MMO->getAAInfo()) { 1044 if (const Value *MMOV = MMO->getValue()) { 1045 SmallVector<Value *, 4> Objs; 1046 getUnderlyingObjectsForCodeGen(MMOV, Objs, MF->getDataLayout()); 1047 1048 if (Objs.empty()) 1049 MayHaveConflictingAAMD = true; 1050 else 1051 for (Value *V : Objs) { 1052 // If this memory location comes from a known stack slot 1053 // that is not remapped, we continue checking. 1054 // Otherwise, we need to invalidate AA infomation. 1055 const AllocaInst *AI = dyn_cast_or_null<AllocaInst>(V); 1056 if (AI && MergedAllocas.count(AI)) { 1057 MayHaveConflictingAAMD = true; 1058 break; 1059 } 1060 } 1061 } 1062 } 1063 if (MayHaveConflictingAAMD) { 1064 NewMMOs.push_back(MF->getMachineMemOperand(MMO, AAMDNodes())); 1065 ReplaceMemOps = true; 1066 } else { 1067 NewMMOs.push_back(MMO); 1068 } 1069 } 1070 1071 // If any memory operand is updated, set memory references of 1072 // this instruction. 1073 if (ReplaceMemOps) 1074 I.setMemRefs(*MF, NewMMOs); 1075 } 1076 1077 // Rewrite MachineMemOperands that reference old frame indices. 1078 for (auto E : enumerate(SSRefs)) 1079 if (!E.value().empty()) { 1080 const PseudoSourceValue *NewSV = 1081 MF->getPSVManager().getFixedStack(SlotRemap.find(E.index())->second); 1082 for (MachineMemOperand *Ref : E.value()) 1083 Ref->setValue(NewSV); 1084 } 1085 1086 // Update the location of C++ catch objects for the MSVC personality routine. 1087 if (WinEHFuncInfo *EHInfo = MF->getWinEHFuncInfo()) 1088 for (WinEHTryBlockMapEntry &TBME : EHInfo->TryBlockMap) 1089 for (WinEHHandlerType &H : TBME.HandlerArray) 1090 if (H.CatchObj.FrameIndex != std::numeric_limits<int>::max() && 1091 SlotRemap.count(H.CatchObj.FrameIndex)) 1092 H.CatchObj.FrameIndex = SlotRemap[H.CatchObj.FrameIndex]; 1093 1094 LLVM_DEBUG(dbgs() << "Fixed " << FixedMemOp << " machine memory operands.\n"); 1095 LLVM_DEBUG(dbgs() << "Fixed " << FixedDbg << " debug locations.\n"); 1096 LLVM_DEBUG(dbgs() << "Fixed " << FixedInstr << " machine instructions.\n"); 1097 } 1098 1099 void StackColoring::removeInvalidSlotRanges() { 1100 for (MachineBasicBlock &BB : *MF) 1101 for (MachineInstr &I : BB) { 1102 if (I.getOpcode() == TargetOpcode::LIFETIME_START || 1103 I.getOpcode() == TargetOpcode::LIFETIME_END || I.isDebugInstr()) 1104 continue; 1105 1106 // Some intervals are suspicious! In some cases we find address 1107 // calculations outside of the lifetime zone, but not actual memory 1108 // read or write. Memory accesses outside of the lifetime zone are a clear 1109 // violation, but address calculations are okay. This can happen when 1110 // GEPs are hoisted outside of the lifetime zone. 1111 // So, in here we only check instructions which can read or write memory. 1112 if (!I.mayLoad() && !I.mayStore()) 1113 continue; 1114 1115 // Check all of the machine operands. 1116 for (const MachineOperand &MO : I.operands()) { 1117 if (!MO.isFI()) 1118 continue; 1119 1120 int Slot = MO.getIndex(); 1121 1122 if (Slot<0) 1123 continue; 1124 1125 if (Intervals[Slot]->empty()) 1126 continue; 1127 1128 // Check that the used slot is inside the calculated lifetime range. 1129 // If it is not, warn about it and invalidate the range. 