c++: template instantiation during fold_for_warn [PR94038]
Unfortunately, the previous fix to PR94038 is fragile. When the argument to fold_for_warn is a bare CALL_EXPR, then all is well: the result of maybe_constant_value from fold_for_warn (with uid_sensitive=true) is reused via the cv_cache in the subsequent call to maybe_constant_value from cp_fold (with uid_sensitive=false), so we avoid instantiating bar<int>. But when the argument to fold_for_warn is more complex, e.g. an INDIRECT_REF of a CALL_EXPR, as in the testcase below (due to bar<int>() returning const int& which we need to decay to int) then from fold_for_warn we call maybe_constant_value on the INDIRECT_REF, and from cp_fold we call it on the CALL_EXPR, so there is no reuse via the cv_cache and we therefore end up instantiating bar<int>. So for a more robust solution to this general issue of warning flags affecting code generation, it seems that we need a way to globally avoid template instantiation during constexpr evaluation whenever we're performing warning-dependent folding. To that end, this patch replaces the flag constexpr_ctx::uid_sensitive with a global flag uid_sensitive_constexpr_evaluation_p, and enables it during fold_for_warn using an RAII helper. The patch also adds a counter that keeps track of the number of times uid_sensitive_constexpr_evaluation_p is called and returned true, and we use this to determine whether the result of constexpr evaluation was restricted by the flag. This lets us safely update the cv_cache and fold_cache from fold_for_warn in the most common case where the flag did not restrict constexpr evaluation. gcc/cp/ChangeLog: PR c++/94038 * constexpr.c (constexpr_ctx::uid_sensitive): Remove field. (uid_sensitive_constexpr_evaluation_value): Define. (uid_sensitive_constexpr_evaluation_true_counter): Define. (uid_sensitive_constexpr_evaluation_p): Define. (uid_sensitive_constexpr_evaluation_sentinel): Define its constructor. (uid_sensitive_constexpr_evaluation_checker): Define its constructor and its evaluation_restricted_p method. (get_fundef_copy): Remove 'ctx' parameter. Use u_s_c_e_p instead of constexpr_ctx::uid_sensitive. (cxx_eval_call_expression): Use u_s_c_e_p instead, and test it last. Adjust call to get_fundef_copy. (instantiate_cx_fn_r): Test u_s_c_e_p so that we increment the counter if necessary. (cxx_eval_outermost_constant_expr): Remove 'uid_sensitive' parameter. Adjust function body accordingly. (maybe_constant_value): Remove 'uid_sensitive' parameter and adjust function body accordingly. Set up a uid_sensitive_constexpr_evaluation_checker, and use it to conditionally update the cv_cache. * cp-gimplify.c (cp_fold): Set up a uid_sensitive_constexpr_evaluation_checker, and use it to conditionally update the fold_cache. * cp-tree.h (maybe_constant_value): Update declaration. (struct uid_sensitive_constexpr_evaluation_sentinel): Define. (struct sensitive_constexpr_evaluation_checker): Define. * expr.c (fold_for_warn): Set up a uid_sensitive_constexpr_evaluation_sentinel before calling the folding subroutines. Drop all but the first argument to maybe_constant_value. gcc/testsuite/ChangeLog: PR c++/94038 * g++.dg/warn/pr94038-2.C: New test.
This commit is contained in:
Patrick Palka
parent
5855bdfa06
commit
f65a3299a5
@ -1,3 +1,37 @@
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2020-05-21 Patrick Palka <ppalka@redhat.com>
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PR c++/94038
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* constexpr.c (constexpr_ctx::uid_sensitive): Remove field.
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(uid_sensitive_constexpr_evaluation_value): Define.
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(uid_sensitive_constexpr_evaluation_true_counter): Define.
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(uid_sensitive_constexpr_evaluation_p): Define.
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(uid_sensitive_constexpr_evaluation_sentinel): Define its
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constructor.
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(uid_sensitive_constexpr_evaluation_checker): Define its
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constructor and its evaluation_restricted_p method.
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(get_fundef_copy): Remove 'ctx' parameter. Use u_s_c_e_p
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instead of constexpr_ctx::uid_sensitive.
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(cxx_eval_call_expression): Use u_s_c_e_p instead, and test it
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last. Adjust call to get_fundef_copy.
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(instantiate_cx_fn_r): Test u_s_c_e_p so that we increment the
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counter if necessary.
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(cxx_eval_outermost_constant_expr): Remove 'uid_sensitive'
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parameter. Adjust function body accordingly.
