1 //===-- ARMSubtarget.cpp - ARM Subtarget Information ----------------------===//
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 file implements the ARM specific subclass of TargetSubtargetInfo.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "ARM.h"
15 
16 #include "ARMCallLowering.h"
17 #include "ARMLegalizerInfo.h"
18 #include "ARMRegisterBankInfo.h"
19 #include "ARMSubtarget.h"
20 #include "ARMFrameLowering.h"
21 #include "ARMInstrInfo.h"
22 #include "ARMSubtarget.h"
23 #include "ARMTargetMachine.h"
24 #include "MCTargetDesc/ARMMCTargetDesc.h"
25 #include "Thumb1FrameLowering.h"
26 #include "Thumb1InstrInfo.h"
27 #include "Thumb2InstrInfo.h"
28 #include "llvm/ADT/StringRef.h"
29 #include "llvm/ADT/Triple.h"
30 #include "llvm/ADT/Twine.h"
31 #include "llvm/CodeGen/GlobalISel/InstructionSelect.h"
32 #include "llvm/CodeGen/MachineFunction.h"
33 #include "llvm/IR/Function.h"
34 #include "llvm/IR/GlobalValue.h"
35 #include "llvm/MC/MCAsmInfo.h"
36 #include "llvm/MC/MCTargetOptions.h"
37 #include "llvm/Support/CodeGen.h"
38 #include "llvm/Support/CommandLine.h"
39 #include "llvm/Support/TargetParser.h"
40 #include "llvm/Target/TargetOptions.h"
41 
42 using namespace llvm;
43 
44 #define DEBUG_TYPE "arm-subtarget"
45 
46 #define GET_SUBTARGETINFO_TARGET_DESC
47 #define GET_SUBTARGETINFO_CTOR
48 #include "ARMGenSubtargetInfo.inc"
49 
50 static cl::opt<bool>
51 UseFusedMulOps("arm-use-mulops",
52                cl::init(true), cl::Hidden);
53 
54 enum ITMode {
55   DefaultIT,
56   RestrictedIT,
57   NoRestrictedIT
58 };
59 
60 static cl::opt<ITMode>
61 IT(cl::desc("IT block support"), cl::Hidden, cl::init(DefaultIT),
62    cl::ZeroOrMore,
63    cl::values(clEnumValN(DefaultIT, "arm-default-it",
64                          "Generate IT block based on arch"),
65               clEnumValN(RestrictedIT, "arm-restrict-it",
66                          "Disallow deprecated IT based on ARMv8"),
67               clEnumValN(NoRestrictedIT, "arm-no-restrict-it",
68                          "Allow IT blocks based on ARMv7")));
69 
70 /// ForceFastISel - Use the fast-isel, even for subtargets where it is not
71 /// currently supported (for testing only).
72 static cl::opt<bool>
73 ForceFastISel("arm-force-fast-isel",
74                cl::init(false), cl::Hidden);
75 
76 /// initializeSubtargetDependencies - Initializes using a CPU and feature string
77 /// so that we can use initializer lists for subtarget initialization.
78 ARMSubtarget &ARMSubtarget::initializeSubtargetDependencies(StringRef CPU,
79                                                             StringRef FS) {
80   initializeEnvironment();
81   initSubtargetFeatures(CPU, FS);
82   return *this;
83 }
84 
85 ARMFrameLowering *ARMSubtarget::initializeFrameLowering(StringRef CPU,
86                                                         StringRef FS) {
87   ARMSubtarget &STI = initializeSubtargetDependencies(CPU, FS);
88   if (STI.isThumb1Only())
89     return (ARMFrameLowering *)new Thumb1FrameLowering(STI);
90 
91   return new ARMFrameLowering(STI);
92 }
93 
94 ARMSubtarget::ARMSubtarget(const Triple &TT, const std::string &CPU,
95                            const std::string &FS,
96                            const ARMBaseTargetMachine &TM, bool IsLittle)
97     : ARMGenSubtargetInfo(TT, CPU, FS), UseMulOps(UseFusedMulOps),
98       CPUString(CPU), IsLittle(IsLittle), TargetTriple(TT), Options(TM.Options),
99       TM(TM), FrameLowering(initializeFrameLowering(CPU, FS)),
100       // At this point initializeSubtargetDependencies has been called so
101       // we can query directly.
