Bug Summary

File:lib/Target/PowerPC/PPCCTRLoops.cpp
Location:line 307, column 38
Description:Value stored to 'Opcode' is never read

Annotated Source Code

1//===-- PPCCTRLoops.cpp - Identify and generate CTR loops -----------------===//
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 identifies loops where we can generate the PPC branch instructions
11// that decrement and test the count register (CTR) (bdnz and friends).
12//
13// The pattern that defines the induction variable can changed depending on
14// prior optimizations. For example, the IndVarSimplify phase run by 'opt'
15// normalizes induction variables, and the Loop Strength Reduction pass
16// run by 'llc' may also make changes to the induction variable.
17//
18// Criteria for CTR loops:
19// - Countable loops (w/ ind. var for a trip count)
20// - Try inner-most loops first
21// - No nested CTR loops.
22// - No function calls in loops.
23//
24//===----------------------------------------------------------------------===//
25
26#include "llvm/Transforms/Scalar.h"
27#include "PPC.h"
28#include "PPCTargetMachine.h"
29#include "llvm/ADT/STLExtras.h"
30#include "llvm/ADT/Statistic.h"
31#include "llvm/Analysis/LoopInfo.h"
32#include "llvm/Analysis/ScalarEvolutionExpander.h"
33#include "llvm/Analysis/TargetLibraryInfo.h"
34#include "llvm/IR/Constants.h"
35#include "llvm/IR/DerivedTypes.h"
36#include "llvm/IR/Dominators.h"
37#include "llvm/IR/InlineAsm.h"
38#include "llvm/IR/Instructions.h"
39#include "llvm/IR/IntrinsicInst.h"
40#include "llvm/IR/Module.h"
41#include "llvm/IR/ValueHandle.h"
42#include "llvm/PassSupport.h"
43#include "llvm/Support/CommandLine.h"
44#include "llvm/Support/Debug.h"
45#include "llvm/Support/raw_ostream.h"
46#include "llvm/Transforms/Utils/BasicBlockUtils.h"
47#include "llvm/Transforms/Utils/Local.h"
48#include "llvm/Transforms/Utils/LoopUtils.h"
49
50#ifndef NDEBUG
51#include "llvm/CodeGen/MachineDominators.h"
52#include "llvm/CodeGen/MachineFunction.h"
53#include "llvm/CodeGen/MachineFunctionPass.h"
54#include "llvm/CodeGen/MachineRegisterInfo.h"
55#endif
56
57#include <algorithm>
58#include <vector>
59
60using namespace llvm;
61
62#define DEBUG_TYPE"ctrloops" "ctrloops"
63
64#ifndef NDEBUG
65static cl::opt<int> CTRLoopLimit("ppc-max-ctrloop", cl::Hidden, cl::init(-1));
66#endif
67
68STATISTIC(NumCTRLoops, "Number of loops converted to CTR loops")static llvm::Statistic NumCTRLoops = { "ctrloops", "Number of loops converted to CTR loops"
, 0, 0 };
69
70namespace llvm {
71 void initializePPCCTRLoopsPass(PassRegistry&);
72#ifndef NDEBUG
73 void initializePPCCTRLoopsVerifyPass(PassRegistry&);
74#endif
75}
76
77namespace {
78 struct PPCCTRLoops : public FunctionPass {
79
80#ifndef NDEBUG
81 static int Counter;
82#endif
83
84 public:
85 static char ID;
86
87 PPCCTRLoops() : FunctionPass(ID), TM(nullptr) {
88 initializePPCCTRLoopsPass(*PassRegistry::getPassRegistry());
89 }
90 PPCCTRLoops(PPCTargetMachine &TM) : FunctionPass(ID), TM(&TM) {
91 initializePPCCTRLoopsPass(*PassRegistry::getPassRegistry());
92 }
93
94 bool runOnFunction(Function &F) override;
95
96 void getAnalysisUsage(AnalysisUsage &AU) const override {
97 AU.addRequired<LoopInfoWrapperPass>();
98 AU.addPreserved<LoopInfoWrapperPass>();
99 AU.addRequired<DominatorTreeWrapperPass>();
100 AU.addPreserved<DominatorTreeWrapperPass>();
101 AU.addRequired<ScalarEvolutionWrapperPass>();
102 }
103
104 private:
105 bool mightUseCTR(const Triple &TT, BasicBlock *BB);
106 bool convertToCTRLoop(Loop *L);
107
108 private:
109 PPCTargetMachine *TM;
110 LoopInfo *LI;
111 ScalarEvolution *SE;
112 const DataLayout *DL;
113 DominatorTree *DT;
