CIRCT 20.0.0git
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IMConstProp.cpp
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1//===- IMConstProp.cpp - Intermodule ConstProp and DCE ----------*- C++ -*-===//
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// This implements SCCP:
10// https://www.cs.wustl.edu/~cytron/531Pages/f11/Resources/Papers/cprop.pdf
11//
12//===----------------------------------------------------------------------===//
13
20#include "circt/Support/APInt.h"
21#include "mlir/IR/Iterators.h"
22#include "mlir/IR/Threading.h"
23#include "mlir/Pass/Pass.h"
24#include "llvm/ADT/APSInt.h"
25#include "llvm/ADT/TinyPtrVector.h"
26#include "llvm/Support/Debug.h"
27#include "llvm/Support/ScopedPrinter.h"
28
29namespace circt {
30namespace firrtl {
31#define GEN_PASS_DEF_IMCONSTPROP
32#include "circt/Dialect/FIRRTL/Passes.h.inc"
33} // namespace firrtl
34} // namespace circt
35
36using namespace circt;
37using namespace firrtl;
38
39#define DEBUG_TYPE "IMCP"
40
41/// Return true if this is a wire or register.
42static bool isWireOrReg(Operation *op) {
43 return isa<WireOp, RegResetOp, RegOp>(op);
44}
45
46/// Return true if this is an aggregate indexer.
47static bool isAggregate(Operation *op) {
48 return isa<SubindexOp, SubaccessOp, SubfieldOp, OpenSubfieldOp,
49 OpenSubindexOp, RefSubOp>(op);
50}
51
52// Return true if this forwards input to output.
53// Implies has appropriate visit method that propagates changes.
54static bool isNodeLike(Operation *op) {
55 return isa<NodeOp, RefResolveOp, RefSendOp>(op);
56}
57
58/// Return true if this is a wire or register we're allowed to delete.
59static bool isDeletableWireOrRegOrNode(Operation *op) {
60 if (!isWireOrReg(op) && !isa<NodeOp>(op))
61 return false;
62
63 // Always allow deleting wires of probe-type.
64 if (type_isa<RefType>(op->getResult(0).getType()))
65 return true;
66
67 // Otherwise, don't delete if has anything keeping it around or unknown.
68 return AnnotationSet(op).empty() && !hasDontTouch(op) &&
69 hasDroppableName(op) && !cast<Forceable>(op).isForceable();
70}
71
72//===----------------------------------------------------------------------===//
73// Pass Infrastructure
74//===----------------------------------------------------------------------===//
75
76namespace {
77/// This class represents a single lattice value. A lattive value corresponds to
78/// the various different states that a value in the SCCP dataflow analysis can
79/// take. See 'Kind' below for more details on the different states a value can
80/// take.
81class LatticeValue {
82 enum Kind {
83 /// A value with a yet-to-be-determined value. This state may be changed to
84 /// anything, it hasn't been processed by IMConstProp.
85 Unknown,
86
87 /// A value that is known to be a constant. This state may be changed to
88 /// overdefined.
89 Constant,
90
91 /// A value that cannot statically be determined to be a constant. This
92 /// state cannot be changed.
93 Overdefined
94 };
95
96public:
97 /// Initialize a lattice value with "Unknown".
98 /*implicit*/ LatticeValue() : valueAndTag(nullptr, Kind::Unknown) {}
99 /// Initialize a lattice value with a constant.
100 /*implicit*/ LatticeValue(IntegerAttr attr)
101 : valueAndTag(attr, Kind::Constant) {}
102 /*implicit*/ LatticeValue(StringAttr attr)
103 : valueAndTag(attr, Kind::Constant) {}
104
105 static LatticeValue getOverdefined() {
106 LatticeValue result;
107 result.markOverdefined();
108 return result;
109 }
110
111 bool isUnknown() const { return valueAndTag.getInt() == Kind::Unknown; }
112 bool isConstant() const { return valueAndTag.getInt() == Kind::Constant; }
113 bool isOverdefined() const {
114 return valueAndTag.getInt() == Kind::Overdefined;
115 }
116
117 /// Mark the lattice value as overdefined.
118 void markOverdefined() {
119 valueAndTag.setPointerAndInt(nullptr, Kind::Overdefined);
120 }
121
122 /// Mark the lattice value as constant.
123 void markConstant(IntegerAttr value) {
124 valueAndTag.setPointerAndInt(value, Kind::Constant);
125 }
126
127 /// If this lattice is constant or invalid value, return the attribute.
128 /// Returns nullptr otherwise.
129 Attribute getValue() const { return valueAndTag.getPointer(); }
130
131 /// If this is in the constant state, return the attribute.
132 Attribute getConstant() const {
134 return getValue();
135 }
136
137 /// Merge in the value of the 'rhs' lattice into this one. Returns true if the
138 /// lattice value changed.
139 bool mergeIn(LatticeValue rhs) {
140 // If we are already overdefined, or rhs is unknown, there is nothing to do.
141 if (isOverdefined() || rhs.isUnknown())
142 return false;
143
144 // If we are unknown, just take the value of rhs.
145 if (isUnknown()) {
146 valueAndTag = rhs.valueAndTag;
147 return true;
148 }
149
150 // Otherwise, if this value doesn't match rhs go straight to overdefined.
151 // This happens when we merge "3" and "4" from two different instance sites
152 // for example.
153 if (valueAndTag != rhs.valueAndTag) {
154 markOverdefined();
155 return true;
156 }
157 return false;
158 }
159
160 bool operator==(const LatticeValue &other) const {
161 return valueAndTag == other.valueAndTag;
162 }
163 bool operator!=(const LatticeValue &other) const {
164 return valueAndTag != other.valueAndTag;
165 }
166
167private:
168 /// The attribute value if this is a constant and the tag for the element
169 /// kind. The attribute is an IntegerAttr (or BoolAttr) or StringAttr.
