PrologEpilogInserter.cpp revision f7a0c0de6d73df8f24438234485b7950323b3d44
1//===-- PrologEpilogInserter.cpp - Insert Prolog/Epilog code in function --===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This pass is responsible for finalizing the functions frame layout, saving 11// callee saved registers, and for emitting prolog & epilog code for the 12// function. 13// 14// This pass must be run after register allocation. After this pass is 15// executed, it is illegal to construct MO_FrameIndex operands. 16// 17// This pass provides an optional shrink wrapping variant of prolog/epilog 18// insertion, enabled via --shrink-wrap. See ShrinkWrapping.cpp. 19// 20//===----------------------------------------------------------------------===// 21 22#include "PrologEpilogInserter.h" 23#include "llvm/CodeGen/MachineDominators.h" 24#include "llvm/CodeGen/MachineLoopInfo.h" 25#include "llvm/CodeGen/MachineInstr.h" 26#include "llvm/CodeGen/MachineFrameInfo.h" 27#include "llvm/CodeGen/MachineModuleInfo.h" 28#include "llvm/CodeGen/MachineRegisterInfo.h" 29#include "llvm/CodeGen/RegisterScavenging.h" 30#include "llvm/Target/TargetMachine.h" 31#include "llvm/Target/TargetRegisterInfo.h" 32#include "llvm/Target/TargetFrameInfo.h" 33#include "llvm/Target/TargetInstrInfo.h" 34#include "llvm/Support/CommandLine.h" 35#include "llvm/Support/Compiler.h" 36#include "llvm/ADT/IndexedMap.h" 37#include "llvm/ADT/STLExtras.h" 38#include <climits> 39 40using namespace llvm; 41 42char PEI::ID = 0; 43 44static RegisterPass<PEI> 45X("prologepilog", "Prologue/Epilogue Insertion"); 46 47/// createPrologEpilogCodeInserter - This function returns a pass that inserts 48/// prolog and epilog code, and eliminates abstract frame references. 49/// 50FunctionPass *llvm::createPrologEpilogCodeInserter() { return new PEI(); } 51 52/// runOnMachineFunction - Insert prolog/epilog code and replace abstract 53/// frame indexes with appropriate references. 54/// 55bool PEI::runOnMachineFunction(MachineFunction &Fn) { 56 const Function* F = Fn.getFunction(); 57 const TargetRegisterInfo *TRI = Fn.getTarget().getRegisterInfo(); 58 RS = TRI->requiresRegisterScavenging(Fn) ? new RegScavenger() : NULL; 59 FrameIndexVirtualScavenging = TRI->requiresFrameIndexScavenging(Fn); 60 61 // Get MachineModuleInfo so that we can track the construction of the 62 // frame. 63 if (MachineModuleInfo *MMI = getAnalysisIfAvailable<MachineModuleInfo>()) 64 Fn.getFrameInfo()->setMachineModuleInfo(MMI); 65 66 // Calculate the MaxCallFrameSize and HasCalls variables for the function's 67 // frame information. Also eliminates call frame pseudo instructions. 68 calculateCallsInformation(Fn); 69 70 // Allow the target machine to make some adjustments to the function 71 // e.g. UsedPhysRegs before calculateCalleeSavedRegisters. 72 TRI->processFunctionBeforeCalleeSavedScan(Fn, RS); 73 74 // Scan the function for modified callee saved registers and insert spill code 75 // for any callee saved registers that are modified. 76 calculateCalleeSavedRegisters(Fn); 77 78 // Determine placement of CSR spill/restore code: 79 // - with shrink wrapping, place spills and restores to tightly 80 // enclose regions in the Machine CFG of the function where 81 // they are used. Without shrink wrapping 82 // - default (no shrink wrapping), place all spills in the 83 // entry block, all restores in return blocks. 84 placeCSRSpillsAndRestores(Fn); 85 86 // Add the code to save and restore the callee saved registers 87 if (!F->hasFnAttr(Attribute::Naked)) 88 insertCSRSpillsAndRestores(Fn); 89 90 // Allow the target machine to make final modifications to the function 91 // before the frame layout is finalized. 92 TRI->processFunctionBeforeFrameFinalized(Fn); 93 94 // Calculate actual frame offsets for all abstract stack objects... 95 calculateFrameObjectOffsets(Fn); 96 97 // Add prolog and epilog code to the function. This function is required 98 // to align the stack frame as necessary for any stack variables or 99 // called functions. Because of this, calculateCalleeSavedRegisters 100 // must be called before this function in order to set the HasCalls 101 // and MaxCallFrameSize variables. 