114 const TargetLibraryInfo *LibInfo;
115 bool PreserveLCSSA;
116 };
117
118 char PPCCTRLoops::ID = 0;
119#ifndef NDEBUG
120 int PPCCTRLoops::Counter = 0;
121#endif
122
123#ifndef NDEBUG
124 struct PPCCTRLoopsVerify : public MachineFunctionPass {
125 public:
126 static char ID;
127
128 PPCCTRLoopsVerify() : MachineFunctionPass(ID) {
129 initializePPCCTRLoopsVerifyPass(*PassRegistry::getPassRegistry());
130 }
131
132 void getAnalysisUsage(AnalysisUsage &AU) const override {
133 AU.addRequired<MachineDominatorTree>();
134 MachineFunctionPass::getAnalysisUsage(AU);
135 }
136
137 bool runOnMachineFunction(MachineFunction &MF) override;
138
139 private:
140 MachineDominatorTree *MDT;
141 };
142
143 char PPCCTRLoopsVerify::ID = 0;
144#endif // NDEBUG
145} // end anonymous namespace
146
147INITIALIZE_PASS_BEGIN(PPCCTRLoops, "ppc-ctr-loops", "PowerPC CTR Loops",static void* initializePPCCTRLoopsPassOnce(PassRegistry &
Registry) {
148 false, false)static void* initializePPCCTRLoopsPassOnce(PassRegistry &
Registry) {
149INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)initializeDominatorTreeWrapperPassPass(Registry);
150INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)initializeLoopInfoWrapperPassPass(Registry);
151INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)initializeScalarEvolutionWrapperPassPass(Registry);
152INITIALIZE_PASS_END(PPCCTRLoops, "ppc-ctr-loops", "PowerPC CTR Loops",PassInfo *PI = new PassInfo("PowerPC CTR Loops", "ppc-ctr-loops"
, & PPCCTRLoops ::ID, PassInfo::NormalCtor_t(callDefaultCtor
< PPCCTRLoops >), false, false); Registry.registerPass(
*PI, true); return PI; } void llvm::initializePPCCTRLoopsPass
(PassRegistry &Registry) { static volatile sys::cas_flag initialized
= 0; sys::cas_flag old_val = sys::CompareAndSwap(&initialized
, 1, 0); if (old_val == 0) { initializePPCCTRLoopsPassOnce(Registry
); sys::MemoryFence(); ; ; initialized = 2; ; } else { sys::cas_flag
tmp = initialized; sys::MemoryFence(); while (tmp != 2) { tmp
= initialized; sys::MemoryFence(); } } ; }
153 false, false)PassInfo *PI = new PassInfo("PowerPC CTR Loops", "ppc-ctr-loops"
, & PPCCTRLoops ::ID, PassInfo::NormalCtor_t(callDefaultCtor
< PPCCTRLoops >), false, false); Registry.registerPass(
*PI, true); return PI; } void llvm::initializePPCCTRLoopsPass
(PassRegistry &Registry) { static volatile sys::cas_flag initialized
= 0; sys::cas_flag old_val = sys::CompareAndSwap(&initialized
, 1, 0); if (old_val == 0) { initializePPCCTRLoopsPassOnce(Registry
); sys::MemoryFence(); ; ; initialized = 2; ; } else { sys::cas_flag
tmp = initialized; sys::MemoryFence(); while (tmp != 2) { tmp
= initialized; sys::MemoryFence(); } } ; }
154
155FunctionPass *llvm::createPPCCTRLoops(PPCTargetMachine &TM) {
156 return new PPCCTRLoops(TM);
157}
158
159#ifndef NDEBUG
160INITIALIZE_PASS_BEGIN(PPCCTRLoopsVerify, "ppc-ctr-loops-verify",static void* initializePPCCTRLoopsVerifyPassOnce(PassRegistry
&Registry) {
161 "PowerPC CTR Loops Verify", false, false)static void* initializePPCCTRLoopsVerifyPassOnce(PassRegistry
&Registry) {
162INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)initializeMachineDominatorTreePass(Registry);
163INITIALIZE_PASS_END(PPCCTRLoopsVerify, "ppc-ctr-loops-verify",PassInfo *PI = new PassInfo("PowerPC CTR Loops Verify", "ppc-ctr-loops-verify"
, & PPCCTRLoopsVerify ::ID, PassInfo::NormalCtor_t(callDefaultCtor
< PPCCTRLoopsVerify >), false, false); Registry.registerPass
(*PI, true); return PI; } void llvm::initializePPCCTRLoopsVerifyPass
(PassRegistry &Registry) { static volatile sys::cas_flag initialized
= 0; sys::cas_flag old_val = sys::CompareAndSwap(&initialized
