From 6ba0b38f4b9a163297514ff1acec7e66078dede1 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Tue, 14 Apr 2026 12:45:34 +0300
Subject: [PATCH] cgen: cgen doesn't create temporaries for arguments with
 multiple references (fixes #22749)

---
 vlib/v/gen/c/fn.v                             | 49 +++++++++++++++++++
 .../tests/pointers/multi_ref_call_arg_test.v  | 24 +++++++++
 2 files changed, 73 insertions(+)
 create mode 100644 vlib/v/tests/pointers/multi_ref_call_arg_test.v

diff --git a/vlib/v/gen/c/fn.v b/vlib/v/gen/c/fn.v
index 69db40b1d..0166f9fb9 100644
--- a/vlib/v/gen/c/fn.v
+++ b/vlib/v/gen/c/fn.v
@@ -5989,6 +5989,52 @@ fn (mut g Gen) keep_alive_call_postgen(node ast.CallExpr, tmp_cnt_save int) {
 	}
 }
 
+fn (mut g Gen) write_multi_ref_arg(arg ast.CallArg, arg_typ ast.Type, expected_type ast.Type, lang ast.Language) bool {
+	if lang != .v || g.is_json_fn || !expected_type.is_ptr() || expected_type.has_option_or_result()
+		|| expected_type.nr_muls() <= 1 || expected_type.nr_muls() <= arg_typ.nr_muls()
+		|| arg_typ.has_flag(.shared_f) || expected_type.has_flag(.shared_f) {
+		return false
+	}
+	expected_deref_type := expected_type.deref()
+	expected_deref_sym := g.table.sym(expected_deref_type)
+	arg_sym := g.table.sym(arg_typ)
+	if expected_deref_sym.kind in [.interface, .sum_type] || arg_sym.kind == .function
+		|| arg.expr is ast.None {
+		return false
+	}
+	if arg.expr is ast.Ident
+		&& (arg.expr.language == .c || g.table.is_interface_smartcast(arg.expr.obj)) {
+		return false
+	}
+	// Build the first reference level from the original storage when possible,
+	// then materialize deeper levels through compound-literal temporaries.
+	extra_refs := expected_type.nr_muls() - arg_typ.nr_muls()
+	for level := extra_refs - 1; level > 0; level-- {
+		ref_type := arg_typ.set_nr_muls(arg_typ.nr_muls() + level)
+		g.write('ADDR(${g.styp(ref_type)}, ')
+	}
+	old_arg_no_auto_deref := g.arg_no_auto_deref
+	if arg.expr.is_auto_deref_var() {
+		g.arg_no_auto_deref = true
+	}
+	defer {
+		g.arg_no_auto_deref = old_arg_no_auto_deref
+	}
+	is_auto_heap_ident := arg.expr is ast.Ident && g.resolved_ident_is_auto_heap(arg.expr)
+	if is_auto_heap_ident {
+		g.write_raw_receiver_expr(arg.expr)
+	} else if arg.expr.is_lvalue() {
+		g.write('&')
+		g.expr(arg.expr)
+	} else {
+		g.write('ADDR(${g.styp(arg_typ)}, ')
+		g.expr_with_cast(arg.expr, arg_typ, arg_typ)
+		g.write(')')
+	}
+	g.write(')'.repeat(extra_refs - 1))
+	return true
+}
+
 @[inline]
 fn (mut g Gen) ref_or_deref_arg(arg ast.CallArg, expected_type_ ast.Type, lang ast.Language, is_smartcast bool) {
 	g.ref_or_deref_arg_ex(arg, expected_type_, lang, is_smartcast, false)
@@ -6129,6 +6175,9 @@ fn (mut g Gen) ref_or_deref_arg_ex(arg ast.CallArg, expected_type_ ast.Type, lan
 		g.expr_with_cast(arg.expr, arg_typ, expected_type)
 		return
 	}
+	if g.write_multi_ref_arg(arg, arg_typ, expected_type, lang) {
+		return
+	}
 	is_auto_heap_ident := arg.expr is ast.Ident && g.resolved_ident_is_auto_heap(arg.expr)
 	mut needs_closing := false
 	old_inside_smartcast := g.inside_smartcast
diff --git a/vlib/v/tests/pointers/multi_ref_call_arg_test.v b/vlib/v/tests/pointers/multi_ref_call_arg_test.v
new file mode 100644
index 000000000..7c437db5a
--- /dev/null
+++ b/vlib/v/tests/pointers/multi_ref_call_arg_test.v
@@ -0,0 +1,24 @@
+fn takes_quad_ref(x &&&&int) {
+	unsafe {
+		****x = 5
+	}
+}
+
+fn takes_triple_ref(x &&&int) {
+	unsafe {
+		***x = 7
+	}
+}
+
+fn test_call_arg_with_multi_ref_from_value() {
+	mut y := 4
+	takes_quad_ref(y)
+	assert y == 5
+}
+
+fn test_call_arg_with_multi_ref_from_ref() {
+	mut y := 4
+	p := &y
+	takes_triple_ref(p)
+	assert y == 7
+}
-- 
2.39.5