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digitalmars.D.bugs - [Issue 259] New: Comparing signed to unsigned does not generate an error

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           Summary: Comparing signed to unsigned does not generate an error
           Product: D
           Version: 0.163
          Platform: PC
        OS/Version: Windows
            Status: NEW
          Keywords: spec
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla digitalmars.com
        ReportedBy: lio lunesu.com


From the book of Bright,
http://www.digitalmars.com/d/expression.html#RelExpression

"It is an error to have one operand be signed and the other unsigned for a <,
<=, > or >= expression. Use casts to make both operands signed or both operands
unsigned."

...yet...

#import std.conv;
#int main( char[] args[] ) {
#       int i = toInt(args[1]);
#       uint u = toUint(args[2]);
#       if (i < u)
#               return 1;
#       else 
#               return 0;
#}

...compiled with "dmd", "dmd -debug" or "dmd -release" does not give an error
message, neither at compile time, nor at run time.


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Jul 20 2006
next sibling parent Thomas Kuehne <thomas-dloop kuehne.cn> writes:
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

d-bugmail puremagic.com schrieb am 2006-07-20:
 http://d.puremagic.com/issues/show_bug.cgi?id=259
 From the book of Bright,
 http://www.digitalmars.com/d/expression.html#RelExpression

 "It is an error to have one operand be signed and the other unsigned for a <,
<=, > or >= expression. Use casts to make both operands signed or both operands
 unsigned."

 ...yet...

 #import std.conv;
 #int main( char[] args[] ) {
 #       int i = toInt(args[1]);
 #       uint u = toUint(args[2]);
 #       if (i < u)
 #               return 1;
 #       else 
 #               return 0;
 #}

 ...compiled with "dmd", "dmd -debug" or "dmd -release" does not give an error
 message, neither at compile time, nor at run time.
Added to DStress as http://dstress.kuehne.cn/nocompile/o/opCmp_08_A.d http://dstress.kuehne.cn/nocompile/o/opCmp_08_B.d http://dstress.kuehne.cn/nocompile/o/opCmp_08_C.d http://dstress.kuehne.cn/nocompile/o/opCmp_08_D.d http://dstress.kuehne.cn/nocompile/o/opCmp_08_E.d http://dstress.kuehne.cn/nocompile/o/opCmp_08_F.d http://dstress.kuehne.cn/nocompile/o/opCmp_08_G.d http://dstress.kuehne.cn/nocompile/o/opCmp_08_H.d http://dstress.kuehne.cn/nocompile/o/opCmp_08_I.d http://dstress.kuehne.cn/nocompile/o/opCmp_08_J.d http://dstress.kuehne.cn/nocompile/o/opCmp_08_K.d http://dstress.kuehne.cn/nocompile/o/opCmp_08_L.d http://dstress.kuehne.cn/nocompile/o/opCmp_08_M.d http://dstress.kuehne.cn/nocompile/o/opCmp_08_N.d http://dstress.kuehne.cn/nocompile/o/opCmp_08_O.d http://dstress.kuehne.cn/nocompile/o/opCmp_08_P.d Thomas -----BEGIN PGP SIGNATURE----- iD8DBQFE8DkSLK5blCcjpWoRAvd4AJ9n86OSH7vfqYKSxBQHFupEzG9/OgCfasr1 EMOV+he335iGTfu8g/Ff45g= =v3rD -----END PGP SIGNATURE-----
Aug 26 2006
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smjg iname.com changed:

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                 CC|                            |o.dathe gmx.de




------- Comment #2 from smjg iname.com  2009-02-22 11:45 -------
*** Bug 2205 has been marked as a duplicate of this bug. ***


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------- Comment #3 from clugdbug yahoo.com.au  2009-02-23 02:28 -------
Note that it's critical than any fix for this bug should not make code like the
following fail to compile:

uint a = 5;
if (a > 2) { ... }

Otherwise the cure would be worse than the disease <g>.


