diff options
| -rw-r--r-- | gcc/cp/constexpr.cc | 63 | ||||
| -rw-r--r-- | gcc/testsuite/g++.dg/diagnostic/constexpr3.C | 33 |
2 files changed, 95 insertions, 1 deletions
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc index 8bd5c4a..0ca4370 100644 --- a/gcc/cp/constexpr.cc +++ b/gcc/cp/constexpr.cc @@ -3381,6 +3381,61 @@ ok: } } +/* *TP was not deemed constant by reduced_constant_expression_p. Explain + why and suggest what could be done about it. */ + +static tree +verify_constant_explain_r (tree *tp, int *walk_subtrees, void *) +{ + bool ref_p = false; + + /* No need to look into types or unevaluated operands. */ + if (TYPE_P (*tp) || unevaluated_p (TREE_CODE (*tp))) + { + *walk_subtrees = false; + return NULL_TREE; + } + + switch (TREE_CODE (*tp)) + { + CASE_CONVERT: + if (TREE_CODE (TREE_OPERAND (*tp, 0)) != ADDR_EXPR) + break; + ref_p = TYPE_REF_P (TREE_TYPE (*tp)); + *tp = TREE_OPERAND (*tp, 0); + gcc_fallthrough (); + case ADDR_EXPR: + { + tree op = TREE_OPERAND (*tp, 0); + if (VAR_P (op) + && DECL_DECLARED_CONSTEXPR_P (op) + && !TREE_STATIC (op) + /* ??? We should also say something about temporaries. */ + && !DECL_ARTIFICIAL (op)) + { + if (ref_p) + inform (location_of (*tp), "reference to %qD is not a constant " + "expression", op); + else + inform (location_of (*tp), "pointer to %qD is not a constant " + "expression", op); + const location_t op_loc = DECL_SOURCE_LOCATION (op); + rich_location richloc (line_table, op_loc); + richloc.add_fixit_insert_before (op_loc, "static "); + inform (&richloc, + "address of non-static constexpr variable %qD may differ on " + "each invocation of the enclosing function; add %<static%> " + "to give it a constant address", op); + } + break; + } + default: + break; + } + + return NULL_TREE; +} + /* Some expressions may have constant operands but are not constant themselves, such as 1/0. Call this function to check for that condition. @@ -3398,7 +3453,13 @@ verify_constant (tree t, bool allow_non_constant, bool *non_constant_p, && t != void_node) { if (!allow_non_constant) - error ("%q+E is not a constant expression", t); + { + auto_diagnostic_group d; + error_at (cp_expr_loc_or_input_loc (t), + "%q+E is not a constant expression", t); + cp_walk_tree_without_duplicates (&t, verify_constant_explain_r, + nullptr); + } *non_constant_p = true; } if (TREE_OVERFLOW_P (t)) diff --git a/gcc/testsuite/g++.dg/diagnostic/constexpr3.C b/gcc/testsuite/g++.dg/diagnostic/constexpr3.C new file mode 100644 index 0000000..39ddf01 --- /dev/null +++ b/gcc/testsuite/g++.dg/diagnostic/constexpr3.C @@ -0,0 +1,33 @@ +// PR c++/91483 +// { dg-do compile { target c++14 } } + +struct X { + int const& var; +}; + +struct A { + A *ap = this; +}; + +constexpr A +foo () +{ + return {}; +} + +void +test () +{ + constexpr int i = 42; // { dg-message "may differ on each invocation" } + + constexpr X x{i}; // { dg-error "not a constant expression" } + // { dg-message "reference to .i. is not a constant expression" "" { target *-*-* } .-1 } + constexpr const int *p = &i; // { dg-error "not a constant expression" } + // { dg-message "pointer to .i. is not a constant expression" "" { target *-*-* } .-1 } + + constexpr A a = foo (); // { dg-error "not a constant expression" } + // { dg-message "pointer to .a. is not a constant expression|may differ" "" { target *-*-* } .-1 } + + constexpr const int *q = __builtin_launder (&i); // { dg-error "not a constant expression" } + // { dg-message "pointer to .i. is not a constant expression" "" { target *-*-* } .-1 } +} |