a big array of structure will make clangd very slow

[asd-a]

for example:

pair<int,int>hack_clangd[1<<20];

then clangd will be slow

[HighCommander4]

I suspect this is the upstream bug llvm/llvm-project#51054

[sam-mccall]

I relanded the fix from that bug but it still feels sluggish.

#include <utility>
std::pair<int, int> hack_clangd[1<<20];

time bin/clang -fsyntax-only ~/test.cc
________________________________________________________
Executed in    1.97 secs   fish           external 
   usr time  1778.03 millis  820.00 micros  1777.21 millis 
   sys time  192.02 millis  324.00 micros  191.70 millis 

[fishBone000]

This problem still exists, even on 18.1.3.

#include <bits/stdc++.h>

struct s_t {

};

// Large memory consumption: 6+GB
// std::pair<int, int> tree[int(10e7)];
// s_t tree[int(10e7)];

// No effect
// int tree[int(10e7)];

int main() {
}

Uncomment corresponding lines to see the effect.

For std::pair<int, int>, each time I edit the src code in my IDE (nvim), e.g. delete a character, add a character, or delete lines, a memory consumption spike can be observed (6+GB).
The spike gets much smaller if the array is smaller, e.g. ~1GB for 10e6, and much smaller if less than 10e5.

For s_t, it is kind of strange:
The memory consumption goes up by 6GB, and never goes down, unlike std::pair<int, int> which looks like a spike.