bpo-43693: Eliminate unused "fast locals". (gh-26587)

Currently, if an arg value escapes (into the closure for an inner function) we end up allocating two indices in the fast locals even though only one gets used.  Additionally, using the lower index would be better in some cases, such as with no-arg `super()`.  To address this, we update the compiler to fix the offsets so each variable only gets one "fast local".  As a consequence, now some cell offsets are interspersed with the locals (only when an arg escapes to an inner function).

https://bugs.python.org/issue43693

1 files changed, 21 insertions, 21 deletions

diff --git a/Lib/test/test_dis.py b/Lib/test/test_dis.py
index b81fcb5..41dd939 100644
--- a/Lib/test/test_dis.py
+++ b/Lib/test/test_dis.py
@@ -427,9 +427,9 @@ def _h(y):
     return foo
 
 dis_nested_0 = """\
-              0 MAKE_CELL                2 (y)
+              0 MAKE_CELL                0 (y)
 
-%3d           2 LOAD_CLOSURE             2 (y)
+%3d           2 LOAD_CLOSURE             0 (y)
               4 BUILD_TUPLE              1
               6 LOAD_CONST               1 (<code object foo at 0x..., file "%s", line %d>)
               8 LOAD_CONST               2 ('_h.<locals>.foo')
@@ -446,14 +446,14 @@ dis_nested_0 = """\
 
 dis_nested_1 = """%s
 Disassembly of <code object foo at 0x..., file "%s", line %d>:
-              0 MAKE_CELL                1 (x)
+              0 MAKE_CELL                0 (x)
 
-%3d           2 LOAD_CLOSURE             1 (x)
+%3d           2 LOAD_CLOSURE             0 (x)
               4 BUILD_TUPLE              1
               6 LOAD_CONST               1 (<code object <listcomp> at 0x..., file "%s", line %d>)
               8 LOAD_CONST               2 ('_h.<locals>.foo.<locals>.<listcomp>')
              10 MAKE_FUNCTION            8 (closure)
-             12 LOAD_DEREF               2 (y)
+             12 LOAD_DEREF               1 (y)
              14 GET_ITER
              16 CALL_FUNCTION            1
              18 RETURN_VALUE
@@ -966,19 +966,19 @@ expected_jumpy_line = 1
 
 Instruction = dis.Instruction
 expected_opinfo_outer = [
-  Instruction(opname='MAKE_CELL', opcode=135, arg=3, argval='a', argrepr='a', offset=0, starts_line=None, is_jump_target=False),
-  Instruction(opname='MAKE_CELL', opcode=135, arg=4, argval='b', argrepr='b', offset=2, starts_line=None, is_jump_target=False),
+  Instruction(opname='MAKE_CELL', opcode=135, arg=0, argval='a', argrepr='a', offset=0, starts_line=None, is_jump_target=False),
+  Instruction(opname='MAKE_CELL', opcode=135, arg=1, argval='b', argrepr='b', offset=2, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_CONST', opcode=100, arg=8, argval=(3, 4), argrepr='(3, 4)', offset=4, starts_line=2, is_jump_target=False),
-  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=3, argval='a', argrepr='a', offset=6, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=4, argval='b', argrepr='b', offset=8, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=0, argval='a', argrepr='a', offset=6, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=1, argval='b', argrepr='b', offset=8, starts_line=None, is_jump_target=False),
   Instruction(opname='BUILD_TUPLE', opcode=102, arg=2, argval=2, argrepr='', offset=10, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_CONST', opcode=100, arg=3, argval=code_object_f, argrepr=repr(code_object_f), offset=12, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_CONST', opcode=100, arg=4, argval='outer.<locals>.f', argrepr="'outer.<locals>.f'", offset=14, starts_line=None, is_jump_target=False),
   Instruction(opname='MAKE_FUNCTION', opcode=132, arg=9, argval=9, argrepr='defaults, closure', offset=16, starts_line=None, is_jump_target=False),
   Instruction(opname='STORE_FAST', opcode=125, arg=2, argval='f', argrepr='f', offset=18, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_GLOBAL', opcode=116, arg=0, argval='print', argrepr='print', offset=20, starts_line=7, is_jump_target=False),
-  Instruction(opname='LOAD_DEREF', opcode=137, arg=3, argval='a', argrepr='a', offset=22, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_DEREF', opcode=137, arg=4, argval='b', argrepr='b', offset=24, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_DEREF', opcode=137, arg=0, argval='a', argrepr='a', offset=22, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_DEREF', opcode=137, arg=1, argval='b', argrepr='b', offset=24, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_CONST', opcode=100, arg=5, argval='', argrepr="''", offset=26, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_CONST', opcode=100, arg=6, argval=1, argrepr='1', offset=28, starts_line=None, is_jump_target=False),
   Instruction(opname='BUILD_LIST', opcode=103, arg=0, argval=0, argrepr='', offset=30, starts_line=None, is_jump_target=False),
@@ -991,23 +991,23 @@ expected_opinfo_outer = [
 ]
 
