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/SlotIndexes.h" 40 #include "llvm/CodeGen/TargetOpcodes.h" 41 #include "llvm/CodeGen/WinEHFuncInfo.h" 42 #include "llvm/Config/llvm-config.h" 43 #include "llvm/IR/Constants.h" 44 #include "llvm/IR/DebugInfoMetadata.h" 45 #include "llvm/IR/Instructions.h" 46 #include "llvm/IR/Metadata.h" 47 #include "llvm/IR/Use.h" 48 #include "llvm/IR/Value.h" 49 #include "llvm/InitializePasses.h" 50 #include "llvm/Pass.h" 51 #include "llvm/Support/Casting.h" 52 #include "llvm/Support/CommandLine.h" 53 #include "llvm/Support/Compiler.h" 54 #include "llvm/Support/Debug.h" 55 #include "llvm/Support/raw_ostream.h" 56 #include <algorithm> 57 #include <cassert> 58 #include <limits> 59 #include <memory> 60 #include <utility> 61 62 using namespace llvm; 63 64 #define DEBUG_TYPE "stack-coloring" 65 66 static cl::opt<bool> 67 DisableColoring("no-stack-coloring", 68 cl::init(false), cl::Hidden, 69 cl::desc("Disable stack coloring")); 70 71 /// The user may write code that uses allocas outside of the declared lifetime 72 /// zone. This can happen when the user returns a reference to a local 73 /// data-structure. We can detect these cases and decide not to optimize the 74 /// code. If this flag is enabled, we try to save the user. This option 75 /// is treated as overriding LifetimeStartOnFirstUse below. 76 static cl::opt<bool> 77 ProtectFromEscapedAllocas("protect-from-escaped-allocas", 78 cl::init(false), cl::Hidden, 79 cl::desc("Do not optimize lifetime zones that " 80 "are broken")); 81 82 /// Enable enhanced dataflow scheme for lifetime analysis (treat first 83 /// use of stack slot as start of slot lifetime, as opposed to looking 84 /// for LIFETIME_START marker). See "Implementation notes" below for 85 /// more info. 86 static cl::opt<bool> 87 LifetimeStartOnFirstUse("stackcoloring-lifetime-start-on-first-use", 88 cl::init(true), cl::Hidden, 89 cl::desc("Treat stack lifetimes as starting on first use, not on START marker.")); 90 91 92 STATISTIC(NumMarkerSeen, "Number of lifetime markers found."); 93 STATISTIC(StackSpaceSaved, "Number of bytes saved due to merging slots."); 94 STATISTIC(StackSlotMerged, "Number of stack slot merged."); 95 STATISTIC(EscapedAllocas, "Number of allocas that escaped the lifetime region"); 96 97 //===----------------------------------------------------------------------===// 98 // StackColoring Pass 99 //===----------------------------------------------------------------------===// 100 // 101 // Stack Coloring reduces stack usage by merging stack slots when they 102 // can't be used together. For example, consider the following C program: 103 // 104 // void bar(char *, int); 105 // void foo(bool var) { 106 // A: { 107 // char z[4096]; 108 // bar(z, 0); 109 // } 110 // 111 // char *p; 112 // char x[4096]; 113 // char y[4096]; 114 // if (var) { 115 // p = x; 116 // } else { 117 // bar(y, 1); 118 // p = y + 1024; 119 // } 120 // B: 121 // bar(p, 2); 122 // } 123 // 124 // Naively-compiled, this program would use 12k of stack space. However, the 125 // stack slot corresponding to `z` is always destroyed before either of the 126 // stack slots for `x` or `y` are used, and then `x` is only used if `var` 127 // is true, while `y` is only used if `var` is false. So in no time are 2 128 // of the stack slots used together, and therefore we can merge them, 129 // compiling the function using only a single 4k alloca: 130 // 131 // void foo(bool var) { // equivalent 132 // char x[4096]; 133 // char *p; 134 // bar(x, 0); 135 // if (var) { 136 // p = x; 137 // } else { 138 // bar(x, 1); 139 // p = x + 1024; 140 // } 141 // bar(p, 2); 142 // } 143 // 144 // This is an important optimization if we want stack space to be under 145 // control in large functions, both open-coded ones and ones created by 146 // inlining. 147 // 148 // Implementation Notes: 149 // --------------------- 150 // 151 // An important part of the above reasoning is that `z` can't be accessed 152 // while the latter 2 calls to `bar` are running. This is justified because 153 // `z`'s lifetime is over after we exit from block `A:`, so any further 154 // accesses to it would be UB. The way we represent this information 155 // in LLVM is by having frontends delimit blocks with `lifetime.start` 156 // and `lifetime.end` intrinsics. 157 // 158 // The effect of these intrinsics seems to be as follows (maybe I should 159 // specify this in the reference?): 160 // 161 // L1) at start, each stack-slot is marked as *out-of-scope*, unless no 162 // lifetime intrinsic refers to that stack slot, in which case 163 // it is marked as *in-scope*. 164 // L2) on a `lifetime.start`, a stack slot is marked as *in-scope* and 165 // the stack slot is overwritten with `undef`. 166 // L3) on a `lifetime.end`, a stack slot is marked as *out-of-scope*. 167 // L4) on function exit, all stack slots are marked as *out-of-scope*. 168 // L5) `lifetime.end` is a no-op when called on a slot that is already 169 // *out-of-scope*. 170 // L6) memory accesses to *out-of-scope* stack slots are UB. 171 // L7) when a stack-slot is marked as *out-of-scope*, all pointers to it 172 // are invalidated, unless the slot is "degenerate". This is used to 173 // justify not marking slots as in-use until the pointer to them is 174 // used, but feels a bit hacky in the presence of things like LICM. See 175 // the "Degenerate Slots" section for more details. 176 // 177 // Now, let's ground stack coloring on these rules. We'll define a slot 178 // as *in-use* at a (dynamic) point in execution if it either can be 179 // written to at that point, or if it has a live and non-undef content 180 // at that point. 181 // 182 // Obviously, slots that are never *in-use* together can be merged, and 183 // in our example `foo`, the slots for `x`, `y` and `z` are never 184 // in-use together (of course, sometimes slots that *are* in-use together 185 // might still be mergable, but we don't care about that here). 