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source: src/ResolvExpr/SatisfyAssertions.cpp @ ded6c2a6

ast-experimental

Last change on this file since ded6c2a6 was 251ce80, checked in by Fangren Yu <f37yu@…>, 18 months ago
remove reference to symbol table in unify
Property mode set to `100644`
File size: 20.3 KB

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1	//
2	// Cforall Version 1.0.0 Copyright (C) 2015 University of Waterloo
3	//
4	// The contents of this file are covered under the licence agreement in the
5	// file "LICENCE" distributed with Cforall.
6	//
7	// SatisfyAssertions.cpp --
8	//
9	// Author : Aaron B. Moss
10	// Created On : Mon Jun 10 17:45:00 2019
11	// Last Modified By : Andrew Beach
12	// Last Modified On : Tue Oct 1 13:56:00 2019
13	// Update Count : 2
14	//
15
16	#include "SatisfyAssertions.hpp"
17
18	#include <algorithm>
19	#include <cassert>
20	#include <sstream>
21	#include <string>
22	#include <unordered_map>
23	#include <vector>
24
25	#include "AdjustExprType.hpp"
26	#include "Candidate.hpp"
27	#include "CandidateFinder.hpp"
28	#include "CommonType.hpp"
29	#include "Cost.h"
30	#include "RenameVars.h"
31	#include "SpecCost.hpp"
32	#include "typeops.h"
33	#include "Unify.h"
34	#include "AST/Decl.hpp"
35	#include "AST/Expr.hpp"
36	#include "AST/Node.hpp"
37	#include "AST/Pass.hpp"
38	#include "AST/Print.hpp"
39	#include "AST/SymbolTable.hpp"
40	#include "AST/TypeEnvironment.hpp"
41	#include "FindOpenVars.h"
42	#include "Common/FilterCombos.h"
43	#include "Common/Indenter.h"
44	#include "GenPoly/GenPoly.h"
45	#include "SymTab/Mangler.h"
46
47	namespace ResolvExpr {
48
49	// in CandidateFinder.cpp; unique ID for assertion satisfaction
50	extern UniqueId globalResnSlot;
51
52	namespace {
53	/// Post-unification assertion satisfaction candidate
54	struct AssnCandidate {
55	ast::SymbolTable::IdData cdata; ///< Satisfying declaration
56	ast::ptr< ast::Type > adjType; ///< Satisfying type
57	ast::TypeEnvironment env; ///< Post-unification environment
58	ast::AssertionSet have; ///< Post-unification have-set
59	ast::AssertionSet need; ///< Post-unification need-set
60	ast::OpenVarSet open; ///< Post-unification open-var-set
61	ast::UniqueId resnSlot; ///< Slot for any recursive assertion IDs
62
63	AssnCandidate(
64	const ast::SymbolTable::IdData c, const ast::Type * at, ast::TypeEnvironment && e,
65	ast::AssertionSet && h, ast::AssertionSet && n, ast::OpenVarSet && o, ast::UniqueId rs )
66	: cdata( c ), adjType( at ), env( std::move( e ) ), have( std::move( h ) ),
67	need( std::move( n ) ), open( std::move( o ) ), resnSlot( rs ) {}
68	};
69
70	/// List of assertion satisfaction candidates
71	using AssnCandidateList = std::vector< AssnCandidate >;
72
73	/// Reference to a single deferred item
74	struct DeferRef {
75	const ast::VariableExpr * expr;
76	const ast::AssertionSetValue & info;
77	const AssnCandidate & match;
78	};
79
80	/// Wrapper for the deferred items from a single assertion satisfaction.
81	/// Acts like an indexed list of DeferRef
82	struct DeferItem {
83	const ast::VariableExpr * expr;
84	const ast::AssertionSetValue & info;
85	AssnCandidateList matches;
86
87	DeferItem(
88	const ast::VariableExpr * d, const ast::AssertionSetValue & i, AssnCandidateList && ms )
89	: expr( d ), info( i ), matches( std::move( ms ) ) {}
90
91	bool empty() const { return matches.empty(); }
92
93	AssnCandidateList::size_type size() const { return matches.size(); }
94
95	DeferRef operator[] ( unsigned i ) const { return { expr, info, matches[i] }; }
96	};
97
98	/// List of deferred satisfaction items
99	using DeferList = std::vector< DeferItem >;
100
101	/// Set of assertion satisfactions, grouped by resolution ID
102	using InferCache = std::unordered_map< ast::UniqueId, ast::InferredParams >;
103
104	/// Lexicographically-ordered vector of costs.
