[Bug c/60083] New: Duplicate conversion warnings from negative integer to unsigned type (gcc-4.3 emits only one warning)

[Bug c/60083] New: Duplicate conversion warnings from negative integer to unsigned type (gcc-4.3 emits only one warning)

[chengniansun at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60083

            Bug ID: 60083
           Summary: Duplicate conversion warnings from negative integer to
                    unsigned type (gcc-4.3 emits only one warning)
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: chengniansun at gmail dot com

I have the following code, and gcc-trunk emits duplicate warnings on the
implicit conversion from negative long long to unsigned short. 

Moreover, if I turn on -O1, gcc emits only one warning, but the message changes
to "large integer implicitly truncated to unsigned type".

Lastly, gcc-4.3 only emits one warning for this conversion. 


$: cat s.c
int *const a = 0;
unsigned fn1() {
  unsigned short s = ~0x4578ADBCAA1DE677LL ^ a == 0;
  return s;
}
$: gcc-trunk -c -Wconversion s.c
s.c: In function ‘fn1’:
s.c:3:22: warning: negative integer implicitly converted to unsigned type
[-Wsign-conversion]
   unsigned short s = ~0x4578ADBCAA1DE677LL ^ a == 0;
                      ^
s.c:3:22: warning: negative integer implicitly converted to unsigned type
[-Wsign-conversion]
$: gcc-trunk -c -O1 -Wconversion s.c
s.c: In function ‘fn1’:
s.c:3:22: warning: large integer implicitly truncated to unsigned type
[-Woverflow]
   unsigned short s = ~0x4578ADBCAA1DE677LL ^ a == 0;
                      ^
$: gcc-4.3 -c -O1 -Wconversion s.c
s.c: In function ‘fn1’:
s.c:3: warning: large integer implicitly truncated to unsigned type
$:
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idW748

--- Comment #54 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
(In reply to Marek Polacek from comment #53)
> So fixed on the trunk?

yes, fixed on trunk.

[Bug c/60083] Duplicate conversion warnings from negative integer to unsigned type (gcc-4.3 emits only one warning)

[chengniansun at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60083

--- Comment #1 from Chengnian Sun <chengniansun at gmail dot com> ---
I think the following case is similar to the reported case. The only difference
is the message content. The following case also triggers "gcc -O0" to emit two
duplicate warnings. But "gcc -O1" emits only one warning.

$: cat s.c
extern short fn2(short, short);
unsigned long g;
void fn1() {
  int const l = 0;
  fn2(((g = l != 0) < 10LL) | 91608LL, 0);
}
$: gcc-trunk -c -Wconversion -std=c99 s.c
s.c: In function ‘fn1’:
s.c:5:7: warning: conversion to ‘short int’ alters ‘long long int’ constant
value [-Wconversion]
   fn2(((g = l != 0) < 10LL) | 91608LL, 0);
       ^
s.c:5:7: warning: conversion to ‘short int’ alters ‘long long int’ constant
value [-Wconversion]
$: gcc-trunk -c -Wconversion -std=c99 s.c -O1
s.c: In function ‘fn1’:
s.c:5:7: warning: conversion to ‘short int’ from ‘long long int’ may alter its
value [-Wconversion]
   fn2(((g = l != 0) < 10LL) | 91608LL, 0);
       ^
$:
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To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/60083] Duplicate conversion warnings from negative integer to unsigned type (gcc-4.3 emits only one warning)
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id`083

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-02-07
                 CC|                            |mpolacek at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Yeah, I bet we'll have tons of those ;/.