From d49c5c35b7e897b0b127ee0bc1ea77beaa7432fd Mon Sep 17 00:00:00 2001
From: John Hawthorn <john@hawthorn.email>
Date: Sat, 4 Sep 2021 01:35:22 -0700
Subject: [PATCH] Allow calling variadic cfuncs with many args

We have a check to ensure we don't have to push args on the stack to
call a cfunc with many args. However we never need to use the stack for
variadic cfuncs, so we shouldn't care about the number of arguments.
---
 test/ruby/test_yjit.rb | 14 ++++++++++++++
 yjit_codegen.c         |  2 +-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/test/ruby/test_yjit.rb b/test/ruby/test_yjit.rb
index 94989dae9e..20f8046df7 100644
--- a/test/ruby/test_yjit.rb
+++ b/test/ruby/test_yjit.rb
@@ -204,6 +204,20 @@ def to_s
     RUBY
   end
 
+  # Tests calling a variadic cfunc with many args
+  def test_build_large_struct
+    assert_compiles(<<~RUBY, insns: %i[opt_send_without_block], min_calls: 2)
+      ::Foo = Struct.new(:a, :b, :c, :d, :e, :f, :g, :h)
+
+      def build_foo
+        ::Foo.new(:a, :b, :c, :d, :e, :f, :g, :h)
+      end
+
+      build_foo
+      build_foo
+    RUBY
+  end
+
   def test_fib_recursion
     assert_compiles(<<~'RUBY', insns: %i[opt_le opt_minus opt_plus opt_send_without_block], result: 34)
       def fib(n)
diff --git a/yjit_codegen.c b/yjit_codegen.c
index c90610794c..bfc6064ba3 100644
--- a/yjit_codegen.c
+++ b/yjit_codegen.c
@@ -2830,7 +2830,7 @@ gen_send_cfunc(jitstate_t *jit, ctx_t *ctx, const struct rb_callinfo *ci, const
     }
 
     // Don't JIT functions that need C stack arguments for now
-    if (argc + 1 > NUM_C_ARG_REGS) {
+    if (cfunc->argc >= 0 && argc + 1 > NUM_C_ARG_REGS) {
         GEN_COUNTER_INC(cb, send_cfunc_toomany_args);
         return YJIT_CANT_COMPILE;
     }