LLVM  8.0.0svn
WebAssemblyTargetMachine.cpp
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1 //===- WebAssemblyTargetMachine.cpp - Define TargetMachine for WebAssembly -==//
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 /// \file
11 /// This file defines the WebAssembly-specific subclass of TargetMachine.
12 ///
13 //===----------------------------------------------------------------------===//
14 
17 #include "WebAssembly.h"
21 #include "llvm/CodeGen/Passes.h"
24 #include "llvm/IR/Function.h"
27 #include "llvm/Transforms/Scalar.h"
28 #include "llvm/Transforms/Utils.h"
29 using namespace llvm;
30 
31 #define DEBUG_TYPE "wasm"
32 
33 // Emscripten's asm.js-style exception handling
35  "enable-emscripten-cxx-exceptions",
36  cl::desc("WebAssembly Emscripten-style exception handling"),
37  cl::init(false));
38 
39 // Emscripten's asm.js-style setjmp/longjmp handling
41  "enable-emscripten-sjlj",
42  cl::desc("WebAssembly Emscripten-style setjmp/longjmp handling"),
43  cl::init(false));
44 
46  // Register the target.
51 
52  // Register backend passes
53  auto &PR = *PassRegistry::getPassRegistry();
78 }
79 
80 //===----------------------------------------------------------------------===//
81 // WebAssembly Lowering public interface.
82 //===----------------------------------------------------------------------===//
83 
85  if (!RM.hasValue()) {
86  // Default to static relocation model. This should always be more optimial
87  // than PIC since the static linker can determine all global addresses and
88  // assume direct function calls.
89  return Reloc::Static;
90  }
91  return *RM;
92 }
93 
94 /// Create an WebAssembly architecture model.
95 ///
97  const Target &T, const Triple &TT, StringRef CPU, StringRef FS,
98  const TargetOptions &Options, Optional<Reloc::Model> RM,
100  : LLVMTargetMachine(T,
101  TT.isArch64Bit() ? "e-m:e-p:64:64-i64:64-n32:64-S128"
102  : "e-m:e-p:32:32-i64:64-n32:64-S128",
103  TT, CPU, FS, Options, getEffectiveRelocModel(RM),
104  getEffectiveCodeModel(CM, CodeModel::Large), OL),
105  TLOF(new WebAssemblyTargetObjectFile()) {
106  // WebAssembly type-checks instructions, but a noreturn function with a return
107  // type that doesn't match the context will cause a check failure. So we lower
108  // LLVM 'unreachable' to ISD::TRAP and then lower that to WebAssembly's
109  // 'unreachable' instructions which is meant for that case.
110  this->Options.TrapUnreachable = true;
111 
112  // WebAssembly treats each function as an independent unit. Force
113  // -ffunction-sections, effectively, so that we can emit them independently.
114  this->Options.FunctionSections = true;
115  this->Options.DataSections = true;
116  this->Options.UniqueSectionNames = true;
117 
118  initAsmInfo();
119 
120  // Note that we don't use setRequiresStructuredCFG(true). It disables
121  // optimizations than we're ok with, and want, such as critical edge
122  // splitting and tail merging.
123 }
124 
126 
127 const WebAssemblySubtarget *
129  Attribute CPUAttr = F.getFnAttribute("target-cpu");
130  Attribute FSAttr = F.getFnAttribute("target-features");
131 
132  std::string CPU = !CPUAttr.hasAttribute(Attribute::None)
133  ? CPUAttr.getValueAsString().str()
134  : TargetCPU;
135  std::string FS = !FSAttr.hasAttribute(Attribute::None)
136  ? FSAttr.getValueAsString().str()
137  : TargetFS;
138 
139  auto &I = SubtargetMap[CPU + FS];
140  if (!I) {
141  // This needs to be done before we create a new subtarget since any
142  // creation will depend on the TM and the code generation flags on the
143  // function that reside in TargetOptions.
