X86Subtarget.cpp revision 360784 
1//===-- X86Subtarget.cpp - X86 Subtarget Information ----------------------===//
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 file implements the X86 specific subclass of TargetSubtargetInfo.
10//
11//===----------------------------------------------------------------------===//
12
13#include "X86.h"
14
15#include "X86CallLowering.h"
16#include "X86LegalizerInfo.h"
17#include "X86MacroFusion.h"
18#include "X86RegisterBankInfo.h"
19#include "X86Subtarget.h"
20#include "MCTargetDesc/X86BaseInfo.h"
21#include "X86TargetMachine.h"
22#include "llvm/ADT/Triple.h"
23#include "llvm/CodeGen/GlobalISel/CallLowering.h"
24#include "llvm/CodeGen/GlobalISel/InstructionSelect.h"
25#include "llvm/IR/Attributes.h"
26#include "llvm/IR/ConstantRange.h"
27#include "llvm/IR/Function.h"
28#include "llvm/IR/GlobalValue.h"
29#include "llvm/Support/Casting.h"
30#include "llvm/Support/CodeGen.h"
31#include "llvm/Support/CommandLine.h"
32#include "llvm/Support/Debug.h"
33#include "llvm/Support/ErrorHandling.h"
34#include "llvm/Support/raw_ostream.h"
35#include "llvm/Target/TargetMachine.h"
36
37#if defined(_MSC_VER)
38#include <intrin.h>
39#endif
40
41using namespace llvm;
42
43#define DEBUG_TYPE "subtarget"
44
45#define GET_SUBTARGETINFO_TARGET_DESC
46#define GET_SUBTARGETINFO_CTOR
47#include "X86GenSubtargetInfo.inc"
48
49// Temporary option to control early if-conversion for x86 while adding machine
50// models.
51static cl::opt<bool>
52X86EarlyIfConv("x86-early-ifcvt", cl::Hidden,
53               cl::desc("Enable early if-conversion on X86"));
54
55
56/// Classify a blockaddress reference for the current subtarget according to how
57/// we should reference it in a non-pcrel context.
58unsigned char X86Subtarget::classifyBlockAddressReference() const {
59  return classifyLocalReference(nullptr);
60}
61
62/// Classify a global variable reference for the current subtarget according to
63/// how we should reference it in a non-pcrel context.
64unsigned char
65X86Subtarget::classifyGlobalReference(const GlobalValue *GV) const {
66  return classifyGlobalReference(GV, *GV->getParent());
67}
68
69unsigned char
70X86Subtarget::classifyLocalReference(const GlobalValue *GV) const {
71  // If we're not PIC, it's not very interesting.
72  if (!isPositionIndependent())
73    return X86II::MO_NO_FLAG;
74
75  if (is64Bit()) {
76    // 64-bit ELF PIC local references may use GOTOFF relocations.
77    if (isTargetELF()) {
78      switch (TM.getCodeModel()) {
79      // 64-bit small code model is simple: All rip-relative.
80      case CodeModel::Tiny:
81        llvm_unreachable("Tiny codesize model not supported on X86");
82      case CodeModel::Small:
83      case CodeModel::Kernel:
84        return X86II::MO_NO_FLAG;
85
86      // The large PIC code model uses GOTOFF.
87      case CodeModel::Large:
88        return X86II::MO_GOTOFF;
89
90      // Medium is a hybrid: RIP-rel for code, GOTOFF for DSO local data.
91      case CodeModel::Medium:
92        if (isa<Function>(GV))
93          return X86II::MO_NO_FLAG; // All code is RIP-relative
94        return X86II::MO_GOTOFF;    // Local symbols use GOTOFF.
95      }
96      llvm_unreachable("invalid code model");
97    }
98
99    // Otherwise, this is either a RIP-relative reference or a 64-bit movabsq,
100    // both of which use MO_NO_FLAG.
101    return X86II::MO_NO_FLAG;
102  }
103
104  // The COFF dynamic linker just patches the executable sections.
