Clang spell checker is slow

[Quuxplusone]

Bugzilla Link	PR17698
Status	NEW
Importance	P normal
Reported by	Óscar Fuentes (ofv@wanadoo.es)
Reported on	2013-10-25 14:09:14 -0700
Last modified on	2019-07-11 15:52:57 -0700
Version	trunk
Hardware	PC Linux
CC	jryans@gmail.com, llvm-bugs@lists.llvm.org, rafael@espindo.la
Fixed by commit(s)
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This test case:

#include "boost/asio.hpp"
double mainf();
int mainf() {
  foo(sdafo_2, 0);
  return 0;
}

takes this time to compile:

Time (seconds)  Command
6.8             clang -c -std=c++11 test.cpp
4.8             clang -c test.cpp

    (after replacing `sdafo_2' with `x')
1.0             clang -c test.cpp

    (after replacing `sdafo_2' with `o_2')
2.8             clang -c test.cpp

Note how Clang needs a long time to compute the diagnostic about `sdafo_2'
after reporting the diagnostic about the illegal overload of `mainf'.

[Quuxplusone]

Forgot to mention that compiling the preprocessed source halves the compile time. That is, preprocessing and then compiling the resulting output takes half the time of compiling the original file.

[Quuxplusone]

-fno-spell-checking makes the slowness go away.

[Quuxplusone]

Just to add one more data point to this issue: after making a simple change on a C++ source file, clang seemed stuck while compiling it. After 2 minutes I killed the process thinking that it was in a infinite loop. Then remembered this issue and tried to compile with g++. Sure enough, there was a typo introduced by the change. After fixing the typo clang compiled the C++ file in a few seconds.