1 //===-- WebAssemblyCallIndirectFixup.cpp - Fix call_indirects -------------===//
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 converts pseudo call_indirect instructions into real
12 /// call_indirects.
13 ///
14 /// The order of arguments for a call_indirect is the arguments to the function
15 /// call, followed by the function pointer. There's no natural way to express
16 /// a machineinstr with varargs followed by one more arg, so we express it as
17 /// the function pointer followed by varargs, then rewrite it here.
18 ///
19 /// We need to rewrite the order of the arguments on the machineinstrs
20 /// themselves so that register stackification knows the order they'll be
21 /// executed in.
22 ///
23 //===----------------------------------------------------------------------===//
24 
25 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h" // for WebAssembly::ARGUMENT_*
26 #include "WebAssembly.h"
27 #include "WebAssemblyMachineFunctionInfo.h"
28 #include "WebAssemblySubtarget.h"
29 #include "llvm/Analysis/AliasAnalysis.h"
30 #include "llvm/CodeGen/LiveIntervals.h"
31 #include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
32 #include "llvm/CodeGen/MachineDominators.h"
33 #include "llvm/CodeGen/MachineInstrBuilder.h"
34 #include "llvm/CodeGen/MachineRegisterInfo.h"
35 #include "llvm/CodeGen/Passes.h"
36 #include "llvm/Support/Debug.h"
37 #include "llvm/Support/raw_ostream.h"
38 using namespace llvm;
39 
40 #define DEBUG_TYPE "wasm-call-indirect-fixup"
41 
42 namespace {
43 class WebAssemblyCallIndirectFixup final : public MachineFunctionPass {
44   StringRef getPassName() const override {
45     return "WebAssembly CallIndirect Fixup";
46   }
47 
48   bool runOnMachineFunction(MachineFunction &MF) override;
49 
50 public:
51   static char ID; // Pass identification, replacement for typeid
52   WebAssemblyCallIndirectFixup() : MachineFunctionPass(ID) {}
53 };
54 } // end anonymous namespace
55 
56 char WebAssemblyCallIndirectFixup::ID = 0;
57 INITIALIZE_PASS(WebAssemblyCallIndirectFixup, DEBUG_TYPE,
58                 "Rewrite call_indirect argument orderings", false, false)
59 
60 FunctionPass *llvm::createWebAssemblyCallIndirectFixup() {
61   return new WebAssemblyCallIndirectFixup();
62 }
63 
64 static unsigned GetNonPseudoCallIndirectOpcode(const MachineInstr &MI) {
65   switch (MI.getOpcode()) {
66     using namespace WebAssembly;
67   case PCALL_INDIRECT_VOID: return CALL_INDIRECT_VOID;
68   case PCALL_INDIRECT_I32: return CALL_INDIRECT_I32;
69   case PCALL_INDIRECT_I64: return CALL_INDIRECT_I64;
70   case PCALL_INDIRECT_F32: return CALL_INDIRECT_F32;
71   case PCALL_INDIRECT_F64: return CALL_INDIRECT_F64;
72   case PCALL_INDIRECT_v16i8: return CALL_INDIRECT_v16i8;
73   case PCALL_INDIRECT_v8i16: return CALL_INDIRECT_v8i16;
74   case PCALL_INDIRECT_v4i32: return CALL_INDIRECT_v4i32;
75   case PCALL_INDIRECT_v4f32: return CALL_INDIRECT_v4f32;
76   default: return INSTRUCTION_LIST_END;
77   }
78 }
79 
80 static bool IsPseudoCallIndirect(const MachineInstr &MI) {
81   return GetNonPseudoCallIndirectOpcode(MI) !=
82          WebAssembly::INSTRUCTION_LIST_END;
83 }
84 
85 bool WebAssemblyCallIndirectFixup::runOnMachineFunction(MachineFunction &MF) {
86   LLVM_DEBUG(dbgs() << "********** Fixing up CALL_INDIRECTs **********\n"
87                     << MF.getName() << '\n');
88 
89   bool Changed = false;
90   const WebAssemblyInstrInfo *TII =
91       MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
92 
93   for (MachineBasicBlock &MBB : MF) {
94     for (MachineInstr &MI : MBB) {
95       if (IsPseudoCallIndirect(MI)) {
96         LLVM_DEBUG(dbgs() << "Found call_indirect: " << MI << '\n');
97 
98         // Rewrite pseudo to non-pseudo
99         const MCInstrDesc &Desc = TII->get(GetNonPseudoCallIndirectOpcode(MI));
100         MI.setDesc(Desc);
101 
102         // Rewrite argument order
103         SmallVector<MachineOperand, 8> Ops;
104 
105         // Set up a placeholder for the type signature immediate.
106         Ops.push_back(MachineOperand::CreateImm(0));
107 
108         // Set up the flags immediate, which currently has no defined flags
109         // so it's always zero.
110         Ops.push_back(MachineOperand::CreateImm(0));
111 
112         for (const MachineOperand &MO :
113                  make_range(MI.operands_begin() +
114                                 MI.getDesc().getNumDefs() + 1,
115                             MI.operands_begin() +
116                                 MI.getNumExplicitOperands()))
117           Ops.push_back(MO);
118         Ops.push_back(MI.getOperand(MI.getDesc().getNumDefs()));
119 
120         // Replace the instructions operands.
121         while (MI.getNumOperands() > MI.getDesc().getNumDefs())
122           MI.RemoveOperand(MI.getNumOperands() - 1);
123         for (const MachineOperand &MO : Ops)
124           MI.addOperand(MO);
125 
126         LLVM_DEBUG(dbgs() << "  After transform: " << MI);
127         Changed = true;
128       }
129     }
130   }
131 
132   LLVM_DEBUG(dbgs() << "\nDone fixing up CALL_INDIRECTs\n\n");
133 
134   return Changed;
135 }
136 
137