, 1, 0); if (old_val == 0) { initializePPCCTRLoopsVerifyPassOnce
(Registry); sys::MemoryFence(); ; ; initialized = 2; ; } else
{ sys::cas_flag tmp = initialized; sys::MemoryFence(); while
(tmp != 2) { tmp = initialized; sys::MemoryFence(); } } ; }
164 "PowerPC CTR Loops Verify", false, false)PassInfo *PI = new PassInfo("PowerPC CTR Loops Verify", "ppc-ctr-loops-verify"
, & PPCCTRLoopsVerify ::ID, PassInfo::NormalCtor_t(callDefaultCtor
< PPCCTRLoopsVerify >), false, false); Registry.registerPass
(*PI, true); return PI; } void llvm::initializePPCCTRLoopsVerifyPass
(PassRegistry &Registry) { static volatile sys::cas_flag initialized
= 0; sys::cas_flag old_val = sys::CompareAndSwap(&initialized
, 1, 0); if (old_val == 0) { initializePPCCTRLoopsVerifyPassOnce
(Registry); sys::MemoryFence(); ; ; initialized = 2; ; } else
{ sys::cas_flag tmp = initialized; sys::MemoryFence(); while
(tmp != 2) { tmp = initialized; sys::MemoryFence(); } } ; }
165
166FunctionPass *llvm::createPPCCTRLoopsVerify() {
167 return new PPCCTRLoopsVerify();
168}
169#endif // NDEBUG
170
171bool PPCCTRLoops::runOnFunction(Function &F) {
172 LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
173 SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
174 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
175 DL = &F.getParent()->getDataLayout();
176 auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>();
177 LibInfo = TLIP ? &TLIP->getTLI() : nullptr;
178 PreserveLCSSA = mustPreserveAnalysisID(LCSSAID);
179
180 bool MadeChange = false;
181
182 for (LoopInfo::iterator I = LI->begin(), E = LI->end();
183 I != E; ++I) {
184 Loop *L = *I;
185 if (!L->getParentLoop())
186 MadeChange |= convertToCTRLoop(L);
187 }
188
189 return MadeChange;
190}
191
192static bool isLargeIntegerTy(bool Is32Bit, Type *Ty) {
193 if (IntegerType *ITy = dyn_cast<IntegerType>(Ty))
194 return ITy->getBitWidth() > (Is32Bit ? 32U : 64U);
195
196 return false;
197}
198
199// Determining the address of a TLS variable results in a function call in
200// certain TLS models.
201static bool memAddrUsesCTR(const PPCTargetMachine *TM,
202 const Value *MemAddr) {
203 const auto *GV = dyn_cast<GlobalValue>(MemAddr);
204 if (!GV) {
205 // Recurse to check for constants that refer to TLS global variables.
206 if (const auto *CV = dyn_cast<Constant>(MemAddr))
207 for (const auto &CO : CV->operands())
208 if (memAddrUsesCTR(TM, CO))
209 return true;
210
211 return false;
212 }
213
214 if (!GV->isThreadLocal())
215 return false;
216 if (!TM)
217 return true;
218 TLSModel::Model Model = TM->getTLSModel(GV);
219 return Model == TLSModel::GeneralDynamic || Model == TLSModel::LocalDynamic;
220}
221
222bool PPCCTRLoops::mightUseCTR(const Triple &TT, BasicBlock *BB) {
223 for (BasicBlock::iterator J = BB->begin(), JE = BB->end();
224 J != JE; ++J) {
225 if (CallInst *CI = dyn_cast<CallInst>(J)) {
226 if (InlineAsm *IA = dyn_cast<InlineAsm>(CI->getCalledValue())) {
227 // Inline ASM is okay, unless it clobbers the ctr register.
228 InlineAsm::ConstraintInfoVector CIV = IA->ParseConstraints();
229 for (unsigned i = 0, ie = CIV.size(); i < ie; ++i) {
230 InlineAsm::ConstraintInfo &C = CIV[i];
231 if (C.Type != InlineAsm::isInput)
232 for (unsigned j = 0, je = C.Codes.size(); j < je; ++j)
233 if (StringRef(C.Codes[j]).equals_lower("{ctr}"))
234 return true;
235 }
236
237 continue;
238 }
239
240 if (!TM)
241 return true;
242 const TargetLowering *TLI =
243 TM->getSubtargetImpl(*BB->getParent())->getTargetLowering();
244
245 if (Function *F = CI->getCalledFunction()) {
246 // Most intrinsics don't become function calls, but some might.