105	/// Lexicographic order comes from default operator< on std::vector.
106	using CostVec = std::vector< Cost >;
107
108	/// Flag for state iteration
109	enum IterateFlag { IterateState };
110
111	/// Intermediate state for satisfying a set of assertions
112	struct SatState {
113	CandidateRef cand; ///< Candidate assertion is rooted on
114	ast::AssertionList need; ///< Assertions to find
115	ast::AssertionSet newNeed; ///< Recursive assertions from current satisfied assertions
116	DeferList deferred; ///< Deferred matches
117	InferCache inferred; ///< Cache of already-inferred assertions
118	CostVec costs; ///< Disambiguating costs of recursive assertion satisfaction
119	ast::SymbolTable symtab; ///< Name lookup (depends on previous assertions)
120
121	/// Initial satisfaction state for a candidate
122	SatState( CandidateRef & c, const ast::SymbolTable & syms )
123	: cand( c ), need(), newNeed(), deferred(), inferred(), costs{ Cost::zero },
124	symtab( syms ) { need.swap( c->need ); }
125
126	/// Update satisfaction state for next step after previous state
127	SatState( SatState && o, IterateFlag )
128	: cand( std::move( o.cand ) ), need( o.newNeed.begin(), o.newNeed.end() ), newNeed(),
129	deferred(), inferred( std::move( o.inferred ) ), costs( std::move( o.costs ) ),
130	symtab( o.symtab ) { costs.emplace_back( Cost::zero ); }
131
132	/// Field-wise next step constructor
133	SatState(
134	CandidateRef && c, ast::AssertionSet && nn, InferCache && i, CostVec && cs,
135	ast::SymbolTable && syms )
136	: cand( std::move( c ) ), need( nn.begin(), nn.end() ), newNeed(), deferred(),
137	inferred( std::move( i ) ), costs( std::move( cs ) ), symtab( std::move( syms ) )
138	{ costs.emplace_back( Cost::zero ); }
139	};
140
141	/// Adds a captured assertion to the symbol table
142	void addToSymbolTable( const ast::AssertionSet & have, ast::SymbolTable & symtab ) {
143	for ( auto & i : have ) {
144	if ( i.second.isUsed ) { symtab.addId( i.first->var ); }
145	}
146	}
147
148	/// Binds a single assertion, updating satisfaction state
149	void bindAssertion(
150	const ast::VariableExpr * expr, const ast::AssertionSetValue & info, CandidateRef & cand,
151	AssnCandidate & match, InferCache & inferred
152	) {
153	const ast::DeclWithType * candidate = match.cdata.id;
154	assertf( candidate->uniqueId,
155	"Assertion candidate does not have a unique ID: %s", toString( candidate ).c_str() );
156
157	ast::Expr * varExpr = match.cdata.combine( cand->expr->location, cand->cvtCost );
158	varExpr->result = match.adjType;
159	if ( match.resnSlot ) { varExpr->inferred.resnSlots().emplace_back( match.resnSlot ); }
160
161	// place newly-inferred assertion in proper location in cache
162	inferred[ info.resnSlot ][ expr->var->uniqueId ] = ast::ParamEntry{
163	candidate->uniqueId, candidate, match.adjType, expr->result, varExpr };
164	}
165
166	/// Satisfy a single assertion
167	bool satisfyAssertion( ast::AssertionList::value_type & assn, SatState & sat, bool allowConversion = false, bool skipUnbound = false) {
168	// skip unused assertions
169	if ( ! assn.second.isUsed ) return true;
170
171	// find candidates that unify with the desired type
172	AssnCandidateList matches;
173
174	std::vector<ast::SymbolTable::IdData> candidates;
175	auto kind = ast::SymbolTable::getSpecialFunctionKind(assn.first->var->name);
176	if (kind != ast::SymbolTable::SpecialFunctionKind::NUMBER_OF_KINDS) {
177	// prefilter special decls by argument type, if already known
178	ast::ptr<ast::Type> thisArgType = assn.first->result.strict_as<ast::PointerType>()->base
179	.strict_as<ast::FunctionType>()->params[0]
180	.strict_as<ast::ReferenceType>()->base;
181	sat.cand->env.apply(thisArgType);
182
183	std::string otypeKey = "";
184	if (thisArgType.as<ast::PointerType>()) otypeKey = Mangle::Encoding::pointer;
185	else if (!isUnboundType(thisArgType)) otypeKey = Mangle::mangle(thisArgType, Mangle::Type \| Mangle::NoGenericParams);
186	else if (skipUnbound) return false;
187
188	candidates = sat.symtab.specialLookupId(kind, otypeKey);
189	}
190	else {
191	candidates = sat.symtab.lookupId(assn.first->var->name);
192	}
193	for ( const ast::SymbolTable::IdData & cdata : candidates ) {
194	const ast::DeclWithType * candidate = cdata.id;
195
196	// ignore deleted candidates.
