[Bug preprocessor/48383] New: Line continuations handled incorrectly in 4.5 and above

["dg at cowlark dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48383

           Summary: Line continuations handled incorrectly in 4.5 and
                    above
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: preprocessor
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: dg@cowlark.com


Given the following test file:

foo \
bar

...then if I preprocess it with gcc 4.4 (using gcc -E), I get this:

foo bar

...but if I preprocess it with gcc 4.5 or 4.6, I get this:

foo
 bar

This would appear to me to violate 5.1.1.2.1.2 of the C99 draft, which states:

> Each instance of a backslash character (\) immediately followed by a new-line
> character is deleted, splicing physical source lines to form logical source
> lines.

Given that the following test file:

foo\
bar

...always preprocesses to this:

foobar

...then I suspect that what we've got here is an optimisation to keep line
number information correct on the 'bar' token; the reasoning would presumably
be that since C (and C++) treats newlines like all other whitespace, it makes
no difference whether the 'bar' token is on the same line or a new line.
Unfortunately, I believe the spec doesn't allow this behaviour.

(This is actually biting us because we're using cpp to preprocess files before
passing them to a perl script, and are relying on cpp to glue line
continuations together. As of gcc 4.5, this is no longer happening.)