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[mypyc] Don't explicitly assign NULL values in setup functions #15379

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Merged
JukkaL merged 1 commit into from
Jun 12, 2023
Merged

[mypyc] Don't explicitly assign NULL values in setup functions #15379

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Don't explicitly assign NULL values in setup functions: 
While investigating something unrelated I stumbled across the `*_setup`
functions, and I noticed that they contain a lot of code that looks like this:

```c
self->abc = NULL;
self->xyz = NULL;
// ...
```

Something told me that assigning `NULL` to a bunch of fields is propably not
needed, and when looking at the docs for `tp_alloc()` I found this reference to
[`allocfunc`](https://docs.python.org/3/c-api/typeobj.html#c.allocfunc), the
typedef for `tp_alloc()`:

> It should return a pointer to a block of memory of adequate length for the
> instance, suitably aligned, **and initialized to zeros**, ...

Emphasis is mine.

Basically I added a simple check that removes lines similar to above which
assigns `NULL` values in setup functions. This removes about ~4100 lines from
the C file when self-compiling.
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@dosisod
dosisod committed Jun 6, 2023
commit 2fbf70914c66b186df1da71f870ed44793d64757
7 changes: 6 additions & 1 deletion mypyc/codegen/emitclass.py
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Original file line number Diff line number Diff line change
Expand Up @@ -578,7 +578,12 @@ def generate_setup_for_class(

for base in reversed(cl.base_mro):
for attr, rtype in base.attributes.items():
emitter.emit_line(rf"self->{emitter.attr(attr)} = {emitter.c_undefined_value(rtype)};")
value = emitter.c_undefined_value(rtype)

# We don't need to set this field to NULL since tp_alloc() already
# zero-initializes `self`.
if value != "NULL":
emitter.emit_line(rf"self->{emitter.attr(attr)} = {value};")

# Initialize attributes to default values, if necessary
if defaults_fn is not None:
Expand Down