Re: Possible bug in RVO?
On Monday, 4 April 2016 at 21:31:08 UTC, Ali Çehreli wrote:
On 04/04/2016 09:36 AM, Anonymouse wrote:
On Monday, 4 April 2016 at 03:55:26 UTC, Yuxuan Shui wrote:
[...]
assert(x.aa.length > 0); // <-- boom
[...]
No idea myself but that's where it seems to go wrong.
Looks like a bug. Just to make it more visible:
auto clobber(ref Set x, ref Set o) {
writefln("entered clobber- x.aa: %s", x.aa);
Set ret;
writefln("did not touch x.aa - x.aa: %s", x.aa);
ret.aa = x.aa;
return ret;
}
x.aa changes during the second call:
entered clobber- x.aa: [1:true]
did not touch x.aa - x.aa: [1:true]
entered clobber- x.aa: [1:true]
did not touch x.aa - x.aa: [] <-- What happened?
Ali
I filed an bug report here:
https://issues.dlang.org/show_bug.cgi?id=15869
Re: Possible bug in RVO?
On 04/04/2016 09:36 AM, Anonymouse wrote:
On Monday, 4 April 2016 at 03:55:26 UTC, Yuxuan Shui wrote:
On Monday, 4 April 2016 at 03:28:01 UTC, Yuxuan Shui wrote:
auto clobber(ref Set x, ref Set o) {
Set ret;
ret.aa = x.aa;
assert(x.aa.length > 0); // <-- boom
return ret;
}
No idea myself but that's where it seems to go wrong.
Looks like a bug. Just to make it more visible:
auto clobber(ref Set x, ref Set o) {
writefln("entered clobber- x.aa: %s", x.aa);
Set ret;
writefln("did not touch x.aa - x.aa: %s", x.aa);
ret.aa = x.aa;
return ret;
}
x.aa changes during the second call:
entered clobber- x.aa: [1:true]
did not touch x.aa - x.aa: [1:true]
entered clobber- x.aa: [1:true]
did not touch x.aa - x.aa: [] <-- What happened?
Ali
Re: Possible bug in RVO?
On Monday, 4 April 2016 at 03:55:26 UTC, Yuxuan Shui wrote:
On Monday, 4 April 2016 at 03:28:01 UTC, Yuxuan Shui wrote:
auto clobber(ref Set x, ref Set o) {
Set ret;
ret.aa = x.aa;
assert(x.aa.length > 0); // <-- boom
return ret;
}
No idea myself but that's where it seems to go wrong.
Re: Possible bug in RVO?
On Monday, 4 April 2016 at 03:28:01 UTC, Yuxuan Shui wrote:
I have encountered a weird bug.
I defined a Set class, which has a opBinary!"-". And somehow
this:
auto tmp = set_a-set_b;
produces different results as this:
set_a = set_a-set_b;
the latter will produce an empty set.
I tried to reduce the source code to get a test case. But this
problem just goes away after removing some code.
Any ideas what I could have done wrong?
A slightly more reduced test case:
struct Set {
void insert(ulong v) {
aa[v] = true;
}
@disable this(this);
bool[ulong] aa;
}
auto clobber(ref Set x, ref Set o) {
Set ret;
ret.aa = x.aa;
return ret;
}
struct XX {
Set a, b, tmp;
this(int n) {
a.insert(1);
//a.aa[1] = true; <--- Swap above line with this doesn't
trigger the bug
tmp = a.clobber(b);
a = a.clobber(b);
}
}
void main(){
import std.stdio;
XX xx = XX(0);
writeln(xx.a.aa.length);
writeln(xx.tmp.aa.length);
}
Re: Possible bug in RVO?
On Monday, 4 April 2016 at 03:55:26 UTC, Yuxuan Shui wrote: On Monday, 4 April 2016 at 03:28:01 UTC, Yuxuan Shui wrote: I have encountered a weird bug. I defined a Set class, which has a opBinary!"-". And somehow this: auto tmp = set_a-set_b; produces different results as this: set_a = set_a-set_b; the latter will produce an empty set. I tried to reduce the source code to get a test case. But this problem just goes away after removing some code. Any ideas what I could have done wrong? A slightly more reduced test case: And LDC has the same problem with the first test case, but not with the second one.
Re: Possible bug in RVO?
On Monday, 4 April 2016 at 03:28:01 UTC, Yuxuan Shui wrote:
I have encountered a weird bug.
I defined a Set class, which has a opBinary!"-". And somehow
this:
auto tmp = set_a-set_b;
produces different results as this:
set_a = set_a-set_b;
the latter will produce an empty set.
I tried to reduce the source code to get a test case. But this
problem just goes away after removing some code.
Any ideas what I could have done wrong?
OK, I think I got a test case:
import std.traits;
struct Set {
public:
void insert(ulong v) {
aa[v] = true;
}
size_t size() const {
return aa.length;
}
auto opBinary(string op)(ref Set o) const {
Set ret;
foreach(k; aa.byKey)
if (k !in o.aa)
ret.insert(k);
return ret;
}
@disable this(this);
bool[ulong] aa;
}
struct XX {
Set a, b, tmp;
this(int n) {
a.insert(n);
tmp = a-b;
a = a-b;
}
}
void main(){
import std.stdio;
XX xx = XX(1000);
writeln(xx.a.size);
writeln(xx.tmp.size);
}
This does not happen when 'a' is on stack, that's why I was
having trouble reproducing it.
I don't think this is valid code, because Set has disabled
post-blit, 'a = a-b' should report an error. However, I don't
think current behavior of dmd is correct either.
Possible bug in RVO?
I have encountered a weird bug. I defined a Set class, which has a opBinary!"-". And somehow this: auto tmp = set_a-set_b; produces different results as this: set_a = set_a-set_b; the latter will produce an empty set. I tried to reduce the source code to get a test case. But this problem just goes away after removing some code. Any ideas what I could have done wrong?