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------- Comment #4 from ddparnell bigpond.com  2009-02-23 02:34 -------
Even more critical, any fix for this bug should not make code like the
following fail to compile:

uint a = 5;
if (a > -2) { ... }


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------- Comment #5 from 2korden gmail.com  2009-02-23 07:40 -------
(In reply to comment #4)
 Even more critical, any fix for this bug should not make code like the
 following fail to compile:
 
 uint a = 5;
 if (a > -2) { ... }
 
Why not? This is obviously a bug! --
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------- Comment #6 from jarrett.billingsley gmail.com  2009-02-23 07:53 -------
(In reply to comment #5)
 uint a = 5;
 if (a > -2) { ... }
 
Why not? This is obviously a bug!
Agreed. I can't tell you how many times I've done something stupid like: for(uint i = something; i >= 0; i--) { /* yay, infinite loop! */ } A nontrivial condition that always results in an infinite loop should never be accepted. --
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Qian Xu <qian.xu funkwerk-itk.com> changed:

           What    |Removed                     |Added
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                 CC|                            |qian.xu funkwerk-itk.com




--- Comment #7 from Qian Xu <qian.xu funkwerk-itk.com>  2009-07-22 00:31:06 PDT
---
Is there any official response to this issue? It was reported at 2006, but the
status is still "NEW"

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--- Comment #8 from Stewart Gordon <smjg iname.com>  2009-07-22 01:17:51 PDT ---
As I look, bug 2006 doesn't seem to have anything to do with this one at all.

But if you find a duplicate of a bug, then mark it as one!

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--- Comment #9 from Qian Xu <qian.xu funkwerk-itk.com>  2009-07-22 01:34:05 PDT
---
(In reply to comment #8)
 As I look, bug 2006 doesn't seem to have anything to do with this one at all.
 
 But if you find a duplicate of a bug, then mark it as one!
sorry, i mean it was reported in year 2006. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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Andrei Alexandrescu <andrei metalanguage.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|                            |andrei metalanguage.com
         AssignedTo|nobody puremagic.com        |andrei metalanguage.com




--- Comment #10 from Andrei Alexandrescu <andrei metalanguage.com>  2009-07-24
18:08:49 PDT ---
This needs to be fixed. I'm taking ownership (though Walter will do all the
work) in order to not forget. I'll add a unittest to TDPL too. Until then let's
vote this up.

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Andrei Alexandrescu <andrei metalanguage.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|andrei metalanguage.com     |bugzilla digitalmars.com
           Severity|normal                      |major




--- Comment #11 from Andrei Alexandrescu <andrei metalanguage.com>  2009-08-24
22:17:42 PDT ---
Reassigning this to Walter. Walter, any chance you could please bump the
priority on fixing this one. I am bumping priority to major, it's an important
bug that is getting rather old.

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Ellery Newcomer <ellery-newcomer utulsa.edu> changed:

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                 CC|                            |ellery-newcomer utulsa.edu




--- Comment #12 from Ellery Newcomer <ellery-newcomer utulsa.edu>  2009-09-03
08:33:41 PDT ---
This morning I've been tinkering with the DMD source, and I've made an edit to
expression.c that appears to fix this issue. How do I submit?

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Don <clugdbug yahoo.com.au> changed:

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                 CC|                            |clugdbug yahoo.com.au




--- Comment #13 from Don <clugdbug yahoo.com.au>  2009-09-03 08:39:48 PDT ---
(In reply to comment #12)
 This morning I've been tinkering with the DMD source, and I've made an edit to
 expression.c that appears to fix this issue. How do I submit?
Either create a patch using SVN, and attach it, or just post the lines you changed (Walter doesn't actually use patch files, as far as I can tell). Search for bugs with keyword 'patch' for examples. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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--- Comment #14 from Ellery Newcomer <ellery-newcomer utulsa.edu>  2009-09-03
13:51:16 PDT ---
Okay, so what I have is it checks for 

signed cmp unsigned 

or vice versa in CmpExp::Semantic just before typeCombine gets called, which
works, but then stuff like

1 < 1u

doesn't. So the idea is 

signed cmp unsigned 

or vice versa is okay if the signed arg is a literal and its value is
nonnegative. 

