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Eval.cc @ fa761c2

Last change on this file since fa761c2 was 8f557161, checked in by Michael Brooks <mlbrooks@…>, 13 months ago

Clarify and fix accuracy in eval public API, on reporting "unable to evaluate."

While the eval internals always used the flag pair valid and cfavalid almost correctly, the public interface exposed the outcome as a single flag, and the various interpretations of this flag were a mess.

Old cfacc treated sizeof(whatever) in some contexts as "known to be zero," which is wrong.
The generally correct answer, which new cfacc now uses is, "unknown now, but GCC will see it as a fine constant."
New tests/eval.cfa captures this fact: is runnable and would fail on old cfacc; it passes with new cfacc.

Property mode set to 100644

File size: 9.9 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	// Eval.cc -- Evaluate parts of the ast at compile time.
8	//
9	// Author : Richard C. Bilson
10	// Created On : Mon May 18 07:44:20 2015
11	// Last Modified By : Peter A. Buhr
12	// Last Modified On : Sat Aug 6 12:11:59 2022
13	// Update Count : 119
14	//
15
16	#include "Eval.h"
17
18	#include <utility> // for pair
19
20	#include "AST/Inspect.hpp"
21	#include "Common/PassVisitor.h"
22	#include "CodeGen/OperatorTable.h" // access: OperatorInfo
23	#include "AST/Pass.hpp"
24	#include "InitTweak/InitTweak.h"
25	#include "SynTree/Expression.h"
26
27	//-------------------------------------------------------------
28	// Old AST
29	struct EvalOld : public WithShortCircuiting {
30	long long int value = 0; // compose the result of the constant expression
31	bool valid = true; // true => constant expression and value is the result
32	// false => not constant expression, e.g., ++i
33	bool cfavalid = true; // true => constant expression and value computable
34	// false => constant expression but value not computable, e.g., sizeof(int)
35
36	void previsit( const BaseSyntaxNode * ) { visit_children = false; }
37	void postvisit( const BaseSyntaxNode * ) { valid = false; }
38
39	void postvisit( const SizeofExpr * ) {
40	}
41
42	void postvisit( const ConstantExpr * expr ) {
43	value = expr->intValue();
44	}
45
46	void postvisit( const CastExpr * expr ) {
47	auto arg = eval(expr->arg);
48	valid = arg.second;
49	value = arg.first;
50	// TODO: perform type conversion on value if valid
51	}
52
53	void postvisit( const VariableExpr * const expr ) {
54	if ( EnumInstType * inst = dynamic_cast<EnumInstType *>(expr->result) ) {
55	if ( EnumDecl * decl = inst->baseEnum ) {
56	if ( decl->valueOf( expr->var, value ) ) { // value filled by valueOf
57	return;
58	}
59	}
60	}
61	valid = false;
62	}
63
64	void postvisit( const ApplicationExpr * expr ) {
65	DeclarationWithType * function = InitTweak::getFunction(const_cast<ApplicationExpr *>(expr));
66	if ( ! function \|\| function->linkage != LinkageSpec::Intrinsic ) { valid = false; return; }
67	const std::string & fname = function->name;
68	assertf( expr->args.size() == 1 \|\| expr->args.size() == 2, "Intrinsic function with %zd arguments: %s", expr->args.size(), fname.c_str() );
69	std::pair<long long int, bool> arg1, arg2;
70	arg1 = eval(expr->args.front());
71	valid = valid && arg1.second;
72	if ( ! valid ) return;
73	if ( expr->args.size() == 2 ) {
74	arg2 = eval(expr->args.back());
75	valid = valid && arg2.second;
76	if ( ! valid ) return;
77	}
78	if (fname == "?+?") {
79	value = arg1.first + arg2.first;
80	} else if (fname == "?-?") {
81	value = arg1.first - arg2.first;
82	} else if (fname == "?*?") {
83	value = arg1.first * arg2.first;
84	} else if (fname == "?/?") {
85	value = arg1.first / arg2.first;
86	} else if (fname == "?%?") {
87	value = arg1.first % arg2.first;
88	} else {
89	valid = false;
90	}
91	// TODO: implement other intrinsic functions