102       InstrInfo(isThumb1Only()
103                     ? (ARMBaseInstrInfo *)new Thumb1InstrInfo(*this)
104                     : !isThumb()
105                           ? (ARMBaseInstrInfo *)new ARMInstrInfo(*this)
106                           : (ARMBaseInstrInfo *)new Thumb2InstrInfo(*this)),
107       TLInfo(TM, *this) {
108 
109   CallLoweringInfo.reset(new ARMCallLowering(*getTargetLowering()));
110   Legalizer.reset(new ARMLegalizerInfo(*this));
111 
112   auto *RBI = new ARMRegisterBankInfo(*getRegisterInfo());
113 
114   // FIXME: At this point, we can't rely on Subtarget having RBI.
115   // It's awkward to mix passing RBI and the Subtarget; should we pass
116   // TII/TRI as well?
117   InstSelector.reset(createARMInstructionSelector(
118       *static_cast<const ARMBaseTargetMachine *>(&TM), *this, *RBI));
119 
120   RegBankInfo.reset(RBI);
121 }
122 
123 const CallLowering *ARMSubtarget::getCallLowering() const {
124   return CallLoweringInfo.get();
125 }
126 
127 const InstructionSelector *ARMSubtarget::getInstructionSelector() const {
128   return InstSelector.get();
129 }
130 
131 const LegalizerInfo *ARMSubtarget::getLegalizerInfo() const {
132   return Legalizer.get();
133 }
134 
135 const RegisterBankInfo *ARMSubtarget::getRegBankInfo() const {
136   return RegBankInfo.get();
137 }
138 
139 bool ARMSubtarget::isXRaySupported() const {
140   // We don't currently suppport Thumb, but Windows requires Thumb.
141   return hasV6Ops() && hasARMOps() && !isTargetWindows();
142 }
143 
144 void ARMSubtarget::initializeEnvironment() {
145   // MCAsmInfo isn't always present (e.g. in opt) so we can't initialize this
146   // directly from it, but we can try to make sure they're consistent when both
147   // available.
148   UseSjLjEH = (isTargetDarwin() && !isTargetWatchABI() &&
149                Options.ExceptionModel == ExceptionHandling::None) ||
150               Options.ExceptionModel == ExceptionHandling::SjLj;
151   assert((!TM.getMCAsmInfo() ||
152           (TM.getMCAsmInfo()->getExceptionHandlingType() ==
153            ExceptionHandling::SjLj) == UseSjLjEH) &&
154          "inconsistent sjlj choice between CodeGen and MC");
155 }
156 
157 void ARMSubtarget::initSubtargetFeatures(StringRef CPU, StringRef FS) {
158   if (CPUString.empty()) {
159     CPUString = "generic";
160 
161     if (isTargetDarwin()) {
162       StringRef ArchName = TargetTriple.getArchName();
163       ARM::ArchKind AK = ARM::parseArch(ArchName);
164       if (AK == ARM::ArchKind::ARMV7S)
165         // Default to the Swift CPU when targeting armv7s/thumbv7s.
166         CPUString = "swift";
167       else if (AK == ARM::ArchKind::ARMV7K)
168         // Default to the Cortex-a7 CPU when targeting armv7k/thumbv7k.
169         // ARMv7k does not use SjLj exception handling.
170         CPUString = "cortex-a7";
171     }
172   }
173 
174   // Insert the architecture feature derived from the target triple into the
175   // feature string. This is important for setting features that are implied
176   // based on the architecture version.
177   std::string ArchFS = ARM_MC::ParseARMTriple(TargetTriple, CPUString);
178   if (!FS.empty()) {
179     if (!ArchFS.empty())
180       ArchFS = (Twine(ArchFS) + "," + FS).str();
181     else
182       ArchFS = FS;
183   }
184   ParseSubtargetFeatures(CPUString, ArchFS);
185 
186   // FIXME: This used enable V6T2 support implicitly for Thumb2 mode.
187   // Assert this for now to make the change obvious.
188   assert(hasV6T2Ops() || !hasThumb2());
189 
190   // Execute only support requires movt support
191   if (genExecuteOnly())
192     assert(hasV8MBaselineOps() && !NoMovt && "Cannot generate execute-only code for this target");
193 
194   // Keep a pointer to static instruction cost data for the specified CPU.