197	// NOTE: this behavior is different from main resolver.
198	// further investigations might be needed to determine
199	// if we should implement the same rule here
200	// (i.e. error if unique best match is deleted)
201	if (candidate->isDeleted && candidate->linkage == ast::Linkage::AutoGen) continue;
202
203	// build independent unification context for candidate
204	ast::AssertionSet have, newNeed;
205	ast::TypeEnvironment newEnv{ sat.cand->env };
206	ast::OpenVarSet newOpen{ sat.cand->open };
207	ast::ptr< ast::Type > toType = assn.first->result;
208	ast::ptr< ast::Type > adjType =
209	renameTyVars( adjustExprType( candidate->get_type(), newEnv, sat.symtab ), GEN_USAGE, false );
210
211	// only keep candidates which unify
212
213	ast::OpenVarSet closed;
214	findOpenVars( toType, newOpen, closed, newNeed, have, FirstClosed );
215	findOpenVars( adjType, newOpen, closed, newNeed, have, FirstOpen );
216	if ( allowConversion ) {
217	if ( auto c = commonType( toType, adjType, newEnv, newNeed, have, newOpen, WidenMode {true, true} ) ) {
218	// set up binding slot for recursive assertions
219	ast::UniqueId crntResnSlot = 0;
220	if ( ! newNeed.empty() ) {
221	crntResnSlot = ++globalResnSlot;
222	for ( auto & a : newNeed ) { a.second.resnSlot = crntResnSlot; }
223	}
224
225	matches.emplace_back(
226	cdata, adjType, std::move( newEnv ), std::move( have ), std::move( newNeed ),
227	std::move( newOpen ), crntResnSlot );
228	}
229	}
230	else {
231	if ( unifyExact( toType, adjType, newEnv, newNeed, have, newOpen, WidenMode {true, true} ) ) {
232	// set up binding slot for recursive assertions
233	ast::UniqueId crntResnSlot = 0;
234	if ( ! newNeed.empty() ) {
235	crntResnSlot = ++globalResnSlot;
236	for ( auto & a : newNeed ) { a.second.resnSlot = crntResnSlot; }
237	}
238
239	matches.emplace_back(
240	cdata, adjType, std::move( newEnv ), std::move( have ), std::move( newNeed ),
241	std::move( newOpen ), crntResnSlot );
242	}
243	}
244	}
245
246	// break if no satisfying match
247	if ( matches.empty() ) return false;
248
249	// defer if too many satisfying matches
250	if ( matches.size() > 1 ) {
251	sat.deferred.emplace_back( assn.first, assn.second, std::move( matches ) );
252	return true;
253	}
254
255	// otherwise bind unique match in ongoing scope
256	AssnCandidate & match = matches.front();
257	addToSymbolTable( match.have, sat.symtab );
258	sat.newNeed.insert( match.need.begin(), match.need.end() );
259	sat.cand->env = std::move( match.env );
260	sat.cand->open = std::move( match.open );
261
262	bindAssertion( assn.first, assn.second, sat.cand, match, sat.inferred );
263	return true;
264	}
265
266	/// Map of candidate return types to recursive assertion satisfaction costs
