1 //- WebAssemblyISelDAGToDAG.cpp - A dag to dag inst selector for WebAssembly -//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 ///
9 /// \file
10 /// This file defines an instruction selector for the WebAssembly target.
11 ///
12 //===----------------------------------------------------------------------===//
13 
14 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
15 #include "WebAssembly.h"
16 #include "WebAssemblyTargetMachine.h"
17 #include "llvm/CodeGen/SelectionDAGISel.h"
18 #include "llvm/IR/Function.h" // To access function attributes.
19 #include "llvm/Support/Debug.h"
20 #include "llvm/Support/KnownBits.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   StringRef getPassName() const override {
46     return "WebAssembly Instruction Selection";
47   }
48 
49   bool runOnMachineFunction(MachineFunction &MF) override {
50     LLVM_DEBUG(dbgs() << "********** ISelDAGToDAG **********\n"
51                          "********** Function: "
52                       << MF.getName() << '\n');
53 
54     ForCodeSize = MF.getFunction().hasFnAttribute(Attribute::OptimizeForSize) ||
55                   MF.getFunction().hasFnAttribute(Attribute::MinSize);
56     Subtarget = &MF.getSubtarget<WebAssemblySubtarget>();
57     return SelectionDAGISel::runOnMachineFunction(MF);
58   }
59 
60   void Select(SDNode *Node) override;
61 
62   bool SelectInlineAsmMemoryOperand(const SDValue &Op, unsigned ConstraintID,
63                                     std::vector<SDValue> &OutOps) override;
64 
65 // Include the pieces autogenerated from the target description.
66 #include "WebAssemblyGenDAGISel.inc"
67 
68 private:
69   // add select functions here...
70 };
71 } // end anonymous namespace
72 
73 void WebAssemblyDAGToDAGISel::Select(SDNode *Node) {
74   // If we have a custom node, we already have selected!
75   if (Node->isMachineOpcode()) {
76     LLVM_DEBUG(errs() << "== "; Node->dump(CurDAG); errs() << "\n");
77     Node->setNodeId(-1);
78     return;
79   }
80 
81   // Few custom selection stuff. If we need WebAssembly-specific selection,
82   // uncomment this block add corresponding case statements.
83   /*
84   switch (Node->getOpcode()) {
85   default:
86     break;
87   }
88   */
89 
90   // Select the default instruction.
91   SelectCode(Node);
92 }
93 
94 bool WebAssemblyDAGToDAGISel::SelectInlineAsmMemoryOperand(
95     const SDValue &Op, unsigned ConstraintID, std::vector<SDValue> &OutOps) {
96   switch (ConstraintID) {
97   case InlineAsm::Constraint_i:
98   case InlineAsm::Constraint_m:
99     // We just support simple memory operands that just have a single address
100     // operand and need no special handling.
101     OutOps.push_back(Op);
102     return false;
103   default:
104     break;
105   }
106 
107   return true;
108 }
109 
110 /// This pass converts a legalized DAG into a WebAssembly-specific DAG, ready
111 /// for instruction scheduling.
112 FunctionPass *llvm::createWebAssemblyISelDag(WebAssemblyTargetMachine &TM,
113                                              CodeGenOpt::Level OptLevel) {
114   return new WebAssemblyDAGToDAGISel(TM, OptLevel);
115 }
116