92	}
93	};
94
95	//-------------------------------------------------------------
96	// New AST
97	struct EvalNew : public ast::WithShortCircuiting {
98	Evaluation result = { 0, true, true };
99
100	void previsit( const ast::Node * ) { visit_children = false; }
101	void postvisit( const ast::Node * ) { result.isEvaluableInGCC = result.hasKnownValue = false; }
102
103	void postvisit( const ast::UntypedExpr * ) {
104	assertf( false, "UntypedExpr in constant expression evaluation" ); // FIX ME, resolve variable
105	}
106
107	void postvisit( const ast::ConstantExpr * expr ) { // only handle int constants
108	result.knownValue = expr->intValue();
109	result.hasKnownValue = true;
110	result.isEvaluableInGCC = true;
111	}
112
113	void postvisit( const ast::SizeofExpr * ) {
114	result.hasKnownValue = false;
115	result.isEvaluableInGCC = true;
116	}
117
118	void postvisit( const ast::AlignofExpr * ) {
119	result.hasKnownValue = false;
120	result.isEvaluableInGCC = true;
121	}
122
123	void postvisit( const ast::OffsetofExpr * ) {
124	result.hasKnownValue = false;
125	result.isEvaluableInGCC = true;
126	}
127
128	void postvisit( const ast::LogicalExpr * expr ) {
129	Evaluation arg1, arg2;
130	arg1 = eval( expr->arg1 );
131	result.isEvaluableInGCC &= arg1.isEvaluableInGCC;
132	if ( ! result.isEvaluableInGCC ) return;
133	arg2 = eval( expr->arg2 );
134	result.isEvaluableInGCC &= arg2.isEvaluableInGCC;
135	if ( ! result.isEvaluableInGCC ) return;
136
137	result.hasKnownValue &= arg1.hasKnownValue;
138	result.hasKnownValue &= arg2.hasKnownValue;
139	if ( ! result.hasKnownValue ) return;
140
141	if ( expr->isAnd ) {
142	result.knownValue = arg1.knownValue && arg2.knownValue;
143	} else {
144	result.knownValue = arg1.knownValue \|\| arg2.knownValue;
145	} // if
146	}
147
148	void postvisit( const ast::ConditionalExpr * expr ) {
149	Evaluation arg1, arg2, arg3;
150	arg1 = eval( expr->arg1 );
151	result.isEvaluableInGCC &= arg1.isEvaluableInGCC;
152	if ( ! result.isEvaluableInGCC ) return;
153	arg2 = eval( expr->arg2 );
154	result.isEvaluableInGCC &= arg2.isEvaluableInGCC;
155	if ( ! result.isEvaluableInGCC ) return;
156	arg3 = eval( expr->arg3 );
157	result.isEvaluableInGCC &= arg3.isEvaluableInGCC;
158	if ( ! result.isEvaluableInGCC ) return;
159
160	result.hasKnownValue &= arg1.hasKnownValue;
161	result.hasKnownValue &= arg2.hasKnownValue;
162	result.hasKnownValue &= arg3.hasKnownValue;
163	if ( ! result.hasKnownValue ) return;
164
165	result.knownValue = arg1.knownValue ? arg2.knownValue : arg3.knownValue;
166	}
167
168	void postvisit( const ast::CastExpr * expr ) {
169	// cfa-cc generates a cast before every constant and many other places, e.g., (int)3,
170	// so we must use the value from the cast argument, even though we lack any basis for evaluating wraparound effects, etc
171	result = eval(expr->arg);
172	}
173
174	void postvisit( const ast::VariableExpr * expr ) {
175	result.hasKnownValue = false;
176	result.isEvaluableInGCC = false;
177	if ( const ast::EnumInstType * inst = dynamic_cast<const ast::EnumInstType *>(expr->result.get()) ) {
178	if ( const ast::EnumDecl * decl = inst->base ) {
179	result.isEvaluableInGCC = true;
180	result.hasKnownValue = decl->valueOf( expr->var, result.knownValue ); // result.knownValue filled by valueOf
181	}
182	}
183	}
184
185	void postvisit( const ast::ApplicationExpr * expr ) {
186	const ast::DeclWithType * function = ast::getFunction(expr);
187	if ( ! function \|\| function->linkage != ast::Linkage::Intrinsic ) {
188	result.isEvaluableInGCC = false;
189	result.hasKnownValue = false;
190	return;
191	}
192	const std::string & fname = function->name;
193	assertf( expr->args.size() == 1 \|\| expr->args.size() == 2, "Intrinsic function with %zd arguments: %s", expr->args.size(), fname.c_str() );
194
