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
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
|
#include <torch/csrc/jit/frontend/convert_to_ssa.h>
#include <torch/csrc/jit/frontend/exit_transforms.h>
#include <torch/csrc/jit/frontend/inline_loop_condition.h>
#include <torch/csrc/jit/frontend/ir_emitter.h>
#include <torch/csrc/jit/frontend/mini_environment.h>
#include <torch/csrc/jit/ir/ir.h>
#include <torch/csrc/jit/ir/ir_views.h>
namespace torch {
namespace jit {
// At the beginning of the pass the Graph has already undergone type checking,
// and writes or reads to a variable are emitted as Loads and Stores in the
// graph.
// a = 1
// print(a)
// is represented as:
// %a.1 : int = prim::Constant[value=1]()
// prim::Store[name="a"](%a.1)
// %a : int = prim::Load[name="a"]()
// prim::Print(%a)
//
// First, this pass recursively adds the Loads & Stores to control flow nodes
// Then the graph is converted to SSA form.
using ValueEnvironment = MiniEnvironment<Value*>;
using TypeEnvironment = MiniEnvironment<TypePtr>;
// Adds Loads & Stores to Loops & Ifs
struct ControlFlowLoadStores {
static void addBlockInput(
Block* b,
const TypePtr& type,
const std::string& name) {
auto g = b->owningGraph();
g->createStore(name, b->addInput(name)->setType(type))
->insertAfter(b->param_node());
}
static void addBlockOutput(
Block* exit_block,
const TypePtr& type,
const std::string& name) {
WithInsertPoint insert(exit_block);
auto g = exit_block->owningGraph();
auto block_exit = g->insertNode(g->createLoad(name, type))->output();
exit_block->registerOutput(block_exit);
}
static void addNodeOutput(
Node* n,
const TypePtr& type,
const std::string& name) {
auto out = n->addOutput()->setType(type);
if (meaningfulName(name)) {
out->setDebugName(name);
}
auto g = n->owningGraph();
g->createStore(name, out)->insertAfter(n);
}
static void addNodeInput(
Node* n,
const TypePtr& type,
const std::string& name) {
auto g = n->owningGraph();
auto inp = g->createLoad(name, type)->insertBefore(n)->output();
n->addInput(inp);
}
void addIfLoadStores(Node* n) {
auto true_block = n->blocks().at(0);
auto false_block = n->blocks().at(1);
auto true_vars = addControlFlowLoadStores(true_block);
auto false_vars = addControlFlowLoadStores(false_block);
std::set<std::string> mutated_variables;
for (auto& v : true_vars->definedVariables()) {
if (false_vars->findInAnyFrame(v)) {
mutated_variables.insert(v);
}
}
for (auto& v : false_vars->definedVariables()) {
if (true_vars->findInAnyFrame(v)) {
mutated_variables.insert(v);
}
}
// Following the same logic as emitIfElseBlocks in ir_emitter.cpp,
// we emit a node output if the variable is defined in each block
// and the types of each block can be unified
for (const auto& x : mutated_variables) {
auto true_type = true_vars->findInAnyFrame(x);
auto false_type = false_vars->findInAnyFrame(x);
auto unified =
unifyTypes(true_type, false_type, /*default_to_union=*/true);
addBlockOutput(true_block, true_type, x);
addBlockOutput(false_block, false_type, x);
addNodeOutput(n, *unified, x);
}
}
// loop_carried_outputs* = Loop(max_trip_count, start_condition,
// loop_carried_inputs*)
// block0(loop_counter, loop_carried_block*) {
// <body>
// -> (continue_condition, loop_carried_block_outputs*)
// }
// all loop_carried_... lists are the same length and represent the value of
// loop-carried variables whose definitions are updated as the loop executes
// in a way that ensure single static assignment.
void addLoopLoadStores(Node* n) {
auto body_block = n->blocks().at(0);
auto loop_vars = addControlFlowLoadStores(body_block);
for (const auto& name : loop_vars->definedVariables()) {
// if the variable local to the loop body, then
// we do not need a loop carried variable for it
auto parent_type = environment_stack->findInAnyFrame(name);
if (!parent_type) {
continue;
}
// since the loop may execute 0 or many times, the output types
// of the loop and the input loop carried dependencies are conservatively
// the union of the output of the body and the input to the loop
auto block_type = loop_vars->findInThisFrame(name);
auto unified_type = unifyTypes(parent_type, block_type).value();
// Insert a store at the beginning of the loop block, so that all
// loads of the variable will use the loop carried value
addNodeInput(n, parent_type, name);
addBlockInput(body_block, unified_type, name);
addBlockOutput(body_block, block_type, name);
addNodeOutput(n, unified_type, name);
}
}
std::shared_ptr<TypeEnvironment> addControlFlowLoadStores(Block* block) {
pushFrame(block);
for (Node* n : block->nodes()) {
switch (n->kind()) {
case prim::If: {
addIfLoadStores(n);
} break;
case prim::Loop: {
addLoopLoadStores(n);
} break;
case prim::Closure: {
for (auto b : n->blocks()) {
addControlFlowLoadStores(b);
}
} break;
case prim::Store: {
environment_stack->setVar(n->s(attr::name), n->input()->type());
} break;
case prim::ComprehensionScope: {
addControlFlowLoadStores(n->blocks().at(0));
} break;
}
}
return popFrame();
}
void pushFrame(Block* b) {
environment_stack = std::make_shared<TypeEnvironment>(b, environment_stack);
}
std::shared_ptr<TypeEnvironment> popFrame() {
auto old_frame = environment_stack;
environment_stack = environment_stack->next;
return old_frame;
}
void run(std::shared_ptr<Graph>& graph) {
addControlFlowLoadStores(graph->block());
}
std::shared_ptr<TypeEnvironment> environment_stack = nullptr;
};
// Given a graph where 1) outputs have been added to control flow nodes and
// 2) loads and stores are represented in the graph, erase the Loads & Stores.
