LLVM talks 1: Clang for Chromium

[bearophile]

There are the videos of the 2011 LLVM Developer Meeting:
http://www.youtube.com/playlist?list=PL970A5BD02C11F80C

Slides too:
http://llvm.org/devmtg/2011-11/

As usual the LLVM talks are quite interesting. I have started to see the videos/slides, it will require some time.

An interesting talk, "Using clang in the Chromium project":
http://www.youtube.com/watch?v=IvL3f8xY7Uw

Slides:
http://llvm.org/devmtg/2011-11/Weber_Wennborg_UsingClangInChromium.pdf

-----------------------------------

It shows some problems found by Clang.


a.cc:2:9: warning: using the result of an assignment as a condition without parentheses [-Wparentheses]
  if (x |= y)
      ~~^~~~
a.cc:2:9: note: use '!=' to turn this compound assignment into an inequality comparison
  if (x |= y)
        ^~
        !=

1 warning generated.



This code doesn't compile with DMD:
Error: assignment cannot be used as a condition, perhaps == was meant?

void main() {
    int x, y;
    if (x = y) {}
}


But this gives no errors:

void main() {
    int x, y;
    if (x |= y) {}
    if (x += y) {}
}


Do you know why DMD forbids assignments as conditions, but it accepts compound assignments there? It looks like a incongruence that's better to remove.

-----------------------------------

10.25 in the video:

a.cc:2:16: warning: operator '?:' has lower precedence than '+'; '+' will be evaluated first
  return x + b ? y : 0;
         ~~~~~ ^
a.cc:2:16: note: place parentheses around the '?:' expression to evaluate it first
  return x + b ? y : 0;
               ^
            (         )

1 warning generated.

They say:

> It's a bug every time!


Given the frequence of bugs caused by the ?: operator, I think something like this will be good to have in D too.

-----------------------------------

a.cc:8:23: warning: argument to ’sizeof’ in ’memset’ call is the same expression as the destination;
  did you mean to dereference it?
  memset(s, 0, sizeof(s));
         ~            ^

1 warning generated.

-----------------------------------

At 14.45-16.39 there is an interesting part, about slide 22 of the PDF. It's about crashes/bugs caused by undefined order of evaluation of function arguments. This is a class of bugs that don't have to happen in D2 code.

Bye,
bearophile