170 llvm::PointerIntPair<Attribute, 2, Kind> valueAndTag;
171};
172} // end anonymous namespace
173
174LLVM_ATTRIBUTE_USED
175static llvm::raw_ostream &operator<<(llvm::raw_ostream &os,
176 const LatticeValue &lattice) {
177 if (lattice.isUnknown())
178 return os << "<Unknown>";
179 if (lattice.isOverdefined())
180 return os << "<Overdefined>";
181 return os << "<" << lattice.getConstant() << ">";
182}
183
184namespace {
185struct IMConstPropPass
186 : public circt::firrtl::impl::IMConstPropBase<IMConstPropPass> {
187
188 void runOnOperation() override;
189 void rewriteModuleBody(FModuleOp module);
190
191 /// Returns true if the given block is executable.
192 bool isBlockExecutable(Block *block) const {
193 return executableBlocks.count(block);
194 }
195
196 bool isOverdefined(FieldRef value) const {
197 auto it = latticeValues.find(value);
198 return it != latticeValues.end() && it->second.isOverdefined();
199 }
200
201 // Mark the given value as overdefined. If the value is an aggregate,
202 // we mark all ground elements as overdefined.
203 void markOverdefined(Value value) {
204 FieldRef fieldRef = getOrCacheFieldRefFromValue(value);
205 auto firrtlType = type_dyn_cast<FIRRTLType>(value.getType());
206 if (!firrtlType || type_isa<PropertyType>(firrtlType)) {
207 markOverdefined(fieldRef);
208 return;
209 }
210
211 walkGroundTypes(firrtlType, [&](uint64_t fieldID, auto, auto) {
212 markOverdefined(fieldRef.getSubField(fieldID));
213 });
214 }
215
216 /// Mark the given value as overdefined. This means that we cannot refine a
217 /// specific constant for this value.
218 void markOverdefined(FieldRef value) {
219 auto &entry = latticeValues[value];
220 if (!entry.isOverdefined()) {
221 LLVM_DEBUG({
222 logger.getOStream()
223 << "Setting overdefined : (" << getFieldName(value).first << ")\n";
224 });
225 entry.markOverdefined();
226 changedLatticeValueWorklist.push_back(value);
227 }
228 }
229
230 /// Merge information from the 'from' lattice value into value. If it
231 /// changes, then users of the value are added to the worklist for
232 /// revisitation.
233 void mergeLatticeValue(FieldRef value, LatticeValue &valueEntry,
234 LatticeValue source) {
235 if (valueEntry.mergeIn(source)) {
236 LLVM_DEBUG({
237 logger.getOStream()
238 << "Changed to " << valueEntry << " : (" << value << ")\n";
239 });
240 changedLatticeValueWorklist.push_back(value);
241 }
242 }
243
244 void mergeLatticeValue(FieldRef value, LatticeValue source) {
245 // Don't even do a map lookup if from has no info in it.
246 if (source.isUnknown())
247 return;
248 mergeLatticeValue(value, latticeValues[value], source);
249 }
250
251 void mergeLatticeValue(FieldRef result, FieldRef from) {
252 // If 'from' hasn't been computed yet, then it is unknown, don't do
253 // anything.
254 auto it = latticeValues.find(from);
255 if (it == latticeValues.end())
256 return;
257 mergeLatticeValue(result, it->second);
258 }
259
260 void mergeLatticeValue(Value result, Value from) {
261 FieldRef fieldRefFrom = getOrCacheFieldRefFromValue(from);
262 FieldRef fieldRefResult = getOrCacheFieldRefFromValue(result);
263 if (!type_isa<FIRRTLType>(result.getType()))
264 return mergeLatticeValue(fieldRefResult, fieldRefFrom);
265 // Special-handle PropertyType's, walkGroundType's doesn't support.
266 if (type_isa<PropertyType>(result.getType()))
267 return mergeLatticeValue(fieldRefResult, fieldRefFrom);
268 walkGroundTypes(type_cast<FIRRTLType>(result.getType()),
269 [&](uint64_t fieldID, auto, auto) {
270 mergeLatticeValue(fieldRefResult.getSubField(fieldID),
271 fieldRefFrom.getSubField(fieldID));
272 });
273 }
274
275 /// setLatticeValue - This is used when a new LatticeValue is computed for
276 /// the result of the specified value that replaces any previous knowledge,
277 /// e.g. because a fold() function on an op returned a new thing. This should
278 /// not be used on operations that have multiple contributors to it, e.g.
279 /// wires or ports.
280 void setLatticeValue(FieldRef value, LatticeValue source) {
281 // Don't even do a map lookup if from has no info in it.
282 if (source.isUnknown())
283 return;
284
285 // If we've changed this value then revisit all the users.
286 auto &valueEntry = latticeValues[value];
287 if (valueEntry != source) {
288 changedLatticeValueWorklist.push_back(value);
289 valueEntry = source;
290 }
291 }
292
293 // This function returns a field ref of the given value. This function caches
294 // the result to avoid extra IR traversal if the value is an aggregate
295 // element.
296 FieldRef getOrCacheFieldRefFromValue(Value value) {
297 if (!value.getDefiningOp() || !isAggregate(value.getDefiningOp()))
298 return FieldRef(value, 0);
299 auto &fieldRef = valueToFieldRef[value];
300 if (fieldRef)
301 return fieldRef;
302 return fieldRef = getFieldRefFromValue(value);
303 }
304
305 /// Return the lattice value for the specified SSA value, extended to the
306 /// width of the specified destType. If allowTruncation is true, then this
307 /// allows truncating the lattice value to the specified type.
308 LatticeValue getExtendedLatticeValue(FieldRef value, FIRRTLType destType,
309 bool allowTruncation = false);
310
311 /// Mark the given block as executable.
312 void markBlockExecutable(Block *block);
313 void markWireOp(WireOp wireOrReg);
314 void markMemOp(MemOp mem);
315
316 void markInvalidValueOp(InvalidValueOp invalid);
317 void markAggregateConstantOp(AggregateConstantOp constant);
318 void markInstanceOp(InstanceOp instance);
319 void markObjectOp(ObjectOp object);
320 template <typename OpTy>
321 void markConstantValueOp(OpTy op);
322
323 void visitConnectLike(FConnectLike connect, FieldRef changedFieldRef);
324 void visitRefSend(RefSendOp send, FieldRef changedFieldRef);
325 void visitRefResolve(RefResolveOp resolve, FieldRef changedFieldRef);
326 void mergeOnlyChangedLatticeValue(Value dest, Value src,
327 FieldRef changedFieldRef);
328 void visitNode(NodeOp node, FieldRef changedFieldRef);
329 void visitOperation(Operation *op, FieldRef changedFieldRef);
330
331private:
332 /// This is the current instance graph for the Circuit.
