lebedev.ri added a comment.
In https://reviews.llvm.org/D38954#906900, @thakis wrote:
> Can you build some large-ish codebase (say, LLVM) with and without this patch
> and make sure that this doesn't measurably add to build perf? (With the
> warning turned on, obviously.)
>
> Other than that, this looks good to me.
Very contrived example:
$ head -n 3 test.cpp
#include <cstddef>
int main(int argc, char* argv[]) {
$ perl -e 'print "if(argv == NULL) return 1;\n"x1000000; print "\n"' >>
test.cpp
$ tail -n 2 test.cpp
}
So this is a file with 1 million comparisons of pointer with `NULL`.
$ time clang -fsyntax-only -Wzero-as-null-pointer-constant -std=c++11
test.cpp -w
real 0m8.197s
user 0m8.071s
sys 0m0.124s
$ time clang -fsyntax-only -Wzero-as-null-pointer-constant -std=c++11
test.cpp -w
real 0m7.881s
user 0m7.728s
sys 0m0.152s
$ time clang -fsyntax-only -Wzero-as-null-pointer-constant -std=c++11
test.cpp -w
real 0m7.212s
user 0m7.063s
sys 0m0.148s
$ time /build/llvm-build-Clang-release/bin/clang -fsyntax-only
-Wzero-as-null-pointer-constant -std=c++11 test.cpp -w
real 0m11.200s
user 0m11.070s
sys 0m0.128s
$ time /build/llvm-build-Clang-release/bin/clang -fsyntax-only
-Wzero-as-null-pointer-constant -std=c++11 test.cpp -w
real 0m11.141s
user 0m11.019s
sys 0m0.121s
$ time /build/llvm-build-Clang-release/bin/clang -fsyntax-only
-Wzero-as-null-pointer-constant -std=c++11 test.cpp -w
real 0m11.254s
user 0m11.127s
sys 0m0.126s
So there absolutely is some penalty, but it does not appear to be huge, at
least on this contrived example.
I *could* try benchmark-building llvm, but i'm still sporadically experiencing
a crash <https://bugs.llvm.org/show_bug.cgi?id=34480>, so the timings will not
be comparable.
================
Comment at: test/SemaCXX/warn-zero-nullptr.cpp:68
+ public:
+// FIXME: this one should *NOT* warn.
+ explicit TemplateClass1(int a, T default_value = 0) {} //
expected-warning{{zero as null pointer constant}} expected-warning{{zero as
null pointer constant}}
----------------
thakis wrote:
> Did you mean to fix this before commit?
Eh, i'm conflicted about this one.
This is more of "for future consideration"
Repository:
rL LLVM
https://reviews.llvm.org/D38954
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