Tuple to constant folding

DinoV · DinoV · commit 9851616f1956 · 2021-01-28T11:14:38.000-08:00
Summary: This implements an optimization that replaces  [LOAD_CONST ...] BUILD_TUPLE with a simple LOAD_CONST with the actual tuple object burned in.   Again we just produce a new Constant AST node whose value is the tuple object.

Test Plan: ./python -m test.test_compiler
diff --git a/compiler/optimizer.py b/compiler/optimizer.py
@@ -1,6 +1,7 @@
 import ast
 import operator
 from ast import Constant, Num, Str, Bytes, Ellipsis, NameConstant, copy_location
+from typing import Iterable, Optional
 from compiler.peephole import safe_multiply, safe_power, safe_mod, safe_lshift
 from compiler.visitor import ASTRewriter
 
@@ -95,3 +96,19 @@ def visitBinOp(self, node: ast.BinOp) -> ast.expr:
                     pass
 
         return self.update_node(node, left=l, right=r)
+
+    def makeConstTuple(self, elts: Iterable[ast.expr]) -> Optional[Constant]:
+        if all(is_const(elt) for elt in elts):
+            return Constant(tuple(get_const_value(elt) for elt in elts))
+
+        return None
+
+    def visitTuple(self, node: ast.Tuple) -> ast.expr:
+        elts = self.walk_list(node.elts)
+
+        if isinstance(node.ctx, ast.Load):
+            res = self.makeConstTuple(elts)
+            if res is not None:
+                return copy_location(res, node)
+
+        return self.update_node(node, elts=elts)
diff --git a/test_compiler/test_py37.py b/test_compiler/test_py37.py
@@ -188,6 +188,9 @@ def test_ast_optimizer(self):
             ("1 + None", "1 + None"),
             ("True + None", "True + None"),
             ("True + 1", "2"),
+            ("(1, 2)", "(1, 2)"),
+            ("(1, 2) * 2", "(1, 2, 1, 2)"),
+            ("(1, --2, abc)", "(1, 2, abc)"),
         ]
         for inp, expected in cases:
             optimizer = AstOptimizer()