145  I = llvm::make_unique<WebAssemblySubtarget>(TargetTriple, CPU, FS, *this);
146  }
147  return I.get();
148 }
149 
150 namespace {
151 class StripThreadLocal final : public ModulePass {
152  // The default thread model for wasm is single, where thread-local variables
153  // are identical to regular globals and should be treated the same. So this
154  // pass just converts all GlobalVariables to NotThreadLocal
155  static char ID;
156 
157 public:
158  StripThreadLocal() : ModulePass(ID) {}
159  bool runOnModule(Module &M) override {
160  for (auto &GV : M.globals())
161  GV.setThreadLocalMode(GlobalValue::ThreadLocalMode::NotThreadLocal);
162  return true;
163  }
164 };
165 char StripThreadLocal::ID = 0;
166 
167 /// WebAssembly Code Generator Pass Configuration Options.
168 class WebAssemblyPassConfig final : public TargetPassConfig {
169 public:
170  WebAssemblyPassConfig(WebAssemblyTargetMachine &TM, PassManagerBase &PM)
171  : TargetPassConfig(TM, PM) {}
172 
173  WebAssemblyTargetMachine &getWebAssemblyTargetMachine() const {
174  return getTM<WebAssemblyTargetMachine>();
175  }
176 
177  FunctionPass *createTargetRegisterAllocator(bool) override;
178 
179  void addIRPasses() override;
180  bool addInstSelector() override;
181  void addPostRegAlloc() override;
182  bool addGCPasses() override { return false; }
183  void addPreEmitPass() override;
184 };
185 } // end anonymous namespace
186 
189  return TargetTransformInfo(WebAssemblyTTIImpl(this, F));
190 }
191 
194  return new WebAssemblyPassConfig(*this, PM);
195 }
196 
197 FunctionPass *WebAssemblyPassConfig::createTargetRegisterAllocator(bool) {
198  return nullptr; // No reg alloc
199 }
200 
201 //===----------------------------------------------------------------------===//
202 // The following functions are called from lib/CodeGen/Passes.cpp to modify
203 // the CodeGen pass sequence.
204 //===----------------------------------------------------------------------===//
205 
206 void WebAssemblyPassConfig::addIRPasses() {
207  if (TM->Options.ThreadModel == ThreadModel::Single) {
208  // In "single" mode, atomics get lowered to non-atomics.
209  addPass(createLowerAtomicPass());
210  addPass(new StripThreadLocal());
211  } else {
212  // Expand some atomic operations. WebAssemblyTargetLowering has hooks which
213  // control specifically what gets lowered.
214  addPass(createAtomicExpandPass());
215  }
216 
217  // Add signatures to prototype-less function declarations
219 
220  // Lower .llvm.global_dtors into .llvm_global_ctors with __cxa_atexit calls.
222 
223  // Fix function bitcasts, as WebAssembly requires caller and callee signatures
224  // to match.
226 
227  // Optimize "returned" function attributes.
228  if (getOptLevel() != CodeGenOpt::None)
230 
231  // If exception handling is not enabled and setjmp/longjmp handling is
232  // enabled, we lower invokes into calls and delete unreachable landingpad
233  // blocks. Lowering invokes when there is no EH support is done in
234  // TargetPassConfig::addPassesToHandleExceptions, but this runs after this
235  // function and SjLj handling expects all invokes to be lowered before.
236  if (!EnableEmException &&
237  TM->Options.ExceptionModel == ExceptionHandling::None) {
238  addPass(createLowerInvokePass());
239  // The lower invoke pass may create unreachable code. Remove it in order not
240  // to process dead blocks in setjmp/longjmp handling.
242  }
243 
244  // Handle exceptions and setjmp/longjmp if enabled.
247  EnableEmSjLj));
248 
250 }
251 
252 bool WebAssemblyPassConfig::addInstSelector() {
254  addPass(
255  createWebAssemblyISelDag(getWebAssemblyTargetMachine(), getOptLevel()));
256  // Run the argument-move pass immediately after the ScheduleDAG scheduler
257  // so that we can fix up the ARGUMENT instructions before anything else
258  // sees them in the wrong place.
260  // Set the p2align operands. This information is present during ISel, however
261  // it's inconvenient to collect. Collect it now, and update the immediate
262  // operands.
264  return false;
265 }
266 
267 void WebAssemblyPassConfig::addPostRegAlloc() {
268  // TODO: The following CodeGen passes don't currently support code containing
269  // virtual registers. Consider removing their restrictions and re-enabling
270  // them.