267	using PruneMap = std::unordered_map< std::string, CostVec >;
268
269	/// Gets the pruning key for a candidate (derived from environment-adjusted return type)
270	std::string pruneKey( const Candidate & cand ) {
271	ast::ptr< ast::Type > resType = cand.expr->result;
272	cand.env.apply( resType );
273	return Mangle::mangleType( resType );
274	}
275
276	/// Associates inferred parameters with an expression
277	struct InferMatcher final {
278	InferCache & inferred;
279
280	InferMatcher( InferCache & inferred ) : inferred( inferred ) {}
281
282	const ast::Expr * postvisit( const ast::Expr * expr ) {
283	// Skip if no slots to find
284	if ( !expr->inferred.hasSlots() ) return expr;
285	// if ( expr->inferred.mode != ast::Expr::InferUnion::Slots ) return expr;
286	std::vector<UniqueId> missingSlots;
287	// find inferred parameters for resolution slots
288	ast::InferredParams * newInferred = new ast::InferredParams();
289	for ( UniqueId slot : expr->inferred.resnSlots() ) {
290	// fail if no matching assertions found
291	auto it = inferred.find( slot );
292	if ( it == inferred.end() ) {
293	// std::cerr << "missing assertion " << slot << std::endl;
294	missingSlots.push_back(slot);
295	continue;
296	}
297
298	// place inferred parameters into new map
299	for ( auto & entry : it->second ) {
300	// recurse on inferParams of resolved expressions
301	entry.second.expr = postvisit( entry.second.expr );
302	auto res = newInferred->emplace( entry );
303	assert( res.second && "all assertions newly placed" );
304	}
305	}
306
307	ast::Expr * ret = mutate( expr );
308	ret->inferred.set_inferParams( newInferred );
309	if (!missingSlots.empty()) ret->inferred.resnSlots() = missingSlots;
310	return ret;
311	}
312	};
313
314	/// Replace ResnSlots with InferParams and add alternative to output list, if it meets pruning
315	/// threshold.
316	void finalizeAssertions(
317	CandidateRef & cand, InferCache & inferred, PruneMap & thresholds, CostVec && costs,
318	CandidateList & out
319	) {
320	// prune if cheaper alternative for same key has already been generated
321	std::string key = pruneKey( *cand );
322	auto it = thresholds.find( key );
323	if ( it != thresholds.end() ) {
324	if ( it->second < costs ) return;
325	} else {
326	thresholds.emplace_hint( it, key, std::move( costs ) );
327	}
328
329	// replace resolution slots with inferred parameters, add to output
330	ast::Pass< InferMatcher > matcher{ inferred };
331	cand->expr = cand->expr->accept( matcher );
332	out.emplace_back( cand );
333	}
334
335	/// Combo iterator that combines candidates into an output list, merging their environments.
336	/// Rejects an appended candidate if environments cannot be merged. See `Common/FilterCombos.h`
337	/// for description of "combo iterator".
