[Bug other/42375] New: trunk hangs during diffutils configure

[Bug other/42375] New: trunk hangs during diffutils configure

[dirtyepic at gentoo dot org]

the attached code from the diffutils configure script is supposed to check for
"working C stack overflow detection" but instead hangs when built with trunk at
-O2 or higher.  4.4.2 works.

$ gcc -v
Using built-in specs.
COLLECT_GCC=/usr/x86_64-unknown-linux-gnu/gcc-bin/4.5.0-pre9999/gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-unknown-linux-gnu/4.5.0-pre9999/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with:
/var/tmp/portage/sys-devel/gcc-4.5.0_pre9999/work/gcc-4.5.0-9999/configure
--prefix=/usr --bindir=/usr/x86_64-unknown-linux-gnu/gcc-bin/4.5.0-pre9999
--includedir=/usr/lib/gcc/x86_64-unknown-linux-gnu/4.5.0-pre9999/include
--datadir=/usr/share/gcc-data/x86_64-unknown-linux-gnu/4.5.0-pre9999
--mandir=/usr/share/gcc-data/x86_64-unknown-linux-gnu/4.5.0-pre9999/man
--infodir=/usr/share/gcc-data/x86_64-unknown-linux-gnu/4.5.0-pre9999/info
--with-gxx-include-dir=/usr/lib/gcc/x86_64-unknown-linux-gnu/4.5.0-pre9999/include/g++-v4
--host=x86_64-unknown-linux-gnu --build=x86_64-unknown-linux-gnu
--disable-altivec --disable-fixed-point --with-ppl --with-cloog --disable-nls
--with-system-zlib --disable-checking --disable-werror --enable-secureplt
--enable-multilib --disable-libmudflap --disable-libssp --enable-libgomp
--enable-cld
--with-python-dir=/share/gcc-data/x86_64-unknown-linux-gnu/4.5.0-pre9999/python
--disable-libgcj --enable-languages=c,c++ --enable-shared
--enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu
--with-bugurl=http://bugs.gentoo.org/ --with-pkgversion='Gentoo SVN'
--enable-lto --enable-checking
Thread model: posix
gcc version 4.5.0-pre9999 20091215 (experimental) rev. 155245 (Gentoo SVN)


-- 
           Summary: trunk hangs during diffutils configure
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: dirtyepic at gentoo dot org
  GCC host triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42375

[Bug other/42375] trunk hangs during diffutils configure

[dirtyepic at gentoo dot org]

------- Comment #1 from dirtyepic at gentoo dot org  2009-12-15 05:24 -------
Created an attachment (id=19303)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=19303&action=view)
conftest.i


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42375

[Bug other/42375] trunk hangs during diffutils configure

[dirtyepic at gentoo dot org]

------- Comment #2 from dirtyepic at gentoo dot org  2009-12-15 05:24 -------
Created an attachment (id=19304)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=19304&action=view)
conftest.c


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42375

[Bug tree-optimization/42375] trunk hangs during diffutils configure

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2009-12-15 13:35 -------
This is a bug in the test.  Early inter-procedural SRA avoids passing array by
reference in the recurse() function and instead passes the first element
which is the only one read.  Thus the function is optimized to
an endless loop.

  static int
  recurse (char *p)
  {
    char array[500];
    array[0] = 1;
    return *p + recurse (array);
  }

  int
  main (void)
  {
    return recurse ("\1");
  }

on i686 (or with -m32) this does not happen - Martin, any idea why?


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jamborm at gcc dot gnu dot
                   |                            |org
          Component|other                       |tree-optimization
   GCC host triplet|x86_64-unknown-linux-gnu    |
 GCC target triplet|                            |i?86-*-*
           Keywords|                            |missed-optimization


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42375

[Bug tree-optimization/42375] trunk hangs during diffutils configure

[jamborm at gcc dot gnu dot org]

------- Comment #4 from jamborm at gcc dot gnu dot org  2009-12-22 14:26 -------
(In reply to comment #3)
> 
> on i686 (or with -m32) this does not happen - Martin, any idea why?
> 

I had to examine the testcase to find out.  It turns out that on i686
is_va_list_type() returns true for this type (char *) and so IPA-SRA
does not even consider it a candidate.  

The test was added because of premature decomposition of alpha stdarg
structures (pretty much the same issue as with early intraprocedural
SRA) and so does not really make sense here.  An easy way out of this
would be to allow scalar is_va_list_type types.  I will make a patch
for next stage 1.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42375