186 // 187 // In this implementation, we successively merge pairs of slots that are 188 // not *in-use* together. We could be smarter - for example, we could merge 189 // a single large slot with 2 small slots, or we could construct the 190 // interference graph and run a "smart" graph coloring algorithm, but with 191 // that aside, how do we find out whether a pair of slots might be *in-use* 192 // together? 193 // 194 // From our rules, we see that *out-of-scope* slots are never *in-use*, 195 // and from (L7) we see that "non-degenerate" slots remain non-*in-use* 196 // until their address is taken. Therefore, we can approximate slot activity 197 // using dataflow. 198 // 199 // A subtle point: naively, we might try to figure out which pairs of 200 // stack-slots interfere by propagating `S in-use` through the CFG for every 201 // stack-slot `S`, and having `S` and `T` interfere if there is a CFG point in 202 // which they are both *in-use*. 203 // 204 // That is sound, but overly conservative in some cases: in our (artificial) 205 // example `foo`, either `x` or `y` might be in use at the label `B:`, but 206 // as `x` is only in use if we came in from the `var` edge and `y` only 207 // if we came from the `!var` edge, they still can't be in use together. 208 // See PR32488 for an important real-life case. 209 // 210 // If we wanted to find all points of interference precisely, we could 211 // propagate `S in-use` and `S&T in-use` predicates through the CFG. That 212 // would be precise, but requires propagating `O(n^2)` dataflow facts. 213 // 214 // However, we aren't interested in the *set* of points of interference 215 // between 2 stack slots, only *whether* there *is* such a point. So we 216 // can rely on a little trick: for `S` and `T` to be in-use together, 217 // one of them needs to become in-use while the other is in-use (or 218 // they might both become in use simultaneously). We can check this 219 // by also keeping track of the points at which a stack slot might *start* 220 // being in-use. 221 // 222 // Exact first use: 223 // ---------------- 224 // 225 // Consider the following motivating example: 226 // 227 // int foo() { 228 // char b1[1024], b2[1024]; 229 // if (...) { 230 // char b3[1024]; 231 // <uses of b1, b3>; 232 // return x; 233 // } else { 234 // char b4[1024], b5[1024]; 235 // <uses of b2, b4, b5>; 236 // return y; 237 // } 238 // } 239 // 240 // In the code above, "b3" and "b4" are declared in distinct lexical 241 // scopes, meaning that it is easy to prove that they can share the 242 // same stack slot. Variables "b1" and "b2" are declared in the same 243 // scope, meaning that from a lexical point of view, their lifetimes 244 // overlap. From a control flow pointer of view, however, the two 245 // variables are accessed in disjoint regions of the CFG, thus it 246 // should be possible for them to share the same stack slot. An ideal 247 // stack allocation for the function above would look like: 248 // 249 // slot 0: b1, b2 250 // slot 1: b3, b4 251 // slot 2: b5 252 // 253 // Achieving this allocation is tricky, however, due to the way 254 // lifetime markers are inserted. Here is a simplified view of the 255 // control flow graph for the code above: 256 // 257 // +------ block 0 -------+ 258 // 0| LIFETIME_START b1, b2 | 259 // 1| <test 'if' condition> | 260 // +-----------------------+ 261 // ./ \. 262 // +------ block 1 -------+ +------ block 2 -------+ 263 // 2| LIFETIME_START b3 | 5| LIFETIME_START b4, b5 | 264 // 3| <uses of b1, b3> | 6| <uses of b2, b4, b5> | 265 // 4| LIFETIME_END b3 | 7| LIFETIME_END b4, b5 | 266 // +-----------------------+ +-----------------------+ 267 // \. /. 268 // +------ block 3 -------+ 269 // 8| <cleanupcode> | 270 // 9| LIFETIME_END b1, b2 | 271 // 10| return | 272 // +-----------------------+ 273 // 274 // If we create live intervals for the variables above strictly based 275 // on the lifetime markers, we'll get the set of intervals on the 276 // left. If we ignore the lifetime start markers and instead treat a 277 // variable's lifetime as beginning with the first reference to the 278 // var, then we get the intervals on the right. 279 // 280 // LIFETIME_START First Use 281 // b1: [0,9] [3,4] [8,9] 282 // b2: [0,9] [6,9] 283 // b3: [2,4] [3,4] 284 // b4: [5,7] [6,7] 285 // b5: [5,7] [6,7] 286 // 287 // For the intervals on the left, the best we can do is overlap two 288 // variables (b3 and b4, for example); this gives us a stack size of 289 // 4*1024 bytes, not ideal. When treating first-use as the start of a 290 // lifetime, we can additionally overlap b1 and b5, giving us a 3*1024 291 // byte stack (better). 292 // 293 // Degenerate Slots: 294 // ----------------- 295 // 296 // Relying entirely on first-use of stack slots is problematic, 297 // however, due to the fact that optimizations can sometimes migrate 298 // uses of a variable outside of its lifetime start/end region. Here 299 // is an example: 300 // 301 // int bar() { 302 // char b1[1024], b2[1024]; 303 // if (...) { 304 // <uses of b2> 305 // return y; 306 // } else { 307 // <uses of b1> 308 // while (...) { 309 // char b3[1024]; 310 // <uses of b3> 311 // } 312 // } 313 // } 314 // 315 // Before optimization, the control flow graph for the code above 316 // might look like the following: 317 // 318 // +------ block 0 -------+ 319 // 0| LIFETIME_START b1, b2 | 320 // 1| <test 'if' condition> | 321 // +-----------------------+ 322 // ./ \. 323 // +------ block 1 -------+ +------- block 2 -------+ 324 // 2| <uses of b2> | 3| <uses of b1> | 325 // +-----------------------+ +-----------------------+ 326 // | | 327 // | +------- block 3 -------+ <-\. 328 // | 4| <while condition> | | 329 // | +-----------------------+ | 330 // | / | | 331 // | / +------- block 4 -------+ 332 // \ / 5| LIFETIME_START b3 | | 333 // \ / 6| <uses of b3> | | 334 // \ / 7| LIFETIME_END b3 | | 335 // \ | +------------------------+ | 336 // \ | \ / 337 // +------ block 5 -----+ \--------------- 338 // 8| <cleanupcode> | 339 // 9| LIFETIME_END b1, b2 | 340 // 10| return | 341 // +---------------------+ 342 // 343 // During optimization, however, it can happen that an instruction 344 // computing an address in "b3" (for example, a loop-invariant GEP) is 345 // hoisted up out of the loop from block 4 to block 2. [Note that 346 // this is not an actual load from the stack, only an instruction that 347 // computes the address to be loaded]. If this happens, there is now a 348 // path leading from the first use of b3 to the return instruction 349 // that does not encounter the b3 LIFETIME_END, hence b3's lifetime is 350 // now larger than if we were computing live intervals strictly based 351 // on lifetime markers. In the example above, this lengthened lifetime 352 // would mean that it would appear illegal to overlap b3 with b2. 