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(maybe_constant_value): Remove 'uid_sensitive' parameter and
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adjust function body accordingly. Set up a
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uid_sensitive_constexpr_evaluation_checker, and use it to
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conditionally update the cv_cache.
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* cp-gimplify.c (cp_fold): Set up a
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uid_sensitive_constexpr_evaluation_checker, and use it to
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conditionally update the fold_cache.
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* cp-tree.h (maybe_constant_value): Update declaration.
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(struct uid_sensitive_constexpr_evaluation_sentinel): Define.
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(struct sensitive_constexpr_evaluation_checker): Define.
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* expr.c (fold_for_warn): Set up a
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uid_sensitive_constexpr_evaluation_sentinel before calling
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the folding subroutines. Drop all but the first argument to
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maybe_constant_value.
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2020-05-20 Marek Polacek <polacek@redhat.com>
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DR 2237
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@ -1089,11 +1089,67 @@ struct constexpr_ctx {
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bool strict;
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/* Whether __builtin_is_constant_evaluated () should be true. */
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bool manifestly_const_eval;
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/* Whether we want to avoid doing anything that will cause extra DECL_UID
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generation. */
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bool uid_sensitive;
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};
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/* This internal flag controls whether we should avoid doing anything during
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constexpr evaluation that would cause extra DECL_UID generation, such as
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template instantiation and function body copying. */
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static bool uid_sensitive_constexpr_evaluation_value;
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/* An internal counter that keeps track of the number of times
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uid_sensitive_constexpr_evaluation_p returned true. */
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static unsigned uid_sensitive_constexpr_evaluation_true_counter;
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/* The accessor for uid_sensitive_constexpr_evaluation_value which also
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increments the corresponding counter. */
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static bool
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uid_sensitive_constexpr_evaluation_p ()
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{
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if (uid_sensitive_constexpr_evaluation_value)
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{
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++uid_sensitive_constexpr_evaluation_true_counter;
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return true;
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}
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else
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return false;
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}
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/* The default constructor for uid_sensitive_constexpr_evaluation_sentinel
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enables the internal flag for uid_sensitive_constexpr_evaluation_p
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during the lifetime of the sentinel object. Upon its destruction, the
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previous value of uid_sensitive_constexpr_evaluation_p is restored. */
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uid_sensitive_constexpr_evaluation_sentinel
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::uid_sensitive_constexpr_evaluation_sentinel ()
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: ovr (uid_sensitive_constexpr_evaluation_value, true)
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{
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}
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/* The default constructor for uid_sensitive_constexpr_evaluation_checker
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records the current number of times that uid_sensitive_constexpr_evaluation_p
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has been called and returned true. */
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uid_sensitive_constexpr_evaluation_checker
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::uid_sensitive_constexpr_evaluation_checker ()
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: saved_counter (uid_sensitive_constexpr_evaluation_true_counter)
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{
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}
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/* Returns true iff uid_sensitive_constexpr_evaluation_p is true, and
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some constexpr evaluation was restricted due to u_s_c_e_p being called
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and returning true during the lifetime of this checker object. */
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bool
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uid_sensitive_constexpr_evaluation_checker::evaluation_restricted_p () const
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{
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return (uid_sensitive_constexpr_evaluation_value
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&& saved_counter != uid_sensitive_constexpr_evaluation_true_counter);
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}
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/* A table of all constexpr calls that have been evaluated by the
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compiler in this translation unit. */
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@ -1156,7 +1212,7 @@ static GTY(()) hash_map<tree, tree> *fundef_copies_table;
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is parms, TYPE is result. */
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static tree
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get_fundef_copy (const constexpr_ctx *ctx, constexpr_fundef *fundef)
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get_fundef_copy (constexpr_fundef *fundef)
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{
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tree copy;
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bool existed;
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@ -1173,7 +1229,7 @@ get_fundef_copy (const constexpr_ctx *ctx, constexpr_fundef *fundef)
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}
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else if (*slot == NULL_TREE)
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{
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if (ctx->uid_sensitive)
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if (uid_sensitive_constexpr_evaluation_p ())
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return NULL_TREE;
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/* We've already used the function itself, so make a copy. */
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@ -2292,8 +2348,8 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree t,
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/* We can't defer instantiating the function any longer. */
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if (!DECL_INITIAL (fun)
