http://d.puremagic.com/issues/show_bug.cgi?id=259


Christian Kamm <kamm-removethis@incasoftware.de> changed:

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--- Comment #20 from Christian Kamm <kamm-removethis@incasoftware.de> 2011-10-10 08:58:59 PDT ---
See
https://github.com/D-Programming-Language/dmd/pull/119
https://github.com/D-Programming-Language/dmd/pull/444
for two possible fixes.

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bearophile_hugs@eml.cc changed:

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--- Comment #21 from bearophile_hugs@eml.cc 2011-11-24 17:45:34 PST ---
See:

https://github.com/D-Programming-Language/dmd/commit/4536fd5e3102fcea168660e9c4d2a2c80d50e7f5

But druntime and Phobos will probably need some changes.

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--- Comment #22 from bearophile_hugs@eml.cc 2011-11-24 19:25:19 PST ---
(In reply to comment #21)

> But druntime and Phobos will probably need some changes.

Keeping this as a warning in the current compiler, and turn it into an (deprecated) error in the next DMD version, will probably allow to update druntime and Phobos.

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--- Comment #23 from bearophile_hugs@eml.cc 2011-11-25 02:32:32 PST ---
I think Walter is willing to accept that patch if someone improves the patch to remove some of its false positives.

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--- Comment #24 from Don <clugdbug@yahoo.com.au> 2011-11-25 04:05:29 PST ---
It seems wrong to me that:

if (-1 < 2u) {...}
fails to compile. Both are in the range -int.max .. int.max, so they can safely
be compared using signed comparison.

The problems with mixed sign are when one operand can be in the range -int.max..0 and the other can be in the range int.max+1u..uint.max. If at least one of the operands is in the polysemous range 0..int.max, there should be no problem.

But, the patch as it stands allows a polysemous-ranged int to be compared with a uint, but does not allow a polysemous-range uint to be compared with an int. At present the spec doesn't give any reason for unsigned to be treated from signed.

The problem is the silly C promotion rule that converts both operands to unsigned (instead, it should generate an error). In any existing C code that works, it works because the signed operand is in the polysemous range. Of course there could be code which relies on (-1<2u) being false. But surely such code is broken.

Do we really need to retain backwards compatibility with broken C code?

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--- Comment #25 from bearophile_hugs@eml.cc 2011-11-25 04:26:23 PST ---
(In reply to comment #24)

Thank you Don.

> Of course there could be code which relies on (-1<2u) being false.
> But surely such code is broken.

I don't like this is in D.

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Jesse Phillips <Jesse.K.Phillips+D@gmail.com> changed:

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   Target Milestone|---                         |2.059


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Denis Shelomovskij <verylonglogin.reg@gmail.com> changed:

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--- Comment #26 from Denis Shelomovskij <verylonglogin.reg@gmail.com> 2013-03-05 10:44:52 MSK ---
Issue state:

dmd pull #444
https://github.com/D-Programming-Language/dmd/pull/444
was merged, then #ifdef'd out as it was "too disruptive" in
https://github.com/D-Programming-Language/dmd/commit/52d8c150ecfbe2cad6672f50094a6ff1230e72e3
then completely removed in dmd pull #1611
https://github.com/D-Programming-Language/dmd/pull/1611

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Walter Bright <bugzilla@digitalmars.com> changed:

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--- Comment #27 from Walter Bright <bugzilla@digitalmars.com> 2013-04-07 01:27:07 PDT ---
I think we're going to have to give up on this one.

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--- Comment #28 from Denis Shelomovskij <verylonglogin.reg@gmail.com> 2013-04-07 20:42:55 MSD ---
(In reply to comment #27)
> I think we're going to have to give up on this one.

Not being able to at least highlight signed to unsigned comparisons in a program is a major lack of functionality. IMHO this is why enhancement Issue 9811 matters as it is the place where we can forget about "disruptiveness" and "is it always and error" questions.

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