[Bug rtl-optimization/67786] New: wrong code at -O2 and -O3 on x86_64-linux-gnu

[Bug rtl-optimization/67786] New: wrong code at -O2 and -O3 on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67786

            Bug ID: 67786
           Summary: wrong code at -O2 and -O3 on x86_64-linux-gnu
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu
  Target Milestone: ---

The current gcc trunk miscompiles the following code on x86_64-linux-gnu at -O2
and -O3 in both 32-bit and 64-bit modes. 

This is a regression from 5.2.x.


$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/6.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-trunk/configure --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 6.0.0 20150930 (experimental) [trunk revision 228291] (GCC) 
$ 
$ gcc-trunk -Os small.c; ./a.out
15
$ gcc-5.2 -O2 small.c; ./a.out
15
$ 
$ gcc-trunk -O2 small.c; ./a.out
-32
$ 
$ 


-------------------------------------


int printf (const char *, ...);

int a, b = 10;
char c;

int
main ()
{
  char d;
  int e = 5;
  for (a = 0; a; a--)
    e = 0;
  c = (b & 15) ^ e;
  d = c > e ? c : c << e;
  printf ("%d\n", d);
  return 0;
}

[Bug rtl-optimization/67786] [6 Regression] wrong code at -O2 and -O3 on x86_64-linux-gnu

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67786

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-09-30
                 CC|                            |ktkachov at gcc dot gnu.org,
                   |                            |mpolacek at gcc dot gnu.org
   Target Milestone|---                         |6.0
            Summary|wrong code at -O2 and -O3   |[6 Regression] wrong code
                   |on x86_64-linux-gnu         |at -O2 and -O3 on
                   |                            |x86_64-linux-gnu
     Ever confirmed|0                           |1

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Started with r227368.

[Bug rtl-optimization/67786] [6 Regression] wrong code at -O2 and -O3 on x86_64-linux-gnu

[ktkachov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67786

ktkachov at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |ktkachov at gcc dot gnu.org

--- Comment #2 from ktkachov at gcc dot gnu.org ---
Confirmed. Looking into it

[Bug rtl-optimization/67786] [6 Regression] wrong code at -O2 and -O3 on x86_64-linux-gnu

[ktkachov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67786

--- Comment #3 from ktkachov at gcc dot gnu.org ---
Patch posted at:
https://gcc.gnu.org/ml/gcc-patches/2015-10/msg00056.html

[Bug rtl-optimization/67786] [6 Regression] wrong code at -O2 and -O3 on x86_64-linux-gnu

[ktkachov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67786

--- Comment #4 from ktkachov at gcc dot gnu.org ---
Author: ktkachov
Date: Fri Oct  2 08:36:45 2015
New Revision: 228375

URL: https://gcc.gnu.org/viewcvs?rev=228375&root=gcc&view=rev
Log:
[RTL ifcvt] PR 67786, 67787: Check that intermediate instructions in the basic
block don't clobber a reg used in condition

        PR rtl-optimization/67786
        PR rtl-optimization/67787
        * ifcvt.c (bb_valid_for_noce_process_p): Reject basic block if
        it modifies a reg used in the condition calculation.

        * gcc.dg/pr67786.c: New test.
        * gcc.dg/pr67787.c: Likewise.


Added:
    trunk/gcc/testsuite/gcc.dg/pr67786.c
    trunk/gcc/testsuite/gcc.dg/pr67787.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/ifcvt.c
    trunk/gcc/testsuite/ChangeLog

[Bug rtl-optimization/67786] [6 Regression] wrong code at -O2 and -O3 on x86_64-linux-gnu

[ktkachov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67786

ktkachov at gcc dot gnu.org changed:

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

--- Comment #5 from ktkachov at gcc dot gnu.org ---
Fixed on trunk.
Thanks for the good testcase

[Bug rtl-optimization/67786] [6 Regression] wrong code at -O2 and -O3 on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67786

--- Comment #6 from Zhendong Su <su at cs dot ucdavis.edu> ---
(In reply to ktkachov from comment #5)
> Fixed on trunk.
> Thanks for the good testcase

Thanks for looking into the PR and for the quick fix.