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From: Jason Merrill <jason@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r11-6324] c++: Fix initializing empty base from prvalue [PR97597] Date: Wed, 23 Dec 2020 22:11:28 +0000 (GMT) [thread overview] Message-ID: <20201223221128.5619B389365E@sourceware.org> (raw) https://gcc.gnu.org/g:612cf351c700b6216209e3f3f4b3a0959bf2dee7 commit r11-6324-g612cf351c700b6216209e3f3f4b3a0959bf2dee7 Author: Jason Merrill <jason@redhat.com> Date: Tue Dec 22 15:41:56 2020 -0500 c++: Fix initializing empty base from prvalue [PR97597] unsafe_return_slot_p wasn't recognizing an empty base as potentially-overlapping, which it definitely is. The change to build_base_path is to make the virtual conversion also recognized by is_empty_base_ref; unsafe_return_slot_p doesn't to handle virtual conversions, but hypothetical future callers might. gcc/cp/ChangeLog: PR c++/97597 * class.c (is_empty_base_ref): New. (build_base_path): Add NOP_EXPR after offset. * cp-tree.h (is_empty_base_ref): Declare it. * call.c (unsafe_return_slot_p): Call it. gcc/testsuite/ChangeLog: PR c++/97597 * g++.dg/init/empty3.C: New test. Diff: --- gcc/cp/call.c | 4 ++++ gcc/cp/class.c | 31 +++++++++++++++++++++++++++++-- gcc/cp/cp-tree.h | 1 + gcc/testsuite/g++.dg/init/empty3.C | 18 ++++++++++++++++++ 4 files changed, 52 insertions(+), 2 deletions(-) diff --git a/gcc/cp/call.c b/gcc/cp/call.c index c2d62e582bf..65a4d73a7e0 100644 --- a/gcc/cp/call.c +++ b/gcc/cp/call.c @@ -8426,6 +8426,10 @@ call_copy_ctor (tree a, tsubst_flags_t complain) bool unsafe_return_slot_p (tree t) { + /* Check empty bases separately, they don't have fields. */ + if (is_empty_base_ref (t)) + return true; + STRIP_NOPS (t); if (TREE_CODE (t) == ADDR_EXPR) t = TREE_OPERAND (t, 0); diff --git a/gcc/cp/class.c b/gcc/cp/class.c index bc0d3d6bf86..fc5502aad98 100644 --- a/gcc/cp/class.c +++ b/gcc/cp/class.c @@ -494,8 +494,6 @@ build_base_path (enum tree_code code, if (want_pointer) target_type = ptr_target_type; - expr = build1 (NOP_EXPR, ptr_target_type, expr); - if (!integer_zerop (offset)) { offset = fold_convert (sizetype, offset); @@ -506,6 +504,8 @@ build_base_path (enum tree_code code, else null_test = NULL; + expr = build1 (NOP_EXPR, ptr_target_type, expr); + indout: if (!want_pointer) { @@ -659,6 +659,33 @@ convert_to_base_statically (tree expr, tree base) return expr; } +/* True IFF EXPR is a reference to an empty base class "subobject", as built in + convert_to_base_statically. We look for the result of the fold_convert + call, a NOP_EXPR from one pointer type to another, where the target is an + empty base of the original type. */ + +bool +is_empty_base_ref (tree expr) +{ + if (TREE_CODE (expr) == INDIRECT_REF) + expr = TREE_OPERAND (expr, 0); + if (TREE_CODE (expr) != NOP_EXPR) + return false; + tree type = TREE_TYPE (expr); + if (!POINTER_TYPE_P (type)) + return false; + type = TREE_TYPE (type); + if (!is_empty_class (type)) + return false; + STRIP_NOPS (expr); + tree fromtype = TREE_TYPE (expr); + if (!POINTER_TYPE_P (fromtype)) + return false; + fromtype = TREE_TYPE (fromtype); + return (CLASS_TYPE_P (fromtype) + && !same_type_ignoring_top_level_qualifiers_p (fromtype, type) + && DERIVED_FROM_P (type, fromtype)); +} \f tree build_vfield_ref (tree datum, tree type) diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h index 6cce9e2b407..fc6a7898475 100644 --- a/gcc/cp/cp-tree.h +++ b/gcc/cp/cp-tree.h @@ -6484,6 +6484,7 @@ extern tree build_base_path (enum tree_code, tree, extern tree convert_to_base (tree, tree, bool, bool, tsubst_flags_t); extern tree convert_to_base_statically (tree, tree); +extern bool is_empty_base_ref (tree); extern tree build_vtbl_ref (tree, tree); extern tree build_vfn_ref (tree, tree); extern tree get_vtable_decl (tree, int); diff --git a/gcc/testsuite/g++.dg/init/empty3.C b/gcc/testsuite/g++.dg/init/empty3.C new file mode 100644 index 00000000000..510338b2a7e --- /dev/null +++ b/gcc/testsuite/g++.dg/init/empty3.C @@ -0,0 +1,18 @@ +// PR c++/97597 + +struct pq { + pq (const pq &); +}; + +struct a9 { + operator pq () const; +}; + +struct zp : pq { + zp (const a9 &k3) : pq (k3) { } +}; + +int main() +{ + zp z = a9(); +}
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