From 03c83cf7aa1110e427beb00ea95767dfaf50d694 Mon Sep 17 00:00:00 2001 From: Patrick Palka Date: Sat, 12 Mar 2022 15:00:49 -0500 Subject: [PATCH] c++: ICE with bad conversion shortcutting [PR104622] When shortcutting bad argument conversions during overload resolution, we assume conversions get computed in sequential order and that therefore the conversion array is incomplete iff the last conversion is missing. But this assumption turns out to be wrong for templates, because during deduction check_non_deducible_conversion can compute an argument conversion out of order. So in the testcase below, at the end of add_template_candidate the conversion array looks like {bad_conv, NULL, good_conv} where the last conversion was computed during deduction and the first one later from add_function_candidate. We need to add this candidate to bad_fns since not all of its argument conversions were computed, but we don't do so because the last conversion isn't missing. This patch fixes this by checking for a missing conversion exhaustively instead. In passing, this cleans up check_non_deducible_conversion given that the only values of 'strict' we expect to see here the enumerators of unification_kind_t. PR c++/104622 gcc/cp/ChangeLog: * call.cc (missing_conversion_p): Define. (add_candidates): Use it. * pt.cc (check_non_deducible_conversion): Change type of strict parameter to unification_kind_t and directly test for DEDUCE_CALL. gcc/testsuite/ChangeLog: * g++.dg/template/conv18.C: New test. --- gcc/cp/call.cc | 13 ++++++++++++- gcc/cp/pt.cc | 6 +++--- gcc/testsuite/g++.dg/template/conv18.C | 14 ++++++++++++++ 3 files changed, 29 insertions(+), 4 deletions(-) create mode 100644 gcc/testsuite/g++.dg/template/conv18.C diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc index d6eed5e..8fe8ef3 100644 --- a/gcc/cp/call.cc +++ b/gcc/cp/call.cc @@ -6023,6 +6023,17 @@ perfect_candidate_p (z_candidate *cand) return true; } +/* True iff one of CAND's argument conversions is NULL. */ + +static bool +missing_conversion_p (const z_candidate *cand) +{ + for (unsigned i = 0; i < cand->num_convs; ++i) + if (!cand->convs[i]) + return true; + return false; +} + /* Add each of the viable functions in FNS (a FUNCTION_DECL or OVERLOAD) to the CANDIDATES, returning an updated list of CANDIDATES. The ARGS are the arguments provided to the call; @@ -6200,7 +6211,7 @@ add_candidates (tree fns, tree first_arg, const vec *args, if (cand->viable == -1 && shortcut_bad_convs - && !cand->convs[cand->reversed () ? 0 : cand->num_convs - 1]) + && missing_conversion_p (cand)) { /* This candidate has been tentatively marked non-strictly viable, and we didn't compute all argument conversions for it (having diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc index f7ee33a..67a49c7 100644 --- a/gcc/cp/pt.cc +++ b/gcc/cp/pt.cc @@ -152,7 +152,7 @@ static tree coerce_innermost_template_parms (tree, tree, tree, tsubst_flags_t, bool, bool); static void tsubst_enum (tree, tree, tree); static bool check_instantiated_args (tree, tree, tsubst_flags_t); -static int check_non_deducible_conversion (tree, tree, int, int, +static int check_non_deducible_conversion (tree, tree, unification_kind_t, int, struct conversion **, bool); static int maybe_adjust_types_for_deduction (tree, unification_kind_t, tree*, tree*, tree); @@ -22287,7 +22287,7 @@ maybe_adjust_types_for_deduction (tree tparms, unify_one_argument. */ static int -check_non_deducible_conversion (tree parm, tree arg, int strict, +check_non_deducible_conversion (tree parm, tree arg, unification_kind_t strict, int flags, struct conversion **conv_p, bool explain_p) { @@ -22307,7 +22307,7 @@ check_non_deducible_conversion (tree parm, tree arg, int strict, if (can_convert_arg (type, parm, NULL_TREE, flags, complain)) return unify_success (explain_p); } - else if (strict != DEDUCE_EXACT) + else if (strict == DEDUCE_CALL) { bool ok = false; tree conv_arg = TYPE_P (arg) ? NULL_TREE : arg; diff --git a/gcc/testsuite/g++.dg/template/conv18.C b/gcc/testsuite/g++.dg/template/conv18.C new file mode 100644 index 0000000..f59f6fd --- /dev/null +++ b/gcc/testsuite/g++.dg/template/conv18.C @@ -0,0 +1,14 @@ +// PR c++/104622 +// { dg-additional-options "-fpermissive" } + +template +struct type_identity { + typedef T type; +}; + +template void f(typename type_identity::type*, T, int*); + +int main() { + const int p = 0; + f(&p, 0, 0); // { dg-warning "invalid conversion" } +} -- 2.7.4