From 3471a61ed0ddef70de8f1bbba85cd1e945fc86fd Mon Sep 17 00:00:00 2001
From: Nathaniel Shead <nathanieloshead@gmail.com>
Date: Sat, 16 Dec 2023 21:34:45 +1100
Subject: [PATCH] c++: Prevent overwriting arguments when merging duplicates
 [PR112588]

When merging duplicate instantiations of function templates, currently
read_function_def overwrites the arguments with that of the existing
duplicate. This is problematic, however, since this means that the
PARM_DECLs in the body of the function definition no longer match with
the PARM_DECLs in the argument list, which causes issues when it comes
to generating RTL.

There doesn't seem to be any reason to do this replacement, so this
patch removes that logic.

	PR c++/112588

gcc/cp/ChangeLog:

	* module.cc (trees_in::read_function_def): Don't overwrite
	arguments.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/merge-16.h: New test.
	* g++.dg/modules/merge-16_a.C: New test.
	* g++.dg/modules/merge-16_b.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
---
 gcc/cp/module.cc                          |  2 --
 gcc/testsuite/g++.dg/modules/merge-16.h   | 10 ++++++++++
 gcc/testsuite/g++.dg/modules/merge-16_a.C |  7 +++++++
 gcc/testsuite/g++.dg/modules/merge-16_b.C |  5 +++++
 4 files changed, 22 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/modules/merge-16.h
 create mode 100644 gcc/testsuite/g++.dg/modules/merge-16_a.C
 create mode 100644 gcc/testsuite/g++.dg/modules/merge-16_b.C

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 350ad15dc62..8db662c0267 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -11703,8 +11703,6 @@ trees_in::read_function_def (tree decl, tree maybe_template)
       DECL_RESULT (decl) = result;
       DECL_INITIAL (decl) = initial;
       DECL_SAVED_TREE (decl) = saved;
-      if (maybe_dup)
-	DECL_ARGUMENTS (decl) = DECL_ARGUMENTS (maybe_dup);
 
       if (context)
 	SET_DECL_FRIEND_CONTEXT (decl, context);
diff --git a/gcc/testsuite/g++.dg/modules/merge-16.h b/gcc/testsuite/g++.dg/modules/merge-16.h
new file mode 100644
index 00000000000..fdb38551103
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/merge-16.h
@@ -0,0 +1,10 @@
+// PR c++/112588
+
+void f(int*);
+
+template <typename T>
+struct S {
+  void g(int n) { f(&n); }
+};
+
+template struct S<void>;
diff --git a/gcc/testsuite/g++.dg/modules/merge-16_a.C b/gcc/testsuite/g++.dg/modules/merge-16_a.C
new file mode 100644
index 00000000000..c243224c875
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/merge-16_a.C
@@ -0,0 +1,7 @@
+// PR c++/112588
+// { dg-additional-options "-fmodules-ts" }
+// { dg-module-cmi merge16 }
+
+module;
+#include "merge-16.h"
+export module merge16;
diff --git a/gcc/testsuite/g++.dg/modules/merge-16_b.C b/gcc/testsuite/g++.dg/modules/merge-16_b.C
new file mode 100644
index 00000000000..8c7b1f0511f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/merge-16_b.C
@@ -0,0 +1,5 @@
+// PR c++/112588
+// { dg-additional-options "-fmodules-ts" }
+
+#include "merge-16.h"
+import merge16;
-- 
2.11.4.GIT