1 /*
2 * Copyright (C) 2016 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include "pc_relative_fixups_mips.h"
18 #include "code_generator_mips.h"
19 #include "intrinsics_mips.h"
20
21 namespace art {
22 namespace mips {
23
24 /**
25 * Finds instructions that need the constant area base as an input.
26 */
27 class PCRelativeHandlerVisitor : public HGraphVisitor {
28 public:
PCRelativeHandlerVisitor(HGraph * graph,CodeGenerator * codegen)29 PCRelativeHandlerVisitor(HGraph* graph, CodeGenerator* codegen)
30 : HGraphVisitor(graph),
31 codegen_(down_cast<CodeGeneratorMIPS*>(codegen)),
32 base_(nullptr) {}
33
MoveBaseIfNeeded()34 void MoveBaseIfNeeded() {
35 if (base_ != nullptr) {
36 // Bring the base closer to the first use (previously, it was in the
37 // entry block) and relieve some pressure on the register allocator
38 // while avoiding recalculation of the base in a loop.
39 base_->MoveBeforeFirstUserAndOutOfLoops();
40 // Computing the base for PC-relative literals will clobber RA with
41 // the NAL instruction on R2. Take a note of this before generating
42 // the method entry.
43 codegen_->ClobberRA();
44 }
45 }
46
47 private:
InitializePCRelativeBasePointer()48 void InitializePCRelativeBasePointer() {
49 // Ensure we only initialize the pointer once.
50 if (base_ != nullptr) {
51 return;
52 }
53 // Insert the base at the start of the entry block, move it to a better
54 // position later in MoveBaseIfNeeded().
55 base_ = new (GetGraph()->GetArena()) HMipsComputeBaseMethodAddress();
56 HBasicBlock* entry_block = GetGraph()->GetEntryBlock();
57 entry_block->InsertInstructionBefore(base_, entry_block->GetFirstInstruction());
58 DCHECK(base_ != nullptr);
59 }
60
VisitLoadClass(HLoadClass * load_class)61 void VisitLoadClass(HLoadClass* load_class) OVERRIDE {
62 HLoadClass::LoadKind load_kind = load_class->GetLoadKind();
63 switch (load_kind) {
64 case HLoadClass::LoadKind::kBootImageLinkTimeAddress:
65 case HLoadClass::LoadKind::kBootImageLinkTimePcRelative:
66 case HLoadClass::LoadKind::kBootImageAddress:
67 case HLoadClass::LoadKind::kBssEntry:
68 // Add a base register for PC-relative literals on R2.
69 InitializePCRelativeBasePointer();
70 load_class->AddSpecialInput(base_);
71 break;
72 default:
73 break;
74 }
75 }
76
VisitLoadString(HLoadString * load_string)77 void VisitLoadString(HLoadString* load_string) OVERRIDE {
78 HLoadString::LoadKind load_kind = load_string->GetLoadKind();
79 switch (load_kind) {
80 case HLoadString::LoadKind::kBootImageLinkTimeAddress:
81 case HLoadString::LoadKind::kBootImageAddress:
82 case HLoadString::LoadKind::kBootImageLinkTimePcRelative:
83 case HLoadString::LoadKind::kBssEntry:
84 // Add a base register for PC-relative literals on R2.
85 InitializePCRelativeBasePointer();
86 load_string->AddSpecialInput(base_);
87 break;
88 default:
89 break;
90 }
91 }
92
VisitPackedSwitch(HPackedSwitch * switch_insn)93 void VisitPackedSwitch(HPackedSwitch* switch_insn) OVERRIDE {
94 if (switch_insn->GetNumEntries() <=
95 InstructionCodeGeneratorMIPS::kPackedSwitchJumpTableThreshold) {
96 return;
97 }
98 // We need to replace the HPackedSwitch with a HMipsPackedSwitch in order to
99 // address the constant area.
100 InitializePCRelativeBasePointer();
101 HGraph* graph = GetGraph();
102 HBasicBlock* block = switch_insn->GetBlock();
103 HMipsPackedSwitch* mips_switch = new (graph->GetArena()) HMipsPackedSwitch(
104 switch_insn->GetStartValue(),
105 switch_insn->GetNumEntries(),
106 switch_insn->InputAt(0),
107 base_,
108 switch_insn->GetDexPc());
109 block->ReplaceAndRemoveInstructionWith(switch_insn, mips_switch);
110 }
111
112 CodeGeneratorMIPS* codegen_;
113
114 // The generated HMipsComputeBaseMethodAddress in the entry block needed as an
115 // input to the HMipsLoadFromConstantTable instructions.
116 HMipsComputeBaseMethodAddress* base_;
117 };
118
Run()119 void PcRelativeFixups::Run() {
120 CodeGeneratorMIPS* mips_codegen = down_cast<CodeGeneratorMIPS*>(codegen_);
121 if (mips_codegen->GetInstructionSetFeatures().IsR6()) {
122 // Do nothing for R6 because it has PC-relative addressing.
123 return;
124 }
125 if (graph_->HasIrreducibleLoops()) {
126 // Do not run this optimization, as irreducible loops do not work with an instruction
127 // that can be live-in at the irreducible loop header.
128 return;
129 }
130 PCRelativeHandlerVisitor visitor(graph_, codegen_);
131 visitor.VisitInsertionOrder();
132 visitor.MoveBaseIfNeeded();
133 }
134
135 } // namespace mips
136 } // namespace art
137