333 InstanceGraph *instanceGraph = nullptr;
334
335 /// This keeps track of the current state of each tracked value.
336 DenseMap<FieldRef, LatticeValue> latticeValues;
337
338 /// The set of blocks that are known to execute, or are intrinsically live.
339 SmallPtrSet<Block *, 16> executableBlocks;
340
341 /// A worklist of values whose LatticeValue recently changed, indicating the
342 /// users need to be reprocessed.
343 SmallVector<FieldRef, 64> changedLatticeValueWorklist;
344
345 // A map to give operations to be reprocessed.
346 DenseMap<FieldRef, llvm::TinyPtrVector<Operation *>> fieldRefToUsers;
347
348 // A map to cache results of getFieldRefFromValue since it's costly traverse
349 // the IR.
350 llvm::DenseMap<Value, FieldRef> valueToFieldRef;
351
352 /// This keeps track of users the instance results that correspond to output
353 /// ports.
354 DenseMap<BlockArgument, llvm::TinyPtrVector<Value>>
355 resultPortToInstanceResultMapping;
356
357#ifndef NDEBUG
358 /// A logger used to emit information during the application process.
359 llvm::ScopedPrinter logger{llvm::dbgs()};
360#endif
361};
362} // end anonymous namespace
363
364// TODO: handle annotations: [[OptimizableExtModuleAnnotation]]
365void IMConstPropPass::runOnOperation() {
366 auto circuit = getOperation();
367 LLVM_DEBUG(
368 { logger.startLine() << "IMConstProp : " << circuit.getName() << "\n"; });
369
370 instanceGraph = &getAnalysis<InstanceGraph>();
371
372 // Mark the input ports of public modules as being overdefined.
373 for (auto module : circuit.getBodyBlock()->getOps<FModuleOp>()) {
374 if (module.isPublic()) {
375 markBlockExecutable(module.getBodyBlock());
376 for (auto port : module.getBodyBlock()->getArguments())
377 markOverdefined(port);
378 }
379 }
380
381 // If a value changed lattice state then reprocess any of its users.
382 while (!changedLatticeValueWorklist.empty()) {
383 FieldRef changedFieldRef = changedLatticeValueWorklist.pop_back_val();
384 for (Operation *user : fieldRefToUsers[changedFieldRef]) {
385 if (isBlockExecutable(user->getBlock()))
386 visitOperation(user, changedFieldRef);
387 }
388 }
389
390 // Rewrite any constants in the modules.
391 mlir::parallelForEach(circuit.getContext(),
392 circuit.getBodyBlock()->getOps<FModuleOp>(),
393 [&](auto op) { rewriteModuleBody(op); });
394
395 // Clean up our state for next time.
396 instanceGraph = nullptr;
397 latticeValues.clear();
398 executableBlocks.clear();
399 assert(changedLatticeValueWorklist.empty());
400 fieldRefToUsers.clear();
401 valueToFieldRef.clear();
402 resultPortToInstanceResultMapping.clear();
403}
404
405/// Return the lattice value for the specified SSA value, extended to the width
406/// of the specified destType. If allowTruncation is true, then this allows
407/// truncating the lattice value to the specified type.
408LatticeValue IMConstPropPass::getExtendedLatticeValue(FieldRef value,
409 FIRRTLType destType,
410 bool allowTruncation) {
411 // If 'value' hasn't been computed yet, then it is unknown.
412 auto it = latticeValues.find(value);
413 if (it == latticeValues.end())
414 return LatticeValue();
415
416 auto result = it->second;
417 // Unknown/overdefined stay whatever they are.
418 if (result.isUnknown() || result.isOverdefined())
419 return result;
420
421 // No extOrTrunc for property types. Return what we have.
422 if (isa<PropertyType>(destType))
423 return result;
424
425 auto constant = result.getConstant();
426
427 // If not property, only support integers.
428 auto intAttr = dyn_cast<IntegerAttr>(constant);
429 assert(intAttr && "unsupported lattice attribute kind");
430 if (!intAttr)
431 return result;
432
433 // No extOrTrunc necessary for bools.
434 if (auto boolAttr = dyn_cast<BoolAttr>(intAttr))
435 return result;
436
437 // Non-base (or non-ref) types are overdefined.
438 auto baseType = getBaseType(destType);
439 if (!baseType)
440 return LatticeValue::getOverdefined();
441
442 // If destType is wider than the source constant type, extend it.
443 auto resultConstant = intAttr.getAPSInt();
444 auto destWidth = baseType.getBitWidthOrSentinel();
445 if (destWidth == -1) // We don't support unknown width FIRRTL.
446 return LatticeValue::getOverdefined();
447 if (resultConstant.getBitWidth() == (unsigned)destWidth)
448 return result; // Already the right width, we're done.
449
450 // Otherwise, extend the constant using the signedness of the source.
451 resultConstant = extOrTruncZeroWidth(resultConstant, destWidth);
452 return LatticeValue(IntegerAttr::get(destType.getContext(), resultConstant));
453}
454
455// NOLINTBEGIN(misc-no-recursion)
456/// Mark a block executable if it isn't already. This does an initial scan of
457/// the block, processing nullary operations like wires, instances, and
458/// constants that only get processed once.
459void IMConstPropPass::markBlockExecutable(Block *block) {
460 if (!executableBlocks.insert(block).second)
461 return; // Already executable.
462
463 // Mark block arguments, which are module ports, with don't touch as
464 // overdefined.
465 for (auto ba : block->getArguments())
466 if (hasDontTouch(ba))
467 markOverdefined(ba);
468
469 for (auto &op : *block) {
470 // Handle each of the special operations in the firrtl dialect.
