On Sat, Mar 14, 2026 at 03:42:04PM -0400, Jason Merrill wrote:
> On 3/14/26 11:04 AM, Nathaniel Shead wrote:
> > Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk/15?
>
> OK.
>
Actually, Linaro showed me that this failed on ARM for a few cases. (It
should have failed on x86_64 too, I would think, I'm not sure why it
didn't.)
Here's a slightly updated version of the patch that includes a more
thorough description about why the old version broke.
Bootstrapped and regtested on x86_64-pc-linux-gnu, and lightly tested on
arm-linux-gnueabihf; OK for trunk/15?
-- >8 --
The crash in the given PR occurs because we've streamed the definition
of an anticipated builtin, but when processing the nonnull attribute we
find that its DECL_ARGUMENTS is null.
Back in r14-8196-g3471a61ed0ddef70de8f1bbba85cd1e945fc86fd I removed the
setting of DECL_ARGUMENTS as this was causing issues where we were
replacing the argument list for existing definitions. This was because
the definition we streamed was referencing those same PARM_DECLs, and if
they diverged we got different parts of the body with different
pointers to the same logical parameter.
In most cases we do not need to adjust DECL_ARGUMENTS because
fn_parms_fini will substitute in the correct DECL_ARGUMENTS from the
existing declaration. But if DECL_ARGUMENTS was not set on the existing
declaration at all, as happens with e.g. anticipated builtins, then we
do need to set them.
PR c++/124477
gcc/cp/ChangeLog:
* module.cc (trees_in::read_function_def): Set DECL_ARGUMENTS if
installing and otherwise missing.
gcc/testsuite/ChangeLog:
* g++.dg/modules/builtin-10_a.C: New test.
* g++.dg/modules/builtin-10_b.C: New test.
Signed-off-by: Nathaniel Shead <[email protected]>
Reviewed-by: Jason Merrill <[email protected]>
---
gcc/cp/module.cc | 7 ++++++
gcc/testsuite/g++.dg/modules/builtin-10_a.C | 24 +++++++++++++++++++++
gcc/testsuite/g++.dg/modules/builtin-10_b.C | 9 ++++++++
3 files changed, 40 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/modules/builtin-10_a.C
create mode 100644 gcc/testsuite/g++.dg/modules/builtin-10_b.C
diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 83d24a3267d..c1dd0767233 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -13217,6 +13217,13 @@ trees_in::read_function_def (tree decl, tree
maybe_template)
DECL_INITIAL (decl) = initial;
DECL_SAVED_TREE (decl) = saved;
+ /* Some entities (like anticipated builtins) were declared without
+ DECL_ARGUMENTS, so update them now. But don't do it if there's
+ already an argument list, because we've already built the
+ definition referencing those merged PARM_DECLs. */
+ if (!DECL_ARGUMENTS (decl))
+ DECL_ARGUMENTS (decl) = DECL_ARGUMENTS (maybe_dup);
+
if (context)
SET_DECL_FRIEND_CONTEXT (decl, context);
if (cexpr.decl)
diff --git a/gcc/testsuite/g++.dg/modules/builtin-10_a.C
b/gcc/testsuite/g++.dg/modules/builtin-10_a.C
new file mode 100644
index 00000000000..b816f4263d5
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/builtin-10_a.C
@@ -0,0 +1,24 @@
+// PR c++/124477
+// { dg-additional-options "-fmodules -Wno-global-module -O3" }
+// { dg-module-cmi M }
+
+module;
+extern "C" {
+ typedef long unsigned int size_t;
+
+ extern void *memset (void *__s, int __c, size_t __n) noexcept (true)
__attribute__ ((__nonnull__ (1)));
+
+ extern
+ __inline
+ __attribute__((__always_inline__))
+ __attribute__((__gnu_inline__))
+ __attribute__((__artificial__))
+ void *
+ __attribute__((__leaf__))
+ memset(void *__dest, int __ch, size_t __len) noexcept(true) {
+ return __builtin___memset_chk(__dest, __ch, __len,
+ __builtin_object_size(__dest, 0));
+ }
+}
+export module M;
+export using ::memset;
diff --git a/gcc/testsuite/g++.dg/modules/builtin-10_b.C
b/gcc/testsuite/g++.dg/modules/builtin-10_b.C
new file mode 100644
index 00000000000..69303666dd2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/builtin-10_b.C
@@ -0,0 +1,9 @@
+// PR c++/124477
+// { dg-additional-options "-fmodules -O3 -fdump-lang-module-alias" }
+
+import M;
+void foo(void *data) {
+ memset(data, 0xFF, 4);
+}
+
+// { dg-final { scan-lang-dump {Deduping '::memset'} module } }
--
2.51.0