This should work fine if sizeof(signed arg) =< sizeof(unsigned arg) because the
value of the signed arg is within the range of the unsigned arg, and
typeCombine should be able to expand the type of the signed arg to that of the
unsigned arg or whatever.
It should work if sizeof(signed arg) > sizeof(unsigned arg) because the value
of the unsigned arg is within the range of the signed arg, and typeCombine
should be able to expand the type of the unsigned arg to that of the signed
arg.

I don't know, maybe this should be happening in typeCombine. Insert the
following in expression.c CmpExp::semantic before the line

typeCombine(sc);


    if ( e1->type->isintegral() && e2->type->isintegral()){
        if(e1->type->isunsigned() ^ e2->type->isunsigned()){
            if(!e1->type->isunsigned() &&
                dynamic_cast<IntegerExp*>(e1) &&
                ((sinteger_t) e1->toInteger()) >= 0) goto JustKidding;
            if(!e2->type->isunsigned() &&
                dynamic_cast<IntegerExp*>(e2) &&
                ((sinteger_t) e2->toInteger()) >= 0) goto JustKidding;
            error("comparing signed and unsigned integers");
        }
        JustKidding:;
    }

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--- Comment #15 from Don <clugdbug yahoo.com.au> 2009-09-08 09:40:30 PDT ---
(In reply to comment #14)
 Okay, so what I have is it checks for 
[snip]
 
 signed cmp unsigned 
 
 or vice versa is okay if the signed arg is a literal and its value is
 nonnegative. 
In D2, it's possible to a lot better than this. With the new D2 rules for implicit conversion between integral types (range-based), it should be enough to require that one of the types must implicitly convert to the other. This doesn't quite work yet, since range-based addition (for example) is not yet implemented. This will mean that stuff like: byte b; uint u; b = -67; if (u < b + 0x100) ... is OK because although b + 0x100 is signed, it can never be less than 1, so it can safely be converted to unsigned. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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--- Comment #16 from Ellery Newcomer <ellery-newcomer utulsa.edu> 2009-09-08
10:43:00 PDT ---
Cool. That sounds like a much better solution than the patch I posted.

Concerning my patch, I just realized that comparison with unsigned and zero
generally doesn't make sense either, except maybe

{unsigned} > 0

so now I have

    if ( e1->type->isintegral() && e2->type->isintegral()){
        if(e1->type->isunsigned() ^ e2->type->isunsigned()){
            if(!e1->type->isunsigned() && dynamic_cast<IntegerExp*>(e1)){
                sinteger_t v1 = ((sinteger_t) e1->toInteger());
                if(v1 > 0) goto JustKidding;
                // 0 < uns or 0 !>= uns okay
                else if(v1 == 0 && (op == TOKlt || op == TOKul))
                    goto JustKidding;
            }else if(dynamic_cast<IntegerExp*>(e2)){
                sinteger_t v2 = ((sinteger_t) e2->toInteger());
                if(v2 > 0) goto JustKidding;
                // uns > 0 or uns !<= 0 okay
                else if(v2 == 0 && (op == TOKgt || op == TOKug))
                    goto JustKidding;
            }
            error("comparing signed and unsigned integers");
        }
        JustKidding:;
    }

in case anyone plans to commit it

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Witold Baryluk <baryluk smp.if.uj.edu.pl> changed:

           What    |Removed                     |Added
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                 CC|                            |baryluk smp.if.uj.edu.pl


--- Comment #17 from Witold Baryluk <baryluk smp.if.uj.edu.pl> 2009-11-18
13:13:14 PST ---
Hi,

I today found remarkable bug:

int k = -1;
uint n = 7;
assert(k < n);


Code above should execute without proble, but dmd it computing false as value
of (k<n) which absolutly nonsensical. casting n to int, resolves problem

int k = -1;
uint n = 7;
assert(k < cast(T)n);

How it can be so long time not resolved?