471 TypeSwitch<Operation *>(&op)
472 .Case<RegOp, RegResetOp>(
473 [&](auto reg) { markOverdefined(op.getResult(0)); })
474 .Case<WireOp>([&](auto wire) { markWireOp(wire); })
475 .Case<ConstantOp, SpecialConstantOp, StringConstantOp,
476 FIntegerConstantOp, BoolConstantOp>(
477 [&](auto constOp) { markConstantValueOp(constOp); })
478 .Case<AggregateConstantOp>(
479 [&](auto aggConstOp) { markAggregateConstantOp(aggConstOp); })
480 .Case<InvalidValueOp>(
481 [&](auto invalid) { markInvalidValueOp(invalid); })
482 .Case<InstanceOp>([&](auto instance) { markInstanceOp(instance); })
483 .Case<ObjectOp>([&](auto obj) { markObjectOp(obj); })
484 .Case<MemOp>([&](auto mem) { markMemOp(mem); })
485 .Case<LayerBlockOp>(
486 [&](auto layer) { markBlockExecutable(layer.getBody(0)); })
487 .Default([&](auto _) {
488 if (isa<mlir::UnrealizedConversionCastOp, VerbatimExprOp,
489 VerbatimWireOp, SubaccessOp>(op) ||
490 op.getNumOperands() == 0) {
491 // Mark operations whose results cannot be tracked as overdefined.
492 // Mark unhandled operations with no operand as well since otherwise
493 // they will remain unknown states until the end.
494 for (auto result : op.getResults())
495 markOverdefined(result);
496 } else if (
497 // Operations that are handled when propagating values, or chasing
498 // indexing.
499 !isAggregate(&op) && !isNodeLike(&op) && op.getNumResults() > 0) {
500 // If an unknown operation has an aggregate operand, mark results as
501 // overdefined since we cannot track the dataflow. Similarly if the
502 // operations create aggregate values, we mark them overdefined.
503
504 // TODO: We should handle aggregate operations such as
505 // vector_create, bundle_create or vector operations.
506
507 bool hasAggregateOperand =
508 llvm::any_of(op.getOperandTypes(), [](Type type) {
509 return type_isa<FVectorType, BundleType>(type);
510 });
511
512 for (auto result : op.getResults())
513 if (hasAggregateOperand ||
514 type_isa<FVectorType, BundleType>(result.getType()))
515 markOverdefined(result);
516 }
517 });
518
519 // This tracks a dependency from field refs to operations which need
520 // to be added to worklist when lattice values change.
521 if (!isAggregate(&op)) {
522 for (auto operand : op.getOperands()) {
523 auto fieldRef = getOrCacheFieldRefFromValue(operand);
524 auto firrtlType = type_dyn_cast<FIRRTLType>(operand.getType());
525 if (!firrtlType)
526 continue;
527 // Special-handle PropertyType's, walkGroundTypes doesn't support.
528 if (type_isa<PropertyType>(firrtlType)) {
529 fieldRefToUsers[fieldRef].push_back(&op);
530 continue;
531 }
532 walkGroundTypes(firrtlType, [&](uint64_t fieldID, auto type, auto) {
533 fieldRefToUsers[fieldRef.getSubField(fieldID)].push_back(&op);
534 });
535 }
536 }
537 }
538}
539// NOLINTEND(misc-no-recursion)
540
541void IMConstPropPass::markWireOp(WireOp wire) {
542 auto type = type_dyn_cast<FIRRTLType>(wire.getResult().getType());
543 if (!type || hasDontTouch(wire.getResult()) || wire.isForceable()) {
544 for (auto result : wire.getResults())
545 markOverdefined(result);
546 return;
547 }
548
549 // Otherwise, this starts out as unknown and is upgraded by connects.
550}
551
552void IMConstPropPass::markMemOp(MemOp mem) {
553 for (auto result : mem.getResults())
554 markOverdefined(result);
555}
556
557template <typename OpTy>
558void IMConstPropPass::markConstantValueOp(OpTy op) {
559 mergeLatticeValue(getOrCacheFieldRefFromValue(op),
560 LatticeValue(op.getValueAttr()));
561}
562
563void IMConstPropPass::markAggregateConstantOp(AggregateConstantOp constant) {
564 walkGroundTypes(constant.getType(), [&](uint64_t fieldID, auto, auto) {
565 mergeLatticeValue(FieldRef(constant, fieldID),
566 LatticeValue(cast<IntegerAttr>(
567 constant.getAttributeFromFieldID(fieldID))));
568 });
569}
570
571void IMConstPropPass::markInvalidValueOp(InvalidValueOp invalid) {
572 markOverdefined(invalid.getResult());
573}
574
575/// Instances have no operands, so they are visited exactly once when their
576/// enclosing block is marked live. This sets up the def-use edges for ports.
577void IMConstPropPass::markInstanceOp(InstanceOp instance) {
578 // Get the module being reference or a null pointer if this is an extmodule.
579 Operation *op = instance.getReferencedModule(*instanceGraph);
580
581 // If this is an extmodule, just remember that any results and inouts are
582 // overdefined.
583 if (!isa<FModuleOp>(op)) {
584 auto module = dyn_cast<FModuleLike>(op);
585 for (size_t resultNo = 0, e = instance.getNumResults(); resultNo != e;
586 ++resultNo) {
587 auto portVal = instance.getResult(resultNo);
588 // If this is an input to the extmodule, we can ignore it.
589 if (module.getPortDirection(resultNo) == Direction::In)
590 continue;
591
592 // Otherwise this is a result from it or an inout, mark it as overdefined.
593 markOverdefined(portVal);
594 }
595 return;
596 }
597
598 // Otherwise this is a defined module.
599 auto fModule = cast<FModuleOp>(op);
600 markBlockExecutable(fModule.getBodyBlock());
601
602 // Ok, it is a normal internal module reference. Populate
603 // resultPortToInstanceResultMapping, and forward any already-computed values.
