https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89665
Bug ID: 89665
Summary: inconsistent macro expansion
Product: gcc
Version: 7.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: preprocessor
Assignee: unassigned at gcc dot gnu.org
Reporter: gciofono at gmail dot com
Target Milestone: ---
Created attachment 45941
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=45941&action=edit
hellomacro.c shows the inconsistent macro expansion of gcc.
The preprocessing of the macros follows a lazy-expansion algorithm that is not
entirely satisfying, nor exactly matching the description of the gcc guide,
paragraph 3.10.6 Argument Prescan.
I find that an argument should be expanded each time it is used, or
(suboptimal) each time it is declared, but the gcc preprocessor does none.
My full gcc version with Ubuntu 18.04 is:
gcc (Ubuntu 7.3.0-27ubuntu1~18.04) 7.3.0
please compile with (includes only stdio.h but it is unavoidable to see the
output):
gcc -v -save-temps -o hm hellomacro.c
the commented result of execution is:
$ ./hm
0-1-2-3-4 << 5 times expansion of __COUNTER__, as expected
x << INCONSISTENCY: no expansion to __COUNTER__, because not used
direcly
5-5-5-5-5 << inconsistency: 1 expansion of counter. 5 times would have been
better
x << inconsistency: 1 expansion of counter, because of it indirect
use, but finally discarded like two lines above
7-7-7-7-7 << output of the current counter (6 is skipped).