353 // 354 // To deal with this such cases, the code in ::collectMarkers() below 355 // tries to identify "degenerate" slots -- those slots where on a single 356 // forward pass through the CFG we encounter a first reference to slot 357 // K before we hit the slot K lifetime start marker. For such slots, 358 // we fall back on using the lifetime start marker as the beginning of 359 // the variable's lifetime. NB: with this implementation, slots can 360 // appear degenerate in cases where there is unstructured control flow: 361 // 362 // if (q) goto mid; 363 // if (x > 9) { 364 // int b[100]; 365 // memcpy(&b[0], ...); 366 // mid: b[k] = ...; 367 // abc(&b); 368 // } 369 // 370 // If in RPO ordering chosen to walk the CFG we happen to visit the b[k] 371 // before visiting the memcpy block (which will contain the lifetime start 372 // for "b" then it will appear that 'b' has a degenerate lifetime. 373 // 374 // Handle Windows Exception with LifetimeStartOnFirstUse: 375 // ----------------- 376 // 377 // There was a bug for using LifetimeStartOnFirstUse in win32. 378 // class Type1 { 379 // ... 380 // ~Type1(){ write memory;} 381 // } 382 // ... 383 // try{ 384 // Type1 V 385 // ... 386 // } catch (Type2 X){ 387 // ... 388 // } 389 // For variable X in catch(X), we put point pX=&(&X) into ConservativeSlots 390 // to prevent using LifetimeStartOnFirstUse. Because pX may merged with 391 // object V which may call destructor after implicitly writing pX. All these 392 // are done in C++ EH runtime libs (through CxxThrowException), and can't 393 // obviously check it in IR level. 394 // 395 // The loader of pX, without obvious writing IR, is usually the first LOAD MI 396 // in EHPad, Some like: 397 // bb.x.catch.i (landing-pad, ehfunclet-entry): 398 // ; predecessors: %bb... 399 // successors: %bb... 400 // %n:gr32 = MOV32rm %stack.pX ... 401 // ... 402 // The Type2** %stack.pX will only be written in EH runtime libs, so we 403 // check the StoreSlots to screen it out. 404 405 namespace { 406 407 /// StackColoring - A machine pass for merging disjoint stack allocations, 408 /// marked by the LIFETIME_START and LIFETIME_END pseudo instructions. 409 class StackColoring : public MachineFunctionPass { 410 MachineFrameInfo *MFI; 411 MachineFunction *MF; 412 413 /// A class representing liveness information for a single basic block. 414 /// Each bit in the BitVector represents the liveness property 415 /// for a different stack slot. 416 struct BlockLifetimeInfo { 417 /// Which slots BEGINs in each basic block. 418 BitVector Begin; 419 420 /// Which slots ENDs in each basic block. 421 BitVector End; 422 423 /// Which slots are marked as LIVE_IN, coming into each basic block. 424 BitVector LiveIn; 425 426 /// Which slots are marked as LIVE_OUT, coming out of each basic block. 427 BitVector LiveOut; 428 }; 429 430 /// Maps active slots (per bit) for each basic block. 431 using LivenessMap = DenseMap<const MachineBasicBlock *, BlockLifetimeInfo>; 432 LivenessMap BlockLiveness; 433 434 /// Maps serial numbers to basic blocks. 435 DenseMap<const MachineBasicBlock *, int> BasicBlocks; 436 437 /// Maps basic blocks to a serial number. 438 SmallVector<const MachineBasicBlock *, 8> BasicBlockNumbering; 439 440 /// Maps slots to their use interval. Outside of this interval, slots 441 /// values are either dead or `undef` and they will not be written to. 442 SmallVector<std::unique_ptr<LiveInterval>, 16> Intervals; 443 444 /// Maps slots to the points where they can become in-use. 445 SmallVector<SmallVector<SlotIndex, 4>, 16> LiveStarts; 446 447 /// VNInfo is used for the construction of LiveIntervals. 448 VNInfo::Allocator VNInfoAllocator; 449 450 /// SlotIndex analysis object. 451 SlotIndexes *Indexes; 452 453 /// The list of lifetime markers found. These markers are to be removed 454 /// once the coloring is done. 455 SmallVector<MachineInstr*, 8> Markers; 456 457 /// Record the FI slots for which we have seen some sort of 458 /// lifetime marker (either start or end). 459 BitVector InterestingSlots; 460 461 /// FI slots that need to be handled conservatively (for these 462 /// slots lifetime-start-on-first-use is disabled). 463 BitVector ConservativeSlots; 464 465 /// Record the FI slots referenced by a 'may write to memory'. 466 BitVector StoreSlots; 467 468 /// Number of iterations taken during data flow analysis. 469 unsigned NumIterations; 470 471 public: 472 static char ID; 473 474 StackColoring() : MachineFunctionPass(ID) { 475 initializeStackColoringPass(*PassRegistry::getPassRegistry()); 476 } 477 478 void getAnalysisUsage(AnalysisUsage &AU) const override; 479 bool runOnMachineFunction(MachineFunction &Func) override; 480 481 private: 482 /// Used in collectMarkers 483 using BlockBitVecMap = DenseMap<const MachineBasicBlock *, BitVector>; 484 485 /// Debug. 486 void dump() const; 487 void dumpIntervals() const; 488 void dumpBB(MachineBasicBlock *MBB) const; 489 void dumpBV(const char *tag, const BitVector &BV) const; 490 491 /// Removes all of the lifetime marker instructions from the function. 492 /// \returns true if any markers were removed. 493 bool removeAllMarkers(); 494 495 /// Scan the machine function and find all of the lifetime markers. 496 /// Record the findings in the BEGIN and END vectors. 497 /// \returns the number of markers found. 498 unsigned collectMarkers(unsigned NumSlot); 499 500 /// Perform the dataflow calculation and calculate the lifetime for each of 501 /// the slots, based on the BEGIN/END vectors. Set the LifetimeLIVE_IN and 502 /// LifetimeLIVE_OUT maps that represent which stack slots are live coming 503 /// in and out blocks. 