195   SchedModel = getSchedModelForCPU(CPUString);
196 
197   // Initialize scheduling itinerary for the specified CPU.
198   InstrItins = getInstrItineraryForCPU(CPUString);
199 
200   // FIXME: this is invalid for WindowsCE
201   if (isTargetWindows())
202     NoARM = true;
203 
204   if (isAAPCS_ABI())
205     stackAlignment = 8;
206   if (isTargetNaCl() || isAAPCS16_ABI())
207     stackAlignment = 16;
208 
209   // FIXME: Completely disable sibcall for Thumb1 since ThumbRegisterInfo::
210   // emitEpilogue is not ready for them. Thumb tail calls also use t2B, as
211   // the Thumb1 16-bit unconditional branch doesn't have sufficient relocation
212   // support in the assembler and linker to be used. This would need to be
213   // fixed to fully support tail calls in Thumb1.
214   //
215   // For ARMv8-M, we /do/ implement tail calls.  Doing this is tricky for v8-M
216   // baseline, since the LDM/POP instruction on Thumb doesn't take LR.  This
217   // means if we need to reload LR, it takes extra instructions, which outweighs
218   // the value of the tail call; but here we don't know yet whether LR is going
219   // to be used. We take the optimistic approach of generating the tail call and
220   // perhaps taking a hit if we need to restore the LR.
221 
222   // Thumb1 PIC calls to external symbols use BX, so they can be tail calls,
223   // but we need to make sure there are enough registers; the only valid
224   // registers are the 4 used for parameters.  We don't currently do this
225   // case.
226 
227   SupportsTailCall = !isThumb() || hasV8MBaselineOps();
228 
229   if (isTargetMachO() && isTargetIOS() && getTargetTriple().isOSVersionLT(5, 0))
230     SupportsTailCall = false;
231 
232   switch (IT) {
233   case DefaultIT:
234     RestrictIT = hasV8Ops();
235     break;
236   case RestrictedIT:
237     RestrictIT = true;
238     break;
239   case NoRestrictedIT:
240     RestrictIT = false;
241     break;
242   }
243 
244   // NEON f32 ops are non-IEEE 754 compliant. Darwin is ok with it by default.
245   const FeatureBitset &Bits = getFeatureBits();
246   if ((Bits[ARM::ProcA5] || Bits[ARM::ProcA8]) && // Where this matters
247       (Options.UnsafeFPMath || isTargetDarwin()))
248     UseNEONForSinglePrecisionFP = true;
249 
250   if (isRWPI())
251     ReserveR9 = true;
252 
253   // FIXME: Teach TableGen to deal with these instead of doing it manually here.
254   switch (ARMProcFamily) {
255   case Others:
256   case CortexA5:
257     break;
258   case CortexA7:
259     LdStMultipleTiming = DoubleIssue;
260     break;
261   case CortexA8:
262     LdStMultipleTiming = DoubleIssue;
263     break;
264   case CortexA9:
265     LdStMultipleTiming = DoubleIssueCheckUnalignedAccess;
266     PreISelOperandLatencyAdjustment = 1;
267     break;
268   case CortexA12:
269     break;
270   case CortexA15:
271     MaxInterleaveFactor = 2;
272     PreISelOperandLatencyAdjustment = 1;
273     PartialUpdateClearance = 12;
274     break;
275   case CortexA17:
276   case CortexA32:
277   case CortexA35:
278   case CortexA53:
279   case CortexA55:
280   case CortexA57:
281   case CortexA72:
282   case CortexA73:
283   case CortexA75:
284   case CortexR4:
285   case CortexR4F:
286   case CortexR5:
287   case CortexR7:
288   case CortexM3:
289   case CortexR52:
290   case ExynosM1:
291   case Kryo:
292     break;
293   case Krait:
294     PreISelOperandLatencyAdjustment = 1;
295     break;
296   case Swift:
297     MaxInterleaveFactor = 2;
298     LdStMultipleTiming = SingleIssuePlusExtras;
299     PreISelOperandLatencyAdjustment = 1;
300     PartialUpdateClearance = 12;
301     break;
302   }
303 }
304 
305 bool ARMSubtarget::isAPCS_ABI() const {