105  if (isTargetCOFF())
106    return X86II::MO_NO_FLAG;
107
108  if (isTargetDarwin()) {
109    // 32 bit macho has no relocation for a-b if a is undefined, even if
110    // b is in the section that is being relocated.
111    // This means we have to use o load even for GVs that are known to be
112    // local to the dso.
113    if (GV && (GV->isDeclarationForLinker() || GV->hasCommonLinkage()))
114      return X86II::MO_DARWIN_NONLAZY_PIC_BASE;
115
116    return X86II::MO_PIC_BASE_OFFSET;
117  }
118
119  return X86II::MO_GOTOFF;
120}
121
122unsigned char X86Subtarget::classifyGlobalReference(const GlobalValue *GV,
123                                                    const Module &M) const {
124  // The static large model never uses stubs.
125  if (TM.getCodeModel() == CodeModel::Large && !isPositionIndependent())
126    return X86II::MO_NO_FLAG;
127
128  // Absolute symbols can be referenced directly.
129  if (GV) {
130    if (Optional<ConstantRange> CR = GV->getAbsoluteSymbolRange()) {
131      // See if we can use the 8-bit immediate form. Note that some instructions
132      // will sign extend the immediate operand, so to be conservative we only
133      // accept the range [0,128).
134      if (CR->getUnsignedMax().ult(128))
135        return X86II::MO_ABS8;
136      else
137        return X86II::MO_NO_FLAG;
138    }
139  }
140
141  if (TM.shouldAssumeDSOLocal(M, GV))
142    return classifyLocalReference(GV);
143
144  if (isTargetCOFF()) {
145    if (GV->hasDLLImportStorageClass())
146      return X86II::MO_DLLIMPORT;
147    return X86II::MO_COFFSTUB;
148  }
149  // Some JIT users use *-win32-elf triples; these shouldn't use GOT tables.
150  if (isOSWindows())
151    return X86II::MO_NO_FLAG;
152
153  if (is64Bit()) {
154    // ELF supports a large, truly PIC code model with non-PC relative GOT
155    // references. Other object file formats do not. Use the no-flag, 64-bit
156    // reference for them.
157    if (TM.getCodeModel() == CodeModel::Large)
158      return isTargetELF() ? X86II::MO_GOT : X86II::MO_NO_FLAG;
159    return X86II::MO_GOTPCREL;
160  }
161
162  if (isTargetDarwin()) {
163    if (!isPositionIndependent())
164      return X86II::MO_DARWIN_NONLAZY;
165    return X86II::MO_DARWIN_NONLAZY_PIC_BASE;
166  }
167
168  return X86II::MO_GOT;
169}
170
171unsigned char
172X86Subtarget::classifyGlobalFunctionReference(const GlobalValue *GV) const {
173  return classifyGlobalFunctionReference(GV, *GV->getParent());
174}
175
176unsigned char
177X86Subtarget::classifyGlobalFunctionReference(const GlobalValue *GV,
178                                              const Module &M) const {
179  if (TM.shouldAssumeDSOLocal(M, GV))
180    return X86II::MO_NO_FLAG;
181
182  // Functions on COFF can be non-DSO local for two reasons:
183  // - They are marked dllimport
184  // - They are extern_weak, and a stub is needed
185  if (isTargetCOFF()) {
186    if (GV->hasDLLImportStorageClass())
187      return X86II::MO_DLLIMPORT;
188    return X86II::MO_COFFSTUB;
189  }
190
191  const Function *F = dyn_cast_or_null<Function>(GV);
192
193  if (isTargetELF()) {
194    if (is64Bit() && F && (CallingConv::X86_RegCall == F->getCallingConv()))
195      // According to psABI, PLT stub clobbers XMM8-XMM15.
196      // In Regcall calling convention those registers are used for passing
197      // parameters. Thus we need to prevent lazy binding in Regcall.
198      return X86II::MO_GOTPCREL;
199    // If PLT must be avoided then the call should be via GOTPCREL.