504 void calculateLocalLiveness(); 505 506 /// Returns TRUE if we're using the first-use-begins-lifetime method for 507 /// this slot (if FALSE, then the start marker is treated as start of lifetime). 508 bool applyFirstUse(int Slot) { 509 if (!LifetimeStartOnFirstUse || ProtectFromEscapedAllocas) 510 return false; 511 if (ConservativeSlots.test(Slot)) 512 return false; 513 return true; 514 } 515 516 /// Examines the specified instruction and returns TRUE if the instruction 517 /// represents the start or end of an interesting lifetime. The slot or slots 518 /// starting or ending are added to the vector "slots" and "isStart" is set 519 /// accordingly. 520 /// \returns True if inst contains a lifetime start or end 521 bool isLifetimeStartOrEnd(const MachineInstr &MI, 522 SmallVector<int, 4> &slots, 523 bool &isStart); 524 525 /// Construct the LiveIntervals for the slots. 526 void calculateLiveIntervals(unsigned NumSlots); 527 528 /// Go over the machine function and change instructions which use stack 529 /// slots to use the joint slots. 530 void remapInstructions(DenseMap<int, int> &SlotRemap); 531 532 /// The input program may contain instructions which are not inside lifetime 533 /// markers. This can happen due to a bug in the compiler or due to a bug in 534 /// user code (for example, returning a reference to a local variable). 535 /// This procedure checks all of the instructions in the function and 536 /// invalidates lifetime ranges which do not contain all of the instructions 537 /// which access that frame slot. 538 void removeInvalidSlotRanges(); 539 540 /// Map entries which point to other entries to their destination. 541 /// A->B->C becomes A->C. 542 void expungeSlotMap(DenseMap<int, int> &SlotRemap, unsigned NumSlots); 543 }; 544 545 } // end anonymous namespace 546 547 char StackColoring::ID = 0; 548 549 char &llvm::StackColoringID = StackColoring::ID; 550 551 INITIALIZE_PASS_BEGIN(StackColoring, DEBUG_TYPE, 552 "Merge disjoint stack slots", false, false) 553 INITIALIZE_PASS_DEPENDENCY(SlotIndexes) 554 INITIALIZE_PASS_END(StackColoring, DEBUG_TYPE, 555 "Merge disjoint stack slots", false, false) 556 557 void StackColoring::getAnalysisUsage(AnalysisUsage &AU) const { 558 AU.addRequired<SlotIndexes>(); 559 MachineFunctionPass::getAnalysisUsage(AU); 560 } 561 562 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) 563 LLVM_DUMP_METHOD void StackColoring::dumpBV(const char *tag, 564 const BitVector &BV) const { 565 dbgs() << tag << " : { "; 566 for (unsigned I = 0, E = BV.size(); I != E; ++I) 567 dbgs() << BV.test(I) << " "; 568 dbgs() << "}\n"; 569 } 570 571 LLVM_DUMP_METHOD void StackColoring::dumpBB(MachineBasicBlock *MBB) const { 572 LivenessMap::const_iterator BI = BlockLiveness.find(MBB); 573 assert(BI != BlockLiveness.end() && "Block not found"); 574 const BlockLifetimeInfo &BlockInfo = BI->second; 575 576 dumpBV("BEGIN", BlockInfo.Begin); 577 dumpBV("END", BlockInfo.End); 578 dumpBV("LIVE_IN", BlockInfo.LiveIn); 579 dumpBV("LIVE_OUT", BlockInfo.LiveOut); 580 } 581 582 LLVM_DUMP_METHOD void StackColoring::dump() const { 583 for (MachineBasicBlock *MBB : depth_first(MF)) { 584 dbgs() << "Inspecting block #" << MBB->getNumber() << " [" 585 << MBB->getName() << "]\n"; 586 dumpBB(MBB); 587 } 588 } 589 590 LLVM_DUMP_METHOD void StackColoring::dumpIntervals() const { 591 for (unsigned I = 0, E = Intervals.size(); I != E; ++I) { 592 dbgs() << "Interval[" << I << "]:\n"; 593 Intervals[I]->dump(); 594 } 595 } 596 #endif 597 598 static inline int getStartOrEndSlot(const MachineInstr &MI) 599 { 600 assert((MI.getOpcode() == TargetOpcode::LIFETIME_START || 601 MI.getOpcode() == TargetOpcode::LIFETIME_END) && 602 "Expected LIFETIME_START or LIFETIME_END op"); 603 const MachineOperand &MO = MI.getOperand(0); 604 int Slot = MO.getIndex(); 605 if (Slot >= 0) 606 return Slot; 607 return -1; 608 } 609 610 // At the moment the only way to end a variable lifetime is with 611 // a VARIABLE_LIFETIME op (which can't contain a start). If things 612 // change and the IR allows for a single inst that both begins 613 // and ends lifetime(s), this interface will need to be reworked. 614 bool StackColoring::isLifetimeStartOrEnd(const MachineInstr &MI, 615 SmallVector<int, 4> &slots, 616 bool &isStart) { 617 if (MI.getOpcode() == TargetOpcode::LIFETIME_START || 618 MI.getOpcode() == TargetOpcode::LIFETIME_END) { 619 int Slot = getStartOrEndSlot(MI); 620 if (Slot < 0) 621 return false; 622 if (!InterestingSlots.test(Slot)) 623 return false; 624 slots.push_back(Slot); 625 if (MI.getOpcode() == TargetOpcode::LIFETIME_END) { 626 isStart = false; 627 return true; 628 } 629 if (!applyFirstUse(Slot)) { 630 isStart = true; 631 return true; 632 } 633 } else if (LifetimeStartOnFirstUse && !ProtectFromEscapedAllocas) { 634 if (!MI.isDebugInstr()) { 635 bool found = false; 636 for (const MachineOperand &MO : MI.operands()) { 637 if (!MO.isFI()) 638 continue; 639 int Slot = MO.getIndex(); 640 if (Slot<0) 641 continue; 642 if (InterestingSlots.test(Slot) && applyFirstUse(Slot)) { 643 slots.push_back(Slot); 644 found = true; 645 } 646 } 647 if (found) { 648 isStart = true; 649 return true; 650 } 651 } 652 } 653 return false; 654 } 655 656 unsigned StackColoring::collectMarkers(unsigned NumSlot) { 657 unsigned MarkersFound = 0; 658 BlockBitVecMap SeenStartMap; 659 InterestingSlots.clear(); 660 InterestingSlots.resize(NumSlot); 661 ConservativeSlots.clear(); 662 ConservativeSlots.resize(NumSlot); 663 StoreSlots.clear(); 664 StoreSlots.resize(NumSlot); 665 666 // number of start and end lifetime ops for each slot 667 SmallVector<int, 8> NumStartLifetimes(NumSlot, 0); 668 SmallVector<int, 8> NumEndLifetimes(NumSlot, 0); 669 SmallVector<int, 8> NumLoadInCatchPad(NumSlot, 0); 670 671 // Step 1: collect markers and populate the "InterestingSlots" 672 // and "ConservativeSlots" sets. 673 for (MachineBasicBlock *MBB : depth_first(MF)) { 674 // Compute the set of slots for which we've seen a START marker but have 675 // not yet seen an END marker at this point in the walk (e.g. on entry 676 // to this bb). 