 expected_opinfo_f = [
-  Instruction(opname='MAKE_CELL', opcode=135, arg=3, argval='c', argrepr='c', offset=0, starts_line=None, is_jump_target=False),
-  Instruction(opname='MAKE_CELL', opcode=135, arg=4, argval='d', argrepr='d', offset=2, starts_line=None, is_jump_target=False),
+  Instruction(opname='MAKE_CELL', opcode=135, arg=0, argval='c', argrepr='c', offset=0, starts_line=None, is_jump_target=False),
+  Instruction(opname='MAKE_CELL', opcode=135, arg=1, argval='d', argrepr='d', offset=2, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_CONST', opcode=100, arg=5, argval=(5, 6), argrepr='(5, 6)', offset=4, starts_line=3, is_jump_target=False),
-  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=5, argval='a', argrepr='a', offset=6, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=6, argval='b', argrepr='b', offset=8, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=3, argval='c', argrepr='c', offset=10, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=4, argval='d', argrepr='d', offset=12, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=3, argval='a', argrepr='a', offset=6, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=4, argval='b', argrepr='b', offset=8, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=0, argval='c', argrepr='c', offset=10, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=1, argval='d', argrepr='d', offset=12, starts_line=None, is_jump_target=False),
   Instruction(opname='BUILD_TUPLE', opcode=102, arg=4, argval=4, argrepr='', offset=14, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_CONST', opcode=100, arg=3, argval=code_object_inner, argrepr=repr(code_object_inner), offset=16, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_CONST', opcode=100, arg=4, argval='outer.<locals>.f.<locals>.inner', argrepr="'outer.<locals>.f.<locals>.inner'", offset=18, starts_line=None, is_jump_target=False),
   Instruction(opname='MAKE_FUNCTION', opcode=132, arg=9, argval=9, argrepr='defaults, closure', offset=20, starts_line=None, is_jump_target=False),
   Instruction(opname='STORE_FAST', opcode=125, arg=2, argval='inner', argrepr='inner', offset=22, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_GLOBAL', opcode=116, arg=0, argval='print', argrepr='print', offset=24, starts_line=5, is_jump_target=False),
-  Instruction(opname='LOAD_DEREF', opcode=137, arg=5, argval='a', argrepr='a', offset=26, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_DEREF', opcode=137, arg=6, argval='b', argrepr='b', offset=28, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_DEREF', opcode=137, arg=3, argval='c', argrepr='c', offset=30, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_DEREF', opcode=137, arg=4, argval='d', argrepr='d', offset=32, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_DEREF', opcode=137, arg=3, argval='a', argrepr='a', offset=26, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_DEREF', opcode=137, arg=4, argval='b', argrepr='b', offset=28, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_DEREF', opcode=137, arg=0, argval='c', argrepr='c', offset=30, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_DEREF', opcode=137, arg=1, argval='d', argrepr='d', offset=32, starts_line=None, is_jump_target=False),
   Instruction(opname='CALL_FUNCTION', opcode=131, arg=4, argval=4, argrepr='', offset=34, starts_line=None, is_jump_target=False),
   Instruction(opname='POP_TOP', opcode=1, arg=None, argval=None, argrepr='', offset=36, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_FAST', opcode=124, arg=2, argval='inner', argrepr='inner', offset=38, starts_line=6, is_jump_target=False),