WebAssemblyCallIndirectFixup.cpp revision 314564 
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/// \brief 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 "WebAssembly.h"
26#include "MCTargetDesc/WebAssemblyMCTargetDesc.h" // for WebAssembly::ARGUMENT_*
27#include "WebAssemblyMachineFunctionInfo.h"
28#include "WebAssemblySubtarget.h"
29#include "llvm/Analysis/AliasAnalysis.h"
30#include "llvm/CodeGen/LiveIntervalAnalysis.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"
38using namespace llvm;
39
40#define DEBUG_TYPE "wasm-call-indirect-fixup"
41
42namespace {
43class WebAssemblyCallIndirectFixup final : public MachineFunctionPass {
44  StringRef getPassName() const override {
45    return "WebAssembly CallIndirect Fixup";
46  }
47
48  bool runOnMachineFunction(MachineFunction &MF) override;
49
50public:
51  static char ID; // Pass identification, replacement for typeid
52  WebAssemblyCallIndirectFixup() : MachineFunctionPass(ID) {}
53};
54} // end anonymous namespace
55
56char WebAssemblyCallIndirectFixup::ID = 0;
57FunctionPass *llvm::createWebAssemblyCallIndirectFixup() {
58  return new WebAssemblyCallIndirectFixup();
59}
60
61static unsigned GetNonPseudoCallIndirectOpcode(const MachineInstr &MI) {
62  switch (MI.getOpcode()) {
63    using namespace WebAssembly;
64  case PCALL_INDIRECT_VOID: return CALL_INDIRECT_VOID;
65  case PCALL_INDIRECT_I32: return CALL_INDIRECT_I32;
66  case PCALL_INDIRECT_I64: return CALL_INDIRECT_I64;
67  case PCALL_INDIRECT_F32: return CALL_INDIRECT_F32;
68  case PCALL_INDIRECT_F64: return CALL_INDIRECT_F64;
69  case PCALL_INDIRECT_v16i8: return CALL_INDIRECT_v16i8;
70  case PCALL_INDIRECT_v8i16: return CALL_INDIRECT_v8i16;
71  case PCALL_INDIRECT_v4i32: return CALL_INDIRECT_v4i32;
72  case PCALL_INDIRECT_v4f32: return CALL_INDIRECT_v4f32;
73  default: return INSTRUCTION_LIST_END;
74  }
75}
76
77static bool IsPseudoCallIndirect(const MachineInstr &MI) {
78  return GetNonPseudoCallIndirectOpcode(MI) !=
79         WebAssembly::INSTRUCTION_LIST_END;
80}
81
82bool WebAssemblyCallIndirectFixup::runOnMachineFunction(MachineFunction &MF) {
83  DEBUG(dbgs() << "********** Fixing up CALL_INDIRECTs **********\n"
84               << MF.getName() << '\n');
85
86  bool Changed = false;
87  const WebAssemblyInstrInfo *TII =
88      MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
89
90  for (MachineBasicBlock &MBB : MF) {
91    for (MachineInstr &MI : MBB) {
92      if (IsPseudoCallIndirect(MI)) {
93        DEBUG(dbgs() << "Found call_indirect: " << MI << '\n');
94
95        // Rewrite pseudo to non-pseudo
96        const MCInstrDesc &Desc = TII->get(GetNonPseudoCallIndirectOpcode(MI));
97        MI.setDesc(Desc);
98
99        // Rewrite argument order
100        auto Uses = MI.explicit_uses();
101        MachineInstr::mop_iterator it = Uses.begin();
102        const MachineOperand MO = *it;
103
104        // Set up the flags immediate, which currently has no defined flags
105        // so it's always zero.
106        it->ChangeToImmediate(0);
107
108        MI.addOperand(MF, MO);
109
110        DEBUG(dbgs() << "  After transform: " << MI);
111        Changed = true;
112      }
113    }
114  }
115
116  DEBUG(dbgs() << "\nDone fixing up CALL_INDIRECTs\n\n");
117
118  return Changed;
119}
120
121