102 if (!F->hasFnAttr(Attribute::Naked)) 103 insertPrologEpilogCode(Fn); 104 105 // Replace all MO_FrameIndex operands with physical register references 106 // and actual offsets. 107 // 108 replaceFrameIndices(Fn); 109 110 // If register scavenging is needed, as we've enabled doing it as a 111 // post-pass, scavenge the virtual registers that frame index elimiation 112 // inserted. 113 if (TRI->requiresRegisterScavenging(Fn) && FrameIndexVirtualScavenging) 114 scavengeFrameVirtualRegs(Fn); 115 116 delete RS; 117 clearAllSets(); 118 return true; 119} 120 121#if 0 122void PEI::getAnalysisUsage(AnalysisUsage &AU) const { 123 AU.setPreservesCFG(); 124 if (ShrinkWrapping || ShrinkWrapFunc != "") { 125 AU.addRequired<MachineLoopInfo>(); 126 AU.addRequired<MachineDominatorTree>(); 127 } 128 AU.addPreserved<MachineLoopInfo>(); 129 AU.addPreserved<MachineDominatorTree>(); 130 MachineFunctionPass::getAnalysisUsage(AU); 131} 132#endif 133 134/// calculateCallsInformation - Calculate the MaxCallFrameSize and HasCalls 135/// variables for the function's frame information and eliminate call frame 136/// pseudo instructions. 137void PEI::calculateCallsInformation(MachineFunction &Fn) { 138 const TargetRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo(); 139 140 unsigned MaxCallFrameSize = 0; 141 bool HasCalls = false; 142 143 // Get the function call frame set-up and tear-down instruction opcode 144 int FrameSetupOpcode = RegInfo->getCallFrameSetupOpcode(); 145 int FrameDestroyOpcode = RegInfo->getCallFrameDestroyOpcode(); 146 147 // Early exit for targets which have no call frame setup/destroy pseudo 148 // instructions. 149 if (FrameSetupOpcode == -1 && FrameDestroyOpcode == -1) 150 return; 151 152 std::vector<MachineBasicBlock::iterator> FrameSDOps; 153 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) 154 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) 155 if (I->getOpcode() == FrameSetupOpcode || 156 I->getOpcode() == FrameDestroyOpcode) { 157 assert(I->getNumOperands() >= 1 && "Call Frame Setup/Destroy Pseudo" 158 " instructions should have a single immediate argument!"); 159 unsigned Size = I->getOperand(0).getImm(); 160 if (Size > MaxCallFrameSize) MaxCallFrameSize = Size; 161 HasCalls = true; 162 FrameSDOps.push_back(I); 163 } else if (I->getOpcode() == TargetInstrInfo::INLINEASM) { 164 // An InlineAsm might be a call; assume it is to get the stack frame 165 // aligned correctly for calls. 166 HasCalls = true; 167 } 168 169 MachineFrameInfo *FFI = Fn.getFrameInfo(); 170 FFI->setHasCalls(HasCalls); 171 FFI->setMaxCallFrameSize(MaxCallFrameSize); 172 173 for (std::vector<MachineBasicBlock::iterator>::iterator 174 i = FrameSDOps.begin(), e = FrameSDOps.end(); i != e; ++i) { 175 MachineBasicBlock::iterator I = *i; 176 177 // If call frames are not being included as part of the stack frame, and 178 // there is no dynamic allocation (therefore referencing frame slots off 179 // sp), leave the pseudo ops alone. We'll eliminate them later. 180 if (RegInfo->hasReservedCallFrame(Fn) || RegInfo->hasFP(Fn)) 181 RegInfo->eliminateCallFramePseudoInstr(Fn, *I->getParent(), I); 182 } 183} 184 185 186/// calculateCalleeSavedRegisters - Scan the function for modified callee saved 187/// registers. 188void PEI::calculateCalleeSavedRegisters(MachineFunction &Fn) { 189 const TargetRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo(); 190 const TargetFrameInfo *TFI = Fn.getTarget().getFrameInfo(); 191 MachineFrameInfo *FFI = Fn.getFrameInfo(); 192 193 // Get the callee saved register list... 194 const unsigned *CSRegs = RegInfo->getCalleeSavedRegs(&Fn); 195 196 // These are used to keep track the callee-save area. Initialize them. 197 MinCSFrameIndex = INT_MAX; 198 MaxCSFrameIndex = 0; 199 200 // Early exit for targets which have no callee saved registers. 201 if (CSRegs == 0 || CSRegs[0] == 0) 202 return; 203 204 // Figure out which *callee saved* registers are modified by the current 205 // function, thus needing to be saved and restored in the prolog/epilog. 