677 BitVector BetweenStartEnd; 678 BetweenStartEnd.resize(NumSlot); 679 for (const MachineBasicBlock *Pred : MBB->predecessors()) { 680 BlockBitVecMap::const_iterator I = SeenStartMap.find(Pred); 681 if (I != SeenStartMap.end()) { 682 BetweenStartEnd |= I->second; 683 } 684 } 685 686 // Walk the instructions in the block to look for start/end ops. 687 for (MachineInstr &MI : *MBB) { 688 if (MI.isDebugInstr()) 689 continue; 690 if (MI.getOpcode() == TargetOpcode::LIFETIME_START || 691 MI.getOpcode() == TargetOpcode::LIFETIME_END) { 692 int Slot = getStartOrEndSlot(MI); 693 if (Slot < 0) 694 continue; 695 InterestingSlots.set(Slot); 696 if (MI.getOpcode() == TargetOpcode::LIFETIME_START) { 697 BetweenStartEnd.set(Slot); 698 NumStartLifetimes[Slot] += 1; 699 } else { 700 BetweenStartEnd.reset(Slot); 701 NumEndLifetimes[Slot] += 1; 702 } 703 const AllocaInst *Allocation = MFI->getObjectAllocation(Slot); 704 if (Allocation) { 705 LLVM_DEBUG(dbgs() << "Found a lifetime "); 706 LLVM_DEBUG(dbgs() << (MI.getOpcode() == TargetOpcode::LIFETIME_START 707 ? "start" 708 : "end")); 709 LLVM_DEBUG(dbgs() << " marker for slot #" << Slot); 710 LLVM_DEBUG(dbgs() 711 << " with allocation: " << Allocation->getName() << "\n"); 712 } 713 Markers.push_back(&MI); 714 MarkersFound += 1; 715 } else { 716 for (const MachineOperand &MO : MI.operands()) { 717 if (!MO.isFI()) 718 continue; 719 int Slot = MO.getIndex(); 720 if (Slot < 0) 721 continue; 722 if (! BetweenStartEnd.test(Slot)) { 723 ConservativeSlots.set(Slot); 724 } 725 // Here we check the StoreSlots to screen catch point out. For more 726 // information, please refer "Handle Windows Exception with 727 // LifetimeStartOnFirstUse" at the head of this file. 728 if (MI.mayStore()) 729 StoreSlots.set(Slot); 730 if (MF->getWinEHFuncInfo() && MBB->isEHPad() && MI.mayLoad()) 731 NumLoadInCatchPad[Slot] += 1; 732 } 733 } 734 } 735 BitVector &SeenStart = SeenStartMap[MBB]; 736 SeenStart |= BetweenStartEnd; 737 } 738 if (!MarkersFound) { 739 return 0; 740 } 741 742 // 1) PR27903: slots with multiple start or end lifetime ops are not 743 // safe to enable for "lifetime-start-on-first-use". 744 // 2) And also not safe for variable X in catch(X) in windows. 745 for (unsigned slot = 0; slot < NumSlot; ++slot) { 746 if (NumStartLifetimes[slot] > 1 || NumEndLifetimes[slot] > 1 || 747 (NumLoadInCatchPad[slot] > 1 && !StoreSlots.test(slot))) 748 ConservativeSlots.set(slot); 749 } 750 LLVM_DEBUG(dumpBV("Conservative slots", ConservativeSlots)); 751 752 // Step 2: compute begin/end sets for each block 753 754 // NOTE: We use a depth-first iteration to ensure that we obtain a 755 // deterministic numbering. 756 for (MachineBasicBlock *MBB : depth_first(MF)) { 757 // Assign a serial number to this basic block. 758 BasicBlocks[MBB] = BasicBlockNumbering.size(); 759 BasicBlockNumbering.push_back(MBB); 760 761 // Keep a reference to avoid repeated lookups. 762 BlockLifetimeInfo &BlockInfo = BlockLiveness[MBB]; 763 764 BlockInfo.Begin.resize(NumSlot); 765 BlockInfo.End.resize(NumSlot); 766 767 SmallVector<int, 4> slots; 768 for (MachineInstr &MI : *MBB) { 769 bool isStart = false; 770 slots.clear(); 771 if (isLifetimeStartOrEnd(MI, slots, isStart)) { 772 if (!isStart) { 773 assert(slots.size() == 1 && "unexpected: MI ends multiple slots"); 774 int Slot = slots[0]; 775 if (BlockInfo.Begin.test(Slot)) { 776 BlockInfo.Begin.reset(Slot); 777 } 778 BlockInfo.End.set(Slot); 779 } else { 780 for (auto Slot : slots) { 781 LLVM_DEBUG(dbgs() << "Found a use of slot #" << Slot); 782 LLVM_DEBUG(dbgs() 783 << " at " << printMBBReference(*MBB) << " index "); 784 LLVM_DEBUG(Indexes->getInstructionIndex(MI).print(dbgs())); 785 const AllocaInst *Allocation = MFI->getObjectAllocation(Slot); 786 if (Allocation) { 787 LLVM_DEBUG(dbgs() 788 << " with allocation: " << Allocation->getName()); 789 } 790 LLVM_DEBUG(dbgs() << "\n"); 791 if (BlockInfo.End.test(Slot)) { 792 BlockInfo.End.reset(Slot); 793 } 794 BlockInfo.Begin.set(Slot); 795 } 796 } 797 } 798 } 799 } 800 801 // Update statistics. 802 NumMarkerSeen += MarkersFound; 803 return MarkersFound; 804 } 805 806 void StackColoring::calculateLocalLiveness() { 807 unsigned NumIters = 0; 808 bool changed = true; 809 while (changed) { 810 changed = false; 811 ++NumIters; 812 813 for (const MachineBasicBlock *BB : BasicBlockNumbering) { 814 // Use an iterator to avoid repeated lookups. 815 LivenessMap::iterator BI = BlockLiveness.find(BB); 816 assert(BI != BlockLiveness.end() && "Block not found"); 817 BlockLifetimeInfo &BlockInfo = BI->second; 818 819 // Compute LiveIn by unioning together the LiveOut sets of all preds. 820 BitVector LocalLiveIn; 821 for (MachineBasicBlock *Pred : BB->predecessors()) { 822 LivenessMap::const_iterator I = BlockLiveness.find(Pred); 823 // PR37130: transformations prior to stack coloring can 824 // sometimes leave behind statically unreachable blocks; these 825 // can be safely skipped here. 826 if (I != BlockLiveness.end()) 827 LocalLiveIn |= I->second.LiveOut; 828 } 829 830 // Compute LiveOut by subtracting out lifetimes that end in this 831 // block, then adding in lifetimes that begin in this block. If 832 // we have both BEGIN and END markers in the same basic block 833 // then we know that the BEGIN marker comes after the END, 834 // because we already handle the case where the BEGIN comes 835 // before the END when collecting the markers (and building the 836 // BEGIN/END vectors). 837 BitVector LocalLiveOut = LocalLiveIn; 838 LocalLiveOut.reset(BlockInfo.End); 839 LocalLiveOut |= BlockInfo.Begin; 840 841 // Update block LiveIn set, noting whether it has changed. 842 if (LocalLiveIn.test(BlockInfo.LiveIn)) { 843 changed = true; 844 BlockInfo.LiveIn |= LocalLiveIn; 845 } 846 847 // Update block LiveOut set, noting whether it has changed. 848 if (LocalLiveOut.test(BlockInfo.LiveOut)) { 849 changed = true; 850 BlockInfo.LiveOut |= LocalLiveOut; 851 } 852 } 853 } // while changed. 854 855 NumIterations = NumIters; 856 } 857 858 void StackColoring::calculateLiveIntervals(unsigned NumSlots) { 859 SmallVector<SlotIndex, 16> Starts; 860 SmallVector<bool, 16> DefinitelyInUse; 861 862 // For each block, find which slots are active within this block 863 // and update the live intervals. 