On Wed, 19 Feb 2025, Marek Polacek wrote:
> I suppose it's safer to leave this for GCC 16, but anyway:
>
> Bootstrapped/regtested on x86_64-pc-linux-gnu.
>
> -- >8 --
> Since r10-7718 the attached tests produce an ICE in verify_address:
>
> error: constant not recomputed when 'ADDR_EXPR' changed
>
> but before that we wrongly rejected the tests with "is not a constant
> expression". This patch fixes both problems.
>
> Since r10-7718 replace_decl_r can replace
>
> {._M_dataplus=&<retval>._M_local_buf, ._M_local_buf=0}
>
> with
>
> {._M_dataplus=&HelloWorld._M_local_buf, ._M_local_buf=0}
>
> The initial &<retval>._M_local_buf was not constant, but since
> HelloWorld is a static VAR_DECL, the resulting &HelloWorld._M_local_buf
> should have been marked as TREE_CONSTANT. And since we're taking
> its address, the whole thing should be TREE_ADDRESSABLE.
>
> PR c++/114913
> PR c++/110822
>
> gcc/cp/ChangeLog:
>
> * constexpr.cc (replace_decl_r): If we've replaced something
> inside of an ADDR_EXPR, call cxx_mark_addressable and
> recompute_tree_invariant_for_addr_expr on the resulting ADDR_EXPR.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp0x/constexpr-nsdmi4.C: New test.
> * g++.dg/cpp0x/constexpr-nsdmi5.C: New test.
> ---
> gcc/cp/constexpr.cc | 17 ++++++++++++++++-
> gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi4.C | 19 +++++++++++++++++++
> gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi5.C | 15 +++++++++++++++
> 3 files changed, 50 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi4.C
> create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi5.C
>
> diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
> index 59dd0668af3..c41454057cb 100644
> --- a/gcc/cp/constexpr.cc
> +++ b/gcc/cp/constexpr.cc
> @@ -2707,7 +2707,22 @@ replace_decl_r (tree *tp, int *walk_subtrees, void
> *data)
> {
> replace_decl_data *d = (replace_decl_data *) data;
>
> - if (*tp == d->decl)
> + /* We could be replacing
> + &<retval>.bar -> &foo.bar
> + where foo is a static VAR_DECL, so we need to recompute TREE_CONSTANT
> + on the ADDR_EXPR around it. */
> + if (TREE_CODE (*tp) == ADDR_EXPR)
> + {
> + d->pset->add (*tp);
> + cp_walk_tree (&TREE_OPERAND (*tp, 0), replace_decl_r, d, nullptr);
> + if (d->changed)
d->changed could already be true if something before the ADDR_EXPR was
replaced. I think we should clear/restore d->changed around the
cp_walk_tree call to accurately track whether anything inside the
ADDR_EXPR was replaced. Otherwise LGTM
> + {
> + cxx_mark_addressable (*tp);
> + recompute_tree_invariant_for_addr_expr (*tp);
> + }
> + *walk_subtrees = 0;
> + }
> + else if (*tp == d->decl)
> {
> *tp = unshare_expr (d->replacement);
> d->changed = true;
> diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi4.C
> b/gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi4.C
> new file mode 100644
> index 00000000000..360470dbccb
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi4.C
> @@ -0,0 +1,19 @@
> +// PR c++/114913
> +// { dg-do compile { target c++11 } }
> +
> +struct strt {
> + char *_M_dataplus;
> + char _M_local_buf = 0;
> + constexpr strt()
> + : _M_dataplus(&_M_local_buf) {}
> + constexpr strt(const strt &)
> + : _M_dataplus(&_M_local_buf) {}
> +};
> +
> +constexpr strt
> +f ()
> +{
> + return {};
> +}
> +constexpr strt HelloWorld = f();
> +const char *a() { return HelloWorld._M_dataplus; }
> diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi5.C
> b/gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi5.C
> new file mode 100644
> index 00000000000..0a0acaa9fdf
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi5.C
> @@ -0,0 +1,15 @@
> +// PR c++/110822
> +// { dg-do compile { target c++11 } }
> +
> +void __ostream_insert(const char*);
> +struct basic_string {
> + const char* _M_p;
> + char _M_local_buf[16] = {};
> + constexpr basic_string() : _M_p(_M_local_buf) {}
> + const char *data() const { return _M_p; }
> +};
> +constexpr basic_string f() { return {}; }
> +constexpr basic_string text = f();
> +int main() {
> + __ostream_insert(text._M_p);
> +}
>
> base-commit: 44d4a1086d965fb5280daf65c7c4a253ad6cc8a1
> --
> 2.48.1
>
>