200    if (((F && F->hasFnAttribute(Attribute::NonLazyBind)) ||
201         (!F && M.getRtLibUseGOT())) &&
202        is64Bit())
203       return X86II::MO_GOTPCREL;
204    return X86II::MO_PLT;
205  }
206
207  if (is64Bit()) {
208    if (F && F->hasFnAttribute(Attribute::NonLazyBind))
209      // If the function is marked as non-lazy, generate an indirect call
210      // which loads from the GOT directly. This avoids runtime overhead
211      // at the cost of eager binding (and one extra byte of encoding).
212      return X86II::MO_GOTPCREL;
213    return X86II::MO_NO_FLAG;
214  }
215
216  return X86II::MO_NO_FLAG;
217}
218
219/// Return true if the subtarget allows calls to immediate address.
220bool X86Subtarget::isLegalToCallImmediateAddr() const {
221  // FIXME: I386 PE/COFF supports PC relative calls using IMAGE_REL_I386_REL32
222  // but WinCOFFObjectWriter::RecordRelocation cannot emit them.  Once it does,
223  // the following check for Win32 should be removed.
224  if (In64BitMode || isTargetWin32())
225    return false;
226  return isTargetELF() || TM.getRelocationModel() == Reloc::Static;
227}
228
229void X86Subtarget::initSubtargetFeatures(StringRef CPU, StringRef FS) {
230  std::string CPUName = CPU;
231  if (CPUName.empty())
232    CPUName = "generic";
233
234  std::string FullFS = FS;
235  if (In64BitMode) {
236    // SSE2 should default to enabled in 64-bit mode, but can be turned off
237    // explicitly.
238    if (!FullFS.empty())
239      FullFS = "+sse2," + FullFS;
240    else
241      FullFS = "+sse2";
242
243    // If no CPU was specified, enable 64bit feature to satisy later check.
244    if (CPUName == "generic") {
245      if (!FullFS.empty())
246        FullFS = "+64bit," + FullFS;
247      else
248        FullFS = "+64bit";
249    }
250  }
251
252  // LAHF/SAHF are always supported in non-64-bit mode.
253  if (!In64BitMode) {
254    if (!FullFS.empty())
255      FullFS = "+sahf," + FullFS;
256    else
257      FullFS = "+sahf";
258  }
259
260  // Parse features string and set the CPU.
261  ParseSubtargetFeatures(CPUName, FullFS);
262
263  // All CPUs that implement SSE4.2 or SSE4A support unaligned accesses of
264  // 16-bytes and under that are reasonably fast. These features were
265  // introduced with Intel's Nehalem/Silvermont and AMD's Family10h
266  // micro-architectures respectively.
267  if (hasSSE42() || hasSSE4A())
268    IsUAMem16Slow = false;
269
270  // It's important to keep the MCSubtargetInfo feature bits in sync with
271  // target data structure which is shared with MC code emitter, etc.
272  if (In64BitMode)
273    ToggleFeature(X86::Mode64Bit);
274  else if (In32BitMode)
275    ToggleFeature(X86::Mode32Bit);
276  else if (In16BitMode)
277    ToggleFeature(X86::Mode16Bit);
278  else
279    llvm_unreachable("Not 16-bit, 32-bit or 64-bit mode!");
280
281  LLVM_DEBUG(dbgs() << "Subtarget features: SSELevel " << X86SSELevel
282                    << ", 3DNowLevel " << X863DNowLevel << ", 64bit "
283                    << HasX86_64 << "\n");
284  if (In64BitMode && !HasX86_64)
285    report_fatal_error("64-bit code requested on a subtarget that doesn't "
286                       "support it!");
287
288  // Stack alignment is 16 bytes on Darwin, Linux, kFreeBSD and Solaris (both
289  // 32 and 64 bit) and for all 64-bit targets.
290  if (StackAlignOverride)
291    stackAlignment = *StackAlignOverride;
292  else if (isTargetDarwin() || isTargetLinux() || isTargetSolaris() ||
293           isTargetKFreeBSD() || In64BitMode)
294    stackAlignment = Align(16);
295
296  // Some CPUs have more overhead for gather. The specified overhead is relative
297  // to the Load operation. "2" is the number provided by Intel architects. This
298  // parameter is used for cost estimation of Gather Op and comparison with
299  // other alternatives.
