Re: issue with each specifically for x86
Matt Gamble wrote: Ok, this has been submitted as a bug. https://issues.dlang.org/show_bug.cgi?id=18573 thank you.
Re: issue with each specifically for x86
On Wednesday, 7 March 2018 at 21:39:58 UTC, ketmar wrote: Matt Gamble wrote: On Wednesday, 7 March 2018 at 21:02:30 UTC, ag0aep6g wrote: On 03/07/2018 09:09 PM, ag0aep6g wrote: [...] With `real` instead of `double` x86_64 is also affected. Wow. Good to know I'm not crazy. I was afk for a bit, sorry. I guess I'm glad I found it and posted. The conversation has gone beyond my realm of understanding. Has anyone tested on 2.079 like Ali wanted. I have not had a chance to install. I was going to wait to post the bug till that was tried. sure, it is still there in git HEAD. it is not the bug that can be fixed "accidentally". %-) Ok, this has been submitted as a bug. https://issues.dlang.org/show_bug.cgi?id=18573 Thanks for the quick responses. Don't know what I'd do with out the community.
Re: issue with each specifically for x86
Matt Gamble wrote:
On Wednesday, 7 March 2018 at 21:02:30 UTC, ag0aep6g wrote:
On 03/07/2018 09:09 PM, ag0aep6g wrote:
double f() { return 1; }
void main()
{
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
double b = 2;
assert(b == 2); /* fails; should pass */
}
With `real` instead of `double` x86_64 is also affected.
Wow. Good to know I'm not crazy. I was afk for a bit, sorry. I guess I'm
glad I found it and posted. The conversation has gone beyond my realm of
understanding. Has anyone tested on 2.079 like Ali wanted. I have not had
a chance to install. I was going to wait to post the bug till that was
tried.
sure, it is still there in git HEAD. it is not the bug that can be fixed
"accidentally". %-)
Re: issue with each specifically for x86
On Wednesday, 7 March 2018 at 21:02:30 UTC, ag0aep6g wrote:
On 03/07/2018 09:09 PM, ag0aep6g wrote:
double f() { return 1; }
void main()
{
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
double b = 2;
assert(b == 2); /* fails; should pass */
}
With `real` instead of `double` x86_64 is also affected.
Wow. Good to know I'm not crazy. I was afk for a bit, sorry. I
guess I'm glad I found it and posted. The conversation has gone
beyond my realm of understanding. Has anyone tested on 2.079 like
Ali wanted. I have not had a chance to install. I was going to
wait to post the bug till that was tried.
Re: issue with each specifically for x86
ag0aep6g wrote:
On 03/07/2018 09:09 PM, ag0aep6g wrote:
double f() { return 1; }
void main()
{
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
double b = 2;
assert(b == 2); /* fails; should pass */
}
With `real` instead of `double` x86_64 is also affected.
yeah. that is 'cause SSE cannot do math with 80-bit floats, and compiler
falls back to FPU in this case.
Re: issue with each specifically for x86
On 03/07/2018 09:09 PM, ag0aep6g wrote:
double f() { return 1; }
void main()
{
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
double b = 2;
assert(b == 2); /* fails; should pass */
}
With `real` instead of `double` x86_64 is also affected.
Re: issue with each specifically for x86
H. S. Teoh wrote:
On Wed, Mar 07, 2018 at 10:21:42PM +0200, ketmar via Digitalmars-d-learn
wrote:
[...]
it looks like ignoring `double` result causes FPU stack imbalance
('cause compiler doesn't insert "FPU pop" instruction), and that
affects the computations.
on 64 bit it doesn't matter, 'cause no FPU is used there.
the fix prolly should be easy: just emit "FPU pop" if function result
is ignored. codegen should have this info at hand, i believe.
Nice catch! Is there a bug filed for this yet? If not, it should be.
btw, this is specific to `cast(void)`. if you'll remove the cast, or do
something like `cast(void)(pred(i)+42);`, the bug won't be there. so it
looks like it is not a codegen bug after all, but glue layer. the codegen
is correctly dropping the result without `cast(void)` (`fstp %st(0)` is
inserted in `main`), but cannot do that if return type information is stripped.
so it looks that glue layer should not strip return type info.