206 const TargetRegisterClass * const *CSRegClasses = 207 RegInfo->getCalleeSavedRegClasses(&Fn); 208 209 std::vector<CalleeSavedInfo> CSI; 210 for (unsigned i = 0; CSRegs[i]; ++i) { 211 unsigned Reg = CSRegs[i]; 212 if (Fn.getRegInfo().isPhysRegUsed(Reg)) { 213 // If the reg is modified, save it! 214 CSI.push_back(CalleeSavedInfo(Reg, CSRegClasses[i])); 215 } else { 216 for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg); 217 *AliasSet; ++AliasSet) { // Check alias registers too. 218 if (Fn.getRegInfo().isPhysRegUsed(*AliasSet)) { 219 CSI.push_back(CalleeSavedInfo(Reg, CSRegClasses[i])); 220 break; 221 } 222 } 223 } 224 } 225 226 if (CSI.empty()) 227 return; // Early exit if no callee saved registers are modified! 228 229 unsigned NumFixedSpillSlots; 230 const TargetFrameInfo::SpillSlot *FixedSpillSlots = 231 TFI->getCalleeSavedSpillSlots(NumFixedSpillSlots); 232 233 // Now that we know which registers need to be saved and restored, allocate 234 // stack slots for them. 235 for (std::vector<CalleeSavedInfo>::iterator 236 I = CSI.begin(), E = CSI.end(); I != E; ++I) { 237 unsigned Reg = I->getReg(); 238 const TargetRegisterClass *RC = I->getRegClass(); 239 240 int FrameIdx; 241 if (RegInfo->hasReservedSpillSlot(Fn, Reg, FrameIdx)) { 242 I->setFrameIdx(FrameIdx); 243 continue; 244 } 245 246 // Check to see if this physreg must be spilled to a particular stack slot 247 // on this target. 248 const TargetFrameInfo::SpillSlot *FixedSlot = FixedSpillSlots; 249 while (FixedSlot != FixedSpillSlots+NumFixedSpillSlots && 250 FixedSlot->Reg != Reg) 251 ++FixedSlot; 252 253 if (FixedSlot == FixedSpillSlots + NumFixedSpillSlots) { 254 // Nope, just spill it anywhere convenient. 255 unsigned Align = RC->getAlignment(); 256 unsigned StackAlign = TFI->getStackAlignment(); 257 258 // We may not be able to satisfy the desired alignment specification of 259 // the TargetRegisterClass if the stack alignment is smaller. Use the 260 // min. 261 Align = std::min(Align, StackAlign); 262 FrameIdx = FFI->CreateStackObject(RC->getSize(), Align, true); 263 if ((unsigned)FrameIdx < MinCSFrameIndex) MinCSFrameIndex = FrameIdx; 264 if ((unsigned)FrameIdx > MaxCSFrameIndex) MaxCSFrameIndex = FrameIdx; 265 } else { 266 // Spill it to the stack where we must. 267 FrameIdx = FFI->CreateFixedObject(RC->getSize(), FixedSlot->Offset); 268 } 269 270 I->setFrameIdx(FrameIdx); 271 } 272 273 FFI->setCalleeSavedInfo(CSI); 274} 275 276/// insertCSRSpillsAndRestores - Insert spill and restore code for 277/// callee saved registers used in the function, handling shrink wrapping. 278/// 279void PEI::insertCSRSpillsAndRestores(MachineFunction &Fn) { 280 // Get callee saved register information. 281 MachineFrameInfo *FFI = Fn.getFrameInfo(); 282 const std::vector<CalleeSavedInfo> &CSI = FFI->getCalleeSavedInfo(); 283 284 FFI->setCalleeSavedInfoValid(true); 285 286 // Early exit if no callee saved registers are modified! 287 if (CSI.empty()) 288 return; 289 290 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo(); 291 MachineBasicBlock::iterator I; 292 293 if (! ShrinkWrapThisFunction) { 294 // Spill using target interface. 295 I = EntryBlock->begin(); 296 if (!TII.spillCalleeSavedRegisters(*EntryBlock, I, CSI)) { 297 for (unsigned i = 0, e = CSI.size(); i != e; ++i) { 298 // Add the callee-saved register as live-in. 299 // It's killed at the spill. 300 EntryBlock->addLiveIn(CSI[i].getReg()); 301 302 // Insert the spill to the stack frame. 303 TII.storeRegToStackSlot(*EntryBlock, I, CSI[i].getReg(), true, 304 CSI[i].getFrameIdx(), CSI[i].getRegClass()); 305 } 306 } 307 308 // Restore using target interface. 309 for (unsigned ri = 0, re = ReturnBlocks.size(); ri != re; ++ri) { 310 MachineBasicBlock* MBB = ReturnBlocks[ri]; 311 I = MBB->end(); --I; 312 313 // Skip over all terminator instructions, which are part of the return 314 // sequence. 