WebAssemblyISelDAGToDAG.cpp revision 321369 
1//- WebAssemblyISelDAGToDAG.cpp - A dag to dag inst selector 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 an instruction selector for the WebAssembly target.
12///
13//===----------------------------------------------------------------------===//
14
15#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
16#include "WebAssembly.h"
17#include "WebAssemblyTargetMachine.h"
18#include "llvm/CodeGen/SelectionDAGISel.h"
19#include "llvm/IR/Function.h" // To access function attributes.
20#include "llvm/Support/Debug.h"
21#include "llvm/Support/KnownBits.h"
22#include "llvm/Support/MathExtras.h"
23#include "llvm/Support/raw_ostream.h"
24using namespace llvm;
25
26#define DEBUG_TYPE "wasm-isel"
27
28//===--------------------------------------------------------------------===//
29/// WebAssembly-specific code to select WebAssembly machine instructions for
30/// SelectionDAG operations.
31///
32namespace {
33class WebAssemblyDAGToDAGISel final : public SelectionDAGISel {
34  /// Keep a pointer to the WebAssemblySubtarget around so that we can make the
35  /// right decision when generating code for different targets.
36  const WebAssemblySubtarget *Subtarget;
37
38  bool ForCodeSize;
39
40public:
41  WebAssemblyDAGToDAGISel(WebAssemblyTargetMachine &tm,
42                          CodeGenOpt::Level OptLevel)
43      : SelectionDAGISel(tm, OptLevel), Subtarget(nullptr), ForCodeSize(false) {
44  }
45
46  StringRef getPassName() const override {
47    return "WebAssembly Instruction Selection";
48  }
49
50  bool runOnMachineFunction(MachineFunction &MF) override {
51    ForCodeSize =
52        MF.getFunction()->hasFnAttribute(Attribute::OptimizeForSize) ||
53        MF.getFunction()->hasFnAttribute(Attribute::MinSize);
54    Subtarget = &MF.getSubtarget<WebAssemblySubtarget>();
55    return SelectionDAGISel::runOnMachineFunction(MF);
56  }
57
58  void Select(SDNode *Node) override;
59
60  bool SelectInlineAsmMemoryOperand(const SDValue &Op, unsigned ConstraintID,
61                                    std::vector<SDValue> &OutOps) override;
62
63// Include the pieces autogenerated from the target description.
64#include "WebAssemblyGenDAGISel.inc"
65
66private:
67  // add select functions here...
68};
69} // end anonymous namespace
70
71void WebAssemblyDAGToDAGISel::Select(SDNode *Node) {
72  // Dump information about the Node being selected.
73  DEBUG(errs() << "Selecting: ");
74  DEBUG(Node->dump(CurDAG));
75  DEBUG(errs() << "\n");
76
77  // If we have a custom node, we already have selected!
78  if (Node->isMachineOpcode()) {
79    DEBUG(errs() << "== "; Node->dump(CurDAG); errs() << "\n");
80    Node->setNodeId(-1);
81    return;
82  }
83
84  // Few custom selection stuff.
85  EVT VT = Node->getValueType(0);
86
87  switch (Node->getOpcode()) {
88  default:
89    break;
90    // If we need WebAssembly-specific selection, it would go here.
91    (void)VT;
92  }
93
94  // Select the default instruction.
95  SelectCode(Node);
96}
97
98bool WebAssemblyDAGToDAGISel::SelectInlineAsmMemoryOperand(
99    const SDValue &Op, unsigned ConstraintID, std::vector<SDValue> &OutOps) {
100  switch (ConstraintID) {
101  case InlineAsm::Constraint_i:
102  case InlineAsm::Constraint_m:
103    // We just support simple memory operands that just have a single address
104    // operand and need no special handling.
105    OutOps.push_back(Op);
106    return false;
107  default:
108    break;
109  }
110
111  return true;
112}
113
114/// This pass converts a legalized DAG into a WebAssembly-specific DAG, ready
115/// for instruction scheduling.
116FunctionPass *llvm::createWebAssemblyISelDag(WebAssemblyTargetMachine &TM,
117                                             CodeGenOpt::Level OptLevel) {
118  return new WebAssemblyDAGToDAGISel(TM, OptLevel);
119}
120