338	class CandidateEnvMerger {
339	/// Current list of merged candidates
340	std::vector< DeferRef > crnt;
341	/// Stack of environments to support backtracking
342	std::vector< ast::TypeEnvironment > envs;
343	/// Stack of open variables to support backtracking
344	std::vector< ast::OpenVarSet > opens;
345	/// Symbol table to use for merges
346	const ast::SymbolTable & symtab;
347
348	public:
349	/// The merged environment/open variables and the list of candidates
350	struct OutType {
351	ast::TypeEnvironment env;
352	ast::OpenVarSet open;
353	std::vector< DeferRef > assns;
354	Cost cost;
355
356	OutType(
357	const ast::TypeEnvironment & e, const ast::OpenVarSet & o,
358	const std::vector< DeferRef > & as, const ast::SymbolTable & symtab )
359	: env( e ), open( o ), assns( as ), cost( Cost::zero ) {
360	// compute combined conversion cost
361	for ( const DeferRef & assn : assns ) {
362	// compute conversion cost from satisfying decl to assertion
363	cost += computeConversionCost(
364	assn.match.adjType, assn.expr->result, false, symtab, env );
365
366	// mark vars+specialization on function-type assertions
367	const ast::FunctionType * func =
368	GenPoly::getFunctionType( assn.match.cdata.id->get_type() );
369	if ( ! func ) continue;
370
371	for ( const auto & param : func->params ) {
372	cost.decSpec( specCost( param ) );
373	}
374
375	cost.incVar( func->forall.size() );
376
377	cost.decSpec( func->assertions.size() );
378	}
379	}
380
381	bool operator< ( const OutType & o ) const { return cost < o.cost; }
382	};
383
384	CandidateEnvMerger(
385	const ast::TypeEnvironment & env, const ast::OpenVarSet & open,
386	const ast::SymbolTable & syms )
387	: crnt(), envs{ env }, opens{ open }, symtab( syms ) {}
388
389	bool append( DeferRef i ) {
390	ast::TypeEnvironment env = envs.back();
391	ast::OpenVarSet open = opens.back();
392	mergeOpenVars( open, i.match.open );
393
394	if ( ! env.combine( i.match.env, open ) ) return false;
395
396	crnt.emplace_back( i );
397	envs.emplace_back( std::move( env ) );
398	opens.emplace_back( std::move( open ) );
399	return true;
400	}
401
402	void backtrack() {
403	crnt.pop_back();
404	envs.pop_back();
405	opens.pop_back();
406	}
407
408	OutType finalize() { return { envs.back(), opens.back(), crnt, symtab }; }
409	};
410
411	/// Limit to depth of recursion of assertion satisfaction
412	static const int recursionLimit = 8;
413	/// Maximum number of simultaneously-deferred assertions to attempt concurrent satisfaction of
414	static const int deferLimit = 10;
415	} // anonymous namespace
416
417	void satisfyAssertions(
418	CandidateRef & cand, const ast::SymbolTable & symtab, CandidateList & out,
419	std::vector<std::string> & errors
420	) {
421	// finish early if no assertions to satisfy
422	if ( cand->need.empty() ) {
423	out.emplace_back( cand );
424	return;
425	}
426
427	// build list of possible combinations of satisfying declarations
428	std::vector< SatState > sats{ SatState{ cand, symtab } };
429	std::vector< SatState > nextSats{};
430
431	// pruning thresholds by result type of output candidates.
432	// Candidates should be generated in sorted order, so no need to retroactively prune
433	PruneMap thresholds;
434
435	// satisfy assertions in breadth-first order over the recursion tree of assertion satisfaction.
436	// Stop recursion at a limited number of levels deep to avoid infinite loops.
437	for ( unsigned level = 0; level < recursionLimit; ++level ) {
438	// for each current mutually-compatible set of assertions
439	for ( SatState & sat : sats ) {
440	bool allowConversion = false;
441	// stop this branch if a better option is already found
442	auto it = thresholds.find( pruneKey( *sat.cand ) );
443	if ( it != thresholds.end() && it->second < sat.costs ) goto nextSat;
444
445	// should a limit be imposed? worst case here is O(n^2) but very unlikely to happen.