315 MachineBasicBlock::iterator I2 = I; 316 while (I2 != MBB->begin() && (--I2)->getDesc().isTerminator()) 317 I = I2; 318 319 bool AtStart = I == MBB->begin(); 320 MachineBasicBlock::iterator BeforeI = I; 321 if (!AtStart) 322 --BeforeI; 323 324 // Restore all registers immediately before the return and any 325 // terminators that preceed it. 326 if (!TII.restoreCalleeSavedRegisters(*MBB, I, CSI)) { 327 for (unsigned i = 0, e = CSI.size(); i != e; ++i) { 328 TII.loadRegFromStackSlot(*MBB, I, CSI[i].getReg(), 329 CSI[i].getFrameIdx(), 330 CSI[i].getRegClass()); 331 assert(I != MBB->begin() && 332 "loadRegFromStackSlot didn't insert any code!"); 333 // Insert in reverse order. loadRegFromStackSlot can insert 334 // multiple instructions. 335 if (AtStart) 336 I = MBB->begin(); 337 else { 338 I = BeforeI; 339 ++I; 340 } 341 } 342 } 343 } 344 return; 345 } 346 347 // Insert spills. 348 std::vector<CalleeSavedInfo> blockCSI; 349 for (CSRegBlockMap::iterator BI = CSRSave.begin(), 350 BE = CSRSave.end(); BI != BE; ++BI) { 351 MachineBasicBlock* MBB = BI->first; 352 CSRegSet save = BI->second; 353 354 if (save.empty()) 355 continue; 356 357 blockCSI.clear(); 358 for (CSRegSet::iterator RI = save.begin(), 359 RE = save.end(); RI != RE; ++RI) { 360 blockCSI.push_back(CSI[*RI]); 361 } 362 assert(blockCSI.size() > 0 && 363 "Could not collect callee saved register info"); 364 365 I = MBB->begin(); 366 367 // When shrink wrapping, use stack slot stores/loads. 368 for (unsigned i = 0, e = blockCSI.size(); i != e; ++i) { 369 // Add the callee-saved register as live-in. 370 // It's killed at the spill. 371 MBB->addLiveIn(blockCSI[i].getReg()); 372 373 // Insert the spill to the stack frame. 374 TII.storeRegToStackSlot(*MBB, I, blockCSI[i].getReg(), 375 true, 376 blockCSI[i].getFrameIdx(), 377 blockCSI[i].getRegClass()); 378 } 379 } 380 381 for (CSRegBlockMap::iterator BI = CSRRestore.begin(), 382 BE = CSRRestore.end(); BI != BE; ++BI) { 383 MachineBasicBlock* MBB = BI->first; 384 CSRegSet restore = BI->second; 385 386 if (restore.empty()) 387 continue; 388 389 blockCSI.clear(); 390 for (CSRegSet::iterator RI = restore.begin(), 391 RE = restore.end(); RI != RE; ++RI) { 392 blockCSI.push_back(CSI[*RI]); 393 } 394 assert(blockCSI.size() > 0 && 395 "Could not find callee saved register info"); 396 397 // If MBB is empty and needs restores, insert at the _beginning_. 398 if (MBB->empty()) { 399 I = MBB->begin(); 400 } else { 401 I = MBB->end(); 402 --I; 403 404 // Skip over all terminator instructions, which are part of the 405 // return sequence. 406 if (! I->getDesc().isTerminator()) { 407 ++I; 408 } else { 409 MachineBasicBlock::iterator I2 = I; 410 while (I2 != MBB->begin() && (--I2)->getDesc().isTerminator()) 411 I = I2; 412 } 413 } 414 415 bool AtStart = I == MBB->begin(); 416 MachineBasicBlock::iterator BeforeI = I; 417 if (!AtStart) 418 --BeforeI; 419 420 // Restore all registers immediately before the return and any 421 // terminators that preceed it. 422 for (unsigned i = 0, e = blockCSI.size(); i != e; ++i) { 423 TII.loadRegFromStackSlot(*MBB, I, blockCSI[i].getReg(), 424 blockCSI[i].getFrameIdx(), 425 blockCSI[i].getRegClass()); 426 assert(I != MBB->begin() && 427 "loadRegFromStackSlot didn't insert any code!"); 428 // Insert in reverse order. loadRegFromStackSlot can insert 429 // multiple instructions. 430 if (AtStart) 431 I = MBB->begin(); 432 else { 433 I = BeforeI; 434 ++I; 435 } 436 } 437 } 438} 439 440/// AdjustStackOffset - Helper function used to adjust the stack frame offset. 441static inline void 442AdjustStackOffset(MachineFrameInfo *FFI, int FrameIdx, 443 bool StackGrowsDown, int64_t &Offset, 444 unsigned &MaxAlign) { 445 // If the stack grows down, add the object size to find the lowest address. 446 if (StackGrowsDown) 447 Offset += FFI->getObjectSize(FrameIdx); 448 449 unsigned Align = FFI->getObjectAlignment(FrameIdx); 450 451 // If the alignment of this object is greater than that of the stack, then 452 // increase the stack alignment to match. 453 MaxAlign = std::max(MaxAlign, Align); 454 455 // Adjust to alignment boundary. 