195	if ( expr->args.size() == 1 ) {
196	// pre/postfix operators ++ and -- => assignment, which is not constant
197	Evaluation arg1;
198	arg1 = eval(expr->args.front());
199	result.isEvaluableInGCC &= arg1.isEvaluableInGCC;
200	if ( ! result.isEvaluableInGCC ) return;
201
202	result.hasKnownValue &= arg1.hasKnownValue;
203	if ( ! result.hasKnownValue ) return;
204
205	if (fname == "+?") {
206	result.knownValue = arg1.knownValue;
207	} else if (fname == "-?") {
208	result.knownValue = -arg1.knownValue;
209	} else if (fname == "~?") {
210	result.knownValue = ~arg1.knownValue;
211	} else if (fname == "!?") {
212	result.knownValue = ! arg1.knownValue;
213	} else {
214	result.isEvaluableInGCC = false;
215	result.hasKnownValue = false;
216	} // if
217	} else { // => expr->args.size() == 2
218	// infix assignment operators => assignment, which is not constant
219	Evaluation arg1, arg2;
220	arg1 = eval(expr->args.front());
221	result.isEvaluableInGCC &= arg1.isEvaluableInGCC;
222	if ( ! result.isEvaluableInGCC ) return;
223	arg2 = eval(expr->args.back());
224	result.isEvaluableInGCC &= arg2.isEvaluableInGCC;
225	if ( ! result.isEvaluableInGCC ) return;
226
227	result.hasKnownValue &= arg1.hasKnownValue;
228	result.hasKnownValue &= arg2.hasKnownValue;
229	if ( ! result.hasKnownValue ) return;
230
231	if (fname == "?+?") {
232	result.knownValue = arg1.knownValue + arg2.knownValue;
233	} else if (fname == "?-?") {
234	result.knownValue = arg1.knownValue - arg2.knownValue;
235	} else if (fname == "?*?") {
236	result.knownValue = arg1.knownValue * arg2.knownValue;
237	} else if (fname == "?/?") {
238	if ( arg2.knownValue ) result.knownValue = arg1.knownValue / arg2.knownValue;
239	} else if (fname == "?%?") {
240	if ( arg2.knownValue ) result.knownValue = arg1.knownValue % arg2.knownValue;
241	} else if (fname == "?<<?") {
242	result.knownValue = arg1.knownValue << arg2.knownValue;
243	} else if (fname == "?>>?") {
244	result.knownValue = arg1.knownValue >> arg2.knownValue;
245	} else if (fname == "?<?") {
246	result.knownValue = arg1.knownValue < arg2.knownValue;
247	} else if (fname == "?>?") {
248	result.knownValue = arg1.knownValue > arg2.knownValue;
249	} else if (fname == "?<=?") {
250	result.knownValue = arg1.knownValue <= arg2.knownValue;
251	} else if (fname == "?>=?") {
252	result.knownValue = arg1.knownValue >= arg2.knownValue;
253	} else if (fname == "?==?") {
254	result.knownValue = arg1.knownValue == arg2.knownValue;
255	} else if (fname == "?!=?") {
256	result.knownValue = arg1.knownValue != arg2.knownValue;
257	} else if (fname == "?&?") {
258	result.knownValue = arg1.knownValue & arg2.knownValue;
259	} else if (fname == "?^?") {
260	result.knownValue = arg1.knownValue ^ arg2.knownValue;
261	} else if (fname == "?\|?") {
262	result.knownValue = arg1.knownValue \| arg2.knownValue;
263	} else {
264	result.isEvaluableInGCC = false;
265	result.hasKnownValue = false;
266	}
267	} // if
268	// TODO: implement other intrinsic functions
269	}
270	};
271
272	std::pair<long long int, bool> eval( const Expression * expr ) {
273	PassVisitor<EvalOld> ev;
274	if ( expr ) {
275	expr->accept( ev );
276	return std::make_pair( ev.pass.value, ev.pass.valid );
277	} else {
278	return std::make_pair( 0, false );
279	}
280	}
281
282	Evaluation eval( const ast::Expr * expr ) {
283	if ( expr ) {
284
285	return ast::Pass<EvalNew>::read(expr);
286	// Evaluation ret = ast::Pass<EvalNew>::read(expr);
287	// ret.knownValue = 777;
288	// return ret;
289
290	} else {
291	return { 0, false, false };
292	}
293	}
294
295	// Local Variables: //
296	// tab-width: 4 //
297	// mode: c++ //
298	// compile-command: "make install" //
299	// End: //

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source: src/Common/Eval.cc @ fa761c2

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