Tested x86_64-pc-linux-gnu. Is the library change OK for trunk?
The library patch checks a couple of macros, but I'm not sure that's necessary;
can we just assume std::launder in construct_at?
-- 8< --
I previously tried to clobber an array as a whole, but fell back on a loop
due to issues with std::construct_at following the resolution of LWG3436.
But the loop seems to make life hard for the optimizers and there was
support for reconsidering LWG3436 when I raised the issue on the reflector,
so let's pursue that direction.
This also fixes some xfails in Warray-bounds-20.C.
libstdc++-v3/ChangeLog:
* include/bits/stl_construct.h (construct_at): Launder instead of
adding an extra array bound.
gcc/cp/ChangeLog:
* init.cc (build_new_1): Clobber a constant-bound array as a whole.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/constexpr-new23.C: Launder instead of
adding an extra array bound.
* g++.dg/warn/Warray-bounds-20.C: Remove xfails, add diags.
---
libstdc++-v3/include/bits/stl_construct.h | 9 +++++++-
gcc/cp/init.cc | 22 ++++++++++++++++----
gcc/testsuite/g++.dg/cpp2a/constexpr-new23.C | 5 ++++-
gcc/testsuite/g++.dg/warn/Warray-bounds-20.C | 10 ++++-----
4 files changed, 35 insertions(+), 11 deletions(-)
diff --git a/libstdc++-v3/include/bits/stl_construct.h
b/libstdc++-v3/include/bits/stl_construct.h
index 98b403c4c71..550e3c7ea3f 100644
--- a/libstdc++-v3/include/bits/stl_construct.h
+++ b/libstdc++-v3/include/bits/stl_construct.h
@@ -104,7 +104,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
static_assert(sizeof...(_Args) == 0, "std::construct_at for array "
"types must not use any arguments to initialize the "
"array");
- return ::new(__loc) _Tp[1]();
+ __loc = ::new(__loc) _Tp();
+#if __cpp_lib_launder
+ return std::launder(__location);
+#elif _GLIBCXX_HAVE_BUILTIN_LAUNDER
+ return __builtin_launder(__location);
+#else
+ return static_cast<_Tp*>(__loc);
+#endif
}
else
return ::new(__loc) _Tp(std::forward<_Args>(__args)...);
diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc
index 3fe476d7eec..1e175ae7670 100644
--- a/gcc/cp/init.cc
+++ b/gcc/cp/init.cc
@@ -3662,11 +3662,11 @@ build_new_1 (vec<tree, va_gc> **placement, tree type,
tree nelts,
tree clobber_expr = NULL_TREE;
if (do_clobber)
{
- tree clobber = build_clobber (elt_type, CLOBBER_OBJECT_BEGIN);
- CONSTRUCTOR_IS_DIRECT_INIT (clobber) = true;
- if (array_p)
+ if (array_p && TREE_CODE (cst_outer_nelts) != INTEGER_CST)
{
/* Clobber each element rather than the array at once. */
+ tree clobber = build_clobber (elt_type, CLOBBER_OBJECT_BEGIN);
+ CONSTRUCTOR_IS_DIRECT_INIT (clobber) = true;
tree maxindex = cp_build_binary_op (input_location,
MINUS_EXPR, outer_nelts,
integer_one_node,
@@ -3677,7 +3677,21 @@ build_new_1 (vec<tree, va_gc> **placement, tree type,
tree nelts,
}
else
{
- tree targ = cp_build_fold_indirect_ref (data_addr);
+ tree targ = data_addr;
+ tree ttype = type;
+ if (array_p)
+ {
+ tree dom
+ = compute_array_index_type (NULL_TREE,
+ CONST_CAST_TREE (cst_outer_nelts),
+ complain);
+ ttype = build_cplus_array_type (type, dom);
+ tree ptype = build_pointer_type (ttype);
+ targ = fold_convert (ptype, targ);
+ }
+ targ = cp_build_fold_indirect_ref (targ);
+ tree clobber = build_clobber (ttype, CLOBBER_OBJECT_BEGIN);
+ CONSTRUCTOR_IS_DIRECT_INIT (clobber) = true;
clobber_expr = cp_build_init_expr (targ, clobber);
}
}
diff --git a/gcc/testsuite/g++.dg/cpp2a/constexpr-new23.C
b/gcc/testsuite/g++.dg/cpp2a/constexpr-new23.C
index 1abbef18fae..dc406985f26 100644
--- a/gcc/testsuite/g++.dg/cpp2a/constexpr-new23.C
+++ b/gcc/testsuite/g++.dg/cpp2a/constexpr-new23.C
@@ -13,7 +13,10 @@ namespace std {
constexpr T* construct_at(T* p)
{
if constexpr (__is_array(T))
- return ::new((void*)p) T[1]();
+ {
+ (void) ::new((void*)p) T();
+ return __builtin_launder (p);
+ }
else
return ::new((void*)p) T();
}
diff --git a/gcc/testsuite/g++.dg/warn/Warray-bounds-20.C
b/gcc/testsuite/g++.dg/warn/Warray-bounds-20.C
index 36f8046fed7..ec91e44f988 100644
--- a/gcc/testsuite/g++.dg/warn/Warray-bounds-20.C
+++ b/gcc/testsuite/g++.dg/warn/Warray-bounds-20.C
@@ -53,18 +53,18 @@ void warn_derived_ctor_access_new_alloc ()
void warn_derived_ctor_access_new_array_decl ()
{
- char b[sizeof (D1) * 2]; // { dg-message "at offset \\d+ into object 'b'
of size 80" "LP64 note" { target { lp64 } xfail { lp64 } } }
- // { dg-message "at offset \\d+ into object 'b'
of size 40" "LP64 note" { target { ilp32 } xfail { ilp32 } } .-1 }
+ char b[sizeof (D1) * 2]; // { dg-message "at offset \\d+ into object 'b'
of size 80" "LP64 note" { target { lp64 } } }
+ // { dg-message "at offset \\d+ into object 'b'
of size 40" "LP64 note" { target { ilp32 } } .-1 }
char *p = b;
++p;
- D1 *q = new (p) D1[2];
+ D1 *q = new (p) D1[2]; // { dg-message "partly outside array bounds" }
sink (q);
}
void warn_derived_ctor_access_new_array_alloc ()
{
- char *p = new char[sizeof (D1) * 2]; // { dg-message "at offset
\\d+ into object of size \\d+ allocated by '\[^\n\r]*operator new\[^\n\r]*"
"note" { xfail *-*-* } }
+ char *p = new char[sizeof (D1) * 2]; // { dg-message "at offset
\\d+ into object of size \\d+ allocated by '\[^\n\r]*operator new\[^\n\r]*"
"note" }
++p;
- D1 *q = new (p) D1[2];
+ D1 *q = new (p) D1[2]; // { dg-message "partly outside array bounds" }
sink (q);
}
base-commit: 5ee5a05da06078975a933be849431eee1d4c6989
--
2.51.0