456 Offset = (Offset + Align - 1) / Align * Align; 457 458 if (StackGrowsDown) { 459 FFI->setObjectOffset(FrameIdx, -Offset); // Set the computed offset 460 } else { 461 FFI->setObjectOffset(FrameIdx, Offset); 462 Offset += FFI->getObjectSize(FrameIdx); 463 } 464} 465 466/// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the 467/// abstract stack objects. 468/// 469void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) { 470 const TargetFrameInfo &TFI = *Fn.getTarget().getFrameInfo(); 471 472 bool StackGrowsDown = 473 TFI.getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown; 474 475 // Loop over all of the stack objects, assigning sequential addresses... 476 MachineFrameInfo *FFI = Fn.getFrameInfo(); 477 478 unsigned MaxAlign = 1; 479 480 // Start at the beginning of the local area. 481 // The Offset is the distance from the stack top in the direction 482 // of stack growth -- so it's always nonnegative. 483 int LocalAreaOffset = TFI.getOffsetOfLocalArea(); 484 if (StackGrowsDown) 485 LocalAreaOffset = -LocalAreaOffset; 486 assert(LocalAreaOffset >= 0 487 && "Local area offset should be in direction of stack growth"); 488 int64_t Offset = LocalAreaOffset; 489 490 // If there are fixed sized objects that are preallocated in the local area, 491 // non-fixed objects can't be allocated right at the start of local area. 492 // We currently don't support filling in holes in between fixed sized 493 // objects, so we adjust 'Offset' to point to the end of last fixed sized 494 // preallocated object. 495 for (int i = FFI->getObjectIndexBegin(); i != 0; ++i) { 496 int64_t FixedOff; 497 if (StackGrowsDown) { 498 // The maximum distance from the stack pointer is at lower address of 499 // the object -- which is given by offset. For down growing stack 500 // the offset is negative, so we negate the offset to get the distance. 501 FixedOff = -FFI->getObjectOffset(i); 502 } else { 503 // The maximum distance from the start pointer is at the upper 504 // address of the object. 505 FixedOff = FFI->getObjectOffset(i) + FFI->getObjectSize(i); 506 } 507 if (FixedOff > Offset) Offset = FixedOff; 508 } 509 510 // First assign frame offsets to stack objects that are used to spill 511 // callee saved registers. 512 if (StackGrowsDown) { 513 for (unsigned i = MinCSFrameIndex; i <= MaxCSFrameIndex; ++i) { 514 // If stack grows down, we need to add size of find the lowest 515 // address of the object. 516 Offset += FFI->getObjectSize(i); 517 518 unsigned Align = FFI->getObjectAlignment(i); 519 // If the alignment of this object is greater than that of the stack, 520 // then increase the stack alignment to match. 521 MaxAlign = std::max(MaxAlign, Align); 522 // Adjust to alignment boundary 523 Offset = (Offset+Align-1)/Align*Align; 524 525 FFI->setObjectOffset(i, -Offset); // Set the computed offset 526 } 527 } else { 528 int MaxCSFI = MaxCSFrameIndex, MinCSFI = MinCSFrameIndex; 529 for (int i = MaxCSFI; i >= MinCSFI ; --i) { 530 unsigned Align = FFI->getObjectAlignment(i); 531 // If the alignment of this object is greater than that of the stack, 532 // then increase the stack alignment to match. 533 MaxAlign = std::max(MaxAlign, Align); 534 // Adjust to alignment boundary 535 Offset = (Offset+Align-1)/Align*Align; 536 537 FFI->setObjectOffset(i, Offset); 538 Offset += FFI->getObjectSize(i); 539 } 540 } 541 542 // Make sure the special register scavenging spill slot is closest to the 543 // frame pointer if a frame pointer is required. 544 const TargetRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo(); 545 if (RS && RegInfo->hasFP(Fn)) { 546 int SFI = RS->getScavengingFrameIndex(); 547 if (SFI >= 0) 548 AdjustStackOffset(FFI, SFI, StackGrowsDown, Offset, MaxAlign); 549 } 550 551 // Make sure that the stack protector comes before the local variables on the 552 // stack. 553 if (FFI->getStackProtectorIndex() >= 0) 554 AdjustStackOffset(FFI, FFI->getStackProtectorIndex(), StackGrowsDown, 555 Offset, MaxAlign); 556 557 // Then assign frame offsets to stack objects that are not used to spill 558 // callee saved registers. 