306   assert(TM.TargetABI != ARMBaseTargetMachine::ARM_ABI_UNKNOWN);
307   return TM.TargetABI == ARMBaseTargetMachine::ARM_ABI_APCS;
308 }
309 bool ARMSubtarget::isAAPCS_ABI() const {
310   assert(TM.TargetABI != ARMBaseTargetMachine::ARM_ABI_UNKNOWN);
311   return TM.TargetABI == ARMBaseTargetMachine::ARM_ABI_AAPCS ||
312          TM.TargetABI == ARMBaseTargetMachine::ARM_ABI_AAPCS16;
313 }
314 bool ARMSubtarget::isAAPCS16_ABI() const {
315   assert(TM.TargetABI != ARMBaseTargetMachine::ARM_ABI_UNKNOWN);
316   return TM.TargetABI == ARMBaseTargetMachine::ARM_ABI_AAPCS16;
317 }
318 
319 bool ARMSubtarget::isROPI() const {
320   return TM.getRelocationModel() == Reloc::ROPI ||
321          TM.getRelocationModel() == Reloc::ROPI_RWPI;
322 }
323 bool ARMSubtarget::isRWPI() const {
324   return TM.getRelocationModel() == Reloc::RWPI ||
325          TM.getRelocationModel() == Reloc::ROPI_RWPI;
326 }
327 
328 bool ARMSubtarget::isGVIndirectSymbol(const GlobalValue *GV) const {
329   if (!TM.shouldAssumeDSOLocal(*GV->getParent(), GV))
330     return true;
331 
332   // 32 bit macho has no relocation for a-b if a is undefined, even if b is in
333   // the section that is being relocated. This means we have to use o load even
334   // for GVs that are known to be local to the dso.
335   if (isTargetMachO() && TM.isPositionIndependent() &&
336       (GV->isDeclarationForLinker() || GV->hasCommonLinkage()))
337     return true;
338 
339   return false;
340 }
341 
342 bool ARMSubtarget::isGVInGOT(const GlobalValue *GV) const {
343   return isTargetELF() && TM.isPositionIndependent() &&
344          !TM.shouldAssumeDSOLocal(*GV->getParent(), GV);
345 }
346 
347 unsigned ARMSubtarget::getMispredictionPenalty() const {
348   return SchedModel.MispredictPenalty;
349 }
350 
351 bool ARMSubtarget::enableMachineScheduler() const {
352   // Enable the MachineScheduler before register allocation for subtargets
353   // with the use-misched feature.
354   return useMachineScheduler();
355 }
356 
357 // This overrides the PostRAScheduler bit in the SchedModel for any CPU.
358 bool ARMSubtarget::enablePostRAScheduler() const {
359   if (disablePostRAScheduler())
360     return false;
361   // Don't reschedule potential IT blocks.
362   return !isThumb1Only();
363 }
364 
365 bool ARMSubtarget::enableAtomicExpand() const { return hasAnyDataBarrier(); }
366 
367 bool ARMSubtarget::useStride4VFPs(const MachineFunction &MF) const {
368   // For general targets, the prologue can grow when VFPs are allocated with
369   // stride 4 (more vpush instructions). But WatchOS uses a compact unwind
370   // format which it's more important to get right.
371   return isTargetWatchABI() || (isSwift() && !MF.getFunction().optForMinSize());
372 }
373 
374 bool ARMSubtarget::useMovt(const MachineFunction &MF) const {
375   // NOTE Windows on ARM needs to use mov.w/mov.t pairs to materialise 32-bit
376   // immediates as it is inherently position independent, and may be out of
377   // range otherwise.
378   return !NoMovt && hasV8MBaselineOps() &&
379          (isTargetWindows() || !MF.getFunction().optForMinSize() || genExecuteOnly());
380 }
381 
382 bool ARMSubtarget::useFastISel() const {
383   // Enable fast-isel for any target, for testing only.
384   if (ForceFastISel)
385     return true;
386 
387   // Limit fast-isel to the targets that are or have been tested.
388   if (!hasV6Ops())
389     return false;
390 
391   // Thumb2 support on iOS; ARM support on iOS, Linux and NaCl.
392   return TM.Options.EnableFastISel &&
393          ((isTargetMachO() && !isThumb1Only()) ||
394           (isTargetLinux() && !isThumb()) || (isTargetNaCl() && !isThumb()));
395 }
396