struct EraseLoadStores {
void eraseBlockLoadStores(Block* block) {
pushFrame(block);
for (auto it = block->nodes().begin(); it != block->nodes().end();) {
auto n = *it;
it++;
switch (n->kind()) {
case prim::Store: {
environment_stack->setVar(n->s(attr::name), n->input());
n->destroy();
} break;
case prim::Load: {
auto name = n->s(attr::name);
auto var = environment_stack->findInAnyFrame(name);
TORCH_INTERNAL_ASSERT(
var, "Typechecking should ensure the variable name is set");
n->output()->replaceAllUsesWith(var);
n->destroy();
} break;
case prim::ComprehensionScope: {
// writes within a local variable scope do not leak into
// the rest of the graph
auto body = n->blocks().at(0);
eraseBlockLoadStores(body);
// inline the local variable scope into the graph
for (auto it_cmpr = body->nodes().begin();
it_cmpr != body->nodes().end();) {
Node* body_node = *it_cmpr;
it_cmpr++;
body_node->moveBefore(n);
}
n->destroy();
} break;
default: {
for (auto b : n->blocks()) {
eraseBlockLoadStores(b);
}
} break;
}
}
popFrame();
}
void pushFrame(Block* b) {
environment_stack =
std::make_shared<ValueEnvironment>(b, environment_stack);
}
std::shared_ptr<ValueEnvironment> popFrame() {
auto old_frame = environment_stack;
environment_stack = environment_stack->next;
return old_frame;
}
void run(std::shared_ptr<Graph>& graph) {
eraseBlockLoadStores(graph->block());
}
std::shared_ptr<ValueEnvironment> environment_stack = nullptr;
};
// This pass transforms Breaks & Continues to be LoopContinuations,
// of the form LoopContinuations(%loop_continue_condition, *loop_carried_vars)
// Break Statements have the condition set to false, and Continue statements
// inline the loop condition as the first input.
struct LoopContinuations {
public:
void run(std::shared_ptr<Graph>& graph) {
run(graph->block());
}
private:
void addLoopCarriedOutputs(Node* n) {
auto g = n->owningGraph();
WithInsertPoint insert(n);
// NOLINTNEXTLINE(clang-analyzer-core.CallAndMessage)
auto continuation = curr_loop_->blocks().at(0)->return_node();
for (auto out : continuation->inputs()) {
auto load_node = out->node();
TORCH_INTERNAL_ASSERT(load_node->kind() == prim::Load);
auto new_load =
g->insertNode(g->createClone(load_node, [](Value* v) { return v; }));
n->addInput(new_load->output());
}
}
void assignExitContinuations(Block* block) {
for (auto it = block->nodes().begin(); it != block->nodes().end();) {
Node* n = *it;
it++;
switch (n->kind()) {
case prim::If: {
assignExitContinuations(n->blocks().at(0));
assignExitContinuations(n->blocks().at(1));
} break;
case prim::Closure: {
LoopContinuations closure_block;
closure_block.run(n->blocks().at(0));
} break;
case prim::Loop: {
Node* prev_loop = curr_loop_;
curr_loop_ = n;
assignExitContinuations(n->blocks().at(0));
curr_loop_ = prev_loop;
} break;
case prim::ContinueStmt: {
auto loop_continuation =
graph_->create(prim::LoopContinuation, 0)->insertAfter(n);
auto header_block = loop_continuation->addBlock();
// NOLINTNEXTLINE(clang-analyzer-core.CallAndMessage)
auto pre_header = curr_loop_->blocks().at(1);
header_block->cloneFrom(pre_header, [](Value* v) { return v; });
InlineBlockBeforeNode(n, header_block);
loop_continuation->addInput(header_block->outputs().at(0));
loop_continuation->eraseBlock(0);
addLoopCarriedOutputs(loop_continuation);
n->destroy();
} break;
case prim::BreakStmt: {
auto loop_exit =
graph_->create(prim::LoopContinuation, 0)->insertAfter(n);
// first input is the loop continue condition - break sets false
loop_exit->addInput(false_val_);
addLoopCarriedOutputs(loop_exit);
n->destroy();
} break;
}
}
}
void run(Block* b) {
{
graph_ = b->owningGraph();
WithInsertPoint guard(b->nodes().front());
false_val_ = graph_->insertConstant(false);
}
assignExitContinuations(b);
}
Graph* graph_ = nullptr;
Value* false_val_ = nullptr;
Node* curr_loop_ = nullptr;
};
// Converting to SSA works in multiple parts. First, we add control flow
// loads and stores to the graph. Now that control flow outputs are set,
// we can set remove Break & Continue to have the correct continuations to the
// end of the block (LoopContinuation). Then we inline the loop condition into
// the graph. Then, we erase Loads & Stores. Finally, we remove
// LoopContinuations from the graph.
void ConvertToSSA(std::shared_ptr<Graph>& graph) {
ControlFlowLoadStores ctrl;
ctrl.run(graph);
LoopContinuations exit_vars;
exit_vars.run(graph);
InlineLoopCondition(graph);
EraseLoadStores erase_loads_stores;
erase_loads_stores.run(graph);
TransformExits(graph);
}
} // namespace jit
} // namespace torch
|
