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"
38using namespace llvm;
39
40#define DEBUG_TYPE "wasm-argument-move"
41
42namespace {
43class WebAssemblyArgumentMove final : public MachineFunctionPass {
44public:
45 static char ID; // Pass identification, replacement for typeid
46 WebAssemblyArgumentMove() : MachineFunctionPass(ID) {}
47
48 StringRef getPassName() const override { return "WebAssembly Argument Move"; }
49
50 void getAnalysisUsage(AnalysisUsage &AU) const override {
51 AU.setPreservesCFG();
52 AU.addPreserved<MachineBlockFrequencyInfoWrapperPass>();
53 AU.addPreservedID(ID&: MachineDominatorsID);
54 MachineFunctionPass::getAnalysisUsage(AU);
55 }
56
57 bool runOnMachineFunction(MachineFunction &MF) override;
58};
59} // end anonymous namespace
60
61char WebAssemblyArgumentMove::ID = 0;
62INITIALIZE_PASS(WebAssemblyArgumentMove, DEBUG_TYPE,
63 "Move ARGUMENT instructions for WebAssembly", false, false)
64
65FunctionPass *llvm::createWebAssemblyArgumentMove() {
66 return new WebAssemblyArgumentMove();
67}
68
69bool 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(Opc: 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(x: InsertPt, y: EntryMBB.end())) {
90 if (WebAssembly::isArgument(Opc: MI.getOpcode())) {
91 EntryMBB.insert(I: InsertPt, MI: MI.removeFromParent());
92 Changed = true;
93 }
94 }
95
96 return Changed;
97}
98