559 for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) { 560 if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex) 561 continue; 562 if (RS && (int)i == RS->getScavengingFrameIndex()) 563 continue; 564 if (FFI->isDeadObjectIndex(i)) 565 continue; 566 if (FFI->getStackProtectorIndex() == (int)i) 567 continue; 568 569 AdjustStackOffset(FFI, i, StackGrowsDown, Offset, MaxAlign); 570 } 571 572 // Make sure the special register scavenging spill slot is closest to the 573 // stack pointer. 574 if (RS && !RegInfo->hasFP(Fn)) { 575 int SFI = RS->getScavengingFrameIndex(); 576 if (SFI >= 0) 577 AdjustStackOffset(FFI, SFI, StackGrowsDown, Offset, MaxAlign); 578 } 579 580 if (!RegInfo->targetHandlesStackFrameRounding()) { 581 // If we have reserved argument space for call sites in the function 582 // immediately on entry to the current function, count it as part of the 583 // overall stack size. 584 if (FFI->hasCalls() && RegInfo->hasReservedCallFrame(Fn)) 585 Offset += FFI->getMaxCallFrameSize(); 586 587 // Round up the size to a multiple of the alignment. If the function has 588 // any calls or alloca's, align to the target's StackAlignment value to 589 // ensure that the callee's frame or the alloca data is suitably aligned; 590 // otherwise, for leaf functions, align to the TransientStackAlignment 591 // value. 592 unsigned StackAlign; 593 if (FFI->hasCalls() || FFI->hasVarSizedObjects() || 594 (RegInfo->needsStackRealignment(Fn) && FFI->getObjectIndexEnd() != 0)) 595 StackAlign = TFI.getStackAlignment(); 596 else 597 StackAlign = TFI.getTransientStackAlignment(); 598 // If the frame pointer is eliminated, all frame offsets will be relative 599 // to SP not FP; align to MaxAlign so this works. 600 StackAlign = std::max(StackAlign, MaxAlign); 601 unsigned AlignMask = StackAlign - 1; 602 Offset = (Offset + AlignMask) & ~uint64_t(AlignMask); 603 } 604 605 // Update frame info to pretend that this is part of the stack... 606 FFI->setStackSize(Offset - LocalAreaOffset); 607 608 // Remember the required stack alignment in case targets need it to perform 609 // dynamic stack alignment. 610 if (MaxAlign > FFI->getMaxAlignment()) 611 FFI->setMaxAlignment(MaxAlign); 612} 613 614 615/// insertPrologEpilogCode - Scan the function for modified callee saved 616/// registers, insert spill code for these callee saved registers, then add 617/// prolog and epilog code to the function. 618/// 619void PEI::insertPrologEpilogCode(MachineFunction &Fn) { 620 const TargetRegisterInfo *TRI = Fn.getTarget().getRegisterInfo(); 621 622 // Add prologue to the function... 623 TRI->emitPrologue(Fn); 624 625 // Add epilogue to restore the callee-save registers in each exiting block 626 for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) { 627 // If last instruction is a return instruction, add an epilogue 628 if (!I->empty() && I->back().getDesc().isReturn()) 629 TRI->emitEpilogue(Fn, *I); 630 } 631} 632 633 634/// replaceFrameIndices - Replace all MO_FrameIndex operands with physical 635/// register references and actual offsets. 636/// 637void PEI::replaceFrameIndices(MachineFunction &Fn) { 638 if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do? 639 640 const TargetMachine &TM = Fn.getTarget(); 641 assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!"); 642 const TargetRegisterInfo &TRI = *TM.getRegisterInfo(); 643 const TargetFrameInfo *TFI = TM.getFrameInfo(); 644 bool StackGrowsDown = 645 TFI->getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown; 646 int FrameSetupOpcode = TRI.getCallFrameSetupOpcode(); 647 int FrameDestroyOpcode = TRI.getCallFrameDestroyOpcode(); 648 649 for (MachineFunction::iterator BB = Fn.begin(), 650 E = Fn.end(); BB != E; ++BB) { 651 int SPAdj = 0; // SP offset due to call frame setup / destroy. 652 if (RS && !FrameIndexVirtualScavenging) RS->enterBasicBlock(BB); 653 654 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) { 655 656 if (I->getOpcode() == FrameSetupOpcode || 657 I->getOpcode() == FrameDestroyOpcode) { 658 // Remember how much SP has been adjusted to create the call 659 // frame. 