271 
272  // These functions all require the NoVRegs property.
273  disablePass(&MachineCopyPropagationID);
274  disablePass(&PostRAMachineSinkingID);
275  disablePass(&PostRASchedulerID);
276  disablePass(&FuncletLayoutID);
277  disablePass(&StackMapLivenessID);
278  disablePass(&LiveDebugValuesID);
279  disablePass(&PatchableFunctionID);
280  disablePass(&ShrinkWrapID);
281 
283 }
284 
285 void WebAssemblyPassConfig::addPreEmitPass() {
287 
288  // Restore __stack_pointer global after an exception is thrown.
290 
291  // Now that we have a prologue and epilogue and all frame indices are
292  // rewritten, eliminate SP and FP. This allows them to be stackified,
293  // colored, and numbered with the rest of the registers.
295 
296  // Rewrite pseudo call_indirect instructions as real instructions.
297  // This needs to run before register stackification, because we change the
298  // order of the arguments.
300 
301  if (getOptLevel() != CodeGenOpt::None) {
302  // LiveIntervals isn't commonly run this late. Re-establish preconditions.
304 
305  // Depend on LiveIntervals and perform some optimizations on it.
307 
308  // Prepare store instructions for register stackifying.
310 
311  // Mark registers as representing wasm's value stack. This is a key
312  // code-compression technique in WebAssembly. We run this pass (and
313  // StoreResults above) very late, so that it sees as much code as possible,
314  // including code emitted by PEI and expanded by late tail duplication.
315  addPass(createWebAssemblyRegStackify());
316 
317  // Run the register coloring pass to reduce the total number of registers.
318  // This runs after stackification so that it doesn't consider registers
319  // that become stackified.
320  addPass(createWebAssemblyRegColoring());
321  }
322 
323  // Eliminate multiple-entry loops. Do this before inserting explicit get_local
324  // and set_local operators because we create a new variable that we want
325  // converted into a local.
327 
328  // Insert explicit get_local and set_local operators.
330 
331  // Do various transformations for exception handling
333 
334  // Sort the blocks of the CFG into topological order, a prerequisite for
335  // BLOCK and LOOP markers.
336  addPass(createWebAssemblyCFGSort());
337 
338  // Insert BLOCK and LOOP markers.
339  addPass(createWebAssemblyCFGStackify());
340 
341  // Lower br_unless into br_if.
343 
344  // Perform the very last peephole optimizations on the code.
345  if (getOptLevel() != CodeGenOpt::None)
346  addPass(createWebAssemblyPeephole());
347 
348  // Create a mapping from LLVM CodeGen virtual registers to wasm registers.
350 }
static GCMetadataPrinterRegistry::Add< ErlangGCPrinter > X("erlang", "erlang-compatible garbage collector")
FunctionPass * createWebAssemblyLowerBrUnless()
CodeModel::Model getEffectiveCodeModel(Optional< CodeModel::Model > CM, CodeModel::Model Default)
Helper method for getting the code model, returning Default if CM does not have a value...
ModulePass * createWebAssemblyLowerEmscriptenEHSjLj(bool DoEH, bool DoSjLj)
static PassRegistry * getPassRegistry()
getPassRegistry - Access the global registry object, which is automatically initialized at applicatio...
LLVM_NODISCARD std::string str() const
str - Get the contents as an std::string.
Definition: StringRef.h:228
static cl::opt< bool > EnableEmSjLj("enable-emscripten-sjlj", cl::desc("WebAssembly Emscripten-style setjmp/longjmp handling"), cl::init(false))
This class represents lattice values for constants.
Definition: AllocatorList.h:24
FunctionPass * createWebAssemblyCFGSort()
void initializeWebAssemblyOptimizeLiveIntervalsPass(PassRegistry &)
virtual void addIRPasses()
Add common target configurable passes that perform LLVM IR to IR transforms following machine indepen...
FunctionPass * createWebAssemblyArgumentMove()
A Module instance is used to store all the information related to an LLVM module. ...
Definition: Module.h:64
Triple TargetTriple
Triple string, CPU name, and target feature strings the TargetMachine instance is created with...
