[PATCH]rs6000: avoid peeking eof after __vector keyword

Jiufu Guo guojiufu@linux.ibm.com
Tue Mar 22 05:50:39 GMT 2022


Hi!

Segher Boessenkool <segher@kernel.crashing.org> writes:

> On Mon, Mar 21, 2022 at 02:14:08PM -0400, David Edelsohn wrote:
>> On Mon, Mar 21, 2022 at 5:13 AM Jiufu Guo <guojiufu@linux.ibm.com> wrote:
>> > There is a rare corner case: where __vector is followed only with ";"
>> > and near the end of the file.
>
>> This is okay. Maybe a tweak to the comment, see below.
>
> This whole function could use some restructuring / rewriting to make
> clearer what it actually does.  See the function comment:
>
> /* Called to decide whether a conditional macro should be expanded.
>    Since we have exactly one such macro (i.e, 'vector'), we do not
>    need to examine the 'tok' parameter.  */
>
> ... followed by 17 uses of "tok".  Yes, some of those overwrite the
> function argument, but that doesn't make it any better!  :-P
>
> Some factoring would help, too, perhaps.

Thanks for your review!

I am also confused about it when I check this function for the first
time. In the function, 'tok' is used directly at the beginning, and
then it is overwritten by cpp_peek_token.
>From the history of this function, the first version of this function
contains this 'inconsistency' between comments and implementations. :-P

With check related code, it seems this function is used to predicate
if a conditional macro should be expanded by peeking two or more
tokens.
The context-sensitive macros are vector/bool/pixel.  Correponding
keywords __vector/__bool/__pixel are unconditional.
Based on those related codes, the behavior of function
rs6000_macro_to_expand would be checking if the 'vector' token is
followed by bool/__bool or pixel/__pixel.  To do this the 'tok' has to
be 'examined'.

>From this understanding, we may just update the comment.
While the patch does not cover this.


BR,
Jiufu

>
>
> Segher


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