fix: do not optimize built-in calls

Sentences like:
 LET c = USR(x)
are optimized if c var is not used. But
the built-in call must be executed if it has side-effects.

Thse builtins are: IN, RND and USR

Author: boriel

src/api/optimize.py

@@ -321,16 +321,20 @@ def visit_LET(self, node):
         lvalue = node.children[0]
         if self.O_LEVEL > 1 and not lvalue.accessed:
             warning_not_used(lvalue.lineno, lvalue.name, fname=lvalue.filename)
-            block = symbols.BLOCK(
-                *[
-                    symbols.CALL(x.entry, x.args, x.lineno, lvalue.filename)
-                    for x in self.filter_inorder(
-                        node.children[1],
-                        lambda x: x.token == "FUNCCALL",
-                        lambda x: x.token != "FUNCTION",
-                    )
-                ]
-            )
+            nodes = [
+                symbols.CALL(x.entry, x.args, x.lineno, lvalue.filename) if x.token == "FUNCCALL" else x
+                for x in self.filter_inorder(
+                    node.children[1],
+                    lambda x: x.token in ("FUNCCALL", "BUILTIN"),
+                    lambda x: x.token != "FUNCTION",
+                )
+                if x.token == "FUNCCALL" or getattr(x, "fname") in {"IN", "RND", "USR"}
+            ]
+            for node_ in nodes:
+                if node_.token == "BUILTIN":
+                    node_.discard_result = True
+
+            block = symbols.BLOCK(*nodes)
             yield block
         else:
             yield (yield self.generic_visit(node))

src/arch/z80/visitor/translator.py

@@ -152,6 +152,8 @@ def visit_BUILTIN(self, node):
         att = f"visit_{node.fname}"
         if hasattr(bvisitor, att):
             yield getattr(bvisitor, att)(node)
+            if node.discard_result:
+                self.ic_fparam(node.type_, optemps.new_t())
             return
 
         raise InvalidBuiltinFunctionError(node.fname)

src/symbols/builtin.py

@@ -13,7 +13,7 @@
 
 
 class SymbolBUILTIN(Symbol):
-    """Defines an BUILTIN function e.g. INKEY$(), RND() or LEN"""
+    """Defines a BUILTIN function e.g. INKEY$(), RND() or LEN"""
 
     def __init__(self, lineno, fname, type_=None, *operands):
         assert isinstance(lineno, int)
@@ -22,6 +22,7 @@ def __init__(self, lineno, fname, type_=None, *operands):
         self.lineno = lineno
         self.fname = fname
         self.type_ = type_
+        self.discard_result = False  # Whether to discard the return value of the function
 
     @property
     def type_(self):