================ @@ -10,11 +10,68 @@ // //===----------------------------------------------------------------------===// +/* + * A note on implementation: + * + * As per the C++ standard, constraints are normalized [temp.constr.normal] + * and the normal form is used both for subsumption, and constraint checking. + * Both depend on a parameter mapping that substitutes lazily. In particular, + * we should not substitute in unused arguments. + * + * Clang follows the order of operations prescribed by the standard. + * + * Normalization happens prior to satisfaction and subsumption + * and is handled by `NormalizedConstraint`. + * + * Clang preserves in the normalized form intermediate concept-ids + * (ConceptIdConstraint) This is used for diagnostics only and no substitution + * happens in a ConceptIdConstraint if its expression is satisfied. + * + * The normal form of the associated constraints of a declaration is cached in + * Sema::NormalizationCache such that it is only computed once. + * + * a `NormalizedConstraint` is a recursive data structure, where each node + * contains a parameter maping, represented by the indexes of all parameter + * being used. + * + * Checking satisfaction is done by ConstraintSatisfactionChecker, recursively + * walking NormalizedConstraint. At each level, we substitute the outermost + * level of the template arguments referenced in the parameter mapping of a + * normalized expression (MultiLevelTemplateArgumentList). + * + * template <typename T> + * concept A = __is_same(T, int); + * + * template <typename U> + * concept B = A<U> && __is_same(U, int); + * + * The normal form of b is is `__is_same(T, int) /T->U, innermost level/ ---------------- erichkeane wrote:
```suggestion * The normal form of B is is `__is_same(T, int) /T->U, innermost level/ ``` https://github.com/llvm/llvm-project/pull/141776 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
