From 589c94da22ec71fe8518878e801e88b05deffe18 Mon Sep 17 00:00:00 2001
From: Jakub Jelinek <jakub@redhat.com>
Date: Fri, 21 Mar 2025 12:17:45 +0100
Subject: [PATCH] fnsplit: Set musttail call during function splitting if there
 are musttail calls [PR119376]

The just posted inliner patch can regress musttail calls if we perform
function splitting and then inline the outlined body back into the original
(or inline both the small function and outlined large body into something
else).
If there are any musttail calls, I think we need to call the outlined
body using a musttail call, so that the inliner will preserve musttail
attributes in the body.

2025-03-21  Jakub Jelinek  <jakub@redhat.com>

	PR ipa/119376
	* ipa-split.cc (split_function): Call gimple_call_set_must_tail
	on the call to outlined partition if has_musttail and
	!add_tsan_func_exit.

	* g++.dg/opt/musttail1.C: New test.
---
 gcc/ipa-split.cc                     |  2 ++
 gcc/testsuite/g++.dg/opt/musttail1.C | 35 ++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/opt/musttail1.C

diff --git a/gcc/ipa-split.cc b/gcc/ipa-split.cc
index ff562e2a636..729fb79af52 100644
--- a/gcc/ipa-split.cc
+++ b/gcc/ipa-split.cc
@@ -1473,6 +1473,8 @@ split_function (basic_block return_bb, class split_point *split_point,
 	args_to_pass[i] = arg;
       }
   call = gimple_build_call_vec (node->decl, args_to_pass);
+  if (cur_node->get_fun ()->has_musttail && !add_tsan_func_exit)
+    gimple_call_set_must_tail (call, true);
   gimple_set_block (call, DECL_INITIAL (current_function_decl));
   args_to_pass.release ();
 
diff --git a/gcc/testsuite/g++.dg/opt/musttail1.C b/gcc/testsuite/g++.dg/opt/musttail1.C
new file mode 100644
index 00000000000..5fe8ab6bd39
--- /dev/null
+++ b/gcc/testsuite/g++.dg/opt/musttail1.C
@@ -0,0 +1,35 @@
+// PR ipa/119376
+// { dg-do compile { target musttail } }
+// { dg-options "-O2 -fdump-tree-optimized" }
+// { dg-final { scan-tree-dump-times "  \[^\n\r]* = foo \\\(\[^\n\r]*\\\); \\\[tail call\\\] \\\[must tail call\\\]" 2 "optimized" } }
+// { dg-final { scan-tree-dump-times "  \[^\n\r]* = foo \\\(\[^\n\r]*\\\); \\\[tail call\\\]" 3 "optimized" } }
+
+int foo (int x);
+typedef int (*F) (int);
+int v;
+
+inline int
+bar (int x)
+{
+  if (__builtin_expect (x == 42, 1))
+    return 1;
+  [[gnu::musttail]] return foo (x + v * (x | v) * (x & v) * (x - v) * (x + v * v));
+}
+
+int
+baz (int x)
+{
+  [[gnu::musttail]] return bar (x);
+}
+
+int
+qux (int x)
+{
+  return bar (x + 1);
+}
+
+F
+corge ()
+{
+  return &bar;
+}
-- 
2.47.2