[cocci] how to check a for "don't care" state of a variable?

[Kees Cook <keescook@chromium.org>]

Hi!

I was looking at doing some conversions for this[1], and I wasn't sure
how to check for removing a variable assignment if there was either no
more uses or the next use was an assignment itself.

i.e.:

	var = 1;
	other = func(var);

turns into:

	other = func(1);

but this would not:

	var = 1;
	other = func(var);
	report(var);

without getting confused by:

	var = 1;
	other = func(var);
	var = 5;



@multi_line@
identifier randfunc =~ "get_random_int|prandom_u32|get_random_u32";
identifier RAND;
expression E;
type TYPE;
@@

(
-       RAND = randfunc();
        ... when != RAND
-       RAND %= (E);
+       RAND = prandom_u32_max(E);
|
-       RAND = randfunc();
        ... when != RAND
-       ((TYPE)RAND % (E))
+       prandom_u32_max(E)
// This is wrong: we need to check that RAND is either assigned or never
// accessed again
)


I thought I could do this:

	... when != RAND
	<... RAND = EXP; ...>

But this appears to be invalid syntax...

-Kees

[1] https://lore.kernel.org/lkml/202210071241.445289C5@keescook/

-- 
Kees Cook