1130 LiveInterval *Interval = &*Intervals[Slot]; 1131 SlotIndex Index = Indexes->getInstructionIndex(I); 1132 if (Interval->find(Index) == Interval->end()) { 1133 Interval->clear(); 1134 LLVM_DEBUG(dbgs() << "Invalidating range #" << Slot << "\n"); 1135 EscapedAllocas++; 1136 } 1137 } 1138 } 1139 } 1140 1141 void StackColoring::expungeSlotMap(DenseMap<int, int> &SlotRemap, 1142 unsigned NumSlots) { 1143 // Expunge slot remap map. 1144 for (unsigned i=0; i < NumSlots; ++i) { 1145 // If we are remapping i 1146 if (SlotRemap.count(i)) { 1147 int Target = SlotRemap[i]; 1148 // As long as our target is mapped to something else, follow it. 1149 while (SlotRemap.count(Target)) { 1150 Target = SlotRemap[Target]; 1151 SlotRemap[i] = Target; 1152 } 1153 } 1154 } 1155 } 1156 1157 bool StackColoring::runOnMachineFunction(MachineFunction &Func) { 1158 LLVM_DEBUG(dbgs() << "********** Stack Coloring **********\n" 1159 << "********** Function: " << Func.getName() << '\n'); 1160 MF = &Func; 1161 MFI = &MF->getFrameInfo(); 1162 Indexes = &getAnalysis<SlotIndexes>(); 1163 BlockLiveness.clear(); 1164 BasicBlocks.clear(); 1165 BasicBlockNumbering.clear(); 1166 Markers.clear(); 1167 Intervals.clear(); 1168 LiveStarts.clear(); 1169 VNInfoAllocator.Reset(); 1170 1171 unsigned NumSlots = MFI->getObjectIndexEnd(); 1172 1173 // If there are no stack slots then there are no markers to remove. 1174 if (!NumSlots) 1175 return false; 1176 1177 SmallVector<int, 8> SortedSlots; 1178 SortedSlots.reserve(NumSlots); 1179 Intervals.reserve(NumSlots); 1180 LiveStarts.resize(NumSlots); 1181 1182 unsigned NumMarkers = collectMarkers(NumSlots); 1183 1184 unsigned TotalSize = 0; 1185 LLVM_DEBUG(dbgs() << "Found " << NumMarkers << " markers and " << NumSlots 1186 << " slots\n"); 1187 LLVM_DEBUG(dbgs() << "Slot structure:\n"); 1188 1189 for (int i=0; i < MFI->getObjectIndexEnd(); ++i) { 1190 LLVM_DEBUG(dbgs() << "Slot #" << i << " - " << MFI->getObjectSize(i) 1191 << " bytes.\n"); 1192 TotalSize += MFI->getObjectSize(i); 1193 } 1194 1195 LLVM_DEBUG(dbgs() << "Total Stack size: " << TotalSize << " bytes\n\n"); 1196 1197 // Don't continue because there are not enough lifetime markers, or the 1198 // stack is too small, or we are told not to optimize the slots. 1199 if (NumMarkers < 2 || TotalSize < 16 || DisableColoring || 1200 skipFunction(Func.getFunction())) { 1201 LLVM_DEBUG(dbgs() << "Will not try to merge slots.\n"); 1202 return removeAllMarkers(); 1203 } 1204 1205 for (unsigned i=0; i < NumSlots; ++i) { 1206 std::unique_ptr<LiveInterval> LI(new LiveInterval(i, 0)); 1207 LI->getNextValue(Indexes->getZeroIndex(), VNInfoAllocator); 1208 Intervals.push_back(std::move(LI)); 1209 SortedSlots.push_back(i); 1210 } 1211 1212 // Calculate the liveness of each block. 1213 calculateLocalLiveness(); 1214 LLVM_DEBUG(dbgs() << "Dataflow iterations: " << NumIterations << "\n"); 1215 LLVM_DEBUG(dump()); 1216 1217 // Propagate the liveness information. 1218 calculateLiveIntervals(NumSlots); 1219 LLVM_DEBUG(dumpIntervals()); 1220 1221 // Search for allocas which are used outside of the declared lifetime 1222 // markers. 1223 if (ProtectFromEscapedAllocas) 1224 removeInvalidSlotRanges(); 1225 1226 // Maps old slots to new slots. 1227 DenseMap<int, int> SlotRemap; 1228 unsigned RemovedSlots = 0; 1229 unsigned ReducedSize = 0; 1230 1231 // Do not bother looking at empty intervals. 