247 // sin, cos, exp and log are always calls.
248 unsigned Opcode;
249 if (F->getIntrinsicID() != Intrinsic::not_intrinsic) {
250 switch (F->getIntrinsicID()) {
251 default: continue;
252 // If we have a call to ppc_is_decremented_ctr_nonzero, or ppc_mtctr
253 // we're definitely using CTR.
254 case Intrinsic::ppc_is_decremented_ctr_nonzero:
255 case Intrinsic::ppc_mtctr:
256 return true;
257
258// VisualStudio defines setjmp as _setjmp
259#if defined(_MSC_VER) && defined(setjmp) && \
260 !defined(setjmp_undefined_for_msvc)
261# pragma push_macro("setjmp")
262# undef setjmp
263# define setjmp_undefined_for_msvc
264#endif
265
266 case Intrinsic::setjmp:
267
268#if defined(_MSC_VER) && defined(setjmp_undefined_for_msvc)
269 // let's return it to _setjmp state
270# pragma pop_macro("setjmp")
271# undef setjmp_undefined_for_msvc
272#endif
273
274 case Intrinsic::longjmp:
275
276 // Exclude eh_sjlj_setjmp; we don't need to exclude eh_sjlj_longjmp
277 // because, although it does clobber the counter register, the
278 // control can't then return to inside the loop unless there is also
279 // an eh_sjlj_setjmp.
280 case Intrinsic::eh_sjlj_setjmp:
281
282 case Intrinsic::memcpy:
283 case Intrinsic::memmove:
284 case Intrinsic::memset:
285 case Intrinsic::powi:
286 case Intrinsic::log:
287 case Intrinsic::log2:
288 case Intrinsic::log10:
289 case Intrinsic::exp:
290 case Intrinsic::exp2:
291 case Intrinsic::pow:
292 case Intrinsic::sin:
293 case Intrinsic::cos:
294 return true;
295 case Intrinsic::copysign:
296 if (CI->getArgOperand(0)->getType()->getScalarType()->
297 isPPC_FP128Ty())
298 return true;
299 else
300 continue; // ISD::FCOPYSIGN is never a library call.
301 case Intrinsic::sqrt: Opcode = ISD::FSQRT; break;
302 case Intrinsic::floor: Opcode = ISD::FFLOOR; break;
303 case Intrinsic::ceil: Opcode = ISD::FCEIL; break;
304 case Intrinsic::trunc: Opcode = ISD::FTRUNC; break;
305 case Intrinsic::rint: Opcode = ISD::FRINT; break;
306 case Intrinsic::nearbyint: Opcode = ISD::FNEARBYINT; break;
307 case Intrinsic::round: Opcode = ISD::FROUND; break;
Value stored to 'Opcode' is never read
308 }
309 }
310
311 // PowerPC does not use [US]DIVREM or other library calls for
312 // operations on regular types which are not otherwise library calls
313 // (i.e. soft float or atomics). If adapting for targets that do,
314 // additional care is required here.
315
316 LibFunc::Func Func;
317 if (!F->hasLocalLinkage() && F->hasName() && LibInfo &&
318 LibInfo->getLibFunc(F->getName(), Func) &&
319 LibInfo->hasOptimizedCodeGen(Func)) {
320 // Non-read-only functions are never treated as intrinsics.
321 if (!CI->onlyReadsMemory())
322 return true;
323
324 // Conversion happens only for FP calls.
325 if (!CI->getArgOperand(0)->getType()->isFloatingPointTy())
326 return true;
327
328 switch (Func) {
329 default: return true;
330 case LibFunc::copysign:
331 case LibFunc::copysignf:
332 continue; // ISD::FCOPYSIGN is never a library call.
333 case LibFunc::copysignl:
334 return true;
335 case LibFunc::fabs:
336 case LibFunc::fabsf:
337 case LibFunc::fabsl:
338 continue; // ISD::FABS is never a library call.