864 for (const MachineBasicBlock &MBB : *MF) { 865 Starts.clear(); 866 Starts.resize(NumSlots); 867 DefinitelyInUse.clear(); 868 DefinitelyInUse.resize(NumSlots); 869 870 // Start the interval of the slots that we previously found to be 'in-use'. 871 BlockLifetimeInfo &MBBLiveness = BlockLiveness[&MBB]; 872 for (int pos = MBBLiveness.LiveIn.find_first(); pos != -1; 873 pos = MBBLiveness.LiveIn.find_next(pos)) { 874 Starts[pos] = Indexes->getMBBStartIdx(&MBB); 875 } 876 877 // Create the interval for the basic blocks containing lifetime begin/end. 878 for (const MachineInstr &MI : MBB) { 879 SmallVector<int, 4> slots; 880 bool IsStart = false; 881 if (!isLifetimeStartOrEnd(MI, slots, IsStart)) 882 continue; 883 SlotIndex ThisIndex = Indexes->getInstructionIndex(MI); 884 for (auto Slot : slots) { 885 if (IsStart) { 886 // If a slot is already definitely in use, we don't have to emit 887 // a new start marker because there is already a pre-existing 888 // one. 889 if (!DefinitelyInUse[Slot]) { 890 LiveStarts[Slot].push_back(ThisIndex); 891 DefinitelyInUse[Slot] = true; 892 } 893 if (!Starts[Slot].isValid()) 894 Starts[Slot] = ThisIndex; 895 } else { 896 if (Starts[Slot].isValid()) { 897 VNInfo *VNI = Intervals[Slot]->getValNumInfo(0); 898 Intervals[Slot]->addSegment( 899 LiveInterval::Segment(Starts[Slot], ThisIndex, VNI)); 900 Starts[Slot] = SlotIndex(); // Invalidate the start index 901 DefinitelyInUse[Slot] = false; 902 } 903 } 904 } 905 } 906 907 // Finish up started segments 908 for (unsigned i = 0; i < NumSlots; ++i) { 909 if (!Starts[i].isValid()) 910 continue; 911 912 SlotIndex EndIdx = Indexes->getMBBEndIdx(&MBB); 913 VNInfo *VNI = Intervals[i]->getValNumInfo(0); 914 Intervals[i]->addSegment(LiveInterval::Segment(Starts[i], EndIdx, VNI)); 915 } 916 } 917 } 918 919 bool StackColoring::removeAllMarkers() { 920 unsigned Count = 0; 921 for (MachineInstr *MI : Markers) { 922 MI->eraseFromParent(); 923 Count++; 924 } 925 Markers.clear(); 926 927 LLVM_DEBUG(dbgs() << "Removed " << Count << " markers.\n"); 928 return Count; 929 } 930 931 void StackColoring::remapInstructions(DenseMap<int, int> &SlotRemap) { 932 unsigned FixedInstr = 0; 933 unsigned FixedMemOp = 0; 934 unsigned FixedDbg = 0; 935 936 // Remap debug information that refers to stack slots. 937 for (auto &VI : MF->getVariableDbgInfo()) { 938 if (!VI.Var) 939 continue; 940 if (SlotRemap.count(VI.Slot)) { 941 LLVM_DEBUG(dbgs() << "Remapping debug info for [" 942 << cast<DILocalVariable>(VI.Var)->getName() << "].\n"); 943 VI.Slot = SlotRemap[VI.Slot]; 944 FixedDbg++; 945 } 946 } 947 948 // Keep a list of *allocas* which need to be remapped. 949 DenseMap<const AllocaInst*, const AllocaInst*> Allocas; 950 951 // Keep a list of allocas which has been affected by the remap. 952 SmallPtrSet<const AllocaInst*, 32> MergedAllocas; 953 954 for (const std::pair<int, int> &SI : SlotRemap) { 955 const AllocaInst *From = MFI->getObjectAllocation(SI.first); 956 const AllocaInst *To = MFI->getObjectAllocation(SI.second); 957 assert(To && From && "Invalid allocation object"); 958 Allocas[From] = To; 959 960 // If From is before wo, its possible that there is a use of From between 961 // them. 962 if (From->comesBefore(To)) 963 const_cast<AllocaInst*>(To)->moveBefore(const_cast<AllocaInst*>(From)); 964 965 // AA might be used later for instruction scheduling, and we need it to be 966 // able to deduce the correct aliasing releationships between pointers 967 // derived from the alloca being remapped and the target of that remapping. 968 // The only safe way, without directly informing AA about the remapping 969 // somehow, is to directly update the IR to reflect the change being made 970 // here. 971 Instruction *Inst = const_cast<AllocaInst *>(To); 972 if (From->getType() != To->getType()) { 973 BitCastInst *Cast = new BitCastInst(Inst, From->getType()); 974 Cast->insertAfter(Inst); 975 Inst = Cast; 976 } 977 978 // We keep both slots to maintain AliasAnalysis metadata later. 979 MergedAllocas.insert(From); 980 MergedAllocas.insert(To); 981 982 // Transfer the stack protector layout tag, but make sure that SSPLK_AddrOf 983 // does not overwrite SSPLK_SmallArray or SSPLK_LargeArray, and make sure 984 // that SSPLK_SmallArray does not overwrite SSPLK_LargeArray. 985 MachineFrameInfo::SSPLayoutKind FromKind 986 = MFI->getObjectSSPLayout(SI.first); 987 MachineFrameInfo::SSPLayoutKind ToKind = MFI->getObjectSSPLayout(SI.second); 988 if (FromKind != MachineFrameInfo::SSPLK_None && 989 (ToKind == MachineFrameInfo::SSPLK_None || 990 (ToKind != MachineFrameInfo::SSPLK_LargeArray && 991 FromKind != MachineFrameInfo::SSPLK_AddrOf))) 992 MFI->setObjectSSPLayout(SI.second, FromKind); 993 994 // The new alloca might not be valid in a llvm.dbg.declare for this 995 // variable, so undef out the use to make the verifier happy. 996 AllocaInst *FromAI = const_cast<AllocaInst *>(From); 997 if (FromAI->isUsedByMetadata()) 998 ValueAsMetadata::handleRAUW(FromAI, UndefValue::get(FromAI->getType())); 999 for (auto &Use : FromAI->uses()) { 1000 if (BitCastInst *BCI = dyn_cast<BitCastInst>(Use.get())) 1001 if (BCI->isUsedByMetadata()) 1002 ValueAsMetadata::handleRAUW(BCI, UndefValue::get(BCI->getType())); 1003 } 1004 1005 // Note that this will not replace uses in MMOs (which we'll update below), 1006 // or anywhere else (which is why we won't delete the original 1007 // instruction). 1008 FromAI->replaceAllUsesWith(Inst); 1009 } 1010 1011 // Remap all instructions to the new stack slots. 1012 std::vector<std::vector<MachineMemOperand *>> SSRefs( 1013 MFI->getObjectIndexEnd()); 1014 for (MachineBasicBlock &BB : *MF) 1015 for (MachineInstr &I : BB) { 1016 // Skip lifetime markers. We'll remove them soon. 1017 if (I.getOpcode() == TargetOpcode::LIFETIME_START || 1018 I.getOpcode() == TargetOpcode::LIFETIME_END) 1019 continue; 1020 1021 // Update the MachineMemOperand to use the new alloca. 1022 for (MachineMemOperand *MMO : I.memoperands()) { 1023 // We've replaced IR-level uses of the remapped allocas, so we only 1024 // need to replace direct uses here. 1025 const AllocaInst *AI = dyn_cast_or_null<AllocaInst>(MMO->getValue()); 1026 if (!AI) 1027 continue; 1028 1029 if (!Allocas.count(AI)) 1030 continue; 1031 1032 MMO->setValue(Allocas[AI]); 1033 FixedMemOp++; 1034 } 1035 1036 // Update all of the machine instruction operands. 