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&& !ctx->uid_sensitive
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&& DECL_TEMPLOID_INSTANTIATION (fun))
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&& DECL_TEMPLOID_INSTANTIATION (fun)
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&& !uid_sensitive_constexpr_evaluation_p ())
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{
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location_t save_loc = input_location;
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input_location = loc;
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@ -2454,7 +2510,7 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree t,
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gcc_assert (at_eof >= 2 && ctx->quiet);
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*non_constant_p = true;
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}
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else if (tree copy = get_fundef_copy (ctx, new_call.fundef))
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else if (tree copy = get_fundef_copy (new_call.fundef))
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{
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tree body, parms, res;
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releasing_vec ctors;
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@ -6485,7 +6541,8 @@ instantiate_cx_fn_r (tree *tp, int *walk_subtrees, void */*data*/)
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&& DECL_DECLARED_CONSTEXPR_P (*tp)
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&& !DECL_INITIAL (*tp)
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&& !trivial_fn_p (*tp)
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&& DECL_TEMPLOID_INSTANTIATION (*tp))
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&& DECL_TEMPLOID_INSTANTIATION (*tp)
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&& !uid_sensitive_constexpr_evaluation_p ())
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{
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++function_depth;
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instantiate_decl (*tp, /*defer_ok*/false, /*expl_inst*/false);
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@ -6552,8 +6609,7 @@ cxx_eval_outermost_constant_expr (tree t, bool allow_non_constant,
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bool strict = true,
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bool manifestly_const_eval = false,
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bool constexpr_dtor = false,
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tree object = NULL_TREE,
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bool uid_sensitive = false)
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tree object = NULL_TREE)
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{
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auto_timevar time (TV_CONSTEXPR);
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@ -6569,8 +6625,7 @@ cxx_eval_outermost_constant_expr (tree t, bool allow_non_constant,
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constexpr_global_ctx global_ctx;
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constexpr_ctx ctx = { &global_ctx, NULL, NULL, NULL, NULL, NULL, NULL,
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allow_non_constant, strict,
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manifestly_const_eval || !allow_non_constant,
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uid_sensitive };
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manifestly_const_eval || !allow_non_constant };
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tree type = initialized_type (t);
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tree r = t;
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@ -6660,8 +6715,7 @@ cxx_eval_outermost_constant_expr (tree t, bool allow_non_constant,
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auto_vec<tree, 16> cleanups;
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global_ctx.cleanups = &cleanups;
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if (!uid_sensitive)
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instantiate_constexpr_fns (r);
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instantiate_constexpr_fns (r);
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r = cxx_eval_constant_expression (&ctx, r,
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false, &non_constant_p, &overflow_p);
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@ -6909,14 +6963,12 @@ fold_simple (tree t)
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Otherwise, if T does not have TREE_CONSTANT set, returns T.
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Otherwise, returns a version of T without TREE_CONSTANT.
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MANIFESTLY_CONST_EVAL is true if T is manifestly const-evaluated
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as per P0595. UID_SENSITIVE is true if we can't do anything that
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would affect DECL_UID ordering. */
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as per P0595. */
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static GTY((deletable)) hash_map<tree, tree> *cv_cache;
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tree
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maybe_constant_value (tree t, tree decl, bool manifestly_const_eval,
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bool uid_sensitive)
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maybe_constant_value (tree t, tree decl, bool manifestly_const_eval)
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{
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tree r;
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@ -6934,8 +6986,7 @@ maybe_constant_value (tree t, tree decl, bool manifestly_const_eval,
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return t;
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if (manifestly_const_eval)
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return cxx_eval_outermost_constant_expr (t, true, true, true, false,
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decl, uid_sensitive);
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return cxx_eval_outermost_constant_expr (t, true, true, true, false, decl);
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if (cv_cache == NULL)
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cv_cache = hash_map<tree, tree>::create_ggc (101);
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@ -6950,14 +7001,15 @@ maybe_constant_value (tree t, tree decl, bool manifestly_const_eval,
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return r;
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}
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r = cxx_eval_outermost_constant_expr (t, true, true, false, false,
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decl, uid_sensitive);
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uid_sensitive_constexpr_evaluation_checker c;
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r = cxx_eval_outermost_constant_expr (t, true, true, false, false, decl);
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gcc_checking_assert (r == t
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|| CONVERT_EXPR_P (t)
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|| TREE_CODE (t) == VIEW_CONVERT_EXPR
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|| (TREE_CONSTANT (t) && !TREE_CONSTANT (r))
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|| !cp_tree_equal (r, t));
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cv_cache->put (t, r);
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if (!c.evaluation_restricted_p ())
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cv_cache->put (t, r);
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return r;
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}
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@ -2447,6 +2447,8 @@ cp_fold (tree x)
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if (tree *cached = fold_cache->get (x))
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return *cached;
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uid_sensitive_constexpr_evaluation_checker c;