339 case LibFunc::sqrt:
340 case LibFunc::sqrtf:
341 case LibFunc::sqrtl:
342 Opcode = ISD::FSQRT; break;
343 case LibFunc::floor:
344 case LibFunc::floorf:
345 case LibFunc::floorl:
346 Opcode = ISD::FFLOOR; break;
347 case LibFunc::nearbyint:
348 case LibFunc::nearbyintf:
349 case LibFunc::nearbyintl:
350 Opcode = ISD::FNEARBYINT; break;
351 case LibFunc::ceil:
352 case LibFunc::ceilf:
353 case LibFunc::ceill:
354 Opcode = ISD::FCEIL; break;
355 case LibFunc::rint:
356 case LibFunc::rintf:
357 case LibFunc::rintl:
358 Opcode = ISD::FRINT; break;
359 case LibFunc::round:
360 case LibFunc::roundf:
361 case LibFunc::roundl:
362 Opcode = ISD::FROUND; break;
363 case LibFunc::trunc:
364 case LibFunc::truncf:
365 case LibFunc::truncl:
366 Opcode = ISD::FTRUNC; break;
367 }
368
369 auto &DL = CI->getModule()->getDataLayout();
370 MVT VTy = TLI->getSimpleValueType(DL, CI->getArgOperand(0)->getType(),
371 true);
372 if (VTy == MVT::Other)
373 return true;
374
375 if (TLI->isOperationLegalOrCustom(Opcode, VTy))
376 continue;
377 else if (VTy.isVector() &&
378 TLI->isOperationLegalOrCustom(Opcode, VTy.getScalarType()))
379 continue;
380
381 return true;
382 }
383 }
384
385 return true;
386 } else if (isa<BinaryOperator>(J) &&
387 J->getType()->getScalarType()->isPPC_FP128Ty()) {
388 // Most operations on ppc_f128 values become calls.
389 return true;
390 } else if (isa<UIToFPInst>(J) || isa<SIToFPInst>(J) ||
391 isa<FPToUIInst>(J) || isa<FPToSIInst>(J)) {
392 CastInst *CI = cast<CastInst>(J);
393 if (CI->getSrcTy()->getScalarType()->isPPC_FP128Ty() ||
394 CI->getDestTy()->getScalarType()->isPPC_FP128Ty() ||
395 isLargeIntegerTy(TT.isArch32Bit(), CI->getSrcTy()->getScalarType()) ||
396 isLargeIntegerTy(TT.isArch32Bit(), CI->getDestTy()->getScalarType()))
397 return true;
398 } else if (isLargeIntegerTy(TT.isArch32Bit(),
399 J->getType()->getScalarType()) &&
400 (J->getOpcode() == Instruction::UDiv ||
401 J->getOpcode() == Instruction::SDiv ||
402 J->getOpcode() == Instruction::URem ||
403 J->getOpcode() == Instruction::SRem)) {
404 return true;
405 } else if (TT.isArch32Bit() &&
406 isLargeIntegerTy(false, J->getType()->getScalarType()) &&
407 (J->getOpcode() == Instruction::Shl ||
408 J->getOpcode() == Instruction::AShr ||
409 J->getOpcode() == Instruction::LShr)) {
410 // Only on PPC32, for 128-bit integers (specifically not 64-bit
411 // integers), these might be runtime calls.
412 return true;
413 } else if (isa<IndirectBrInst>(J) || isa<InvokeInst>(J)) {
414 // On PowerPC, indirect jumps use the counter register.
415 return true;
416 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(J)) {
417 if (!TM)
418 return true;
419 const TargetLowering *TLI =
420 TM->getSubtargetImpl(*BB->getParent())->getTargetLowering();
421
422 if (SI->getNumCases() + 1 >= (unsigned)TLI->getMinimumJumpTableEntries())
423 return true;
424 }
425 for (Value *Operand : J->operands())
426 if (memAddrUsesCTR(TM, Operand))
427 return true;
428 }
429
430 return false;
431}
432
433bool PPCCTRLoops::convertToCTRLoop(Loop *L) {
434 bool MadeChange = false;
435
436 const Triple TT =
437 Triple(L->getHeader()->getParent()->getParent()->getTargetTriple());
438 if (!TT.isArch32Bit() && !TT.isArch64Bit())
439 return MadeChange; // Unknown arch. type.
440
441 // Process nested loops first.
442 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I) {
443 MadeChange |= convertToCTRLoop(*I);
444 DEBUG(dbgs() << "Nested loop converted\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("ctrloops")) { dbgs() << "Nested loop converted\n"; } }
while (0);
445 }
446
447 // If a nested loop has been converted, then we can't convert this loop.
