Re: [PATCH] preprocessor: Fix tracking of system header state [PR60014, PR60723]

[Jeff Law <jeffreyalaw@gmail.com>]

On 10/8/22 15:18, Lewis Hyatt via Gcc-patches wrote:
> The token_streamer class (which implements gcc mode -E and
> -save-temps/-no-integrated-cpp) needs to keep track whether the last tokens
> output were in a system header, so that it can generate line marker
> annotations as necessary for a downstream consumer to reconstruct the
> state. The logic for tracking it, which was added by r5-1863 to resolve
> PR60723, has some edge case issues as revealed by the three new test
> cases. The first, coming from the original PR60014, was incidentally fixed by
> r9-1926 for unrelated reasons. The other two were still failing on master
> prior to this commit. Such code paths were not realizable prior to r13-1544,
> which made it possible for the token streamer to see CPP_PRAGMA tokens in more
> contexts.
>
> The two main issues being corrected here are:
>
> 1) print.prev_was_system_token needs to indicate whether the previous token
> output was in a system location. However, it was not being set on every token,
> only on those that triggered the main code path; specifically it was not
> triggered on a CPP_PRAGMA token. Testcase 2 covers this case.
>
> 2) The token_streamer uses a variable "line_marker_emitted" to remember
> whether a line marker has been emitted while processing a given token, so that
> it wouldn't be done more than once in case multiple conditions requiring a
> line marker are true. There was no reason for this to be a member variable
> that retains its value from token to token, since it is just needed for
> tracking the state locally while processing a single given token. The fact
> that it could retain its value for a subsequent token is rather difficult to
> observe, but testcase 3 demonstrates incorrect behavior resulting from
> that. Moving this to a local variable also simplifies understanding the
> control flow going forward.
>
> gcc/c-family/ChangeLog:
>
> 	PR preprocessor/60014
> 	PR preprocessor/60723
> 	* c-ppoutput.cc (class token_streamer): Remove member
> 	line_marker_emitted to...
> 	(token_streamer::stream): ...a local variable here. Set
> 	print.prev_was_system_token on all code paths.
>
> gcc/testsuite/ChangeLog:
>
> 	PR preprocessor/60014
> 	PR preprocessor/60723
> 	* gcc.dg/cpp/pr60014-1.c: New test.
> 	* gcc.dg/cpp/pr60014-1.h: New test.
> 	* gcc.dg/cpp/pr60014-2.c: New test.
> 	* gcc.dg/cpp/pr60014-2.h: New test.
> 	* gcc.dg/cpp/pr60014-3.c: New test.
> 	* gcc.dg/cpp/pr60014-3.h: New test.

OK

jeff