On Sat, Jan 24, 2026 at 04:57:44PM +0800, Jason Merrill wrote:
> On 1/24/26 4:41 PM, Nathaniel Shead wrote:
> > Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk?
> >
> > -- >8 --
> >
> > This fixes two issues with cp_fold_non_odr_use_1:
> >
> > - When called to fold away a reference, it considers the use to not be
> > an lvalue and so 'maybe_constant_value' folds all the way through the
> > nested INDIRECT_REF to a prvalue. Fixed by forcing the expression
> > to be an ADDR_EXPR before calling 'maybe_constant_value', and then
> > folding it away afterwards.
>
> For the REFERENCE_REF case it would make sense to pass its op0 to
> fold_non_odr rather than the ref itself; we already convert_from_reference
> the result.
>
Right, makes sense; thanks. Here's an updated patch that does this
which passes bootstrap and regtest on x86_64-pc-linux-gnu, OK for trunk?
-- >8 --
This fixes two issues with cp_fold_non_odr_use_1:
- When called to fold away a reference, it considers the use to not be
an lvalue and so 'maybe_constant_value' folds all the way through the
nested INDIRECT_REF to a prvalue. Fixed by folding the op0 of the
INDIRECT_REF rather than the ref itself.
- When used to fold away the initializing expression for an INIT_EXPR,
it doesn't mark any new TARGET_EXPRs as eliding. Fixed by reapplying
'set_target_expr_eliding' for the initializer of an INIT_EXPR if it
got modified during ff_only_non_odr walk.
PR c++/123557
PR c++/123738
gcc/cp/ChangeLog:
* cp-gimplify.cc (cp_fold): Pass op0 to cp_fold_non_odr_use_1
when folding a reference. Reapply set_target_expr_eliding on
the initializing expression of an INIT_EXPR.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/constexpr-ice22.C: New test.
* g++.dg/cpp2a/constexpr-ref2.C: New test.
Signed-off-by: Nathaniel Shead <[email protected]>
Reviewed-by: Jason Merrill <[email protected]>
---
gcc/cp/cp-gimplify.cc | 12 ++++++++----
gcc/testsuite/g++.dg/cpp0x/constexpr-ice22.C | 14 ++++++++++++++
gcc/testsuite/g++.dg/cpp2a/constexpr-ref2.C | 19 +++++++++++++++++++
3 files changed, 41 insertions(+), 4 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-ice22.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/constexpr-ref2.C
diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc
index 3c0f415fa87..1189c100527 100644
--- a/gcc/cp/cp-gimplify.cc
+++ b/gcc/cp/cp-gimplify.cc
@@ -3411,9 +3411,9 @@ cp_fold (tree x, fold_flags_t flags)
used as lvalues. */
if ((flags & ff_only_non_odr) && REFERENCE_REF_P (x))
{
- tree r = cp_fold_non_odr_use_1 (x);
- if (r != x)
- return convert_from_reference (cp_fold (r, flags));
+ op0 = cp_fold_non_odr_use_1 (TREE_OPERAND (x, 0));
+ if (op0 != TREE_OPERAND (x, 0))
+ return convert_from_reference (cp_fold (op0, flags));
}
goto unary;
@@ -3560,7 +3560,11 @@ cp_fold (tree x, fold_flags_t flags)
if (op0 == error_mark_node || op1 == error_mark_node)
x = error_mark_node;
else if (op0 != TREE_OPERAND (x, 0) || op1 != TREE_OPERAND (x, 1))
- x = build2_loc (loc, code, TREE_TYPE (x), op0, op1);
+ {
+ if (code == INIT_EXPR && op1 != TREE_OPERAND (x, 1))
+ set_target_expr_eliding (op1);
+ x = build2_loc (loc, code, TREE_TYPE (x), op0, op1);
+ }
break;
}
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-ice22.C
b/gcc/testsuite/g++.dg/cpp0x/constexpr-ice22.C
new file mode 100644
index 00000000000..900c8053a92
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-ice22.C
@@ -0,0 +1,14 @@
+// PR c++/123557
+// { dg-do compile { target c++11 } }
+
+struct a {
+ a() = default;
+ a(a const &) = default;
+ a(a &&);
+};
+struct c {
+ c();
+ a e;
+};
+constexpr a b;
+c::c() : e(b) {}
diff --git a/gcc/testsuite/g++.dg/cpp2a/constexpr-ref2.C
b/gcc/testsuite/g++.dg/cpp2a/constexpr-ref2.C
new file mode 100644
index 00000000000..659beed3a25
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/constexpr-ref2.C
@@ -0,0 +1,19 @@
+// PR c++/123738
+// { dg-do compile { target c++20 } }
+
+struct OStringLiteral {
+ int str = 0;
+};
+
+template<auto L> struct OStringHolder {
+ static constexpr auto & literal = L;
+};
+
+struct OString {
+ template<auto L> constexpr OString(OStringHolder<L> const &):
+ p(&OStringHolder<L>::literal.str) {}
+ int const * p;
+};
+
+
+constexpr OString s = OStringHolder<OStringLiteral{}>{};
--
2.51.0