448 if (MadeChange)
449 return MadeChange;
450
451#ifndef NDEBUG
452 // Stop trying after reaching the limit (if any).
453 int Limit = CTRLoopLimit;
454 if (Limit >= 0) {
455 if (Counter >= CTRLoopLimit)
456 return false;
457 Counter++;
458 }
459#endif
460
461 // We don't want to spill/restore the counter register, and so we don't
462 // want to use the counter register if the loop contains calls.
463 for (Loop::block_iterator I = L->block_begin(), IE = L->block_end();
464 I != IE; ++I)
465 if (mightUseCTR(TT, *I))
466 return MadeChange;
467
468 SmallVector<BasicBlock*, 4> ExitingBlocks;
469 L->getExitingBlocks(ExitingBlocks);
470
471 BasicBlock *CountedExitBlock = nullptr;
472 const SCEV *ExitCount = nullptr;
473 BranchInst *CountedExitBranch = nullptr;
474 for (SmallVectorImpl<BasicBlock *>::iterator I = ExitingBlocks.begin(),
475 IE = ExitingBlocks.end(); I != IE; ++I) {
476 const SCEV *EC = SE->getExitCount(L, *I);
477 DEBUG(dbgs() << "Exit Count for " << *L << " from block " <<do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("ctrloops")) { dbgs() << "Exit Count for " << *L
<< " from block " << (*I)->getName() <<
": " << *EC << "\n"; } } while (0)
478 (*I)->getName() << ": " << *EC << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("ctrloops")) { dbgs() << "Exit Count for " << *L
<< " from block " << (*I)->getName() <<
": " << *EC << "\n"; } } while (0);
479 if (isa<SCEVCouldNotCompute>(EC))
480 continue;
481 if (const SCEVConstant *ConstEC = dyn_cast<SCEVConstant>(EC)) {
482 if (ConstEC->getValue()->isZero())
483 continue;
484 } else if (!SE->isLoopInvariant(EC, L))
485 continue;
486
487 if (SE->getTypeSizeInBits(EC->getType()) > (TT.isArch64Bit() ? 64 : 32))
488 continue;
489
490 // We now have a loop-invariant count of loop iterations (which is not the
491 // constant zero) for which we know that this loop will not exit via this
492 // exisiting block.
493
494 // We need to make sure that this block will run on every loop iteration.
495 // For this to be true, we must dominate all blocks with backedges. Such
496 // blocks are in-loop predecessors to the header block.
497 bool NotAlways = false;
498 for (pred_iterator PI = pred_begin(L->getHeader()),
499 PIE = pred_end(L->getHeader()); PI != PIE; ++PI) {
500 if (!L->contains(*PI))
501 continue;
502
503 if (!DT->dominates(*I, *PI)) {
504 NotAlways = true;
505 break;
506 }
507 }
508
509 if (NotAlways)
510 continue;
511
512 // Make sure this blocks ends with a conditional branch.
513 Instruction *TI = (*I)->getTerminator();
514 if (!TI)
515 continue;
516
517 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
518 if (!BI->isConditional())
519 continue;
520
521 CountedExitBranch = BI;
522 } else
523 continue;
524
525 // Note that this block may not be the loop latch block, even if the loop
526 // has a latch block.
527 CountedExitBlock = *I;
528 ExitCount = EC;
529 break;
530 }
531
532 if (!CountedExitBlock)
533 return MadeChange;
534
535 BasicBlock *Preheader = L->getLoopPreheader();
536
537 // If we don't have a preheader, then insert one. If we already have a
538 // preheader, then we can use it (except if the preheader contains a use of
539 // the CTR register because some such uses might be reordered by the
540 // selection DAG after the mtctr instruction).
541 if (!Preheader || mightUseCTR(TT, Preheader))
542 Preheader = InsertPreheaderForLoop(L, DT, LI, PreserveLCSSA);
543 if (!Preheader)
544 return MadeChange;
545
546 DEBUG(dbgs() << "Preheader for exit count: " << Preheader->getName() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("ctrloops")) { dbgs() << "Preheader for exit count: " <<
Preheader->getName() << "\n"; } } while (0);
547
548 // Insert the count into the preheader and replace the condition used by the
549 // selected branch.
