WebAssemblyTargetMachine.cpp revision 296417 
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/// \brief This file defines the WebAssembly-specific subclass of TargetMachine.
12///
13//===----------------------------------------------------------------------===//
14
15#include "WebAssembly.h"
16#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
17#include "WebAssemblyTargetMachine.h"
18#include "WebAssemblyTargetObjectFile.h"
19#include "WebAssemblyTargetTransformInfo.h"
20#include "llvm/CodeGen/MachineFunctionPass.h"
21#include "llvm/CodeGen/Passes.h"
22#include "llvm/CodeGen/RegAllocRegistry.h"
23#include "llvm/IR/Function.h"
24#include "llvm/Support/CommandLine.h"
25#include "llvm/Support/TargetRegistry.h"
26#include "llvm/Target/TargetOptions.h"
27#include "llvm/Transforms/Scalar.h"
28using namespace llvm;
29
30#define DEBUG_TYPE "wasm"
31
32extern "C" void LLVMInitializeWebAssemblyTarget() {
33  // Register the target.
34  RegisterTargetMachine<WebAssemblyTargetMachine> X(TheWebAssemblyTarget32);
35  RegisterTargetMachine<WebAssemblyTargetMachine> Y(TheWebAssemblyTarget64);
36}
37
38//===----------------------------------------------------------------------===//
39// WebAssembly Lowering public interface.
40//===----------------------------------------------------------------------===//
41
42/// Create an WebAssembly architecture model.
43///
44WebAssemblyTargetMachine::WebAssemblyTargetMachine(
45    const Target &T, const Triple &TT, StringRef CPU, StringRef FS,
46    const TargetOptions &Options, Reloc::Model RM, CodeModel::Model CM,
47    CodeGenOpt::Level OL)
48    : LLVMTargetMachine(T,
49                        TT.isArch64Bit() ? "e-m:e-p:64:64-i64:64-n32:64-S128"
50                                         : "e-m:e-p:32:32-i64:64-n32:64-S128",
51                        TT, CPU, FS, Options, RM, CM, OL),
52      TLOF(make_unique<WebAssemblyTargetObjectFile>()) {
53  // WebAssembly type-checks expressions, but a noreturn function with a return
54  // type that doesn't match the context will cause a check failure. So we lower
55  // LLVM 'unreachable' to ISD::TRAP and then lower that to WebAssembly's
56  // 'unreachable' expression which is meant for that case.
57  this->Options.TrapUnreachable = true;
58
59  initAsmInfo();
60
61  // We need a reducible CFG, so disable some optimizations which tend to
62  // introduce irreducibility.
63  setRequiresStructuredCFG(true);
64}
65
66WebAssemblyTargetMachine::~WebAssemblyTargetMachine() {}
67
68const WebAssemblySubtarget *
69WebAssemblyTargetMachine::getSubtargetImpl(const Function &F) const {
70  Attribute CPUAttr = F.getFnAttribute("target-cpu");
71  Attribute FSAttr = F.getFnAttribute("target-features");
72
73  std::string CPU = !CPUAttr.hasAttribute(Attribute::None)
74                        ? CPUAttr.getValueAsString().str()
75                        : TargetCPU;
76  std::string FS = !FSAttr.hasAttribute(Attribute::None)
77                       ? FSAttr.getValueAsString().str()
78                       : TargetFS;
79
80  auto &I = SubtargetMap[CPU + FS];
81  if (!I) {
82    // This needs to be done before we create a new subtarget since any
83    // creation will depend on the TM and the code generation flags on the
84    // function that reside in TargetOptions.
85    resetTargetOptions(F);
86    I = llvm::make_unique<WebAssemblySubtarget>(TargetTriple, CPU, FS, *this);
87  }
88  return I.get();
89}
90
91namespace {
92/// WebAssembly Code Generator Pass Configuration Options.
