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 /// 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"
24 using 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 ///
32 namespace {
33 class 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 
40 public:
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     LLVM_DEBUG(dbgs() << "********** ISelDAGToDAG **********\n"
52                          "********** Function: "
53                       << MF.getName() << '\n');
54 
55     ForCodeSize = MF.getFunction().hasFnAttribute(Attribute::OptimizeForSize) ||
56                   MF.getFunction().hasFnAttribute(Attribute::MinSize);
57     Subtarget = &MF.getSubtarget<WebAssemblySubtarget>();
58     return SelectionDAGISel::runOnMachineFunction(MF);
59   }
60 
61   void Select(SDNode *Node) override;
62 
63   bool SelectInlineAsmMemoryOperand(const SDValue &Op, unsigned ConstraintID,
64                                     std::vector<SDValue> &OutOps) override;
65 
66 // Include the pieces autogenerated from the target description.
67 #include "WebAssemblyGenDAGISel.inc"
68 
69 private:
70   // add select functions here...
71 };
72 } // end anonymous namespace
73 
74 void WebAssemblyDAGToDAGISel::Select(SDNode *Node) {
75   // If we have a custom node, we already have selected!
76   if (Node->isMachineOpcode()) {
77     LLVM_DEBUG(errs() << "== "; Node->dump(CurDAG); errs() << "\n");
78     Node->setNodeId(-1);
79     return;
80   }
81 
82   // Few custom selection stuff. If we need WebAssembly-specific selection,
83   // uncomment this block add corresponding case statements.
84   /*
85   switch (Node->getOpcode()) {
86   default:
87     break;
88   }
89   */
90 
91   // Select the default instruction.
92   SelectCode(Node);
93 }
94 
95 bool WebAssemblyDAGToDAGISel::SelectInlineAsmMemoryOperand(
96     const SDValue &Op, unsigned ConstraintID, std::vector<SDValue> &OutOps) {
97   switch (ConstraintID) {
98   case InlineAsm::Constraint_i:
99   case InlineAsm::Constraint_m:
100     // We just support simple memory operands that just have a single address
101     // operand and need no special handling.
102     OutOps.push_back(Op);
103     return false;
104   default:
105     break;
106   }
107 
108   return true;
109 }
110 
111 /// This pass converts a legalized DAG into a WebAssembly-specific DAG, ready
112 /// for instruction scheduling.
113 FunctionPass *llvm::createWebAssemblyISelDag(WebAssemblyTargetMachine &TM,
114                                              CodeGenOpt::Level OptLevel) {
115   return new WebAssemblyDAGToDAGISel(TM, OptLevel);
116 }
117