Definition: TargetMachine.h:78
This file a TargetTransformInfo::Concept conforming object specific to the WebAssembly target machine...
unsigned DataSections
Emit data into separate sections.
char & FuncletLayoutID
This pass lays out funclets contiguously.
FunctionPass * createWebAssemblyPeephole()
void initializeWebAssemblyRegStackifyPass(PassRegistry &)
void initializeWebAssemblyArgumentMovePass(PassRegistry &)
F(f)
void initializeWebAssemblyFixIrreducibleControlFlowPass(PassRegistry &)
This file contains the entry points for global functions defined in the LLVM WebAssembly back-end...
virtual void addPreEmitPass()
This pass may be implemented by targets that want to run passes immediately before machine code is em...
static GCMetadataPrinterRegistry::Add< OcamlGCMetadataPrinter > Y("ocaml", "ocaml 3.10-compatible collector")
FunctionPass * createWebAssemblyRegStackify()
FunctionPass * createWebAssemblyOptimizeReturned()
void initializeWebAssemblyStoreResultsPass(PassRegistry &)
This file declares the WebAssembly-specific subclass of TargetLoweringObjectFile. ...
void resetTargetOptions(const Function &F) const
Reset the target options based on the function&#39;s attributes.
FunctionPass * createWebAssemblyRegNumbering()
FunctionPass * createWebAssemblyEHRestoreStackPointer()
FunctionPass * createLowerInvokePass()
Definition: LowerInvoke.cpp:86
void initializeWebAssemblyRegNumberingPass(PassRegistry &)
No attributes have been set.
Definition: Attributes.h:72
void initializeWebAssemblyExceptionInfoPass(PassRegistry &)
void initializeOptimizeReturnedPass(PassRegistry &)
FunctionPass * createWebAssemblyRegColoring()
Target-Independent Code Generator Pass Configuration Options.
This file declares the WebAssembly-specific subclass of TargetMachine.
RegisterTargetMachine - Helper template for registering a target machine implementation, for use in the target machine initialization function.
unsigned FunctionSections
Emit functions into separate sections.
FunctionPass * createUnreachableBlockEliminationPass()
createUnreachableBlockEliminationPass - The LLVM code generator does not work well with unreachable b...
unsigned UniqueSectionNames
ModulePass * createWebAssemblyAddMissingPrototypes()
void initializeWebAssemblyExplicitLocalsPass(PassRegistry &)
initializer< Ty > init(const Ty &Val)
Definition: CommandLine.h:419
bool hasAttribute(AttrKind Val) const
Return true if the attribute is present.
Definition: Attributes.cpp:202
CodeGenOpt::Level getOptLevel() const
Returns the optimization level: None, Less, Default, or Aggressive.
void initializeWebAssemblyPeepholePass(PassRegistry &)
FunctionPass * createWebAssemblyISelDag(WebAssemblyTargetMachine &TM, CodeGenOpt::Level OptLevel)
This pass converts a legalized DAG into a WebAssembly-specific DAG, ready for instruction scheduling...
static Reloc::Model getEffectiveRelocModel(Optional< Reloc::Model > RM)
FunctionPass * createWebAssemblyCallIndirectFixup()
ModulePass * createWebAssemblyLowerGlobalDtors()
char & PostRAMachineSinkingID
This pass perform post-ra machine sink for COPY instructions.
This file provides WebAssembly-specific target descriptions.
void initializeWebAssemblyCallIndirectFixupPass(PassRegistry &)
virtual bool addInstSelector()
addInstSelector - This method should install an instruction selector pass, which converts from LLVM c...
char & LiveDebugValuesID
LiveDebugValues pass.
This class describes a target machine that is implemented with the LLVM target-independent code gener...
void initializeWebAssemblyReplacePhysRegsPass(PassRegistry &)
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:285
FunctionPass * createWebAssemblySetP2AlignOperands()
void initializeWebAssemblyLowerEmscriptenEHSjLjPass(PassRegistry &)
char & MachineCopyPropagationID
MachineCopyPropagation - This pass performs copy propagation on machine instructions.
static cl::opt< bool > EnableEmException("enable-emscripten-cxx-exceptions", cl::desc("WebAssembly Emscripten-style exception handling"), cl::init(false))
void initializeWebAssemblyLateEHPreparePass(PassRegistry &)
Triple - Helper class for working with autoconf configuration names.