93class WebAssemblyPassConfig final : public TargetPassConfig {
94public:
95  WebAssemblyPassConfig(WebAssemblyTargetMachine *TM, PassManagerBase &PM)
96      : TargetPassConfig(TM, PM) {}
97
98  WebAssemblyTargetMachine &getWebAssemblyTargetMachine() const {
99    return getTM<WebAssemblyTargetMachine>();
100  }
101
102  FunctionPass *createTargetRegisterAllocator(bool) override;
103
104  void addIRPasses() override;
105  bool addInstSelector() override;
106  bool addILPOpts() override;
107  void addPreRegAlloc() override;
108  void addPostRegAlloc() override;
109  void addPreEmitPass() override;
110};
111} // end anonymous namespace
112
113TargetIRAnalysis WebAssemblyTargetMachine::getTargetIRAnalysis() {
114  return TargetIRAnalysis([this](const Function &F) {
115    return TargetTransformInfo(WebAssemblyTTIImpl(this, F));
116  });
117}
118
119TargetPassConfig *
120WebAssemblyTargetMachine::createPassConfig(PassManagerBase &PM) {
121  return new WebAssemblyPassConfig(this, PM);
122}
123
124FunctionPass *WebAssemblyPassConfig::createTargetRegisterAllocator(bool) {
125  return nullptr; // No reg alloc
126}
127
128//===----------------------------------------------------------------------===//
129// The following functions are called from lib/CodeGen/Passes.cpp to modify
130// the CodeGen pass sequence.
131//===----------------------------------------------------------------------===//
132
133void WebAssemblyPassConfig::addIRPasses() {
134  if (TM->Options.ThreadModel == ThreadModel::Single)
135    // In "single" mode, atomics get lowered to non-atomics.
136    addPass(createLowerAtomicPass());
137  else
138    // Expand some atomic operations. WebAssemblyTargetLowering has hooks which
139    // control specifically what gets lowered.
140    addPass(createAtomicExpandPass(TM));
141
142  // Optimize "returned" function attributes.
143  addPass(createWebAssemblyOptimizeReturned());
144
145  TargetPassConfig::addIRPasses();
146}
147
148bool WebAssemblyPassConfig::addInstSelector() {
149  (void)TargetPassConfig::addInstSelector();
150  addPass(
151      createWebAssemblyISelDag(getWebAssemblyTargetMachine(), getOptLevel()));
152  // Run the argument-move pass immediately after the ScheduleDAG scheduler
153  // so that we can fix up the ARGUMENT instructions before anything else
154  // sees them in the wrong place.
155  addPass(createWebAssemblyArgumentMove());
156  return false;
157}
158
159bool WebAssemblyPassConfig::addILPOpts() {
160  (void)TargetPassConfig::addILPOpts();
161  return true;
162}
163
164void WebAssemblyPassConfig::addPreRegAlloc() {
165  TargetPassConfig::addPreRegAlloc();
166
167  // Prepare store instructions for register stackifying.
168  addPass(createWebAssemblyStoreResults());
169}
170
171void WebAssemblyPassConfig::addPostRegAlloc() {
172  // TODO: The following CodeGen passes don't currently support code containing
173  // virtual registers. Consider removing their restrictions and re-enabling
174  // them.
175  //
176  // We use our own PrologEpilogInserter which is very slightly modified to
177  // tolerate virtual registers.
178  disablePass(&PrologEpilogCodeInserterID);
179  // Fails with: should be run after register allocation.
180  disablePass(&MachineCopyPropagationID);
181
182  // Mark registers as representing wasm's expression stack.
183  addPass(createWebAssemblyRegStackify());
184
185  // Run the register coloring pass to reduce the total number of registers.
186  addPass(createWebAssemblyRegColoring());
187
188  TargetPassConfig::addPostRegAlloc();
189
190  // Run WebAssembly's version of the PrologEpilogInserter. Target-independent
191  // PEI runs after PostRegAlloc and after ShrinkWrap. Putting it here will run
192  // PEI before ShrinkWrap but otherwise in the same position in the order.
193  addPass(createWebAssemblyPEI());
194}
195
196void WebAssemblyPassConfig::addPreEmitPass() {
197  TargetPassConfig::addPreEmitPass();
198
199  // Put the CFG in structured form; insert BLOCK and LOOP markers.
200  addPass(createWebAssemblyCFGStackify());
201
202  // Lower br_unless into br_if.
203  addPass(createWebAssemblyLowerBrUnless());
204
205  // Create a mapping from LLVM CodeGen virtual registers to wasm registers.
206  addPass(createWebAssemblyRegNumbering());
207
208  // Perform the very last peephole optimizations on the code.
209  addPass(createWebAssemblyPeephole());
210}
211