550 MadeChange = true;
551
552 SCEVExpander SCEVE(*SE, Preheader->getModule()->getDataLayout(), "loopcnt");
553 LLVMContext &C = SE->getContext();
554 Type *CountType = TT.isArch64Bit() ? Type::getInt64Ty(C) :
555 Type::getInt32Ty(C);
556 if (!ExitCount->getType()->isPointerTy() &&
557 ExitCount->getType() != CountType)
558 ExitCount = SE->getZeroExtendExpr(ExitCount, CountType);
559 ExitCount = SE->getAddExpr(ExitCount, SE->getOne(CountType));
560 Value *ECValue =
561 SCEVE.expandCodeFor(ExitCount, CountType, Preheader->getTerminator());
562
563 IRBuilder<> CountBuilder(Preheader->getTerminator());
564 Module *M = Preheader->getParent()->getParent();
565 Value *MTCTRFunc = Intrinsic::getDeclaration(M, Intrinsic::ppc_mtctr,
566 CountType);
567 CountBuilder.CreateCall(MTCTRFunc, ECValue);
568
569 IRBuilder<> CondBuilder(CountedExitBranch);
570 Value *DecFunc =
571 Intrinsic::getDeclaration(M, Intrinsic::ppc_is_decremented_ctr_nonzero);
572 Value *NewCond = CondBuilder.CreateCall(DecFunc, {});
573 Value *OldCond = CountedExitBranch->getCondition();
574 CountedExitBranch->setCondition(NewCond);
575
576 // The false branch must exit the loop.
577 if (!L->contains(CountedExitBranch->getSuccessor(0)))
578 CountedExitBranch->swapSuccessors();
579
580 // The old condition may be dead now, and may have even created a dead PHI
581 // (the original induction variable).
582 RecursivelyDeleteTriviallyDeadInstructions(OldCond);
583 DeleteDeadPHIs(CountedExitBlock);
584
585 ++NumCTRLoops;
586 return MadeChange;
587}
588
589#ifndef NDEBUG
590static bool clobbersCTR(const MachineInstr *MI) {
591 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
592 const MachineOperand &MO = MI->getOperand(i);
593 if (MO.isReg()) {
594 if (MO.isDef() && (MO.getReg() == PPC::CTR || MO.getReg() == PPC::CTR8))
595 return true;
596 } else if (MO.isRegMask()) {
597 if (MO.clobbersPhysReg(PPC::CTR) || MO.clobbersPhysReg(PPC::CTR8))
598 return true;
599 }
600 }
601
602 return false;
603}
604
605static bool verifyCTRBranch(MachineBasicBlock *MBB,
606 MachineBasicBlock::iterator I) {
607 MachineBasicBlock::iterator BI = I;
608 SmallSet<MachineBasicBlock *, 16> Visited;
609 SmallVector<MachineBasicBlock *, 8> Preds;
610 bool CheckPreds;
611
612 if (I == MBB->begin()) {
613 Visited.insert(MBB);
614 goto queue_preds;
615 } else
616 --I;
617
618check_block:
619 Visited.insert(MBB);
620 if (I == MBB->end())
621 goto queue_preds;
622
623 CheckPreds = true;
624 for (MachineBasicBlock::iterator IE = MBB->begin();; --I) {
625 unsigned Opc = I->getOpcode();
626 if (Opc == PPC::MTCTRloop || Opc == PPC::MTCTR8loop) {
627 CheckPreds = false;
628 break;
629 }
630
631 if (I != BI && clobbersCTR(I)) {
632 DEBUG(dbgs() << "BB#" << MBB->getNumber() << " (" <<do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("ctrloops")) { dbgs() << "BB#" << MBB->getNumber
() << " (" << MBB->getFullName() << ") instruction "
<< *I << " clobbers CTR, invalidating " <<
"BB#" << BI->getParent()->getNumber() << " ("
<< BI->getParent()->getFullName() << ") instruction "
<< *BI << "\n"; } } while (0)
633 MBB->getFullName() << ") instruction " << *I <<do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("ctrloops")) { dbgs() << "BB#" << MBB->getNumber
() << " (" << MBB->getFullName() << ") instruction "
<< *I << " clobbers CTR, invalidating " <<
"BB#" << BI->getParent()->getNumber() << " ("
<< BI->getParent()->getFullName() << ") instruction "
<< *BI << "\n"; } } while (0)
634 " clobbers CTR, invalidating " << "BB#" <<do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("ctrloops")) { dbgs() << "BB#" << MBB->getNumber
() << " (" << MBB->getFullName() << ") instruction "
<< *I << " clobbers CTR, invalidating " <<
"BB#" << BI->getParent()->getNumber() << " ("
<< BI->getParent()->getFullName() << ") instruction "
<< *BI << "\n"; } } while (0)