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Andrei Alexandrescu <andrei metalanguage.com> changed:

           What    |Removed                     |Added
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           Severity|major                       |critical


--- Comment #18 from Andrei Alexandrescu <andrei metalanguage.com> 2010-11-26
10:43:45 PST ---
Escalating severity of this dangerous issue. Has 11 votes, too.

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Éric Estièvenart <eric.estievenart free.fr> changed:

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                 CC|                            |eric.estievenart free.fr


--- Comment #19 from Éric Estièvenart <eric.estievenart free.fr> 2011-01-14
11:55:24 PST ---
Indeed this is rather critical; I hit it in a simple precondition like:
void insert( Object o, int ndx = -1 ) // -1 means last
  in { assert( ndx >= -1 && ndx <= somearray.length ); }

forcing to add a cast everywhere would be very painful...

The following code should compile without error and pass:
void main()
{
  uint ulen = 0;
  int ndx = -1;
  assert( -1 <= ulen );
  assert( ndx <= ulen );
}

If it generates warnings is another issue...

// This one should compile too
void func2()
{
  uint u;
  // should not compile (or at least warn): always yields to true
  static assert( !is( typeof( u >= 0 ) ) );
  static assert( !is( typeof( u >= -1 ) ) );
}

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

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                 CC|                            |kamm-removethis incasoftwar
                   |                            |e.de


--- 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:

           What    |Removed                     |Added
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                 CC|                            |bearophile_hugs eml.cc


--- 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. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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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. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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Jesse Phillips <Jesse.K.Phillips+D gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |Jesse.K.Phillips+D gmail.co
                   |                            |m
   Target Milestone|---                         |2.059


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

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                 CC|                            |verylonglogin.reg gmail.com


--- 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:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |WONTFIX


--- 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. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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--- Comment #29 from Andrei Alexandrescu <andrei erdani.com> 2013-04-07
15:03:49 PDT ---
(In reply to comment #27)
 I think we're going to have to give up on this one.
This is a bit abrupt. What was the decision process? I just shared an anecdote about a few major bugs at work caused by this exact behavior. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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--- Comment #30 from Walter Bright <bugzilla digitalmars.com> 2013-04-07
15:49:14 PDT ---
(In reply to comment #29)
 This is a bit abrupt. What was the decision process? I just shared an anecdote
 about a few major bugs at work caused by this exact behavior.
It's been 7 years of discussion now without an answer that works. I don't think it's abrupt! -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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--- Comment #31 from Stewart Gordon <smjg iname.com> 2013-04-07 16:02:40 PDT ---
(In reply to comment #30)
 (In reply to comment #29)
 This is a bit abrupt. What was the decision process? I just shared an anecdote
 about a few major bugs at work caused by this exact behavior.
It's been 7 years of discussion now without an answer that works. I don't think it's abrupt!
How does pull request 119 not work? And why haven't you written a fix yourself in these 7 years - or even made a single comment on this bug until now? -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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--- Comment #32 from Walter Bright <bugzilla digitalmars.com> 2013-04-07
16:50:41 PDT ---
(In reply to comment #31)
 How does pull request 119 not work?
Follow the links & comments https://github.com/D-Programming-Language/dmd/pull/119 If you want to discuss that further, please post there.
 And why haven't you written a fix yourself in these 7 years - or even made a
 single comment on this bug until now?
I've discussed it extensively on the n.g. This isn't the only place it's come up. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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Andrei Alexandrescu <andrei erdani.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|WONTFIX                     |


--- Comment #33 from Andrei Alexandrescu <andrei erdani.com> 2013-04-07
17:24:25 PDT ---
Reopening. The entire discussion makes it obvious this needs a fix. It's
critical and has 20 votes, probably more than probably any other bug. Closing
this without any explanation is straight the opposite of listening to the
community. Thanks.

