ZJIT: Fix a splitting condition for LHS

Author: k0kubun

test/ruby/test_zjit.rb

@@ -86,6 +86,14 @@ def test(a, b, c) = a + b + c
     }, call_threshold: 2
   end
 
+  def test_opt_plus_left_imm
+    assert_compiles '3', %q{
+      def test(a) = 1 + a
+      test(1) # profile opt_plus
+      test(2)
+    }, call_threshold: 2
+  end
+
   # Test argument ordering
   def test_opt_minus
     assert_compiles '2', %q{

zjit/src/backend/x86_64/mod.rs

@@ -183,7 +183,7 @@ impl Assembler
                                     *left = asm.load(*left);
                                 },
                                 // The first operand can't be an immediate value
-                                (Opnd::Value(_), _) => {
+                                (Opnd::UImm(_), _) => {
                                     *left = asm.load(*left);
                                 }
                                 _ => {}