1 //===-- WebAssemblyLowerBrUnless.cpp - Lower br_unless --------------------===//
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 lowers br_unless into br_if with an inverted condition.
11 ///
12 /// br_unless is not currently in the spec, but it's very convenient for LLVM
13 /// to use. This pass allows LLVM to use it, for now.
14 ///
15 //===----------------------------------------------------------------------===//
16
17 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
18 #include "WebAssembly.h"
19 #include "WebAssemblyMachineFunctionInfo.h"
20 #include "WebAssemblySubtarget.h"
21 #include "llvm/CodeGen/MachineFunctionPass.h"
22 #include "llvm/CodeGen/MachineInstrBuilder.h"
23 #include "llvm/Support/Debug.h"
24 #include "llvm/Support/raw_ostream.h"
25 using namespace llvm;
26
27 #define DEBUG_TYPE "wasm-lower-br_unless"
28
29 namespace {
30 class WebAssemblyLowerBrUnless final : public MachineFunctionPass {
getPassName() const31 StringRef getPassName() const override {
32 return "WebAssembly Lower br_unless";
33 }
34
getAnalysisUsage(AnalysisUsage & AU) const35 void getAnalysisUsage(AnalysisUsage &AU) const override {
36 AU.setPreservesCFG();
37 MachineFunctionPass::getAnalysisUsage(AU);
38 }
39
40 bool runOnMachineFunction(MachineFunction &MF) override;
41
42 public:
43 static char ID; // Pass identification, replacement for typeid
WebAssemblyLowerBrUnless()44 WebAssemblyLowerBrUnless() : MachineFunctionPass(ID) {}
45 };
46 } // end anonymous namespace
47
48 char WebAssemblyLowerBrUnless::ID = 0;
49 INITIALIZE_PASS(WebAssemblyLowerBrUnless, DEBUG_TYPE,
50 "Lowers br_unless into inverted br_if", false, false)
51
createWebAssemblyLowerBrUnless()52 FunctionPass *llvm::createWebAssemblyLowerBrUnless() {
53 return new WebAssemblyLowerBrUnless();
54 }
55
runOnMachineFunction(MachineFunction & MF)56 bool WebAssemblyLowerBrUnless::runOnMachineFunction(MachineFunction &MF) {
57 LLVM_DEBUG(dbgs() << "********** Lowering br_unless **********\n"
58 "********** Function: "
59 << MF.getName() << '\n');
60
61 auto &MFI = *MF.getInfo<WebAssemblyFunctionInfo>();
62 const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
63 auto &MRI = MF.getRegInfo();
64
65 for (auto &MBB : MF) {
66 for (MachineInstr &MI : llvm::make_early_inc_range(MBB)) {
67 if (MI.getOpcode() != WebAssembly::BR_UNLESS)
68 continue;
69
70 Register Cond = MI.getOperand(1).getReg();
71 bool Inverted = false;
72
73 // Attempt to invert the condition in place.
74 if (MFI.isVRegStackified(Cond)) {
75 assert(MRI.hasOneDef(Cond));
76 MachineInstr *Def = MRI.getVRegDef(Cond);
77 switch (Def->getOpcode()) {
78 using namespace WebAssembly;
79 case EQ_I32:
80 Def->setDesc(TII.get(NE_I32));
81 Inverted = true;
82 break;
83 case NE_I32:
84 Def->setDesc(TII.get(EQ_I32));
85 Inverted = true;
86 break;
87 case GT_S_I32:
88 Def->setDesc(TII.get(LE_S_I32));
89 Inverted = true;
90 break;
91 case GE_S_I32:
92 Def->setDesc(TII.get(LT_S_I32));
93 Inverted = true;
94 break;
95 case LT_S_I32:
96 Def->setDesc(TII.get(GE_S_I32));
97 Inverted = true;
98 break;
99 case LE_S_I32:
100 Def->setDesc(TII.get(GT_S_I32));
101 Inverted = true;
102 break;
103 case GT_U_I32:
104 Def->setDesc(TII.get(LE_U_I32));
105 Inverted = true;
106 break;
107 case GE_U_I32:
108 Def->setDesc(TII.get(LT_U_I32));
109 Inverted = true;
110 break;
111 case LT_U_I32:
112 Def->setDesc(TII.get(GE_U_I32));
113 Inverted = true;
114 break;
115 case LE_U_I32:
116 Def->setDesc(TII.get(GT_U_I32));
117 Inverted = true;
118 break;
119 case EQ_I64:
120 Def->setDesc(TII.get(NE_I64));
121 Inverted = true;
122 break;
123 case NE_I64:
124 Def->setDesc(TII.get(EQ_I64));
125 Inverted = true;
126 break;
127 case GT_S_I64:
128 Def->setDesc(TII.get(LE_S_I64));
129 Inverted = true;
130 break;
131 case GE_S_I64:
132 Def->setDesc(TII.get(LT_S_I64));
133 Inverted = true;
134 break;
135 case LT_S_I64:
136 Def->setDesc(TII.get(GE_S_I64));
137 Inverted = true;
138 break;
139 case LE_S_I64:
140 Def->setDesc(TII.get(GT_S_I64));
141 Inverted = true;
142 break;
143 case GT_U_I64:
144 Def->setDesc(TII.get(LE_U_I64));
145 Inverted = true;
146 break;
147 case GE_U_I64:
148 Def->setDesc(TII.get(LT_U_I64));
149 Inverted = true;
150 break;
151 case LT_U_I64:
152 Def->setDesc(TII.get(GE_U_I64));
153 Inverted = true;
154 break;
155 case LE_U_I64:
156 Def->setDesc(TII.get(GT_U_I64));
157 Inverted = true;
158 break;
159 case EQ_F32:
160 Def->setDesc(TII.get(NE_F32));
161 Inverted = true;
162 break;
163 case NE_F32:
164 Def->setDesc(TII.get(EQ_F32));
165 Inverted = true;
166 break;
167 case EQ_F64:
168 Def->setDesc(TII.get(NE_F64));
169 Inverted = true;
170 break;
171 case NE_F64:
172 Def->setDesc(TII.get(EQ_F64));
173 Inverted = true;
174 break;
175 case EQZ_I32: {
176 // Invert an eqz by replacing it with its operand.
177 Cond = Def->getOperand(1).getReg();
178 Def->eraseFromParent();
179 Inverted = true;
180 break;
181 }
182 default:
183 break;
184 }
185 }
186
187 // If we weren't able to invert the condition in place. Insert an
188 // instruction to invert it.
189 if (!Inverted) {
190 Register Tmp = MRI.createVirtualRegister(&WebAssembly::I32RegClass);
191 BuildMI(MBB, &MI, MI.getDebugLoc(), TII.get(WebAssembly::EQZ_I32), Tmp)
192 .addReg(Cond);
193 MFI.stackifyVReg(MRI, Tmp);
194 Cond = Tmp;
195 Inverted = true;
196 }
197
198 // The br_unless condition has now been inverted. Insert a br_if and
199 // delete the br_unless.
200 assert(Inverted);
201 BuildMI(MBB, &MI, MI.getDebugLoc(), TII.get(WebAssembly::BR_IF))
202 .add(MI.getOperand(0))
203 .addReg(Cond);
204 MBB.erase(&MI);
205 }
206 }
207
208 return true;
209 }
210