https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115832
Bug ID: 115832
Summary: Very slow compilation with certain flags and std::sort
Product: gcc
Version: 12.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: faisal.irl2004 at gmail dot com
Target Milestone: ---
Created attachment 58611
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58611&action=edit
compiler output of g++ -v
C++ compilation time seems to blow up unreasonably when compiling with
the flags:
-D_GLIBCXX_DEBUG -fsanitize=undefined -O2
In particular, calling something even simple like std::sort() will blow up
compilation time by 5x with these flags. Using any proper subset of these flags
seems to speed up compilation time by at least 5x as well. Using precompiled
headers doesn't help with compilation time much either. I have provided a
minimal test case to illustrate the problem:
A.cpp:
#include <vector>
#include <algorithm>
#define MAXN (int) 10
/*
time g++ A.cpp -D_GLIBCXX_DEBUG -fsanitize=undefined -O2
Removing any one of these 3 flags speeds up compilation by atleast 5x
*/
int main() {
std::vector<int> arr(MAXN);
for (int i = 0; i < MAXN; i++) {
arr[i] = i + 10;
}
// std::sort(arr.begin(), arr.end()); /* Uncomment this to blow up compile
time */
return arr[0];
}
Without std::sort
time g++ A.cpp -D_GLIBCXX_DEBUG -fsanitize=undefined -O2
real 0m0.308s
user 0m0.272s
sys 0m0.035s
With std::sort
time g++ A.cpp -D_GLIBCXX_DEBUG -fsanitize=undefined -O2
real 0m4.175s
user 0m4.062s
sys 0m0.108s
Using precompiled headers also only brings it down to ~4s.
I have attached the preprocessed file and the compiler output of:
g++ -v -save-temps A.cpp -D_GLIBCXX_DEBUG -fsanitize=undefined -O2 &>
compiler_output
(This is run with std::sort present)