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--- Comment #34 from Walter Bright <bugzilla digitalmars.com> 2013-04-07
17:50:06 PDT ---
I don't mind if it is reopened. It's just that it's sat at the top of the
"critical" bug list forever with no movement towards a solution. I'd like to
get this resolved one way or another.

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--- Comment #35 from Andrei Alexandrescu <andrei erdani.com> 2013-04-07
18:38:23 PDT ---
Great. Here's a solution Walter and I just discussed:

Consider a comparison a < b, a <= b, a > b, or a >= b, in which a and b are
integral types of different signedness. Without loss of generality, let's
consider a is signed and b is unsigned and the comparison is a < b. Then we
have the following cases:

1. If a.sizeof > b.sizeof, then a < b is lowered into a < cast(typeof(a)) b.
Then signed comparison proceeds normally. This is a classic value-based
conversion dating from the C days, and we do it in D as well.

2. Otherwise, if a is determined through Value Range Propagation to be greater
than or equal to zero, then a < b is lowered into cast(U) a < b, where U is the
unsigned variant of typeof(a). Then unsigned comparison proceeds normally.

3. Otherwise, the comparison is in error. The error message may recommend using
the std.traits.unsigned function, which executes a size-informed cast.

Walter, if you agree with this resolution please mark this as "preapproved".

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--- Comment #36 from Andrei Alexandrescu <andrei erdani.com> 2013-04-07
18:57:27 PDT ---
Preapproved FTW! Who wants to implement this?

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Andrei Alexandrescu <andrei erdani.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|bugzilla digitalmars.com    |nobody puremagic.com


--- Comment #37 from Andrei Alexandrescu <andrei erdani.com> 2013-04-07
19:05:56 PDT ---
Resetting asignee to default. If anyone wants to work on this, please assign it
to yourself!

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--- Comment #38 from bearophile_hugs eml.cc 2013-04-07 19:29:00 PDT ---
(In reply to comment #35)

 3. Otherwise, the comparison is in error. The error message may recommend using
 the std.traits.unsigned function, which executes a size-informed cast.
This is the source of unsigned: auto unsigned(T)(T x) if (isIntegral!T) { static if (is(Unqual!T == byte )) return cast(ubyte ) x; else static if (is(Unqual!T == short)) return cast(ushort) x; else static if (is(Unqual!T == int )) return cast(uint ) x; else static if (is(Unqual!T == long )) return cast(ulong ) x; else { static assert(T.min == 0, "Bug in either unsigned or isIntegral"); return cast(Unqual!T) x; } } Is it better to use template constraints there? And isn't it better for unsigned to accept only unsigned Ts? -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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--- Comment #39 from Andrei Alexandrescu <andrei erdani.com> 2013-04-08
07:21:23 PDT ---
Thanks Lionello for taking this over. I thought of one more case this morning
so let me insert in the food chain:

(Recall a is signed and b is unsigned.)

==============

1. If a.sizeof > b.sizeof, then a < b is lowered into a < cast(typeof(a)) b.
Then signed comparison proceeds normally. This is a classic value-based
conversion dating from the C days, and we do it in D as well.

2. Otherwise, if a is determined through Value Range Propagation to be greater
than or equal to zero, then a < b is lowered into cast(U) a < b, where U is the
unsigned variant of typeof(a). Then unsigned comparison proceeds normally.

3. (NEW) Otherwise, if b is determined through Value Range Propagation to be
less than or equal to typeof(b).max / 2, then a < b is lowered into a < cast(S)
b, where S is the signed variant of typeof(b). Then signed comparison proceeds
normally.

4. Otherwise, the comparison is in error. The error message may recommend using
the std.traits.unsigned function, which executes a size-informed cast.

==============

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--- Comment #40 from Stewart Gordon <smjg iname.com> 2013-04-08 15:57:45 PDT ---
Sounds good but ... given that people have been trying for 7 years without
success to implement the basic rule from the spec, how many more years can we
realistically expect it to be before this new scheme being suggested is in the
compiler?

