Difference between revisions of "Testing removal of ifdef or configure checks"
(mention that this gets us cpp output (help wiki search)) |
(include hint from Thomas Nagy on getting CPP output for just one file) |
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It is difficult (and time consuming) to prove that the code is unused and that there is no change to the compiled output. | It is difficult (and time consuming) to prove that the code is unused and that there is no change to the compiled output. | ||
| − | ==A script to help== | + | ==A script to help obtain CPP output== |
[[File:Gcc-E.py.txt]] is a Python script that wraps gcc -E (to get the CPP output) to attempt to solve this dilemma, so as to provide a result that can be reasoned with via tools like [https://www.samba.org/ftp/paulus/ dirdiff] | [[File:Gcc-E.py.txt]] is a Python script that wraps gcc -E (to get the CPP output) to attempt to solve this dilemma, so as to provide a result that can be reasoned with via tools like [https://www.samba.org/ftp/paulus/ dirdiff] | ||
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or | or | ||
diff -ur --ignore-matching-lines="^#" /tmp/master-bin/ bin> /tmp/diff | diff -ur --ignore-matching-lines="^#" /tmp/master-bin/ bin> /tmp/diff | ||
| + | |||
| + | ==Getting just one file's CPP output== | ||
| + | Thanks to [https://lists.samba.org/archive/samba-technical/2020-March/134980.html waf author Thomas Nagy] | ||
| + | WAF_CMD_FORMAT=string PYTHONHASHSEED=1 WAF_MAKE=1 ./buildtools/bin/waf -v build | ||
| + | |||
| + | Then just edit the command to add the -E (and perhaps a new output file). | ||
Revision as of 19:20, 14 March 2020
Contents
#ifdef removal is risky
Large-scale removal of "unused" ifdef or the configure checks that produce #defines is an important, but risky task.
It is difficult (and time consuming) to prove that the code is unused and that there is no change to the compiled output.
A script to help obtain CPP output
File:Gcc-E.py.txt is a Python script that wraps gcc -E (to get the CPP output) to attempt to solve this dilemma, so as to provide a result that can be reasoned with via tools like dirdiff
Getting the results
git checkout origin/master git clean -x -f -d CC="gcc -E" ./configure.developer && make -j mv bin /tmp/master-bin git checkout newbranch git clean -x -f -d CC="gcc -E" ./configure.developer && make -j
Reading the results
dirdiff /tmp/master-bin bin
or
diff -ur --ignore-matching-lines="^#" /tmp/master-bin/ bin> /tmp/diff
Getting just one file's CPP output
Thanks to waf author Thomas Nagy
WAF_CMD_FORMAT=string PYTHONHASHSEED=1 WAF_MAKE=1 ./buildtools/bin/waf -v build
Then just edit the command to add the -E (and perhaps a new output file).