https://gcc.gnu.org/g:d91b6c93f98cac71f5588d73191d08ad788e600c
commit r15-2920-gd91b6c93f98cac71f5588d73191d08ad788e600c
Author: Marek Polacek <pola...@redhat.com>
Date: Fri Aug 9 16:14:18 2024 -0400
c++: ICE with NSDMIs and fn arguments [PR116015]
The problem in this PR is that we ended up with
{.rows=(&<PLACEHOLDER_EXPR struct Widget>)->n,
.outer_stride=(&<PLACEHOLDER_EXPR struct MatrixLayout>)->rows}
that is, two PLACEHOLDER_EXPRs for different types on the same level
in one { }. That should not happen; we may, for instance, neglect to
replace a PLACEHOLDER_EXPR due to CONSTRUCTOR_PLACEHOLDER_BOUNDARY on
the constructor.
The same problem happened in PR100252, which I fixed by introducing
replace_placeholders_for_class_temp_r. That didn't work here, though,
because r_p_for_c_t_r only works for non-eliding TARGET_EXPRs: replacing
a PLACEHOLDER_EXPR with a temporary that is going to be elided will
result in a crash in gimplify_var_or_parm_decl when it encounters such
a loose decl.
But leaving the PLACEHOLDER_EXPRs in is also bad because then we end
up with this PR.
TARGET_EXPRs for function arguments are elided in gimplify_arg. The
argument will get a real temporary only in get_formal_tmp_var. One
idea was to use the temporary that is going to be elided anyway, and
then replace_decl it with the real object once we get it. But that
didn't work out: one problem is that we elide the TARGET_EXPR for an
argument before we create the real temporary for the argument, and
when we get it, the context that this was a TARGET_EXPR for an argument
has been lost. We're also in the middle end territory now, even though
this is a C++-specific problem.
A solution is to simply stop eliding TARGET_EXPRs whose initializer is
a CONSTRUCTOR. Such copies can't be (at the moment) elided anyway. But
not eliding all TARGET_EXPRs would be a pessimization.
PR c++/116015
gcc/cp/ChangeLog:
* call.cc (convert_for_arg_passing): Don't set_target_expr_eliding
when the TARGET_EXPR initializer is a CONSTRUCTOR.
gcc/ChangeLog:
* gimplify.cc (gimplify_arg): Do not strip a TARGET_EXPR whose
initializer is a CONSTRUCTOR.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/nsdmi-aggr23.C: New test.
Diff:
---
gcc/cp/call.cc | 7 +++++--
gcc/gimplify.cc | 17 ++++++++++++++++-
gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr23.C | 26 ++++++++++++++++++++++++++
3 files changed, 47 insertions(+), 3 deletions(-)
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 94015db4e650..0fe679aae9fe 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -9468,8 +9468,11 @@ convert_for_arg_passing (tree type, tree val,
tsubst_flags_t complain)
if (complain & tf_warning)
warn_for_address_of_packed_member (type, val);
- /* gimplify_arg elides TARGET_EXPRs that initialize a function argument. */
- if (SIMPLE_TARGET_EXPR_P (val))
+ /* gimplify_arg elides TARGET_EXPRs that initialize a function argument,
+ unless the initializer is a CONSTRUCTOR. In that case, we fail to
+ elide the copy anyway. See that function for more information. */
+ if (SIMPLE_TARGET_EXPR_P (val)
+ && TREE_CODE (TARGET_EXPR_INITIAL (val)) != CONSTRUCTOR)
set_target_expr_eliding (val);
return val;
diff --git a/gcc/gimplify.cc b/gcc/gimplify.cc
index 71cc6c38d807..26a216e151d6 100644
--- a/gcc/gimplify.cc
+++ b/gcc/gimplify.cc
@@ -3760,7 +3760,22 @@ gimplify_arg (tree *arg_p, gimple_seq *pre_p, location_t
call_location,
{
tree init = TARGET_EXPR_INITIAL (*arg_p);
if (init
- && !VOID_TYPE_P (TREE_TYPE (init)))
+ && !VOID_TYPE_P (TREE_TYPE (init))
+ /* Currently, due to c++/116015, it is not desirable to
+ strip a TARGET_EXPR whose initializer is a {}. The
+ problem is that if we do elide it, we also have to
+ replace all the occurrences of the slot temporary in the
+ initializer with the temporary created for the argument.
+ But we do not have that temporary yet so the replacement
+ would be quite awkward and it might be needed to resort
+ back to a PLACEHOLDER_EXPR. Note that stripping the
+ TARGET_EXPR wouldn't help anyway, as gimplify_expr would
+ just allocate a temporary to store the CONSTRUCTOR into.
+ (FIXME PR116375.)
+
+ See convert_for_arg_passing for the C++ code that marks
+ the TARGET_EXPR as eliding or not. */
+ && TREE_CODE (init) != CONSTRUCTOR)
*arg_p = init;
}
}
diff --git a/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr23.C
b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr23.C
new file mode 100644
index 000000000000..2f5b8ca97bf7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr23.C
@@ -0,0 +1,26 @@
+// PR c++/116015
+// { dg-do compile { target c++14 } }
+// { dg-additional-options "-Wno-c++20-extensions" }
+
+struct MatrixLayout {
+ int rows = 0;
+ int outer_stride = rows;
+};
+struct Matrix {
+ Matrix(MatrixLayout m) {}
+};
+struct Widget {
+ int n = 5;
+ Matrix A0{{}};
+ Matrix A1{{n}};
+ Matrix A1_{{.rows = n}};
+ Matrix A2{{n, n}};
+};
+
+int
+main ()
+{
+ Widget w{};
+ Widget w1;
+ Widget w2 = {};
+}
