[Bug middle-end/33315] New: If condition not getting eliminated

[Bug middle-end/33315] New: If condition not getting eliminated

[pranav dot bhandarkar at gmail dot com]

if ( x == 8 ) statement1
if ( x != 8 ) statement1
if ( x == 9 ) statement2
if ( x != 9 ) statement2
should be replaced by

statement1
statement2

However this doesnt happen and compare and jumps do get generated.


-- 
           Summary: If condition not getting eliminated
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pranav dot bhandarkar at gmail dot com
GCC target triplet: arm-none-eabi


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33315

[Bug middle-end/33315] If condition not getting eliminated

[pranav dot bhandarkar at gmail dot com]

------- Comment #1 from pranav dot bhandarkar at gmail dot com  2007-09-05 19:03 -------
Created an attachment (id=14158)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=14158&action=view)
Sample Testcase


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33315

[Bug middle-end/33315] [4.3 Regression] If condition not getting eliminated

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2007-09-05 20:34 -------
This is related to PR32306 and to the fact that we don't have a code hoisting
pass.  And related to PR30905 because cross-jumping fixes this up on the
rtl-level for both gcc 4.1 and 4.2:

test:
        pushl   %ebp
        movl    %esp, %ebp
        popl    %ebp
        movl    $0, a
        movl    $0, a+4
        movl    $0, a+8
        ret


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |spark at gcc dot gnu dot org
  BugsThisDependsOn|                            |30905
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |missed-optimization
   Last reconfirmed|0000-00-00 00:00:00         |2007-09-05 20:34:09
               date|                            |
            Summary|If condition not getting    |[4.3 Regression] If
                   |eliminated                  |condition not getting
                   |                            |eliminated
   Target Milestone|---                         |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33315

[Bug middle-end/33315] [4.3 Regression] If condition not getting eliminated

[mmitchel at gcc dot gnu dot org]

-- 

mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33315

[Bug middle-end/33315] If condition not getting eliminated

[steven at gcc dot gnu dot org]

------- Comment #3 from steven at gcc dot gnu dot org  2007-11-10 00:27 -------
As a missed optimization, this bug adds new information.  But as a regression,
this is a dup of bug 30905.


-- 

steven at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[4.3 Regression] If         |If condition not getting
                   |condition not getting       |eliminated
                   |eliminated                  |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33315

[Bug middle-end/33315] If condition not getting eliminated

[j at uriah dot heep dot sax dot de]

------- Comment #4 from j at uriah dot heep dot sax dot de  2007-11-23 10:57 -------
Is the missed optimization in the following code the same?

volatile unsigned char *reg_a = (unsigned char *)42;
volatile unsigned char *reg_b = (unsigned char *)34;

extern void a(void);
extern void b(void);
extern void c(void);

void
decide(void)
{
        signed char diff;

        diff = *reg_a - *reg_b;

        if (diff < 0)
                a();
        else if (diff == 0)
                b();
        else if (diff > 0)
                c();
}

The third "if" statement is partially executed: it apparently remembered
that diff could not be less than 0, but it still tests against 0 even
though that test has just been done before.  Verified on both, the AVR
and i386 target.

Interestingly, by just reordering the code, the third condition will
be eliminated by GCC 4.x (but not by GCC 3.x):

volatile unsigned char *reg_a = (unsigned char *)42;
volatile unsigned char *reg_b = (unsigned char *)34;

extern void a(void);
extern void b(void);
extern void c(void);

void
decide(void)
{
        signed char diff;

        diff = *reg_a - *reg_b;

        if (diff < 0)
                a();
        else if (diff > 0)
                c();
        else if (diff == 0)
                b();
}

If someone thinks that's an entirely different thing than the subject of this
bug, please tell me so, and I'll submit a separate one.


-- 

j at uriah dot heep dot sax dot de changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |j at uriah dot heep dot sax
                   |                            |dot de


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33315

[Bug middle-end/33315] If condition not getting eliminated

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.0                       |---


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33315

[Bug middle-end/33315] If condition not getting eliminated

[dave at icerasemi dot com]

------- Comment #5 from dave at icerasemi dot com  2008-10-21 08:28 -------
Subject: RE:  If condition not getting eliminated


Hi Ramana,

Please could you add sdkteam-gnu@icerasemi.com - then we all get to see
it ;-)

Cheers,


-----Original Message-----
From: ramana at icerasemi dot com [mailto:gcc-bugzilla@gcc.gnu.org] 
Sent: 21 October 2008 08:04
To: Dave Edwards
Subject: [Bug middle-end/33315] If condition not getting eliminated



-- 

ramana at icerasemi dot com changed:

           What    |Removed                     |Added
------------------------------------------------------------------------
----
                 CC|                            |ramana at icerasemi dot
com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33315

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-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33315

[Bug middle-end/33315] If condition not getting eliminated

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33315

[Bug middle-end/33315] If condition not getting eliminated

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33315

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-02-04 02:33:16 UTC ---
tail merge should be able to do this.  It currently does not though for the
provided testcase in comment #1 but that is PR 52009.
Also note cselim should be able to do it too.