From: Nathaniel Shead <nathanieloshead@gmail.com>
Date: Sat, 16 Dec 2023 10:34:45 +0000 (+1100)
Subject: c++: Prevent overwriting arguments when merging duplicates [PR112588]
X-Git-Tag: basepoints/gcc-15~1943
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=3471a61ed0ddef70de8f1bbba85cd1e945fc86fd;p=thirdparty%2Fgcc.git

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>
---

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 350ad15dc623..8db662c0267f 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 000000000000..fdb38551103b
--- /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 000000000000..c243224c8752
--- /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 000000000000..8c7b1f0511f3
--- /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;