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--- Comment #41 from Andrei Alexandrescu <andrei erdani.com> 2013-04-08
16:14:12 PDT ---
(In reply to comment #40)
 Sounds good but ... given that people have been trying for 7 years without
 success to implement the basic rule from the spec, how many more years can we
 realistically expect it to be before this new scheme being suggested is in the
 compiler?
Now that we have a preapproved solution, a solid VRP implementation, and a much expanded contribution base, I can only assume it'll take days. Lionello? -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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--- Comment #42 from Lionello Lunesu <lio+bugzilla lunesu.com> 2013-04-09
03:02:20 PDT ---
Yes, I'll have this done this week.

For point 1: how to cope with the fact that I can safely cast an uint to long,
but can't cast an int to an ulong (without issues)? 

Surely cast(int)-1 < cast(ulong)1 should evaluate to true? But according to
point 1 it would be rewritten as cast(ulong)-1 < cast(ulong)1 which is
0xFFFFFFFFFFFFFFFF < 0x1 and evaluate to false.

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--- Comment #43 from Stewart Gordon <smjg iname.com> 2013-04-09 05:21:52 PDT ---
(In reply to comment #42)
 Yes, I'll have this done this week.
 For point 1: how to cope with the fact that I can safely cast an uint to long,
 but can't cast an int to an ulong (without issues)? 
 Surely cast(int)-1 < cast(ulong)1 should evaluate to true? But according to
 point 1 it would be rewritten as cast(ulong)-1 < cast(ulong)1 which is
 0xFFFFFFFFFFFFFFFF < 0x1 and evaluate to false.
No. Point 1 is the case where a.sizeof > b.sizeof. This isn't the case here. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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--- Comment #44 from Andrei Alexandrescu <andrei erdani.com> 2013-04-09
08:37:50 PDT ---
Thanks Lionello for working on this! It will make D noticeably better at
bread-and-butter work. Regarding your question - what Stewart said. Let me know
if you hit any snag.

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--- Comment #45 from Lionello Lunesu <lio+bugzilla lunesu.com> 2013-04-10
09:20:22 PDT ---
uint b;
if (b > -2) { ... }

The integral expression -2 doesn't have any size per se, but whole size thing
shouldn't even apply here, since the two expressions have ranges that are
completely disjoint. Points 2 and 3 won't catch this case either and would
cause an error. We could consider all integrals 'long' and apply point 1. Or,
test for disjoint ranges and replace the whole comparison with a constant? (I
have a feeling this optimization might already be happening in a later pass?)

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--- Comment #46 from Andrei Alexandrescu <andrei erdani.com> 2013-04-10
09:45:57 PDT ---
(In reply to comment #45)
 uint b;
 if (b > -2) { ... }
 
 The integral expression -2 doesn't have any size per se, but whole size thing
 shouldn't even apply here, since the two expressions have ranges that are
 completely disjoint. Points 2 and 3 won't catch this case either and would
 cause an error. We could consider all integrals 'long' and apply point 1. Or,
 test for disjoint ranges and replace the whole comparison with a constant? (I
 have a feeling this optimization might already be happening in a later pass?)
I'd say we need to make this an error. If we don't (i.e. make the comparison always true), then we'd silently change behavior. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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--- Comment #47 from Lionello Lunesu <lio+bugzilla lunesu.com> 2013-04-11
19:24:53 PDT ---
https://github.com/D-Programming-Language/dmd/pull/1889

There are many things silently(!) breaking, though, as some templates are not
being chosen because of internal comparison errors.

For example, FormatSpec.width and FormatSpec.precision are ints but often
compared against array lengths (for padding and such). TBH, using negative
width and precision to mean "argument index" is a hack and we'd be better off
changing them to uint and use a flag for the "argument index" case.