300  // TODO: Remove the explicit hasAVX512()?, That would mean we would only
301  // enable gather with a -march.
302  if (hasAVX512() || (hasAVX2() && hasFastGather()))
303    GatherOverhead = 2;
304  if (hasAVX512())
305    ScatterOverhead = 2;
306
307  // Consume the vector width attribute or apply any target specific limit.
308  if (PreferVectorWidthOverride)
309    PreferVectorWidth = PreferVectorWidthOverride;
310  else if (Prefer128Bit)
311    PreferVectorWidth = 128;
312  else if (Prefer256Bit)
313    PreferVectorWidth = 256;
314}
315
316X86Subtarget &X86Subtarget::initializeSubtargetDependencies(StringRef CPU,
317                                                            StringRef FS) {
318  initSubtargetFeatures(CPU, FS);
319  return *this;
320}
321
322X86Subtarget::X86Subtarget(const Triple &TT, StringRef CPU, StringRef FS,
323                           const X86TargetMachine &TM,
324                           MaybeAlign StackAlignOverride,
325                           unsigned PreferVectorWidthOverride,
326                           unsigned RequiredVectorWidth)
327    : X86GenSubtargetInfo(TT, CPU, FS), PICStyle(PICStyles::Style::None),
328      TM(TM), TargetTriple(TT), StackAlignOverride(StackAlignOverride),
329      PreferVectorWidthOverride(PreferVectorWidthOverride),
330      RequiredVectorWidth(RequiredVectorWidth),
331      In64BitMode(TargetTriple.getArch() == Triple::x86_64),
332      In32BitMode(TargetTriple.getArch() == Triple::x86 &&
333                  TargetTriple.getEnvironment() != Triple::CODE16),
334      In16BitMode(TargetTriple.getArch() == Triple::x86 &&
335                  TargetTriple.getEnvironment() == Triple::CODE16),
336      InstrInfo(initializeSubtargetDependencies(CPU, FS)), TLInfo(TM, *this),
337      FrameLowering(*this, getStackAlignment()) {
338  // Determine the PICStyle based on the target selected.
339  if (!isPositionIndependent())
340    setPICStyle(PICStyles::Style::None);
341  else if (is64Bit())
342    setPICStyle(PICStyles::Style::RIPRel);
343  else if (isTargetCOFF())
344    setPICStyle(PICStyles::Style::None);
345  else if (isTargetDarwin())
346    setPICStyle(PICStyles::Style::StubPIC);
347  else if (isTargetELF())
348    setPICStyle(PICStyles::Style::GOT);
349
350  CallLoweringInfo.reset(new X86CallLowering(*getTargetLowering()));
351  Legalizer.reset(new X86LegalizerInfo(*this, TM));
352
353  auto *RBI = new X86RegisterBankInfo(*getRegisterInfo());
354  RegBankInfo.reset(RBI);
355  InstSelector.reset(createX86InstructionSelector(TM, *this, *RBI));
356}
357
358const CallLowering *X86Subtarget::getCallLowering() const {
359  return CallLoweringInfo.get();
360}
361
362InstructionSelector *X86Subtarget::getInstructionSelector() const {
363  return InstSelector.get();
364}
365
366const LegalizerInfo *X86Subtarget::getLegalizerInfo() const {
367  return Legalizer.get();
368}
369
370const RegisterBankInfo *X86Subtarget::getRegBankInfo() const {
371  return RegBankInfo.get();
372}
373
374bool X86Subtarget::enableEarlyIfConversion() const {
375  return hasCMov() && X86EarlyIfConv;
376}
377
378void X86Subtarget::getPostRAMutations(
379    std::vector<std::unique_ptr<ScheduleDAGMutation>> &Mutations) const {
380  Mutations.push_back(createX86MacroFusionDAGMutation());
381}
382