Re: issue with each specifically for x86
H. S. Teoh wrote:
On Wed, Mar 07, 2018 at 10:21:42PM +0200, ketmar via Digitalmars-d-learn
wrote:
[...]
it looks like ignoring `double` result causes FPU stack imbalance
('cause compiler doesn't insert "FPU pop" instruction), and that
affects the computations.
on 64 bit it doesn't matter, 'cause no FPU is used there.
the fix prolly should be easy: just emit "FPU pop" if function result
is ignored. codegen should have this info at hand, i believe.
Nice catch! Is there a bug filed for this yet? If not, it should be.
it seems that no bug is filled yet. feel free to do so. ;-) or maybe OP
should better do it, dunno. definitely not me. ;-)
Re: issue with each specifically for x86
On Wed, Mar 07, 2018 at 10:21:42PM +0200, ketmar via Digitalmars-d-learn wrote:
[...]
> it looks like ignoring `double` result causes FPU stack imbalance
> ('cause compiler doesn't insert "FPU pop" instruction), and that
> affects the computations.
>
> on 64 bit it doesn't matter, 'cause no FPU is used there.
>
> the fix prolly should be easy: just emit "FPU pop" if function result
> is ignored. codegen should have this info at hand, i believe.
Nice catch! Is there a bug filed for this yet? If not, it should be.
T
--
MACINTOSH: Most Applications Crash, If Not, The Operating System Hangs
Re: issue with each specifically for x86
Steven Schveighoffer wrote:
it seems that the only difference between `void` and `double` lambda is one
asm instruction: `fldl (%edi)`. it is presend in `double` labmda, and
absent in `void` lambda.
it looks like ignoring `double` result causes FPU stack imbalance ('cause
compiler doesn't insert "FPU pop" instruction), and that affects the computations.
on 64 bit it doesn't matter, 'cause no FPU is used there.
the fix prolly should be easy: just emit "FPU pop" if function result is
ignored. codegen should have this info at hand, i believe.
Re: issue with each specifically for x86
On 3/7/18 3:09 PM, ag0aep6g wrote:
On 03/07/2018 08:54 PM, Steven Schveighoffer wrote:
Clearly there is some codegen issue here.
It's beautiful:
double f() { return 1; }
void main()
{
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
double b = 2;
assert(b == 2); /* fails; should pass */
}
Are all those calls required? That's one crazy bug.
-Steve
Re: issue with each specifically for x86
On 03/07/2018 08:54 PM, Steven Schveighoffer wrote:
Looking at each, it looks like it does this:
cast(void) unaryFun!pred(r.front);
So I tried this:
auto pred = i => a[i] = a[i-1] + 2;
foreach(i; 1 .. a.length)
cast(void)pred(i);
And I see the -nan value. Remove the cast(void) and I don't see it.
Clearly there is some codegen issue here.
It's beautiful:
double f() { return 1; }
void main()
{
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
cast(void) f();
double b = 2;
assert(b == 2); /* fails; should pass */
}
Re: issue with each specifically for x86
On 3/7/18 1:57 PM, Matt Gamble wrote:
This is a record for me with two 32bit vs 64bit issues in one day. Seems
to be a problem with using "each" under 32bit which can be fixed by
using foreach or switching to x64. Am I doing something wrong or is this
the second bug I've found today?
Below is a silly case, that replicates an error. (i.e. I know I could
use iota(0,9,2).array), but that does not demonstrate the potential bug
and would not fix my actual program.)
import std.range;
import std.algorithm;
import std.stdio;
unittest
{
auto a = new double[9];
a[0] = 0;
iota(1,a.length).each!(i => a[i] = a[i-1] + 2);
writeln(a);
}
//x86, wrong, error
//[-nan, 2, 4, 6, 8, 10, 12, 14, 16]
//First-chance exception: std.format.FormatException Unterminated format
specifier: "%" at C:\D\dmd2\windows\bin\..\..\src\phobos\std\format.d(1175)
//x64, correct
//[0, 2, 4, 6, 8, 10, 12, 14, 16]
unittest
{
auto a = new double[9];
a[0] = 0;
foreach(i; 1..a.length) a[i] = a[i - 1] + 2;
writeln(a);
}
//x86, correct
//[0, 2, 4, 6, 8, 10, 12, 14, 16]
//x64, correct
//[0, 2, 4, 6, 8, 10, 12, 14, 16]
This is windows 10, DMD v2.076.1
It has something to do with the fact that you are returning the value:
iota(1, a.length).each!((i) {a[i] = a[i - 1] + 2;}); // ok
iota(1, a.length).each!((i) {return a[i] = a[i - 1] + 2;}); // shows error
Which is odd to say the least, I don't think each is supposed to do
anything with the return value.
