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 "WebAssemblyUtilities.h"
31#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
32#include "llvm/CodeGen/Passes.h"
33#include "llvm/Support/Debug.h"
34#include "llvm/Support/raw_ostream.h"
35using namespace llvm;
36
37#define DEBUG_TYPE "wasm-argument-move"
38
39namespace {
40class WebAssemblyArgumentMove final : public MachineFunctionPass {
41public:
42 static char ID; // Pass identification, replacement for typeid
43 WebAssemblyArgumentMove() : MachineFunctionPass(ID) {}
44
45 StringRef getPassName() const override { return "WebAssembly Argument Move"; }
46
47 void getAnalysisUsage(AnalysisUsage &AU) const override {
48 AU.setPreservesCFG();
49 AU.addPreserved<MachineBlockFrequencyInfoWrapperPass>();
50 AU.addPreservedID(ID&: MachineDominatorsID);
51 MachineFunctionPass::getAnalysisUsage(AU);
52 }
53
54 bool runOnMachineFunction(MachineFunction &MF) override;
55};
56} // end anonymous namespace
57
58char WebAssemblyArgumentMove::ID = 0;
59INITIALIZE_PASS(WebAssemblyArgumentMove, DEBUG_TYPE,
60 "Move ARGUMENT instructions for WebAssembly", false, false)
61
62FunctionPass *llvm::createWebAssemblyArgumentMove() {
63 return new WebAssemblyArgumentMove();
64}
65
66bool WebAssemblyArgumentMove::runOnMachineFunction(MachineFunction &MF) {
67 LLVM_DEBUG({
68 dbgs() << "********** Argument Move **********\n"
69 << "********** Function: " << MF.getName() << '\n';
70 });
71
72 bool Changed = false;
73 MachineBasicBlock &EntryMBB = MF.front();
74 MachineBasicBlock::iterator InsertPt = EntryMBB.end();
75
76 // Look for the first NonArg instruction.
77 for (MachineInstr &MI : EntryMBB) {
78 if (!WebAssembly::isArgument(Opc: MI.getOpcode())) {
79 InsertPt = MI;
80 break;
81 }
82 }
83
84 // Now move any argument instructions later in the block
85 // to before our first NonArg instruction.
86 for (MachineInstr &MI : llvm::make_range(x: InsertPt, y: EntryMBB.end())) {
87 if (WebAssembly::isArgument(Opc: MI.getOpcode())) {
88 EntryMBB.insert(I: InsertPt, MI: MI.removeFromParent());
89 Changed = true;
90 }
91 }
92
93 return Changed;
94}
95