[Bug c/52326] New: float result incorrect with -O1 and calling external function.

[Bug c/52326] New: float result incorrect with -O1 and calling external function.

[baugesta at cisco dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52326

             Bug #: 52326
           Summary: float result incorrect with -O1 and calling external
                    function.
    Classification: Unclassified
           Product: gcc
           Version: 4.6.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: baugesta@cisco.com


Created attachment 26713
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26713
Two source files, one header file and a Makefile

The sample program attached fails when built with -O1, but not with any other
optimization levels (0,2,3). Unfortunately it only fails when we call an
external function, therefore we had to attach a tgz file instead of a
preprocessed file. 

The tar file contains four files: main.c, foo.c, foo.h and a Makefile. The 
Makefile, which builds two targets (fail and success) can be used to re-create
the problem as well as to build a non-failing version. 

Also, the error only occurs when certain other conditions are met. We've
written a C comment for every condition we found in the source file named
main.c. Please search for the text "NOTE". 

GCC Version:
------------
Our GCC version is 4.6.2. It fails on multiple versions/builds of 4.6.2, both
the one provided with Gentoo and the one provided by Centos 6. The info below
is from my Gentoo host:

COLLECT_GCC=/usr/x86_64-pc-linux-gnu/gcc-bin/4.6.2/gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/4.6.2/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /var/tmp/portage/sys-devel/gcc-4.6.2/work/gcc-4.6.2/configure
--prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/4.6.2
--includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.6.2/include
--datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.6.2
--mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.6.2/man
--infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.6.2/info
--with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.6.2/include/g++-v4
--host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --disable-altivec
--disable-fixed-point --without-ppl --without-cloog --enable-lto --enable-nls
--without-included-gettext --with-system-zlib --disable-werror
--enable-secureplt --enable-multilib --enable-libmudflap --disable-libssp
--enable-libgomp
--with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/4.6.2/python
--enable-checking=release --disable-libgcj --disable-libquadmath
--enable-languages=c,c++ --enable-shared --enable-threads=posix
--enable-__cxa_atexit --enable-clocale=gnu --enable-targets=all
--with-bugurl=http://bugs.gentoo.org/ --with-pkgversion='Gentoo 4.6.2 p1.4,
pie-0.5.0'
Thread model: posix
gcc version 4.6.2 (Gentoo 4.6.2 p1.4, pie-0.5.0) 

The complete command line that triggers the bug:
------------------------------------------------
gcc -o fail -O1 -Wall -Wextra -Wconversion -Werror -Wshadow
-Wmissing-declarations -std=c89 main.c foo.c && ./fail

(Note that it also fails with less arguments, -O1 is all it takes)

Compiler output:
---------------
None


Preprocessed file:
------------------
Due to the nature of the bug, calling an external function, we could not
provide a preprocessed file.

[Bug rtl-optimization/52326] [4.6 Regression] float result incorrect with -O1 and calling external function.

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52326

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|                            |x86_64-*-*
             Status|UNCONFIRMED                 |NEW
      Known to work|                            |4.5.3, 4.7.0
           Keywords|                            |wrong-code
   Last reconfirmed|                            |2012-02-21
          Component|c                           |rtl-optimization
     Ever Confirmed|0                           |1
            Summary|float result incorrect with |[4.6 Regression] float
                   |-O1 and calling external    |result incorrect with -O1
                   |function.                   |and calling external
                   |                            |function.
   Target Milestone|---                         |4.6.3
      Known to fail|                            |4.6.0, 4.6.2

--- Comment #1 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-02-21 13:20:34 UTC ---
Confirmed.  foo.c is unrelated and can be compiled with -O0.  Works with 4.5.3,
fails with 4.6.0 already, works with 4.7.  The tree level looks good to me.

[Bug rtl-optimization/52326] [4.6 Regression] float result incorrect with -O1 and calling external function.

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52326

--- Comment #2 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-02-21 13:27:23 UTC ---
Reduced single-file testcase, fails at -O1:

float fabsf(float x);
void abort (void);

static float minf(float a, float b)
{
  return (a < b) ? a: b;
}

static float maxf(float a, float b)
{
  return (a > b) ? a: b;
}

struct EC {
    float fftout;
    int extragainOn;
};

static float __attribute__((noinline))
foo (float a)
{
  asm("");
  return a;
}

static struct EC * __attribute__((noinline))
ec_create(void)
{
  static struct EC p;

  p.fftout = 1.234567f;
  p.extragainOn = 1;
  return &p;
}

static float ec_process(struct EC *p, float beflev, float estlev)
{
  float fullgCorr;
  float extrag;

  fullgCorr = maxf(0.0f, beflev - estlev) / beflev;
  extrag = 1.0f;

  if (p->extragainOn)
    extrag = minf(1.0f, fullgCorr);

  foo(0.0f);
  return extrag * p->fftout;
}

int main(void)
{
  unsigned int i = 0;
  float beflev[] = {11.6f, 1.0f};
  float estlev[] = {11.5f, 1.0f};
  float output;
  struct EC *p = ec_create();

  /* NOTE: If the for-loop is removed, the error disappears */
  for (i = 0; i < 1; i++)
    output = ec_process(p, beflev[i], estlev[i]);

  if (fabsf(output - 0.010643f) < 1e-5f)
    return 0;
  else
    abort ();
}

[Bug rtl-optimization/52326] [4.6 Regression] float result incorrect with -O1 and calling external function.

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52326

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

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

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-02-21 20:22:59 UTC ---
Works on the trunk since
http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=174664

[Bug target/52326] [4.6 Regression] float result incorrect with -O1 and calling external function.

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52326

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.6.3                       |4.6.4

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-03-01 14:38:02 UTC ---
GCC 4.6.3 is being released.

[Bug target/52326] [4.6 Regression] float result incorrect with -O1 and calling external function.

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52326

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|4.6.4                       |4.7.0

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-04-12 16:17:23 UTC ---
The 4.6 branch has been closed, fixed in GCC 4.7.0.