https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108535
Bug ID: 108535
Summary: RFE: analyzer to allow ifdef inclusion/exclusion like
cppcheck -D/-U
Product: gcc
Version: 12.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: analyzer
Assignee: dmalcolm at gcc dot gnu.org
Reporter: jamie.bainbridge at gmail dot com
Target Milestone: ---
When using code with a lot of #ifdefs, the analyzer can take a long time. It
would be nice if the analyzer could only take some ifdef paths to improve
runtime.
This is common with header-only libraries. Here's an example from stb_image, a
no-dependency image loading library which is popular in game development:
$ wget https://raw.githubusercontent.com/nothings/stb/master/stb_image.h
$ cat > main.c << EOF
#include <math.h>
#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"
int main(void) { return 0; }
EOF
$ gcc-12 --version | head -1
gcc-12 (Ubuntu 12.1.0-2ubuntu1~22.04) 12.1.0
A plain compile completes quickly:
$ time gcc-12 -Wall -Wextra -Wpedantic -o main main.c -lm
real 0m0.322s
user 0m0.290s
sys 0m0.033s
Adding the analyzer makes things worse:
$ time gcc-12 -Wall -Wextra -Wpedantic -fanalyzer -o main main.c -lm
real 0m5.542s
user 0m5.297s
sys 0m0.245s
Adding sanitizers even worse:
$ time gcc-12 -Wall -Wextra -Wpedantic -fanalyzer -fsanitize=address
-fsanitize=leak -fsanitize=undefined -o main main.c -lm
real 0m12.731s
user 0m12.014s
sys 0m0.716s
With cppcheck, analysis time for every path is terrible:
$ time cppcheck --force main.c
...
real 0m40.070s
user 0m40.038s
sys 0m0.024s
(this make's GCC's 5 second analysis look very impressive!)
However I'm able to restrict the number of #ifdef paths that cppcheck takes
with its "-D" option to only check the path(s) provided, this cuts runtime down
to 5% of the above:
$ time cppcheck -D__GNUC__ main.c
...
real 0m2.149s
user 0m2.129s
sys 0m0.020s
Likewise cppcheck has a -U option to exclude #ifdef paths. I would use -U
because maybe I don't care about some paths that this library supports like
STBI_NEON (ARMv7+) or STBI_NO_SIMD (pre-1996 x86 hardware without MMX).
My actual usage right now is to just make my edit-build-run cycle quicker while
I'm still in this rapid development stage, and improving developer experience
seems likely to increase adoption of tools like the analyzer.
For this reason, it would be nice for the GCC analyzer to support an ifdef
include/exclude feature like cppcheck's -D and -U options.
