1 //===-- WebAssemblyArgumentMove.cpp - Argument instruction moving ---------===//
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 moves ARGUMENT instructions after ScheduleDAG scheduling.
11 ///
12 /// Arguments are really live-in registers, however, since we use virtual
13 /// registers and LLVM doesn't support live-in virtual registers, we're
14 /// currently making do with ARGUMENT instructions which are placed at the top
15 /// of the entry block. The trick is to get them to *stay* at the top of the
16 /// entry block.
17 ///
18 /// The ARGUMENTS physical register keeps these instructions pinned in place
19 /// during liveness-aware CodeGen passes, however one thing which does not
20 /// respect this is the ScheduleDAG scheduler. This pass is therefore run
21 /// immediately after that.
22 ///
23 /// This is all hopefully a temporary solution until we find a better solution
24 /// for describing the live-in nature of arguments.
25 ///
26 //===----------------------------------------------------------------------===//
27
28 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
29 #include "WebAssembly.h"
30 #include "WebAssemblyMachineFunctionInfo.h"
31 #include "WebAssemblySubtarget.h"
32 #include "WebAssemblyUtilities.h"
33 #include "llvm/CodeGen/MachineBlockFrequencyInfo.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-argument-move"
41
42 namespace {
43 class WebAssemblyArgumentMove final : public MachineFunctionPass {
44 public:
45 static char ID; // Pass identification, replacement for typeid
WebAssemblyArgumentMove()46 WebAssemblyArgumentMove() : MachineFunctionPass(ID) {}
47
getPassName() const48 StringRef getPassName() const override { return "WebAssembly Argument Move"; }
49
getAnalysisUsage(AnalysisUsage & AU) const50 void getAnalysisUsage(AnalysisUsage &AU) const override {
51 AU.setPreservesCFG();
52 AU.addPreserved<MachineBlockFrequencyInfo>();
53 AU.addPreservedID(MachineDominatorsID);
54 MachineFunctionPass::getAnalysisUsage(AU);
55 }
56
57 bool runOnMachineFunction(MachineFunction &MF) override;
58 };
59 } // end anonymous namespace
60
61 char WebAssemblyArgumentMove::ID = 0;
62 INITIALIZE_PASS(WebAssemblyArgumentMove, DEBUG_TYPE,
63 "Move ARGUMENT instructions for WebAssembly", false, false)
64
createWebAssemblyArgumentMove()65 FunctionPass *llvm::createWebAssemblyArgumentMove() {
66 return new WebAssemblyArgumentMove();
67 }
68
runOnMachineFunction(MachineFunction & MF)69 bool WebAssemblyArgumentMove::runOnMachineFunction(MachineFunction &MF) {
70 LLVM_DEBUG({
71 dbgs() << "********** Argument Move **********\n"
72 << "********** Function: " << MF.getName() << '\n';
73 });
74
75 bool Changed = false;
76 MachineBasicBlock &EntryMBB = MF.front();
77 MachineBasicBlock::iterator InsertPt = EntryMBB.end();
78
79 // Look for the first NonArg instruction.
80 for (MachineInstr &MI : EntryMBB) {
81 if (!WebAssembly::isArgument(MI.getOpcode())) {
82 InsertPt = MI;
83 break;
84 }
85 }
86
87 // Now move any argument instructions later in the block
88 // to before our first NonArg instruction.
89 for (MachineInstr &MI : llvm::make_range(InsertPt, EntryMBB.end())) {
90 if (WebAssembly::isArgument(MI.getOpcode())) {
91 EntryMBB.insert(InsertPt, MI.removeFromParent());
92 Changed = true;
93 }
94 }
95
96 return Changed;
97 }
98