Definition: Triple.h:44
FunctionPass * createWebAssemblyStoreResults()
char & PostRASchedulerID
createPostRAScheduler - This pass performs post register allocation scheduling.
ModulePass * createWebAssemblyFixFunctionBitcasts()
This pass provides access to the codegen interfaces that are needed for IR-level transformations.
void initializeWebAssemblyEHRestoreStackPointerPass(PassRegistry &)
PassManagerBase - An abstract interface to allow code to add passes to a pass manager without having ...
char & StackMapLivenessID
StackMapLiveness - This pass analyses the register live-out set of stackmap/patchpoint intrinsics and...
TargetPassConfig * createPassConfig(PassManagerBase &PM) override
Create a pass configuration object to be used by addPassToEmitX methods for generating a pipeline of ...
Pass * createLowerAtomicPass()
void initializeWebAssemblyLowerBrUnlessPass(PassRegistry &)
FunctionPass * createWebAssemblyFixIrreducibleControlFlow()
Target - Wrapper for Target specific information.
virtual void addPostRegAlloc()
This method may be implemented by targets that want to run passes after register allocation pass pipe...
void initializeWebAssemblyCFGStackifyPass(PassRegistry &)
std::string TargetCPU
Definition: TargetMachine.h:79
char & PatchableFunctionID
This pass implements the "patchable-function" attribute.
bool hasValue() const
Definition: Optional.h:165
StringRef getValueAsString() const
Return the attribute&#39;s value as a string.
Definition: Attributes.cpp:195
FunctionPass * createWebAssemblyLateEHPrepare()
TargetTransformInfo getTargetTransformInfo(const Function &F) override
Get a TargetTransformInfo implementation for the target.
#define I(x, y, z)
Definition: MD5.cpp:58
ModulePass class - This class is used to implement unstructured interprocedural optimizations and ana...
Definition: Pass.h:225
WebAssemblyTargetMachine(const Target &T, const Triple &TT, StringRef CPU, StringRef FS, const TargetOptions &Options, Optional< Reloc::Model > RM, Optional< CodeModel::Model > CM, CodeGenOpt::Level OL, bool JIT)
Create an WebAssembly architecture model.
void LLVMInitializeWebAssemblyTarget()
void initializeWebAssemblyAddMissingPrototypesPass(PassRegistry &)
void initializeFixFunctionBitcastsPass(PassRegistry &)
std::string TargetFS
Definition: TargetMachine.h:80
FunctionPass * createWebAssemblyOptimizeLiveIntervals()
FunctionPass * createWebAssemblyCFGStackify()
void initializeWebAssemblyPrepareForLiveIntervalsPass(PassRegistry &)
void initializeWebAssemblySetP2AlignOperandsPass(PassRegistry &)
void initializeLowerGlobalDtorsPass(PassRegistry &)
FunctionPass * createWebAssemblyPrepareForLiveIntervals()
Attribute getFnAttribute(Attribute::AttrKind Kind) const
Return the attribute for the given attribute kind.
Definition: Function.h:331
iterator_range< global_iterator > globals()
Definition: Module.h:574
char & ShrinkWrapID
ShrinkWrap pass. Look for the best place to insert save and restore.
Definition: ShrinkWrap.cpp:250
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:49
unsigned TrapUnreachable
Emit target-specific trap instruction for &#39;unreachable&#39; IR instructions.
Target & getTheWebAssemblyTarget32()
const WebAssemblySubtarget * getSubtargetImpl(const Function &F) const override
Virtual method implemented by subclasses that returns a reference to that target&#39;s TargetSubtargetInf...
FunctionPass * createWebAssemblyReplacePhysRegs()
void initializeWebAssemblyCFGSortPass(PassRegistry &)
FunctionPass * createAtomicExpandPass()
Target & getTheWebAssemblyTarget64()
FunctionPass * createWebAssemblyExplicitLocals()
void initializeWebAssemblyRegColoringPass(PassRegistry &)