604 for (size_t resultNo = 0, e = instance.getNumResults(); resultNo != e;
605 ++resultNo) {
606 auto instancePortVal = instance.getResult(resultNo);
607 // If this is an input to the instance, it will
608 // get handled when any connects to it are processed.
609 if (fModule.getPortDirection(resultNo) == Direction::In)
610 continue;
611
612 // Otherwise we have a result from the instance. We need to forward results
613 // from the body to this instance result's SSA value, so remember it.
614 BlockArgument modulePortVal = fModule.getArgument(resultNo);
615
616 resultPortToInstanceResultMapping[modulePortVal].push_back(instancePortVal);
617
618 // If there is already a value known for modulePortVal make sure to forward
619 // it here.
620 mergeLatticeValue(instancePortVal, modulePortVal);
621 }
622}
623
624void IMConstPropPass::markObjectOp(ObjectOp obj) {
625 // Mark overdefined for now, not supported.
626 markOverdefined(obj);
627}
628
629static std::optional<uint64_t>
630getFieldIDOffset(FieldRef changedFieldRef, Type connectionType,
631 FieldRef connectedValueFieldRef) {
632 assert(!type_isa<RefType>(connectionType));
633 if (changedFieldRef.getValue() != connectedValueFieldRef.getValue())
634 return {};
635 if (changedFieldRef.getFieldID() >= connectedValueFieldRef.getFieldID() &&
636 changedFieldRef.getFieldID() <=
637 hw::FieldIdImpl::getMaxFieldID(connectionType) +
638 connectedValueFieldRef.getFieldID())
639 return changedFieldRef.getFieldID() - connectedValueFieldRef.getFieldID();
640 return {};
641}
642
643void IMConstPropPass::mergeOnlyChangedLatticeValue(Value dest, Value src,
644 FieldRef changedFieldRef) {
645
646 // Operate on inner type for refs.
647 auto destType = dest.getType();
648 if (auto refType = type_dyn_cast<RefType>(destType))
649 destType = refType.getType();
650
651 if (!isa<FIRRTLType>(destType)) {
652 // If the dest is not FIRRTL type, conservatively mark
653 // all of them overdefined.
654 markOverdefined(src);
655 return markOverdefined(dest);
656 }
657
658 auto fieldRefSrc = getOrCacheFieldRefFromValue(src);
659 auto fieldRefDest = getOrCacheFieldRefFromValue(dest);
660
661 // If a changed field ref is included the source value, find an offset in the
662 // connection.
663 if (auto srcOffset = getFieldIDOffset(changedFieldRef, destType, fieldRefSrc))
664 mergeLatticeValue(fieldRefDest.getSubField(*srcOffset),
665 fieldRefSrc.getSubField(*srcOffset));
666
667 // If a changed field ref is included the dest value, find an offset in the
668 // connection.
669 if (auto destOffset =
670 getFieldIDOffset(changedFieldRef, destType, fieldRefDest))
671 mergeLatticeValue(fieldRefDest.getSubField(*destOffset),
672 fieldRefSrc.getSubField(*destOffset));
673}
674
675void IMConstPropPass::visitConnectLike(FConnectLike connect,
676 FieldRef changedFieldRef) {
677 // Operate on inner type for refs.
678 auto destType = connect.getDest().getType();
679 if (auto refType = type_dyn_cast<RefType>(destType))
680 destType = refType.getType();
681
682 // Mark foreign types as overdefined.
683 if (!isa<FIRRTLType>(destType)) {
684 markOverdefined(connect.getSrc());
685 return markOverdefined(connect.getDest());
686 }
687
688 auto fieldRefSrc = getOrCacheFieldRefFromValue(connect.getSrc());
689 auto fieldRefDest = getOrCacheFieldRefFromValue(connect.getDest());
690 if (auto subaccess = fieldRefDest.getValue().getDefiningOp<SubaccessOp>()) {
691 // If the destination is subaccess, we give up to precisely track
692 // lattice values and mark entire aggregate as overdefined. This code
693 // should be dead unless we stop lowering of subaccess in LowerTypes.
694 Value parent = subaccess.getInput();
695 while (parent.getDefiningOp() &&
696 parent.getDefiningOp()->getNumOperands() > 0)
697 parent = parent.getDefiningOp()->getOperand(0);
698 return markOverdefined(parent);
699 }
700
701 auto propagateElementLattice = [&](uint64_t fieldID, FIRRTLType destType) {
702 auto fieldRefDestConnected = fieldRefDest.getSubField(fieldID);
703 assert(!firrtl::type_isa<FIRRTLBaseType>(destType) ||
704 firrtl::type_cast<FIRRTLBaseType>(destType).isGround());
705
706 // Handle implicit extensions.
707 auto srcValue =
708 getExtendedLatticeValue(fieldRefSrc.getSubField(fieldID), destType);
709 if (srcValue.isUnknown())
710 return;
711
712 // Driving result ports propagates the value to each instance using the
713 // module.
714 if (auto blockArg = dyn_cast<BlockArgument>(fieldRefDest.getValue())) {
715 for (auto userOfResultPort : resultPortToInstanceResultMapping[blockArg])
716 mergeLatticeValue(
717 FieldRef(userOfResultPort, fieldRefDestConnected.getFieldID()),
718 srcValue);
719 // Output ports are wire-like and may have users.
720 return mergeLatticeValue(fieldRefDestConnected, srcValue);
721 }
722
723 auto dest = cast<mlir::OpResult>(fieldRefDest.getValue());
724
725 // For wires and registers, we drive the value of the wire itself, which
726 // automatically propagates to users.
727 if (isWireOrReg(dest.getOwner()))
728 return mergeLatticeValue(fieldRefDestConnected, srcValue);
729
730 // Driving an instance argument port drives the corresponding argument
731 // of the referenced module.
732 if (auto instance = dest.getDefiningOp<InstanceOp>()) {
733 // Update the dest, when its an instance op.
