From: Patrick Palka <ppalka@redhat.com>
Date: Tue, 30 Jan 2024 15:44:56 +0000 (-0500)
Subject: c++: duplicated side effects of xobj arg [PR113640]
X-Git-Tag: basepoints/gcc-15~1508
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0857a00fe3226db8801384743b6d44353dcac9da;p=thirdparty%2Fgcc.git

c++: duplicated side effects of xobj arg [PR113640]

We miscompile the below testcase because keep_unused_object_arg thinks
the object argument of an xobj member function is unused, and so it ends
up duplicating the argument's side effects.

	PR c++/113640

gcc/cp/ChangeLog:

	* call.cc (keep_unused_object_arg): Punt for an xobj member
	function.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp23/explicit-obj-lambda14.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>
---

diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 9de0d77c423f..451a189f7cfb 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -5256,7 +5256,7 @@ keep_unused_object_arg (tree result, tree obj, tree fn)
 {
   if (result == NULL_TREE
       || result == error_mark_node
-      || TREE_CODE (TREE_TYPE (fn)) == METHOD_TYPE
+      || DECL_OBJECT_MEMBER_FUNCTION_P (fn)
       || !TREE_SIDE_EFFECTS (obj))
     return result;
 
diff --git a/gcc/testsuite/g++.dg/cpp23/explicit-obj-lambda14.C b/gcc/testsuite/g++.dg/cpp23/explicit-obj-lambda14.C
new file mode 100644
index 000000000000..5c1d566f9361
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp23/explicit-obj-lambda14.C
@@ -0,0 +1,27 @@
+// PR c++/113640
+// { dg-do run { target c++23 } }
+
+static int total;
+
+struct A {
+  A f(this auto self, int n) {
+    total += n;
+    return self;
+  }
+};
+
+int main() {
+  A a;
+  a.f(1).f(42).f(100);
+  if (total != 143)
+    __builtin_abort();
+
+  auto l = [](this auto self, int n) {
+    total += n;
+    return self;
+  };
+  total = 0;
+  l(1)(42)(100);
+  if (total != 143)
+    __builtin_abort();
+}