1037 for (MachineOperand &MO : I.operands()) { 1038 if (!MO.isFI()) 1039 continue; 1040 int FromSlot = MO.getIndex(); 1041 1042 // Don't touch arguments. 1043 if (FromSlot<0) 1044 continue; 1045 1046 // Only look at mapped slots. 1047 if (!SlotRemap.count(FromSlot)) 1048 continue; 1049 1050 // In a debug build, check that the instruction that we are modifying is 1051 // inside the expected live range. If the instruction is not inside 1052 // the calculated range then it means that the alloca usage moved 1053 // outside of the lifetime markers, or that the user has a bug. 1054 // NOTE: Alloca address calculations which happen outside the lifetime 1055 // zone are okay, despite the fact that we don't have a good way 1056 // for validating all of the usages of the calculation. 1057 #ifndef NDEBUG 1058 bool TouchesMemory = I.mayLoadOrStore(); 1059 // If we *don't* protect the user from escaped allocas, don't bother 1060 // validating the instructions. 1061 if (!I.isDebugInstr() && TouchesMemory && ProtectFromEscapedAllocas) { 1062 SlotIndex Index = Indexes->getInstructionIndex(I); 1063 const LiveInterval *Interval = &*Intervals[FromSlot]; 1064 assert(Interval->find(Index) != Interval->end() && 1065 "Found instruction usage outside of live range."); 1066 } 1067 #endif 1068 1069 // Fix the machine instructions. 1070 int ToSlot = SlotRemap[FromSlot]; 1071 MO.setIndex(ToSlot); 1072 FixedInstr++; 1073 } 1074 1075 // We adjust AliasAnalysis information for merged stack slots. 1076 SmallVector<MachineMemOperand *, 2> NewMMOs; 1077 bool ReplaceMemOps = false; 1078 for (MachineMemOperand *MMO : I.memoperands()) { 1079 // Collect MachineMemOperands which reference 1080 // FixedStackPseudoSourceValues with old frame indices. 1081 if (const auto *FSV = dyn_cast_or_null<FixedStackPseudoSourceValue>( 1082 MMO->getPseudoValue())) { 1083 int FI = FSV->getFrameIndex(); 1084 auto To = SlotRemap.find(FI); 1085 if (To != SlotRemap.end()) 1086 SSRefs[FI].push_back(MMO); 1087 } 1088 1089 // If this memory location can be a slot remapped here, 1090 // we remove AA information. 1091 bool MayHaveConflictingAAMD = false; 1092 if (MMO->getAAInfo()) { 1093 if (const Value *MMOV = MMO->getValue()) { 1094 SmallVector<Value *, 4> Objs; 1095 getUnderlyingObjectsForCodeGen(MMOV, Objs); 1096 1097 if (Objs.empty()) 1098 MayHaveConflictingAAMD = true; 1099 else 1100 for (Value *V : Objs) { 1101 // If this memory location comes from a known stack slot 1102 // that is not remapped, we continue checking. 1103 // Otherwise, we need to invalidate AA infomation. 1104 const AllocaInst *AI = dyn_cast_or_null<AllocaInst>(V); 1105 if (AI && MergedAllocas.count(AI)) { 1106 MayHaveConflictingAAMD = true; 1107 break; 1108 } 1109 } 1110 } 1111 } 1112 if (MayHaveConflictingAAMD) { 1113 NewMMOs.push_back(MF->getMachineMemOperand(MMO, AAMDNodes())); 1114 ReplaceMemOps = true; 1115 } else { 1116 NewMMOs.push_back(MMO); 1117 } 1118 } 1119 1120 // If any memory operand is updated, set memory references of 1121 // this instruction. 1122 if (ReplaceMemOps) 1123 I.setMemRefs(*MF, NewMMOs); 1124 } 1125 1126 // Rewrite MachineMemOperands that reference old frame indices. 1127 for (auto E : enumerate(SSRefs)) 1128 if (!E.value().empty()) { 1129 const PseudoSourceValue *NewSV = 1130 MF->getPSVManager().getFixedStack(SlotRemap.find(E.index())->second); 1131 for (MachineMemOperand *Ref : E.value()) 1132 Ref->setValue(NewSV); 1133 } 1134 1135 // Update the location of C++ catch objects for the MSVC personality routine. 1136 if (WinEHFuncInfo *EHInfo = MF->getWinEHFuncInfo()) 1137 for (WinEHTryBlockMapEntry &TBME : EHInfo->TryBlockMap) 1138 for (WinEHHandlerType &H : TBME.HandlerArray) 1139 if (H.CatchObj.FrameIndex != std::numeric_limits<int>::max() && 1140 SlotRemap.count(H.CatchObj.FrameIndex)) 1141 H.CatchObj.FrameIndex = SlotRemap[H.CatchObj.FrameIndex]; 1142 1143 LLVM_DEBUG(dbgs() << "Fixed " << FixedMemOp << " machine memory operands.\n"); 1144 LLVM_DEBUG(dbgs() << "Fixed " << FixedDbg << " debug locations.\n"); 1145 LLVM_DEBUG(dbgs() << "Fixed " << FixedInstr << " machine instructions.\n"); 1146 (void) FixedMemOp; 1147 (void) FixedDbg; 1148 (void) FixedInstr; 1149 } 1150 1151 void StackColoring::removeInvalidSlotRanges() { 1152 for (MachineBasicBlock &BB : *MF) 1153 for (MachineInstr &I : BB) { 1154 if (I.getOpcode() == TargetOpcode::LIFETIME_START || 1155 I.getOpcode() == TargetOpcode::LIFETIME_END || I.isDebugInstr()) 1156 continue; 1157 1158 // Some intervals are suspicious! In some cases we find address 1159 // calculations outside of the lifetime zone, but not actual memory 1160 // read or write. Memory accesses outside of the lifetime zone are a clear 1161 // violation, but address calculations are okay. This can happen when 1162 // GEPs are hoisted outside of the lifetime zone. 1163 // So, in here we only check instructions which can read or write memory. 1164 if (!I.mayLoad() && !I.mayStore()) 1165 continue; 1166 1167 // Check all of the machine operands. 1168 for (const MachineOperand &MO : I.operands()) { 1169 if (!MO.isFI()) 1170 continue; 1171 1172 int Slot = MO.getIndex(); 1173 1174 if (Slot<0) 1175 continue; 1176 1177 if (Intervals[Slot]->empty()) 1178 continue; 1179 1180 // Check that the used slot is inside the calculated lifetime range. 1181 // If it is not, warn about it and invalidate the range. 