Here we're crashing from potential_constant_expression because it tries
to perform trial evaluation of the first operand '(bool)__r' of the
conjunction (which is overall wrapped in a NON_DEPENDENT_EXPR), but
cxx_eval_constant_expression ICEs on unsupported trees (of which CAST_EXPR
is one). The sequence of events is:
1. build_non_dependent_expr for the array subscript yields
NON_DEPENDENT_EXPR<<<(bool)__r && __s>>> ? 1 : 2
2. cp_build_array_ref calls fold_non_dependent_expr on this subscript
(after this point, processing_template_decl is cleared)
3. during which, the COND_EXPR case of tsubst_copy_and_build calls
fold_non_dependent_expr on the first operand
4. during which, we crash from p_c_e_1 because it attempts trial
evaluation of the CAST_EXPR '(bool)__r'.
Note that even if this crash didn't happen, fold_non_dependent_expr
from cp_build_array_ref would still ultimately be one big no-op here
since neither constexpr evaluation nor tsubst handle NON_DEPENDENT_EXPR.
In light of this and of the observation that we should never see
NON_DEPENDENT_EXPR in a context where a constant expression is needed
(it's used primarily in the build_x_* family of functions), it seems
futile for p_c_e_1 to ever return true for NON_DEPENDENT_EXPR. And the
otherwise inconsistent handling of NON_DEPENDENT_EXPR between p_c_e_1,
cxx_evaluate_constexpr_expression and tsubst apparently leads to weird
bugs such as this one.
PR c++/104507
gcc/cp/ChangeLog:
* constexpr.cc (potential_constant_expression_1)
<case NON_DEPENDENT_EXPR>: Return false instead of recursing.
Assert tf_error isn't set.
gcc/testsuite/ChangeLog:
* g++.dg/template/non-dependent21.C: New test.
case BIND_EXPR:
return RECUR (BIND_EXPR_BODY (t), want_rval);
+ case NON_DEPENDENT_EXPR:
+ /* Treat NON_DEPENDENT_EXPR as non-constant: it's not handled by
+ constexpr evaluation or tsubst, so fold_non_dependent_expr can't
+ do anything useful with it. And we shouldn't see it in a context
+ where a constant expression is strictly required, hence the assert. */
+ gcc_checking_assert (!(flags & tf_error));
+ return false;
+
case CLEANUP_POINT_EXPR:
case MUST_NOT_THROW_EXPR:
case TRY_CATCH_EXPR:
case EH_SPEC_BLOCK:
case EXPR_STMT:
case PAREN_EXPR:
- case NON_DEPENDENT_EXPR:
/* For convenience. */
case LOOP_EXPR:
case EXIT_EXPR:
--- /dev/null
+// PR c++/104507
+
+extern const char *_k_errmsg[];
+
+template<class>
+const char* DoFoo(int __r, int __s) {
+ const char* n = _k_errmsg[(bool)__r && __s ? 1 : 2];
+ return n;
+}