1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
|
// Copyright 2021 yuzu Emulator Project
// Licensed under GPLv2 or any later version
// Refer to the license.txt file included.
// This file implements the SSA rewriting algorithm proposed in
//
// Simple and Efficient Construction of Static Single Assignment Form.
// Braun M., Buchwald S., Hack S., Leißa R., Mallon C., Zwinkau A. (2013)
// In: Jhala R., De Bosschere K. (eds)
// Compiler Construction. CC 2013.
// Lecture Notes in Computer Science, vol 7791.
// Springer, Berlin, Heidelberg
//
// https://link.springer.com/chapter/10.1007/978-3-642-37051-9_6
//
#include <map>
#include <boost/container/flat_map.hpp>
#include "shader_recompiler/frontend/ir/basic_block.h"
#include "shader_recompiler/frontend/ir/function.h"
#include "shader_recompiler/frontend/ir/microinstruction.h"
#include "shader_recompiler/frontend/ir/opcode.h"
#include "shader_recompiler/frontend/ir/pred.h"
#include "shader_recompiler/frontend/ir/reg.h"
#include "shader_recompiler/ir_opt/passes.h"
namespace Shader::Optimization {
namespace {
using ValueMap = boost::container::flat_map<IR::Block*, IR::Value, std::less<IR::Block*>>;
struct DefTable {
[[nodiscard]] ValueMap& operator[](IR::Reg variable) noexcept {
return regs[IR::RegIndex(variable)];
}
[[nodiscard]] ValueMap& operator[](IR::Pred variable) noexcept {
return preds[IR::PredIndex(variable)];
}
std::array<ValueMap, IR::NUM_USER_REGS> regs;
std::array<ValueMap, IR::NUM_USER_PREDS> preds;
};
IR::Opcode UndefOpcode(IR::Reg) noexcept {
return IR::Opcode::Undef32;
}
IR::Opcode UndefOpcode(IR::Pred) noexcept {
return IR::Opcode::Undef1;
}
[[nodiscard]] bool IsPhi(const IR::Inst& inst) noexcept {
return inst.Opcode() == IR::Opcode::Phi;
}
class Pass {
public:
void WriteVariable(auto variable, IR::Block* block, const IR::Value& value) {
current_def[variable].insert_or_assign(block, value);
}
IR::Value ReadVariable(auto variable, IR::Block* block) {
auto& def{current_def[variable]};
if (const auto it{def.find(block)}; it != def.end()) {
return it->second;
}
return ReadVariableRecursive(variable, block);
}
private:
IR::Value ReadVariableRecursive(auto variable, IR::Block* block) {
IR::Value val;
if (const std::span preds{block->ImmediatePredecessors()}; preds.size() == 1) {
val = ReadVariable(variable, preds.front());
} else {
// Break potential cycles with operandless phi
val = IR::Value{&*block->PrependNewInst(block->begin(), IR::Opcode::Phi)};
WriteVariable(variable, block, val);
val = AddPhiOperands(variable, val, block);
}
WriteVariable(variable, block, val);
return val;
}
IR::Value AddPhiOperands(auto variable, const IR::Value& phi, IR::Block* block) {
for (IR::Block* const pred : block->ImmediatePredecessors()) {
phi.Inst()->AddPhiOperand(pred, ReadVariable(variable, pred));
}
return TryRemoveTrivialPhi(phi, block, UndefOpcode(variable));
}
IR::Value TryRemoveTrivialPhi(const IR::Value& phi, IR::Block* block, IR::Opcode undef_opcode) {
IR::Value same;
for (const auto& pair : phi.Inst()->PhiOperands()) {
const IR::Value& op{pair.second};
if (op == same || op == phi) {
// Unique value or self-reference
continue;
}
if (!same.IsEmpty()) {
// The phi merges at least two values: not trivial
return phi;
}
same = op;
}
if (same.IsEmpty()) {
// The phi is unreachable or in the start block
const auto first_not_phi{std::ranges::find_if_not(block->Instructions(), IsPhi)};
same = IR::Value{&*block->PrependNewInst(first_not_phi, undef_opcode)};
}
// Reroute all uses of phi to same and remove phi
phi.Inst()->ReplaceUsesWith(same);
// TODO: Try to recursively remove all phi users, which might have become trivial
return same;
}
DefTable current_def;
};
} // Anonymous namespace
void SsaRewritePass(IR::Function& function) {
Pass pass;
for (const auto& block : function.blocks) {
for (IR::Inst& inst : block->Instructions()) {
switch (inst.Opcode()) {
case IR::Opcode::SetRegister:
if (const IR::Reg reg{inst.Arg(0).Reg()}; reg != IR::Reg::RZ) {
pass.WriteVariable(reg, block.get(), inst.Arg(1));
}
break;
case IR::Opcode::SetPred:
if (const IR::Pred pred{inst.Arg(0).Pred()}; pred != IR::Pred::PT) {
pass.WriteVariable(pred, block.get(), inst.Arg(1));
}
break;
case IR::Opcode::GetRegister:
if (const IR::Reg reg{inst.Arg(0).Reg()}; reg != IR::Reg::RZ) {
inst.ReplaceUsesWith(pass.ReadVariable(reg, block.get()));
}
break;
case IR::Opcode::GetPred:
if (const IR::Pred pred{inst.Arg(0).Pred()}; pred != IR::Pred::PT) {
inst.ReplaceUsesWith(pass.ReadVariable(pred, block.get()));
}
break;
default:
break;
}
}
}
}
} // namespace Shader::Optimization
|
