[Bug c/59264] New: Incorrect order of execution on increament/decrement operator

[Bug c/59264] New: Incorrect order of execution on increament/decrement operator

[smaheshs41 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59264

            Bug ID: 59264
           Summary: Incorrect order of execution on increament/decrement
                    operator
           Product: gcc
           Version: 4.8.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: smaheshs41 at gmail dot com

Created attachment 31281
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=31281&action=edit
The Order of execution of the code is not working properly in the 2nd & 3rd
condition the expected output is 13 but 11 but it works correctly in 1st
condition and the result is 13

As in the program stated it works fine when we have two increament/deacrement
operator and one arithmetic operator(+). But, when we try the same thing with
three increament/deacrement operator and two arithmetic operator(+) out off
three conditions only for one condition the code gets executed correctly for
the remaining two conditions it gives incorrect output.

[Bug c/59264] Incorrect order of execution on increament/decrement operator

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59264

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Your code has undefined behaviour because it modifies the same variables more
than once between sequence points.

[Bug c/59264] Incorrect order of execution on increament/decrement operator

[redi at gcc dot gnu.org]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="UTF-8", Size: 8048 bytes --]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59264

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Instead of reporting a bug, try turning warnings on and fixing them, the
compiler tells you what's wrong with your code:

t.c:2:6: warning: return type of ‘main’ is not ‘int’ [-Wmain]
 void main()
      ^
t.c: In function ‘main’:
t.c:5:3: warning: operation on ‘i’ may be undefined [-Wsequence-point]
  i=++i + ++i + i++;
   ^
t.c:5:3: warning: operation on ‘i’ may be undefined [-Wsequence-point]
t.c:5:3: warning: operation on ‘i’ may be undefined [-Wsequence-point]
t.c:8:3: warning: operation on ‘i’ may be undefined [-Wsequence-point]
  i=i++ + ++i + ++i;
   ^
t.c:8:3: warning: operation on ‘i’ may be undefined [-Wsequence-point]
t.c:8:3: warning: operation on ‘i’ may be undefined [-Wsequence-point]
t.c:11:3: warning: operation on ‘i’ may be undefined [-Wsequence-point]
  i=++i + i++ + ++i;
   ^
t.c:11:3: warning: operation on ‘i’ may be undefined [-Wsequence-point]
t.c:11:3: warning: operation on ‘i’ may be undefined [-Wsequence-point]
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From: "smaheshs41 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/59264] Incorrect order of execution on increament/decrement operator
Date: Sat, 23 Nov 2013 17:13:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59264

--- Comment #3 from Mahesh S <smaheshs41 at gmail dot com> ---
but it gets executed correctly for 1st condition why not for 2nd and 3rd


On Sat, Nov 23, 2013 at 10:36 PM, redi at gcc dot gnu.org <
gcc-bugzilla@gcc.gnu.org> wrote:

> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59264
>
> Jonathan Wakely <redi at gcc dot gnu.org> changed:
>
>            What    |Removed                     |Added
>
> ----------------------------------------------------------------------------
>              Status|UNCONFIRMED                 |RESOLVED
>          Resolution|---                         |INVALID
>
> --- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
> Instead of reporting a bug, try turning warnings on and fixing them, the
> compiler tells you what's wrong with your code:
>
> t.c:2:6: warning: return type of ‘main’ is not ‘int’ [-Wmain]
>  void main()
>       ^
> t.c: In function ‘main’:
> t.c:5:3: warning: operation on ‘i’ may be undefined [-Wsequence-point]
>   i=++i + ++i + i++;
>    ^
> t.c:5:3: warning: operation on ‘i’ may be undefined [-Wsequence-point]
> t.c:5:3: warning: operation on ‘i’ may be undefined [-Wsequence-point]
> t.c:8:3: warning: operation on ‘i’ may be undefined [-Wsequence-point]
>   i=i++ + ++i + ++i;
>    ^
> t.c:8:3: warning: operation on ‘i’ may be undefined [-Wsequence-point]
> t.c:8:3: warning: operation on ‘i’ may be undefined [-Wsequence-point]
> t.c:11:3: warning: operation on ‘i’ may be undefined [-Wsequence-point]
>   i=++i + i++ + ++i;
>    ^
> t.c:11:3: warning: operation on ‘i’ may be undefined [-Wsequence-point]
> t.c:11:3: warning: operation on ‘i’ may be undefined [-Wsequence-point]
>
> --
> You are receiving this mail because:
> You reported the bug.
>
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Subject: [Bug target/58314] SH4 error: 'asm' operand requires impossible reload
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idX314

--- Comment #14 from Oleg Endo <olegendo at gcc dot gnu.org> ---
Created attachment 31283
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id1283&actioníit
re-work movqi / movhi insns

The attached patch seems to fix the problem.
It removes the questionable reg_reg pattern and allows the *movqi / *movhi
pattern to match any memory address.  However, instead of using the "m" memory
constraint, "Sdd" (displacement address mode only) and "Snd" (any address mode
except displacement) are used, so that the R0 reg "z" constraint can be used
appropriately.
The "Snd" memory constraint had to be fixed for this to work.  Some other minor
changes were required for calculating the proper *movqi / *movhi insn size
(which depends on the size of the displacement constant).

CSiBE doesn't show any regressions regarding displacement addressing modes for
SH4 and SH2A and the test cases for this PR compile fine for me.

Although not fully tested yet, could you guys please have a look at it?
Christian, does it fix your Linux build problems, or are there still more / new
ones?

[Bug c/59264] Incorrect order of execution on increament/decrement operator

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59264

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ebotcazou at gcc dot gnu.org

--- Comment #4 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
> but it gets executed correctly for 1st condition why not for 2nd and 3rd

Both executions are correct since the code has undefined behavior.

[Bug c/59264] Incorrect order of execution on increament/decrement operator

[smaheshs41 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59264

--- Comment #5 from Mahesh S <smaheshs41 at gmail dot com> ---
[Bug c/59264] Incorrect order of execution on increament/decrement operator
But it works correctly in Turbo C and Borland C compiler why not in gcc


On Sat, Nov 23, 2013 at 11:23 PM, ebotcazou at gcc dot gnu.org <
gcc-bugzilla@gcc.gnu.org> wrote:

> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59264
>
> Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:
>
>            What    |Removed                     |Added
>
> ----------------------------------------------------------------------------
>                  CC|                            |ebotcazou at gcc dot
> gnu.org
>
> --- Comment #4 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
> > but it gets executed correctly for 1st condition why not for 2nd and 3rd
>
> Both executions are correct since the code has undefined behavior.
>
> --
> You are receiving this mail because:
> You reported the bug.
>

[Bug c/59264] Incorrect order of execution on increament/decrement operator

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59264

--- Comment #6 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
> But it works correctly in Turbo C and Borland C compiler why not in gcc

Well, the point is precisely that all executions, Turbo C, Borland C or GCC,
are equally correct, since the code has undefined behavior...