734 mergeLatticeValue(fieldRefDestConnected, srcValue);
735 auto mod = instance.getReferencedModule<FModuleOp>(*instanceGraph);
736 if (!mod)
737 return;
738
739 BlockArgument modulePortVal = mod.getArgument(dest.getResultNumber());
740
741 return mergeLatticeValue(
742 FieldRef(modulePortVal, fieldRefDestConnected.getFieldID()),
743 srcValue);
744 }
745
746 // Driving a memory result is ignored because these are always treated
747 // as overdefined.
748 if (dest.getDefiningOp<MemOp>())
749 return;
750
751 // For now, don't support const prop into object fields.
752 if (isa_and_nonnull<ObjectSubfieldOp>(dest.getDefiningOp()))
753 return;
754
755 connect.emitError("connectlike operation unhandled by IMConstProp")
756 .attachNote(connect.getDest().getLoc())
757 << "connect destination is here";
758 };
759
760 if (auto srcOffset = getFieldIDOffset(changedFieldRef, destType, fieldRefSrc))
761 propagateElementLattice(
762 *srcOffset,
763 firrtl::type_cast<FIRRTLType>(
764 hw::FieldIdImpl::getFinalTypeByFieldID(destType, *srcOffset)));
765
766 if (auto relativeDest =
767 getFieldIDOffset(changedFieldRef, destType, fieldRefDest))
768 propagateElementLattice(
769 *relativeDest,
770 firrtl::type_cast<FIRRTLType>(
771 hw::FieldIdImpl::getFinalTypeByFieldID(destType, *relativeDest)));
772}
773
774void IMConstPropPass::visitRefSend(RefSendOp send, FieldRef changedFieldRef) {
775 // Send connects the base value (source) to the result (dest).
776 return mergeOnlyChangedLatticeValue(send.getResult(), send.getBase(),
777 changedFieldRef);
778}
779
780void IMConstPropPass::visitRefResolve(RefResolveOp resolve,
781 FieldRef changedFieldRef) {
782 // Resolve connects the ref value (source) to result (dest).
783 // If writes are ever supported, this will need to work differently!
784 return mergeOnlyChangedLatticeValue(resolve.getResult(), resolve.getRef(),
785 changedFieldRef);
786}
787
788void IMConstPropPass::visitNode(NodeOp node, FieldRef changedFieldRef) {
789 if (hasDontTouch(node.getResult()) || node.isForceable()) {
790 for (auto result : node.getResults())
791 markOverdefined(result);
792 return;
793 }
794
795 return mergeOnlyChangedLatticeValue(node.getResult(), node.getInput(),
796 changedFieldRef);
797}
798
799/// This method is invoked when an operand of the specified op changes its
800/// lattice value state and when the block containing the operation is first
801/// noticed as being alive.
802///
803/// This should update the lattice value state for any result values.
804///
805void IMConstPropPass::visitOperation(Operation *op, FieldRef changedField) {
806 // If this is a operation with special handling, handle it specially.
807 if (auto connectLikeOp = dyn_cast<FConnectLike>(op))
808 return visitConnectLike(connectLikeOp, changedField);
809 if (auto sendOp = dyn_cast<RefSendOp>(op))
810 return visitRefSend(sendOp, changedField);
811 if (auto resolveOp = dyn_cast<RefResolveOp>(op))
812 return visitRefResolve(resolveOp, changedField);
813 if (auto nodeOp = dyn_cast<NodeOp>(op))
814 return visitNode(nodeOp, changedField);
815
816 // The clock operand of regop changing doesn't change its result value. All
817 // other registers are over-defined. Aggregate operations also doesn't change
818 // its result value.
819 if (isa<RegOp, RegResetOp>(op) || isAggregate(op))
820 return;
821 // TODO: Handle 'when' operations.
822
823 // If all of the results of this operation are already overdefined (or if
824 // there are no results) then bail out early: we've converged.
825 auto isOverdefinedFn = [&](Value value) {
826 return isOverdefined(getOrCacheFieldRefFromValue(value));
827 };
828 if (llvm::all_of(op->getResults(), isOverdefinedFn))
829 return;
830
831 // To prevent regressions, mark values as overdefined when they are defined
832 // by operations with a large number of operands.
833 if (op->getNumOperands() > 128) {
834 for (auto value : op->getResults())
835 markOverdefined(value);
836 return;
837 }
838
839 // Collect all of the constant operands feeding into this operation. If any
840 // are not ready to be resolved, bail out and wait for them to resolve.
841 SmallVector<Attribute, 8> operandConstants;
842 operandConstants.reserve(op->getNumOperands());
843 bool hasUnknown = false;
844 for (Value operand : op->getOperands()) {
845
846 auto &operandLattice = latticeValues[getOrCacheFieldRefFromValue(operand)];
847
848 // If the operand is an unknown value, then we generally don't want to
849 // process it - we want to wait until the value is resolved to by the SCCP
850 // algorithm.
851 if (operandLattice.isUnknown())
852 hasUnknown = true;
853
854 // Otherwise, it must be constant, invalid, or overdefined. Translate them
855 // into attributes that the fold hook can look at.
856 if (operandLattice.isConstant())
857 operandConstants.push_back(operandLattice.getValue());
858 else
859 operandConstants.push_back({});
860 }
861
862 // Simulate the result of folding this operation to a constant. If folding
863 // fails mark the results as overdefined.
864 SmallVector<OpFoldResult, 8> foldResults;
865 foldResults.reserve(op->getNumResults());
866 if (failed(op->fold(operandConstants, foldResults))) {
867 LLVM_DEBUG({
868 logger.startLine() << "Folding Failed operation : '" << op->getName()
869 << "\n";
870 op->dump();
871 });
872 // If we had unknown arguments, hold off on overdefining
873 if (!hasUnknown)
874 for (auto value : op->getResults())
875 markOverdefined(value);
876 return;
877 }
878
879 LLVM_DEBUG({
880 logger.getOStream() << "\n";
881 logger.startLine() << "Folding operation : '" << op->getName() << "\n";
882 op->dump();
883 logger.getOStream() << "( ";
884 for (auto cst : operandConstants)
885 if (!cst)
886 logger.getOStream() << "{} ";
887 else
888 logger.getOStream() << cst << " ";
889 logger.unindent();
890 logger.getOStream() << ") -> { ";
891 logger.indent();
892 for (auto &r : foldResults) {
893 logger.getOStream() << r << " ";
894 }
895 logger.unindent();
896 logger.getOStream() << "}\n";
897 });
898
899 // If the folding was in-place, keep going. This is surprising, but since
900 // only folder that will do in-place updates is the commutative folder, we
901 // aren't going to stop. We don't update the results, since they didn't
902 // change, the op just got shuffled around.