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--- Comment #48 from Lionello Lunesu <lio+bugzilla lunesu.com> 2013-04-11
19:42:37 PDT ---
// For the record: my test cases. Will add/fix existing unittests as well.
import std.traits;
int i;
uint ui;
long l;
ulong ul;
// 0. same-signed-ness
static assert(__traits(compiles, ui>ul));
static assert(__traits(compiles, ul>ui));
static assert(__traits(compiles, i>l));
static assert(__traits(compiles, l>i));
static assert(__traits(compiles, 1>2));
static assert(!(1>2));
static assert(__traits(compiles, 2>1));
static assert(2>1);
// 1. sizeof(signed) > sizeof(unsigned)
static assert(__traits(compiles, l>ui));
static assert(__traits(compiles, ui>l));
static assert(__traits(compiles, -1L>2));
static assert(!(-1L>2));
static assert(__traits(compiles, 2>-1L));
static assert(2>-1L);
// 2. signed.min >= 0
static assert(__traits(compiles, ui>cast(int)2));
static assert(__traits(compiles, cast(int)2>ui));
static assert(__traits(compiles, ul>cast(int)2));
static assert(__traits(compiles, cast(int)2>ul));
// 3. unsigned.max < typeof(unsigned.max/2)
static assert(__traits(compiles, i>cast(uint)2));
static assert(__traits(compiles, cast(uint)2>i));
static assert(__traits(compiles, cast(int)-1>cast(uint)3));
static assert(__traits(compiles, cast(uint)3>cast(int)-1));
static assert(__traits(compiles, -1>2UL));
static assert(!(-1>2UL));
static assert(__traits(compiles, 2UL>-1));
static assert(2UL>-1);
// error
static assert(!__traits(compiles, ul>-2));
static assert(!__traits(compiles, -2>ul));
static assert(!__traits(compiles, i>ul));
static assert(!__traits(compiles, ul>i));
static assert(!__traits(compiles, l>ul));
static assert(!__traits(compiles, ul>l));
static assert(!__traits(compiles, i>ui));
static assert(!__traits(compiles, ui>i));

void main(){}

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--- Comment #49 from Lionello Lunesu <lio+bugzilla lunesu.com> 2013-04-12
22:01:28 PDT ---
We should probably consider making this a warning or deprecation, instead of an
error. The silent failures within templates make it very hard to fix code.

Warnings and errors during template instantiations are suppressed and the final
"errors instantiating template" doesn't say why (not even with -v; this is
probably worth a filing a separate bug for.) 

I'm having to add a "printf" to expression.c to see those occurrences,
\util\dmd2\src\phobos\std\format.d(1216)
\util\dmd2\src\phobos\std\format.d(1224)
\util\dmd2\src\phobos\std\format.d(1395)

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--- Comment #50 from Lionello Lunesu <lio+bugzilla lunesu.com> 2013-05-03
14:20:12 PDT ---
I've discovered one additional case,

1b. If both types can be cast to the bigger signed type, the cast is safe

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Nick Treleaven <ntrel-public yahoo.co.uk> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ntrel-public yahoo.co.uk


--- Comment #51 from Nick Treleaven <ntrel-public yahoo.co.uk> 2013-08-20
03:11:43 PDT ---
(In reply to comment #47)
 https://github.com/D-Programming-Language/dmd/pull/1889
Update: that was split into two, see: https://github.com/D-Programming-Language/dmd/pull/1913 -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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--- Comment #52 from Lionello Lunesu <lio+bugzilla lunesu.com> 2013-09-07
12:12:57 PDT ---
Also submitted fixes to druntime:
https://github.com/D-Programming-Language/druntime/pull/601

(Note: check the pull requests for the latest info)

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--- Comment #53 from github-bugzilla puremagic.com 2013-09-22 14:11:38 PDT ---
Commit pushed to master at https://github.com/D-Programming-Language/druntime

https://github.com/D-Programming-Language/druntime/commit/439d079dce0079cbacaedd91648d85d2c7d660c0
Merge pull request #601 from lionello/bug259

Bug259: fixed signed-unsigned comparisons in druntime

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