446
447	for (unsigned resetCount = 0; ; ++resetCount) {
448	ast::AssertionList next;
449	resetTyVarRenaming();
450	// make initial pass at matching assertions
451	for ( auto & assn : sat.need ) {
452	// fail early if any assertion is not satisfiable
453	if ( ! satisfyAssertion( assn, sat, allowConversion, !next.empty() ) ) {
454	next.emplace_back(assn);
455	// goto nextSat;
456	}
457	}
458	// success
459	if (next.empty()) break;
460	// fail if nothing resolves
461	else if (next.size() == sat.need.size()) {
462	if (allowConversion) {
463	Indenter tabs{ 3 };
464	std::ostringstream ss;
465	ss << tabs << "Unsatisfiable alternative:\n";
466	print( ss, *sat.cand, ++tabs );
467	ss << (tabs-1) << "Could not satisfy assertion:\n";
468	ast::print( ss, next[0].first, tabs );
469
470	errors.emplace_back( ss.str() );
471	goto nextSat;
472	}
473
474	else {
475	allowConversion = true;
476	continue;
477	}
478	}
479	allowConversion = false;
480	sat.need = std::move(next);
481	}
482
483	if ( sat.deferred.empty() ) {
484	// either add successful match or push back next state
485	if ( sat.newNeed.empty() ) {
486	finalizeAssertions(
487	sat.cand, sat.inferred, thresholds, std::move( sat.costs ), out );
488	} else {
489	nextSats.emplace_back( std::move( sat ), IterateState );
490	}
491	} else if ( sat.deferred.size() > deferLimit ) {
492	// too many deferred assertions to attempt mutual compatibility
493	Indenter tabs{ 3 };
494	std::ostringstream ss;
495	ss << tabs << "Unsatisfiable alternative:\n";
496	print( ss, *sat.cand, ++tabs );
497	ss << (tabs-1) << "Too many non-unique satisfying assignments for assertions:\n";
498	for ( const auto & d : sat.deferred ) {
499	ast::print( ss, d.expr, tabs );
500	}
501
502	errors.emplace_back( ss.str() );
503	goto nextSat;
504	} else {
505	// combine deferred assertions by mutual compatibility
506	std::vector< CandidateEnvMerger::OutType > compatible = filterCombos(
507	sat.deferred, CandidateEnvMerger{ sat.cand->env, sat.cand->open, sat.symtab } );
508
509	// fail early if no mutually-compatible assertion satisfaction
510	if ( compatible.empty() ) {
511	Indenter tabs{ 3 };
512	std::ostringstream ss;
513	ss << tabs << "Unsatisfiable alternative:\n";
514	print( ss, *sat.cand, ++tabs );
515	ss << (tabs-1) << "No mutually-compatible satisfaction for assertions:\n";
516	for ( const auto& d : sat.deferred ) {
517	ast::print( ss, d.expr, tabs );
518	}
519
520	errors.emplace_back( ss.str() );
521	goto nextSat;
522	}
523
524	// sort by cost (for overall pruning order)
525	std::sort( compatible.begin(), compatible.end() );
526
527	// process mutually-compatible combinations
528	for ( auto & compat : compatible ) {
529	// set up next satisfaction state
530	CandidateRef nextCand = std::make_shared<Candidate>(
531	sat.cand->expr, std::move( compat.env ), std::move( compat.open ),
532	ast::AssertionSet{} /* need moved into satisfaction state */,
533	sat.cand->cost, sat.cand->cvtCost );
534
535	ast::AssertionSet nextNewNeed{ sat.newNeed };
536	InferCache nextInferred{ sat.inferred };
537
538	CostVec nextCosts{ sat.costs };
539	nextCosts.back() += compat.cost;
540
541	ast::SymbolTable nextSymtab{ sat.symtab };
542
543	// add compatible assertions to new satisfaction state
544	for ( DeferRef r : compat.assns ) {
545	AssnCandidate match = r.match;
546	addToSymbolTable( match.have, nextSymtab );
547	nextNewNeed.insert( match.need.begin(), match.need.end() );
548
549	bindAssertion( r.expr, r.info, nextCand, match, nextInferred );
550	}
551
552	// either add successful match or push back next state
553	if ( nextNewNeed.empty() ) {
554	finalizeAssertions(
555	nextCand, nextInferred, thresholds, std::move( nextCosts ), out );
556	} else {
557	nextSats.emplace_back(
558	std::move( nextCand ), std::move( nextNewNeed ),
559	std::move( nextInferred ), std::move( nextCosts ),
560	std::move( nextSymtab ) );
561	}
562	}
563	}
564	nextSat:; }
565
566	// finish or reset for next round
567	if ( nextSats.empty() ) return;
568	sats.swap( nextSats );
569	nextSats.clear();
570	}
571
572	// exceeded recursion limit if reaches here
573	if ( out.empty() ) {
574	SemanticError( cand->expr->location, "Too many recursive assertions" );
575	}
576	}
577
578	} // namespace ResolvExpr
579
580	// Local Variables: //
581	// tab-width: 4 //
582	// mode: c++ //
583	// compile-command: "make install" //
584	// End: //

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