I don't get the exception BTW (2.078.1 Windows 10).
Looking at each, it looks like it does this:
cast(void) unaryFun!pred(r.front);
So I tried this:
auto pred = i => a[i] = a[i-1] + 2;
foreach(i; 1 .. a.length)
cast(void)pred(i);
And I see the -nan value. Remove the cast(void) and I don't see it.
Clearly there is some codegen issue here.
-Steve
Re: issue with each specifically for x86
On 03/07/2018 10:57 AM, Matt Gamble wrote:
This is a record for me with two 32bit vs 64bit issues in one day. Seems
to be a problem with using "each" under 32bit which can be fixed by
using foreach or switching to x64. Am I doing something wrong or is this
the second bug I've found today?
Below is a silly case, that replicates an error. (i.e. I know I could
use iota(0,9,2).array), but that does not demonstrate the potential bug
and would not fix my actual program.)
import std.range;
import std.algorithm;
import std.stdio;
unittest
{
auto a = new double[9];
a[0] = 0;
iota(1,a.length).each!(i => a[i] = a[i-1] + 2);
writeln(a);
}
//x86, wrong, error
//[-nan, 2, 4, 6, 8, 10, 12, 14, 16]
//First-chance exception: std.format.FormatException Unterminated format
specifier: "%" at C:\D\dmd2\windows\bin\..\..\src\phobos\std\format.d(1175)
//x64, correct
//[0, 2, 4, 6, 8, 10, 12, 14, 16]
unittest
{
auto a = new double[9];
a[0] = 0;
foreach(i; 1..a.length) a[i] = a[i - 1] + 2;
writeln(a);
}
//x86, correct
//[0, 2, 4, 6, 8, 10, 12, 14, 16]
//x64, correct
//[0, 2, 4, 6, 8, 10, 12, 14, 16]
This is windows 10, DMD v2.076.1
Confirmed on Linux with dmd 2.078.1
It's somehow related to the unused return value of the lambda. The
following code has the same error:
iota(1,a.length).each!((i) {
a[i] = a[i-1] + 2;
return a[i];
});
The error disappears when that return statement is commented-out.
Please file a dmd bug after making sure that 2.079 still has it. (Too
lazy to install right now.)
An ldc that I have handy does not have this bug:
based on DMD v2.073.2 and LLVM 4.0.0
Ali
issue with each specifically for x86
This is a record for me with two 32bit vs 64bit issues in one
day. Seems to be a problem with using "each" under 32bit which
can be fixed by using foreach or switching to x64. Am I doing
something wrong or is this the second bug I've found today?
Below is a silly case, that replicates an error. (i.e. I know I
could use iota(0,9,2).array), but that does not demonstrate the
potential bug and would not fix my actual program.)
import std.range;
import std.algorithm;
import std.stdio;
unittest
{
auto a = new double[9];
a[0] = 0;
iota(1,a.length).each!(i => a[i] = a[i-1] + 2);
writeln(a);
}
//x86, wrong, error
//[-nan, 2, 4, 6, 8, 10, 12, 14, 16]
//First-chance exception: std.format.FormatException Unterminated
format specifier: "%" at
C:\D\dmd2\windows\bin\..\..\src\phobos\std\format.d(1175)
//x64, correct
//[0, 2, 4, 6, 8, 10, 12, 14, 16]
unittest
{
auto a = new double[9];
a[0] = 0;
foreach(i; 1..a.length) a[i] = a[i - 1] + 2;
writeln(a);
}
//x86, correct
//[0, 2, 4, 6, 8, 10, 12, 14, 16]
//x64, correct
//[0, 2, 4, 6, 8, 10, 12, 14, 16]
This is windows 10, DMD v2.076.1