903 if (foldResults.empty())
904 return visitOperation(op, changedField);
905
906 // Merge the fold results into the lattice for this operation.
907 assert(foldResults.size() == op->getNumResults() && "invalid result size");
908 for (unsigned i = 0, e = foldResults.size(); i != e; ++i) {
909 // Merge in the result of the fold, either a constant or a value.
910 LatticeValue resultLattice;
911 OpFoldResult foldResult = foldResults[i];
912 if (Attribute foldAttr = dyn_cast<Attribute>(foldResult)) {
913 if (auto intAttr = dyn_cast<IntegerAttr>(foldAttr))
914 resultLattice = LatticeValue(intAttr);
915 else if (auto strAttr = dyn_cast<StringAttr>(foldAttr))
916 resultLattice = LatticeValue(strAttr);
917 else // Treat unsupported constants as overdefined.
918 resultLattice = LatticeValue::getOverdefined();
919 } else { // Folding to an operand results in its value.
920 resultLattice =
921 latticeValues[getOrCacheFieldRefFromValue(foldResult.get<Value>())];
922 }
923
924 mergeLatticeValue(getOrCacheFieldRefFromValue(op->getResult(i)),
925 resultLattice);
926 }
927}
928
929void IMConstPropPass::rewriteModuleBody(FModuleOp module) {
930 auto *body = module.getBodyBlock();
931 // If a module is unreachable, just ignore it.
932 if (!executableBlocks.count(body))
933 return;
934
935 auto builder = OpBuilder::atBlockBegin(body);
936
937 // Separate the constants we insert from the instructions we are folding and
938 // processing. Leave these as-is until we're done.
939 auto cursor = builder.create<firrtl::ConstantOp>(module.getLoc(), APSInt(1));
940 builder.setInsertionPoint(cursor);
941
942 // Unique constants per <Const,Type> pair, inserted at entry
943 DenseMap<std::pair<Attribute, Type>, Operation *> constPool;
944
945 std::function<Value(Attribute, Type, Location)> getConst =
946 [&](Attribute constantValue, Type type, Location loc) -> Value {
947 auto constIt = constPool.find({constantValue, type});
948 if (constIt != constPool.end()) {
949 auto *cst = constIt->second;
950 // Add location to the constant
951 cst->setLoc(builder.getFusedLoc({cst->getLoc(), loc}));
952 return cst->getResult(0);
953 }
954 OpBuilder::InsertionGuard x(builder);
955 builder.setInsertionPoint(cursor);
956
957 // Materialize reftype "constants" by materializing the constant
958 // and probing it.
959 Operation *cst;
960 if (auto refType = type_dyn_cast<RefType>(type)) {
961 assert(!type_cast<RefType>(type).getForceable() &&
962 "Attempting to materialize rwprobe of constant, shouldn't happen");
963 auto inner = getConst(constantValue, refType.getType(), loc);
964 assert(inner);
965 cst = builder.create<RefSendOp>(loc, inner);
966 } else
967 cst = module->getDialect()->materializeConstant(builder, constantValue,
968 type, loc);
969 assert(cst && "all FIRRTL constants can be materialized");
970 constPool.insert({{constantValue, type}, cst});
971 return cst->getResult(0);
972 };
973
974 // If the lattice value for the specified value is a constant update it and
975 // return true. Otherwise return false.
976 auto replaceValueIfPossible = [&](Value value) -> bool {
977 // Lambda to replace all uses of this value a replacement, unless this is
978 // the destination of a connect. We leave connects alone to avoid upsetting
979 // flow, i.e., to avoid trying to connect to a constant.
980 auto replaceIfNotConnect = [&value](Value replacement) {
981 value.replaceUsesWithIf(replacement, [](OpOperand &operand) {
982 return !isa<FConnectLike>(operand.getOwner()) ||
983 operand.getOperandNumber() != 0;
984 });
985 };
986
987 // TODO: Replace entire aggregate.
988 auto it = latticeValues.find(getFieldRefFromValue(value));
989 if (it == latticeValues.end() || it->second.isOverdefined() ||
990 it->second.isUnknown())
991 return false;
992
993 // Cannot materialize constants for certain types.
994 // TODO: Let materializeConstant tell us what it supports instead of this.
995 // Presently it asserts on unsupported combinations, so check this here.
996 if (!type_isa<FIRRTLBaseType, RefType, FIntegerType, StringType, BoolType>(
997 value.getType()))
998 return false;
999
1000 auto cstValue =
1001 getConst(it->second.getValue(), value.getType(), value.getLoc());
1002
1003 replaceIfNotConnect(cstValue);
1004 return true;
1005 };
1006
1007 // Constant propagate any ports that are always constant.
1008 for (auto &port : body->getArguments())
1009 replaceValueIfPossible(port);
1010
1011 // Walk the IR bottom-up when folding. We often fold entire chains of
1012 // operations into constants, which make the intermediate nodes dead. Going
1013 // bottom up eliminates the users of the intermediate ops, allowing us to
1014 // aggressively delete them.
1015 //
1016 // TODO: Handle WhenOps correctly.
1017 bool aboveCursor = false;
1018 module.walk<mlir::WalkOrder::PostOrder, mlir::ReverseIterator>(
1019 [&](Operation *op) {
1020 auto dropIfDead = [&](Operation *op, const Twine &debugPrefix) {
1021 if (op->use_empty() &&
1022 (wouldOpBeTriviallyDead(op) || isDeletableWireOrRegOrNode(op))) {
1023 LLVM_DEBUG(
1024 { logger.getOStream() << debugPrefix << " : " << op << "\n"; });
1025 ++numErasedOp;
1026 op->erase();
1027 return true;
1028 }
1029 return false;
1030 };
1031
1032 if (aboveCursor) {
1033 // Drop dead constants we materialized.
