On 16-12-2011 13:23, bearophile wrote:
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
I generally don't like that a compiler throws warnings at me for
perfectly valid code. Yes, it *can* be error prone, but most often, I
know what I'm doing and am actually utilizing a language feature.
Personally, I'd make no warnings the default and add an option that
looks for suspicious stuff like if (a = b).
- Alex
