[Bug c/57080] New: Invalid optimization (-O2) when doing double -> int conversion (on big endian archs(?))

[Bug c/57080] New: Invalid optimization (-O2) when doing double -> int conversion (on big endian archs(?))

[ondrej at sury dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57080

             Bug #: 57080
           Summary: Invalid optimization (-O2) when doing double -> int
                    conversion (on big endian archs(?))
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: ondrej@sury.org


Reproduceable on:

Using built-in specs.
COLLECT_GCC=gcc-4.6
COLLECT_LTO_WRAPPER=/usr/lib/gcc/ia64-linux-gnu/4.6/lto-wrapper
Target: ia64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.6.3-15'
--with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.6 --enable-shared --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.6
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object
--disable-libssp --enable-plugin --enable-objc-gc --with-system-libunwind
--enable-checking=release --build=ia64-linux-gnu --host=ia64-linux-gnu
--target=ia64-linux-gnu
Thread model: posix
gcc version 4.6.3 (Debian 4.6.3-15) 

and

Using built-in specs.
COLLECT_GCC=gcc-4.7
COLLECT_LTO_WRAPPER=/usr/lib/gcc/ia64-linux-gnu/4.7/lto-wrapper
Target: ia64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.7.2-5'
--with-bugurl=file:///usr/share/doc/gcc-4.7/README.Bugs
--enable-languages=c,c++,go,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.7 --enable-shared --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.7
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object
--disable-libssp --disable-libitm --enable-plugin --enable-objc-gc
--with-system-libunwind --enable-checking=release --build=ia64-linux-gnu
--host=ia64-linux-gnu --target=ia64-linux-gnu
Thread model: posix
gcc version 4.7.2 (Debian 4.7.2-5) 


This bug manifest itself on ia64, powerpc and s390x (all Big Endian[1]) where
gcc-4.6 is used and the optmized code (-O2) fails to produce correct math
results.

This code from libgd2:src/gd.c:clip_1d:

  *y1 -= m * (*x1 - mindim);

where

  m = (double) -0.050000
  *x1 = -200
  mindim = 0
  *y1 = 15

results in *y1 = 4, which is incorrect value, since it should be 5.

Most simple workaround, which allows gcc to produce correct value:

  *y1 -= (int)(m * (*x1 - mindim));

Assigning to some other variable also works ok:

  int t;
  t = m * (*x1 - mindim);
  *y1 -= t;

Compiling with -O0 also produces correct value.

1. Although SPARC, which should be B-E too, was built correctly.

[Bug c/57080] Invalid optimization (-O2) when doing double -> int conversion (on big endian archs(?))

[ondrej at sury dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57080

--- Comment #1 from Ondřej Surý <ondrej at sury dot org> 2013-04-26 10:27:30 UTC ---
Created attachment 29945
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29945
Generated from gd.c, affected code is in clip_1d function
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Subject: [Bug c++/55708] g++ crashes: constexpr function with reference parameters.
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55708

--- Comment #1 from Daniel Krügler <daniel.kruegler at googlemail dot com> 2013-04-26 10:37:55 UTC ---
gcc 4.9.0 20130421 (experimental) accepts the code on my system (64-bit mingw).
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Subject: [Bug tree-optimization/57075] [4.9 Regression] verify_flow_info failed: control flow in the middle of basic block
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idW075

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> 2013-04-26 10:54:45 UTC ---
Ok, I think I reduced this issue to this:

/* PR tree-optimization/57075 */
/* { dg-do compile } */
/* { dg-options "-O2" } */

extern int baz (void) __attribute__ ((returns_twice));
int __attribute__ ((__leaf__))
foo (void)
{
  return __builtin_printf ("$");
}

void
bar ()
{
  foo ();
  baz ();
}

[Bug c/57080] Invalid optimization (-O2) when doing double -> int conversion (on big endian archs(?))

