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 "WebAssembly.h"
16 #include "MCTargetDesc/WebAssemblyMCTargetDesc.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/MathExtras.h"
22 #include "llvm/Support/raw_ostream.h"
23 using namespace llvm;
24 
25 #define DEBUG_TYPE "wasm-isel"
26 
27 //===--------------------------------------------------------------------===//
28 /// WebAssembly-specific code to select WebAssembly machine instructions for
29 /// SelectionDAG operations.
30 ///
31 namespace {
32 class WebAssemblyDAGToDAGISel final : public SelectionDAGISel {
33   /// Keep a pointer to the WebAssemblySubtarget around so that we can make the
34   /// right decision when generating code for different targets.
35   const WebAssemblySubtarget *Subtarget;
36 
37   bool ForCodeSize;
38 
39 public:
40   WebAssemblyDAGToDAGISel(WebAssemblyTargetMachine &tm,
41                           CodeGenOpt::Level OptLevel)
42       : SelectionDAGISel(tm, OptLevel), Subtarget(nullptr), ForCodeSize(false) {
43   }
44 
45   const char *getPassName() const override {
46     return "WebAssembly Instruction Selection";
47   }
48 
49   bool runOnMachineFunction(MachineFunction &MF) override {
50     ForCodeSize =
51         MF.getFunction()->hasFnAttribute(Attribute::OptimizeForSize) ||
52         MF.getFunction()->hasFnAttribute(Attribute::MinSize);
53     Subtarget = &MF.getSubtarget<WebAssemblySubtarget>();
54     return SelectionDAGISel::runOnMachineFunction(MF);
55   }
56 
57   SDNode *Select(SDNode *Node) override;
58 
59 // Include the pieces autogenerated from the target description.
60 #include "WebAssemblyGenDAGISel.inc"
61 
62 private:
63   // add select functions here...
64 };
65 } // end anonymous namespace
66 
67 SDNode *WebAssemblyDAGToDAGISel::Select(SDNode *Node) {
68   // Dump information about the Node being selected.
69   DEBUG(errs() << "Selecting: ");
70   DEBUG(Node->dump(CurDAG));
71   DEBUG(errs() << "\n");
72 
73   // If we have a custom node, we already have selected!
74   if (Node->isMachineOpcode()) {
75     DEBUG(errs() << "== "; Node->dump(CurDAG); errs() << "\n");
76     Node->setNodeId(-1);
77     return nullptr;
78   }
79 
80   // Few custom selection stuff.
81   SDNode *ResNode = nullptr;
82   EVT VT = Node->getValueType(0);
83 
84   switch (Node->getOpcode()) {
85   default:
86     break;
87     // FIXME: Implement WebAssembly-specific selection.
88     (void)VT;
89   }
90 
91   // Select the default instruction.
92   ResNode = SelectCode(Node);
93 
94   DEBUG(errs() << "=> ");
95   if (ResNode == nullptr || ResNode == Node)
96     DEBUG(Node->dump(CurDAG));
97   else
98     DEBUG(ResNode->dump(CurDAG));
99   DEBUG(errs() << "\n");
100 
101   return ResNode;
102 }
103 
104 /// This pass converts a legalized DAG into a WebAssembly-specific DAG, ready
105 /// for instruction scheduling.
106 FunctionPass *llvm::createWebAssemblyISelDag(WebAssemblyTargetMachine &TM,
107                                              CodeGenOpt::Level OptLevel) {
108   return new WebAssemblyDAGToDAGISel(TM, OptLevel);
109 }
110