1182 LiveInterval *Interval = &*Intervals[Slot]; 1183 SlotIndex Index = Indexes->getInstructionIndex(I); 1184 if (Interval->find(Index) == Interval->end()) { 1185 Interval->clear(); 1186 LLVM_DEBUG(dbgs() << "Invalidating range #" << Slot << "\n"); 1187 EscapedAllocas++; 1188 } 1189 } 1190 } 1191 } 1192 1193 void StackColoring::expungeSlotMap(DenseMap<int, int> &SlotRemap, 1194 unsigned NumSlots) { 1195 // Expunge slot remap map. 1196 for (unsigned i=0; i < NumSlots; ++i) { 1197 // If we are remapping i 1198 if (SlotRemap.count(i)) { 1199 int Target = SlotRemap[i]; 1200 // As long as our target is mapped to something else, follow it. 1201 while (SlotRemap.count(Target)) { 1202 Target = SlotRemap[Target]; 1203 SlotRemap[i] = Target; 1204 } 1205 } 1206 } 1207 } 1208 1209 bool StackColoring::runOnMachineFunction(MachineFunction &Func) { 1210 LLVM_DEBUG(dbgs() << "********** Stack Coloring **********\n" 1211 << "********** Function: " << Func.getName() << '\n'); 1212 MF = &Func; 1213 MFI = &MF->getFrameInfo(); 1214 Indexes = &getAnalysis<SlotIndexes>(); 1215 BlockLiveness.clear(); 1216 BasicBlocks.clear(); 1217 BasicBlockNumbering.clear(); 1218 Markers.clear(); 1219 Intervals.clear(); 1220 LiveStarts.clear(); 1221 VNInfoAllocator.Reset(); 1222 1223 unsigned NumSlots = MFI->getObjectIndexEnd(); 1224 1225 // If there are no stack slots then there are no markers to remove. 1226 if (!NumSlots) 1227 return false; 1228 1229 SmallVector<int, 8> SortedSlots; 1230 SortedSlots.reserve(NumSlots); 1231 Intervals.reserve(NumSlots); 1232 LiveStarts.resize(NumSlots); 1233 1234 unsigned NumMarkers = collectMarkers(NumSlots); 1235 1236 unsigned TotalSize = 0; 1237 LLVM_DEBUG(dbgs() << "Found " << NumMarkers << " markers and " << NumSlots 1238 << " slots\n"); 1239 LLVM_DEBUG(dbgs() << "Slot structure:\n"); 1240 1241 for (int i=0; i < MFI->getObjectIndexEnd(); ++i) { 1242 LLVM_DEBUG(dbgs() << "Slot #" << i << " - " << MFI->getObjectSize(i) 1243 << " bytes.\n"); 1244 TotalSize += MFI->getObjectSize(i); 1245 } 1246 1247 LLVM_DEBUG(dbgs() << "Total Stack size: " << TotalSize << " bytes\n\n"); 1248 1249 // Don't continue because there are not enough lifetime markers, or the 1250 // stack is too small, or we are told not to optimize the slots. 1251 if (NumMarkers < 2 || TotalSize < 16 || DisableColoring || 1252 skipFunction(Func.getFunction())) { 1253 LLVM_DEBUG(dbgs() << "Will not try to merge slots.\n"); 1254 return removeAllMarkers(); 1255 } 1256 1257 for (unsigned i=0; i < NumSlots; ++i) { 1258 std::unique_ptr<LiveInterval> LI(new LiveInterval(i, 0)); 1259 LI->getNextValue(Indexes->getZeroIndex(), VNInfoAllocator); 1260 Intervals.push_back(std::move(LI)); 1261 SortedSlots.push_back(i); 1262 } 1263 1264 // Calculate the liveness of each block. 1265 calculateLocalLiveness(); 1266 LLVM_DEBUG(dbgs() << "Dataflow iterations: " << NumIterations << "\n"); 1267 LLVM_DEBUG(dump()); 1268 1269 // Propagate the liveness information. 1270 calculateLiveIntervals(NumSlots); 1271 LLVM_DEBUG(dumpIntervals()); 1272 1273 // Search for allocas which are used outside of the declared lifetime 1274 // markers. 1275 if (ProtectFromEscapedAllocas) 1276 removeInvalidSlotRanges(); 1277 1278 // Maps old slots to new slots. 1279 DenseMap<int, int> SlotRemap; 1280 unsigned RemovedSlots = 0; 1281 unsigned ReducedSize = 0; 1282 1283 // Do not bother looking at empty intervals. 1284 for (unsigned I = 0; I < NumSlots; ++I) { 1285 if (Intervals[SortedSlots[I]]->empty()) 1286 SortedSlots[I] = -1; 1287 } 1288 1289 // This is a simple greedy algorithm for merging allocas. First, sort the 1290 // slots, placing the largest slots first. Next, perform an n^2 scan and look 1291 // for disjoint slots. When you find disjoint slots, merge the smaller one 1292 // into the bigger one and update the live interval. Remove the small alloca 1293 // and continue. 1294 1295 // Sort the slots according to their size. Place unused slots at the end. 1296 // Use stable sort to guarantee deterministic code generation. 1297 llvm::stable_sort(SortedSlots, [this](int LHS, int RHS) { 1298 // We use -1 to denote a uninteresting slot. Place these slots at the end. 1299 if (LHS == -1) 1300 return false; 1301 if (RHS == -1) 1302 return true; 1303 // Sort according to size. 1304 return MFI->getObjectSize(LHS) > MFI->getObjectSize(RHS); 1305 }); 1306 1307 for (auto &s : LiveStarts) 1308 llvm::sort(s); 1309 1310 bool Changed = true; 1311 while (Changed) { 1312 Changed = false; 1313 for (unsigned I = 0; I < NumSlots; ++I) { 1314 if (SortedSlots[I] == -1) 1315 continue; 1316 1317 for (unsigned J=I+1; J < NumSlots; ++J) { 1318 if (SortedSlots[J] == -1) 1319 continue; 1320 1321 int FirstSlot = SortedSlots[I]; 1322 int SecondSlot = SortedSlots[J]; 1323 1324 // Objects with different stack IDs cannot be merged. 1325 if (MFI->getStackID(FirstSlot) != MFI->getStackID(SecondSlot)) 1326 continue; 1327 1328 LiveInterval *First = &*Intervals[FirstSlot]; 1329 LiveInterval *Second = &*Intervals[SecondSlot]; 1330 auto &FirstS = LiveStarts[FirstSlot]; 1331 auto &SecondS = LiveStarts[SecondSlot]; 1332 assert(!First->empty() && !Second->empty() && "Found an empty range"); 1333 1334 // Merge disjoint slots. This is a little bit tricky - see the 1335 // Implementation Notes section for an explanation. 1336 if (!First->isLiveAtIndexes(SecondS) && 1337 !Second->isLiveAtIndexes(FirstS)) { 1338 Changed = true; 1339 First->MergeSegmentsInAsValue(*Second, First->getValNumInfo(0)); 1340 1341 int OldSize = FirstS.size(); 1342 FirstS.append(SecondS.begin(), SecondS.end()); 1343 auto Mid = FirstS.begin() + OldSize; 1344 std::inplace_merge(FirstS.begin(), Mid, FirstS.end()); 1345 1346 SlotRemap[SecondSlot] = FirstSlot; 1347 SortedSlots[J] = -1; 1348 LLVM_DEBUG(dbgs() << "Merging #" << FirstSlot << " and slots #" 1349 << SecondSlot << " together.\n"); 1350 Align MaxAlignment = std::max(MFI->getObjectAlign(FirstSlot), 1351 MFI->getObjectAlign(SecondSlot)); 1352 1353 assert(MFI->getObjectSize(FirstSlot) >= 1354 MFI->getObjectSize(SecondSlot) && 1355 "Merging a small object into a larger one"); 1356 1357 RemovedSlots+=1; 1358 ReducedSize += MFI->getObjectSize(SecondSlot); 1359 MFI->setObjectAlignment(FirstSlot, MaxAlignment); 1360 MFI->RemoveStackObject(SecondSlot); 1361 } 1362 } 1363 } 1364 }// While changed. 1365 1366 // Record statistics. 1367 StackSpaceSaved += ReducedSize; 1368 StackSlotMerged += RemovedSlots; 1369 LLVM_DEBUG(dbgs() << "Merge " << RemovedSlots << " slots. Saved " 1370 << ReducedSize << " bytes\n"); 1371 1372 // Scan the entire function and update all machine operands that use frame 1373 // indices to use the remapped frame index. 1374 expungeSlotMap(SlotRemap, NumSlots); 1375 remapInstructions(SlotRemap); 1376 1377 return removeAllMarkers(); 1378 } 1379