635 BI->getParent()->getNumber() << " (" <<do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("ctrloops")) { dbgs() << "BB#" << MBB->getNumber
() << " (" << MBB->getFullName() << ") instruction "
<< *I << " clobbers CTR, invalidating " <<
"BB#" << BI->getParent()->getNumber() << " ("
<< BI->getParent()->getFullName() << ") instruction "
<< *BI << "\n"; } } while (0)
636 BI->getParent()->getFullName() << ") instruction " <<do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("ctrloops")) { dbgs() << "BB#" << MBB->getNumber
() << " (" << MBB->getFullName() << ") instruction "
<< *I << " clobbers CTR, invalidating " <<
"BB#" << BI->getParent()->getNumber() << " ("
<< BI->getParent()->getFullName() << ") instruction "
<< *BI << "\n"; } } while (0)
637 *BI << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("ctrloops")) { dbgs() << "BB#" << MBB->getNumber
() << " (" << MBB->getFullName() << ") instruction "
<< *I << " clobbers CTR, invalidating " <<
"BB#" << BI->getParent()->getNumber() << " ("
<< BI->getParent()->getFullName() << ") instruction "
<< *BI << "\n"; } } while (0);
638 return false;
639 }
640
641 if (I == IE)
642 break;
643 }
644
645 if (!CheckPreds && Preds.empty())
646 return true;
647
648 if (CheckPreds) {
649queue_preds:
650 if (MachineFunction::iterator(MBB) == MBB->getParent()->begin()) {
651 DEBUG(dbgs() << "Unable to find a MTCTR instruction for BB#" <<do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("ctrloops")) { dbgs() << "Unable to find a MTCTR instruction for BB#"
<< BI->getParent()->getNumber() << " (" <<
BI->getParent()->getFullName() << ") instruction "
<< *BI << "\n"; } } while (0)
652 BI->getParent()->getNumber() << " (" <<do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("ctrloops")) { dbgs() << "Unable to find a MTCTR instruction for BB#"
<< BI->getParent()->getNumber() << " (" <<
BI->getParent()->getFullName() << ") instruction "
<< *BI << "\n"; } } while (0)
653 BI->getParent()->getFullName() << ") instruction " <<do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("ctrloops")) { dbgs() << "Unable to find a MTCTR instruction for BB#"
<< BI->getParent()->getNumber() << " (" <<
BI->getParent()->getFullName() << ") instruction "
<< *BI << "\n"; } } while (0)
654 *BI << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("ctrloops")) { dbgs() << "Unable to find a MTCTR instruction for BB#"
<< BI->getParent()->getNumber() << " (" <<
BI->getParent()->getFullName() << ") instruction "
<< *BI << "\n"; } } while (0);
655 return false;
656 }
657
658 for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
659 PIE = MBB->pred_end(); PI != PIE; ++PI)
660 Preds.push_back(*PI);
661 }
662
663 do {
664 MBB = Preds.pop_back_val();
665 if (!Visited.count(MBB)) {
666 I = MBB->getLastNonDebugInstr();
667 goto check_block;
668 }
669 } while (!Preds.empty());
670
671 return true;
672}
673
674bool PPCCTRLoopsVerify::runOnMachineFunction(MachineFunction &MF) {
675 MDT = &getAnalysis<MachineDominatorTree>();
676
677 // Verify that all bdnz/bdz instructions are dominated by a loop mtctr before
678 // any other instructions that might clobber the ctr register.
679 for (MachineFunction::iterator I = MF.begin(), IE = MF.end();
680 I != IE; ++I) {
681 MachineBasicBlock *MBB = &*I;
682 if (!MDT->isReachableFromEntry(MBB))
683 continue;
684
685 for (MachineBasicBlock::iterator MII = MBB->getFirstTerminator(),
686 MIIE = MBB->end(); MII != MIIE; ++MII) {
687 unsigned Opc = MII->getOpcode();
688 if (Opc == PPC::BDNZ8 || Opc == PPC::BDNZ ||
689 Opc == PPC::BDZ8 || Opc == PPC::BDZ)
690 if (!verifyCTRBranch(MBB, MII))
691 llvm_unreachable("Invalid PPC CTR loop!")::llvm::llvm_unreachable_internal("Invalid PPC CTR loop!", "/tmp/buildd/llvm-toolchain-snapshot-3.8~svn257205/lib/Target/PowerPC/PPCCTRLoops.cpp"
, 691);
692 }
693 }
694
695 return false;
696}
697#endif // NDEBUG