660 int Size = I->getOperand(0).getImm(); 661 662 if ((!StackGrowsDown && I->getOpcode() == FrameSetupOpcode) || 663 (StackGrowsDown && I->getOpcode() == FrameDestroyOpcode)) 664 Size = -Size; 665 666 SPAdj += Size; 667 668 MachineBasicBlock::iterator PrevI = BB->end(); 669 if (I != BB->begin()) PrevI = prior(I); 670 TRI.eliminateCallFramePseudoInstr(Fn, *BB, I); 671 672 // Visit the instructions created by eliminateCallFramePseudoInstr(). 673 if (PrevI == BB->end()) 674 I = BB->begin(); // The replaced instr was the first in the block. 675 else 676 I = next(PrevI); 677 continue; 678 } 679 680 MachineInstr *MI = I; 681 bool DoIncr = true; 682 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) 683 if (MI->getOperand(i).isFI()) { 684 // Some instructions (e.g. inline asm instructions) can have 685 // multiple frame indices and/or cause eliminateFrameIndex 686 // to insert more than one instruction. We need the register 687 // scavenger to go through all of these instructions so that 688 // it can update its register information. We keep the 689 // iterator at the point before insertion so that we can 690 // revisit them in full. 691 bool AtBeginning = (I == BB->begin()); 692 if (!AtBeginning) --I; 693 694 // If this instruction has a FrameIndex operand, we need to 695 // use that target machine register info object to eliminate 696 // it. 697 int Value; 698 unsigned VReg = 699 TRI.eliminateFrameIndex(MI, SPAdj, &Value, 700 FrameIndexVirtualScavenging ? NULL : RS); 701 if (VReg) { 702 assert (FrameIndexVirtualScavenging && 703 "Not scavenging, but virtual returned from " 704 "eliminateFrameIndex()!"); 705 FrameConstantRegMap[VReg] = FrameConstantEntry(Value, SPAdj); 706 } 707 708 // Reset the iterator if we were at the beginning of the BB. 709 if (AtBeginning) { 710 I = BB->begin(); 711 DoIncr = false; 712 } 713 714 MI = 0; 715 break; 716 } 717 718 if (DoIncr && I != BB->end()) ++I; 719 720 // Update register states. 721 if (RS && !FrameIndexVirtualScavenging && MI) RS->forward(MI); 722 } 723 724 assert(SPAdj == 0 && "Unbalanced call frame setup / destroy pairs?"); 725 } 726} 727 728/// findLastUseReg - find the killing use of the specified register within 729/// the instruciton range. Return the operand number of the kill in Operand. 730static MachineBasicBlock::iterator 731findLastUseReg(MachineBasicBlock::iterator I, MachineBasicBlock::iterator ME, 732 unsigned Reg, unsigned *Operand) { 733 // Scan forward to find the last use of this virtual register 734 for (++I; I != ME; ++I) { 735 MachineInstr *MI = I; 736 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) 737 if (MI->getOperand(i).isReg()) { 738 unsigned OpReg = MI->getOperand(i).getReg(); 739 if (OpReg == 0 || !TargetRegisterInfo::isVirtualRegister(OpReg)) 740 continue; 741 assert (OpReg == Reg 742 && "overlapping use of scavenged index register!"); 743 // If this is the killing use, we're done 744 if (MI->getOperand(i).isKill()) { 745 if (Operand) 746 *Operand = i; 747 return I; 748 } 749 } 750 } 751 // If we hit the end of the basic block, there was no kill of 752 // the virtual register, which is wrong. 753 assert (0 && "scavenged index register never killed!"); 754 return ME; 755} 756 757/// scavengeFrameVirtualRegs - Replace all frame index virtual registers 758/// with physical registers. Use the register scavenger to find an 759/// appropriate register to use. 760void PEI::scavengeFrameVirtualRegs(MachineFunction &Fn) { 761 // Run through the instructions and find any virtual registers. 762 for (MachineFunction::iterator BB = Fn.begin(), 763 E = Fn.end(); BB != E; ++BB) { 764 RS->enterBasicBlock(BB); 765 766 unsigned CurrentVirtReg = 0; 767 unsigned CurrentScratchReg = 0; 768 bool havePrevValue = false; 769 unsigned PrevScratchReg = 0; 770 int PrevValue = 0; 771 MachineInstr *PrevLastUseMI = NULL; 772 unsigned PrevLastUseOp = 0; 773 bool trackingCurrentValue = false; 774 int SPAdj = 0; 775 int Value = 0; 776 777 // The instruction stream may change in the loop, so check BB->end() 778 // directly. 