1034 dropIfDead(op, "Trivially dead materialized constant");
1035 return WalkResult::advance();
1036 }
1037 // Stop once hit the generated constants.
1038 if (op == cursor) {
1039 cursor.erase();
1040 aboveCursor = true;
1041 return WalkResult::advance();
1042 }
1043
1044 // Connects to values that we found to be constant can be dropped.
1045 if (auto connect = dyn_cast<FConnectLike>(op)) {
1046 if (auto *destOp = connect.getDest().getDefiningOp()) {
1047 auto fieldRef = getOrCacheFieldRefFromValue(connect.getDest());
1048 // Don't remove a field-level connection even if the src value is
1049 // constant. If other elements of the aggregate value are not
1050 // constant, the aggregate value cannot be replaced. We can forward
1051 // the constant to its users, so IMDCE (or SV/HW canonicalizer)
1052 // should remove the aggregate if entire aggregate is dead.
1053 auto type = type_dyn_cast<FIRRTLType>(connect.getDest().getType());
1054 if (!type)
1055 return WalkResult::advance();
1056 auto baseType = type_dyn_cast<FIRRTLBaseType>(type);
1057 if (baseType && !baseType.isGround())
1058 return WalkResult::advance();
1059 if (isDeletableWireOrRegOrNode(destOp) &&
1060 !isOverdefined(fieldRef)) {
1061 connect.erase();
1062 ++numErasedOp;
1063 }
1064 }
1065 return WalkResult::advance();
1066 }
1067
1068 // We only fold single-result ops and instances in practice, because
1069 // they are the expressions.
1070 if (op->getNumResults() != 1 && !isa<InstanceOp>(op))
1071 return WalkResult::advance();
1072
1073 // If this operation is already dead, then go ahead and remove it.
1074 if (dropIfDead(op, "Trivially dead"))
1075 return WalkResult::advance();
1076
1077 // Don't "fold" constants (into equivalent), also because they
1078 // may have name hints we'd like to preserve.
1079 if (op->hasTrait<mlir::OpTrait::ConstantLike>())
1080 return WalkResult::advance();
1081
1082 // If the op had any constants folded, replace them.
1083 builder.setInsertionPoint(op);
1084 bool foldedAny = false;
1085 for (auto result : op->getResults())
1086 foldedAny |= replaceValueIfPossible(result);
1087
1088 if (foldedAny)
1089 ++numFoldedOp;
1090
1091 // If the operation folded to a constant then we can probably nuke it.
1092 if (foldedAny && dropIfDead(op, "Made dead"))
1093 return WalkResult::advance();
1094
1095 return WalkResult::advance();
1096 });
1097}
1098
1099std::unique_ptr<mlir::Pass> circt::firrtl::createIMConstPropPass() {
1100 return std::make_unique<IMConstPropPass>();
1101}
assert(baseType &&"element must be base type")
static std::optional< APSInt > getConstant(Attribute operand)
Determine the value of a constant operand for the sake of constant folding.
static bool isNodeLike(Operation *op)
static bool isWireOrReg(Operation *op)
Return true if this is a wire or register.
static bool isAggregate(Operation *op)
Return true if this is an aggregate indexer.
static std::optional< uint64_t > getFieldIDOffset(FieldRef changedFieldRef, Type connectionType, FieldRef connectedValueFieldRef)
static bool isDeletableWireOrRegOrNode(Operation *op)
Return true if this is a wire or register we're allowed to delete.
static unsigned getFieldID(BundleType type, unsigned index)
static Block * getBodyBlock(FModuleLike mod)
This class represents a reference to a specific field or element of an aggregate value.
Definition FieldRef.h:28
FieldRef getSubField(unsigned subFieldID) const
Get a reference to a subfield.
Definition FieldRef.h:62
unsigned getFieldID() const
Get the field ID of this FieldRef, which is a unique identifier mapped to a specific field in a bundl...
Definition FieldRef.h:59
Value getValue() const
Get the Value which created this location.
Definition FieldRef.h:37
Location getLoc() const
Get the location associated with the value of this field ref.
Definition FieldRef.h:67
This class provides a read-only projection over the MLIR attributes that represent a set of annotatio...
This graph tracks modules and where they are instantiated.
connect(destination, source)
Definition support.py:39
FIRRTLBaseType getBaseType(Type type)
If it is a base type, return it as is.
FieldRef getFieldRefFromValue(Value value, bool lookThroughCasts=false)
Get the FieldRef from a value.
void walkGroundTypes(FIRRTLType firrtlType, llvm::function_ref< void(uint64_t, FIRRTLBaseType, bool)> fn)
Walk leaf ground types in the firrtlType and apply the function fn.
bool isConstant(Operation *op)
Return true if the specified operation has a constant value.
std::unique_ptr< mlir::Pass > createIMConstPropPass()
bool hasDontTouch(Value value)
Check whether a block argument ("port") or the operation defining a value has a DontTouch annotation,...
llvm::raw_ostream & operator<<(llvm::raw_ostream &os, const InstanceInfo::LatticeValue &value)
bool hasDroppableName(Operation *op)
Return true if the name is droppable.
std::pair< std::string, bool > getFieldName(const FieldRef &fieldRef, bool nameSafe=false)
Get a string identifier representing the FieldRef.
bool type_isa(Type type)
::mlir::Type getFinalTypeByFieldID(Type type, uint64_t fieldID)
static bool operator==(const ModulePort &a, const ModulePort &b)
Definition HWTypes.h:35
The InstanceGraph op interface, see InstanceGraphInterface.td for more details.
APSInt extOrTruncZeroWidth(APSInt value, unsigned width)
A safe version of APSInt::extOrTrunc that will NOT assert on zero-width signed APSInts.
Definition APInt.cpp:22
bool operator!=(uint64_t a, const FVInt &b)
Definition FVInt.h:651
reg(value, clock, reset=None, reset_value=None, name=None, sym_name=None)
Definition seq.py:21