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code = TREE_CODE (x);
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switch (code)
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{
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@ -2929,10 +2931,13 @@ cp_fold (tree x)
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return org_x;
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}
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fold_cache->put (org_x, x);
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/* Prevent that we try to fold an already folded result again. */
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if (x != org_x)
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fold_cache->put (x, x);
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if (!c.evaluation_restricted_p ())
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{
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fold_cache->put (org_x, x);
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/* Prevent that we try to fold an already folded result again. */
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if (x != org_x)
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fold_cache->put (x, x);
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}
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return x;
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}
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@ -7950,7 +7950,7 @@ extern bool require_potential_rvalue_constant_expression (tree);
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extern tree cxx_constant_value (tree, tree = NULL_TREE);
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extern void cxx_constant_dtor (tree, tree);
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extern tree cxx_constant_init (tree, tree = NULL_TREE);
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extern tree maybe_constant_value (tree, tree = NULL_TREE, bool = false, bool = false);
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extern tree maybe_constant_value (tree, tree = NULL_TREE, bool = false);
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extern tree maybe_constant_init (tree, tree = NULL_TREE, bool = false);
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extern tree fold_non_dependent_expr (tree,
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tsubst_flags_t = tf_warning_or_error,
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@ -7969,6 +7969,27 @@ extern tree fold_sizeof_expr (tree);
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extern void clear_cv_and_fold_caches (bool = true);
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extern tree unshare_constructor (tree CXX_MEM_STAT_INFO);
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/* An RAII sentinel used to restrict constexpr evaluation so that it
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doesn't do anything that causes extra DECL_UID generation. */
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struct uid_sensitive_constexpr_evaluation_sentinel
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{
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temp_override<bool> ovr;
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uid_sensitive_constexpr_evaluation_sentinel ();
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};
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/* Used to determine whether uid_sensitive_constexpr_evaluation_p was
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called and returned true, indicating that we've restricted constexpr
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evaluation in order to avoid UID generation. We use this to control
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updates to the fold_cache and cv_cache. */
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struct uid_sensitive_constexpr_evaluation_checker
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{
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const unsigned saved_counter;
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uid_sensitive_constexpr_evaluation_checker ();
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bool evaluation_restricted_p () const;
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};
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/* In cp-ubsan.c */
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extern void cp_ubsan_maybe_instrument_member_call (tree);
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extern void cp_ubsan_instrument_member_accesses (tree *);
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@ -399,6 +399,11 @@ fold_for_warn (tree x)
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{
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/* C++ implementation. */
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/* Prevent warning-dependent constexpr evaluation from changing
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DECL_UID (which breaks -fcompare-debug) and from instantiating
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templates. */
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uid_sensitive_constexpr_evaluation_sentinel s;
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/* It's not generally safe to fully fold inside of a template, so
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call fold_non_dependent_expr instead. */
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if (processing_template_decl)
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@ -410,7 +415,7 @@ fold_for_warn (tree x)
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return f;
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}
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else if (cxx_dialect >= cxx11)
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x = maybe_constant_value (x, NULL_TREE, false, true);
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x = maybe_constant_value (x);
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return c_fully_fold (x, /*for_init*/false, /*maybe_constp*/NULL);
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}
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@ -1,3 +1,8 @@
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2020-05-21 Patrick Palka <ppalka@redhat.com>
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PR c++/94038
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* g++.dg/warn/pr94038-2.C: New test.
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2020-05-21 Martin Liska <mliska@suse.cz>
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PR target/95229
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28
gcc/testsuite/g++.dg/warn/pr94038-2.C
Normal file
28
gcc/testsuite/g++.dg/warn/pr94038-2.C
Normal file
@ -0,0 +1,28 @@
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// PR c++/94038
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// { dg-do compile { target c++11 } }
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// { dg-additional-options "-O -Wall" }
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static constexpr int x = 0;
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template<typename T>
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constexpr const int&
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foo()
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{
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static_assert(T(1) == 0, "");
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return x;
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}
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template<typename T>
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constexpr const int&
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bar()
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{
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return foo<T>();
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}
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constexpr int
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baz(int a)
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{
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return a;
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}
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static_assert(decltype(baz(bar<int>())){} == 0, "");
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