1232 for (unsigned I = 0; I < NumSlots; ++I) { 1233 if (Intervals[SortedSlots[I]]->empty()) 1234 SortedSlots[I] = -1; 1235 } 1236 1237 // This is a simple greedy algorithm for merging allocas. First, sort the 1238 // slots, placing the largest slots first. Next, perform an n^2 scan and look 1239 // for disjoint slots. When you find disjoint slots, merge the samller one 1240 // into the bigger one and update the live interval. Remove the small alloca 1241 // and continue. 1242 1243 // Sort the slots according to their size. Place unused slots at the end. 1244 // Use stable sort to guarantee deterministic code generation. 1245 llvm::stable_sort(SortedSlots, [this](int LHS, int RHS) { 1246 // We use -1 to denote a uninteresting slot. Place these slots at the end. 1247 if (LHS == -1) 1248 return false; 1249 if (RHS == -1) 1250 return true; 1251 // Sort according to size. 1252 return MFI->getObjectSize(LHS) > MFI->getObjectSize(RHS); 1253 }); 1254 1255 for (auto &s : LiveStarts) 1256 llvm::sort(s); 1257 1258 bool Changed = true; 1259 while (Changed) { 1260 Changed = false; 1261 for (unsigned I = 0; I < NumSlots; ++I) { 1262 if (SortedSlots[I] == -1) 1263 continue; 1264 1265 for (unsigned J=I+1; J < NumSlots; ++J) { 1266 if (SortedSlots[J] == -1) 1267 continue; 1268 1269 int FirstSlot = SortedSlots[I]; 1270 int SecondSlot = SortedSlots[J]; 1271 LiveInterval *First = &*Intervals[FirstSlot]; 1272 LiveInterval *Second = &*Intervals[SecondSlot]; 1273 auto &FirstS = LiveStarts[FirstSlot]; 1274 auto &SecondS = LiveStarts[SecondSlot]; 1275 assert(!First->empty() && !Second->empty() && "Found an empty range"); 1276 1277 // Merge disjoint slots. This is a little bit tricky - see the 1278 // Implementation Notes section for an explanation. 1279 if (!First->isLiveAtIndexes(SecondS) && 1280 !Second->isLiveAtIndexes(FirstS)) { 1281 Changed = true; 1282 First->MergeSegmentsInAsValue(*Second, First->getValNumInfo(0)); 1283 1284 int OldSize = FirstS.size(); 1285 FirstS.append(SecondS.begin(), SecondS.end()); 1286 auto Mid = FirstS.begin() + OldSize; 1287 std::inplace_merge(FirstS.begin(), Mid, FirstS.end()); 1288 1289 SlotRemap[SecondSlot] = FirstSlot; 1290 SortedSlots[J] = -1; 1291 LLVM_DEBUG(dbgs() << "Merging #" << FirstSlot << " and slots #" 1292 << SecondSlot << " together.\n"); 1293 unsigned MaxAlignment = std::max(MFI->getObjectAlignment(FirstSlot), 1294 MFI->getObjectAlignment(SecondSlot)); 1295 1296 assert(MFI->getObjectSize(FirstSlot) >= 1297 MFI->getObjectSize(SecondSlot) && 1298 "Merging a small object into a larger one"); 1299 1300 RemovedSlots+=1; 1301 ReducedSize += MFI->getObjectSize(SecondSlot); 1302 MFI->setObjectAlignment(FirstSlot, MaxAlignment); 1303 MFI->RemoveStackObject(SecondSlot); 1304 } 1305 } 1306 } 1307 }// While changed. 1308 1309 // Record statistics. 1310 StackSpaceSaved += ReducedSize; 1311 StackSlotMerged += RemovedSlots; 1312 LLVM_DEBUG(dbgs() << "Merge " << RemovedSlots << " slots. Saved " 1313 << ReducedSize << " bytes\n"); 1314 1315 // Scan the entire function and update all machine operands that use frame 1316 // indices to use the remapped frame index. 1317 expungeSlotMap(SlotRemap, NumSlots); 1318 remapInstructions(SlotRemap); 1319 1320 return removeAllMarkers(); 1321 } 1322