779 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) { 780 MachineInstr *MI = I; 781 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) 782 if (MI->getOperand(i).isReg()) { 783 MachineOperand &MO = MI->getOperand(i); 784 unsigned Reg = MO.getReg(); 785 if (Reg == 0) 786 continue; 787 if (!TargetRegisterInfo::isVirtualRegister(Reg)) { 788 // If we have a previous scratch reg, check and see if anything 789 // here kills whatever value is in there. 790 if (Reg == PrevScratchReg) { 791 if (MO.isUse()) { 792 // Two-address operands implicitly kill 793 if (MO.isKill() || MI->isRegTiedToDefOperand(i)) { 794 havePrevValue = false; 795 PrevScratchReg = 0; 796 } 797 } else { 798 assert (MO.isDef()); 799 havePrevValue = false; 800 PrevScratchReg = 0; 801 } 802 } 803 continue; 804 } 805 806 // Have we already allocated a scratch register for this virtual? 807 if (Reg != CurrentVirtReg) { 808 // When we first encounter a new virtual register, it 809 // must be a definition. 810 assert(MI->getOperand(i).isDef() && 811 "frame index virtual missing def!"); 812 // We can't have nested virtual register live ranges because 813 // there's only a guarantee of one scavenged register at a time. 814 assert (CurrentVirtReg == 0 && 815 "overlapping frame index virtual registers!"); 816 817 // If the target gave us information about what's in the register, 818 // we can use that to re-use scratch regs. 819 DenseMap<unsigned, FrameConstantEntry>::iterator Entry = 820 FrameConstantRegMap.find(Reg); 821 trackingCurrentValue = Entry != FrameConstantRegMap.end(); 822 if (trackingCurrentValue) { 823 SPAdj = (*Entry).second.second; 824 Value = (*Entry).second.first; 825 } else 826 SPAdj = Value = 0; 827 828 // If the scratch register from the last allocation is still 829 // available, see if the value matches. If it does, just re-use it. 830 if (trackingCurrentValue && havePrevValue && PrevValue == Value) { 831 // FIXME: This assumes that the instructions in the live range 832 // for the virtual register are exclusively for the purpose 833 // of populating the value in the register. That's reasonable 834 // for these frame index registers, but it's still a very, very 835 // strong assumption. Perhaps this implies that the frame index 836 // elimination should be before register allocation, with 837 // conservative heuristics since we'll know less then, and 838 // the reuse calculations done directly when doing the code-gen? 839 840 // Find the last use of the new virtual register. Remove all 841 // instruction between here and there, and update the current 842 // instruction to reference the last use insn instead. 843 MachineBasicBlock::iterator LastUseMI = 844 findLastUseReg(I, BB->end(), Reg, &i); 845 // Remove all instructions up 'til the last use, since they're 846 // just calculating the value we already have. 847 BB->erase(I, LastUseMI); 848 MI = I = LastUseMI; 849 e = MI->getNumOperands(); 850 851 CurrentScratchReg = PrevScratchReg; 852 // Extend the live range of the register 853 PrevLastUseMI->getOperand(PrevLastUseOp).setIsKill(false); 854 RS->setUsed(CurrentScratchReg); 855 } else { 856 CurrentVirtReg = Reg; 857 const TargetRegisterClass *RC = Fn.getRegInfo().getRegClass(Reg); 858 CurrentScratchReg = RS->FindUnusedReg(RC); 859 if (CurrentScratchReg == 0) 860 // No register is "free". Scavenge a register. 861 CurrentScratchReg = RS->scavengeRegister(RC, I, SPAdj); 862 863 PrevValue = Value; 864 } 865 } 866 assert (CurrentScratchReg && "Missing scratch register!"); 867 MI->getOperand(i).setReg(CurrentScratchReg); 868 869 // If this is the last use of the register, stop tracking it. 870 if (MI->getOperand(i).isKill()) { 871 PrevScratchReg = CurrentScratchReg; 872 PrevLastUseMI = MI; 873 PrevLastUseOp = i; 874 CurrentScratchReg = CurrentVirtReg = 0; 875 havePrevValue = trackingCurrentValue; 876 // Re-scan the operands of this instruction to catch definitions 877 // of the scratch register we're using. This is to handle things 878 // like ldr "r2, [scratch]" where scratch is r2. 879 i = 0; 880 } 881 } 882 RS->forward(MI); 883 } 884 } 885} 886