https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93549
--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:c7c09af8ef0fe6671c7733d4d67bb73ecf10fc1b commit r10-6523-gc7c09af8ef0fe6671c7733d4d67bb73ecf10fc1b Author: Jakub Jelinek <ja...@redhat.com> Date: Sat Feb 8 15:11:28 2020 +0100 c++: Handle CONSTRUCTORs without indexes in find_array_ctor_elt [PR93549] My change * typeck2.c (store_init_value): Don't call cp_fully_fold_init on initializers of automatic non-constexpr variables in constexpr functions. - value = cp_fully_fold_init (value); + /* Don't fold initializers of automatic variables in constexpr functions, + that might fold away something that needs to be diagnosed at constexpr + evaluation time. */ + if (!current_function_decl + || !DECL_DECLARED_CONSTEXPR_P (current_function_decl) + || TREE_STATIC (decl)) + value = cp_fully_fold_init (value); from the constexpr new change apparently broke the following testcase. When handling COND_EXPR, we build_vector_from_val, however as the argument we pass to it is not an INTEGER_CST/REAL_CST, but that wrapped in a NON_LVALUE_EXPR location wrapper, we end up with a CONSTRUCTOR and as it is middle-end that builds it, it doesn't bother with indexes. The cp_fully_fold_init call used to fold it into VECTOR_CST in the past, but as we intentionally don't invoke it anymore as it might fold away something that needs to be diagnosed during constexpr evaluation, we end up evaluating ARRAY_REF into the index-less CONSTRUCTOR. The following patch fixes the ICE by teaching find_array_ctor_elt to handle CONSTRUCTORs without indexes (that itself could be still very efficient) and CONSTRUCTORs with some indexes present and others missing (the rules are that if the index on the first element is missing, then it is the array's lowest index (in C/C++ 0) and if other indexes are missing, they are the index of the previous element + 1). Here is a new version, which assumes CONSTRUCTORs with all or none indexes and for CONSTRUCTORs without indexes performs the verification for flag_checking directly in find_array_ctor_elt. For CONSTRUCTORs with indexes, it doesn't do the verification of all elts, because some CONSTRUCTORs can be large, and it "verifies" only what it really needs - if all elts touched during the binary search have indexes, that is actually all we care about because we are sure we found the right elt. It is just if we see a missing index we need assurance that all are missing to be able to directly access it. The assumption then simplifies the patch, for no index CONSTRUCTORs we can use direct access like for CONSTRUCTORs where last elt index is equal to the elt position. If we append right after the last elt, we just should clear the index so that we don't violate the assumption, and if we need a gap between the elts and the elt to be added, we need to add indexes. 2020-02-08 Jakub Jelinek <ja...@redhat.com> PR c++/93549 * constexpr.c (find_array_ctor_elt): If last element has no index, for flag_checking verify all elts have no index. If i is within the elts, return it directly, if it is right after the last elt, append if NULL index, otherwise force indexes on all elts. (cxx_eval_store_expression): Allow cep->index to be NULL. * g++.dg/ext/constexpr-pr93549.C: New test.