[ondrej at sury dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57080

--- Comment #2 from Ondřej Surý <ondrej at sury dot org> 2013-04-26 11:04:19 UTC ---
Maybe I should have said "inconsistent" and this might be related to:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27394
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Subject: [Bug tree-optimization/57075] [4.9 Regression] verify_flow_info failed: control flow in the middle of basic block
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57075

--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> 2013-04-26 11:23:13 UTC ---
b.c: In function ‘bar’:
b.c:17:1: error: control flow in the middle of basic block 2

<bb 2>:
_5 = __builtin_printf ("$");
D.1727 = _5;
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Subject: [Bug tree-optimization/57075] [4.9 Regression] verify_flow_info failed: control flow in the middle of basic block
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--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> 2013-04-26 11:25:38 UTC ---
Ok, that's because printf is considered a possible caller of longjmp but
inlining doesn't split the block before handling the return.

We need to possibly split blocks dependent on stmt_ends_bb_p which depends
on function context.  Similar testcase can be constructed with non-local
gotos, broken before r198192.

[Bug c/57080] Invalid optimization (-O2) when doing double -> int conversion (on big endian archs(?))

[ondrej at sury dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57080

--- Comment #4 from Ondřej Surý <ondrej at sury dot org> 2013-04-26 12:32:20 UTC ---
Yeah, I just came to same conclusion by reading further (PR9325), that it's not
related to PR27394, because we are not hitting the boundaries of the conversion
type.

I understand that the resulting value depends on the time the conversion happen
(e.g. when the fractional part gets discarded), but still I think there's
something wrong when the result depends on the architecture and the
optimization level.
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Subject: [Bug rtl-optimization/57003] [4.8/4.9 Regression] gcc-4.8.0 breaks -O2 optimization with Wine(64) - links/info/bisect of commits included
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idW003

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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

--- Comment #21 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-04-26 13:16:21 UTC ---
Author: jakub
Date: Thu Apr 25 21:49:22 2013
New Revision: 198320

URL: http://gcc.gnu.org/viewcvs?rev\x198320&root=gcc&view=rev
Log:
    PR rtl-optimization/57003
    * regcprop.c (copyprop_hardreg_forward_1): If ksvd.ignore_set_reg,
    call note_stores with kill_clobbered_value callback again after
    killing regs_invalidated_by_call.

    * gcc.target/i386/pr57003.c: New test.

Added:
    trunk/gcc/testsuite/gcc.target/i386/pr57003.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/regcprop.c
    trunk/gcc/testsuite/ChangeLog

Author: jakub
Date: Thu Apr 25 21:50:26 2013
New Revision: 198321

URL: http://gcc.gnu.org/viewcvs?rev\x198321&root=gcc&view=rev
Log:
    PR rtl-optimization/57003
    * regcprop.c (copyprop_hardreg_forward_1): If ksvd.ignore_set_reg,
    call note_stores with kill_clobbered_value callback again after
    killing regs_invalidated_by_call.

    * gcc.target/i386/pr57003.c: New test.

Added:
    branches/gcc-4_8-branch/gcc/testsuite/gcc.target/i386/pr57003.c
Modified:
    branches/gcc-4_8-branch/gcc/ChangeLog
    branches/gcc-4_8-branch/gcc/regcprop.c
    branches/gcc-4_8-branch/gcc/testsuite/ChangeLog

[Bug c/57080] Invalid optimization (-O2) when doing double -> int conversion (on big endian archs(?))

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57080

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> 2013-04-26 16:11:38 UTC ---
(In reply to comment #5)
> I swear I have read the (non) bugs section before reporting the bug. Anyway
> it's do damn confusing that the result can be different on different
> architectures :(.

Rather on older architectures where the fpu was implemented as a stack one
(both 68k and x86 are examples of this).

[Bug c/57080] Invalid optimization (-O2) when doing double -> int conversion (on big endian archs(?))

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57080

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-04-26 17:15:52 UTC ---
I'd say *y1 -= (int)(m * (*x1 - mindim)); isn't a workaround, but a reasonable
thing to do (and less expensive than converting *y1 from int to floating point,
doing subtraction in FPU and converting back.