[Bug lto/56168] New: [4.8 Regression] GCC seems to disregard -fno-builtin when compiling with LTO

[Bug lto/56168] New: [4.8 Regression] GCC seems to disregard -fno-builtin when compiling with LTO

[d.g.gorbachev at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56168

             Bug #: 56168
           Summary: [4.8 Regression] GCC seems to disregard -fno-builtin
                    when compiling with LTO
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: lto
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: d.g.gorbachev@gmail.com


cat > 1.c
extern int printf(const char *, ...);
extern double pow(double, double);

int main(int argc, char **argv)
{
  double d1 = (double) (argc + argv[0][0]);
  double d2 = pow(d1, 1.0 / 3.0);
  printf("%f %f\n", d1 * d1, d2);
  return 0;
}
^D
$ gcc -O -fno-builtin -ffast-math -fno-lto 1.c
/tmp/cc9Il6Md.o:1.c:function main: error: undefined reference to 'pow'
[...]
$ gcc -O -fno-builtin -ffast-math -flto 1.c
/tmp/ccfKmD30.ltrans0.ltrans.o:ccfKmD30.ltrans0.o:function main: error:
undefined reference to 'cbrt'
[...]

R191367 (20120916) - ok, r191654 (20120923) - bug.

[Bug lto/56168] [4.8 Regression] GCC seems to disregard -fno-builtin when compiling with LTO

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56168

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2013-02-01
         AssignedTo|unassigned at gcc dot       |rguenth at gcc dot gnu.org
                   |gnu.org                     |
   Target Milestone|---                         |4.8.0
     Ever Confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> 2013-02-01 09:42:36 UTC ---
-f[no-]builtin-* is a frontend option not supported by LTO (nor by Fortran
for example).  That it controls also middle-end behavior with respect to
LTO streaming 'pow' as a builtin is a bug I suppose (to be analyzed).
Probably caused by

      /* For variables prefer the builtin if one is available.  */
      else if (TREE_CODE (prevailing->symbol.decl) == FUNCTION_DECL)
        {
          for (e = first; e; e = e->symbol.next_sharing_asm_name)
            if (TREE_CODE (e->symbol.decl) == FUNCTION_DECL
                && DECL_BUILT_IN (e->symbol.decl))
              {
                prevailing = e;
                break;
              }
        }

and LTO un-conditionally initializing all builtins (well, and that's needed
unless we can do that lazily during streaming as we stream builtin decls
by their DECL_FUNCTION_CODE ...).

Hm.  I'll have a looksee.

[Bug lto/56168] [4.8 Regression] GCC seems to disregard -fno-builtin when compiling with LTO

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56168

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> 2013-02-01 12:34:53 UTC ---
Created attachment 29328
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29328
patch

We do stream things properly as / not as builtin.  Only we end up replacing
the non-builtin with the prevailing builtin.  It seems to me builtins should
never "prevail" (we do not touch their cgraph nodes either) but we also
should not replace any builtin decl with whatever prevailed (unless maybe
there is a visible definition ...?)

I have a patch but that causes PR55848 to re-appear (also in this testcase):

lto1: error: edge points to wrong declaration:^M
 <function_decl 0x7fb56f8d2a00 pow^M
    type <function_type 0x7fb56f8d1e70^M
...
 Instead of: <function_decl 0x7fb56f7e6f00 __builtin_pow^M
    type <function_type 0x7fb56f7b60a8^M

doesn't happen with -flto-partition=none though.  At LTRANs we again see

  d2_5 = __builtin_pow (d1_3,
3.33333333333333314829616256247390992939472198486328125e-1);
  d3_6 = __builtin_pow (d1_3, 2.0e+0);

which is of course wrong.  Something assumes there is only a single
prevailing cgraph node per symbol?  The callgraph at LTRANS time
looks ok to me:

pow/2 (pow) @0x7f5806f3ca68
  Type: function
  Visibility: undef external public
  previous sharing asm name: 3
  References:
  Referring:
  Read from file: /tmp/ccp4tasf.ltrans0.o
  Function flags:
  Called by: main/1 (1.00 per call)
  Calls:
pow/3 (__builtin_pow) @0x7f5806f3c940
  Type: function
  Visibility: external public
  next sharing asm name: 2
  References:
  Referring:
  Read from file: /tmp/ccp4tasf.ltrans0.o
  Function flags:
  Called by: main/1 (1.00 per call)
main/1 (main) @0x7f5806f3c6f0
  Type: function
  Visibility: prevailing_def public
  References: x.2385/0 (read)
  Referring:
  Read from file: /tmp/ccp4tasf.ltrans0.o
  Function flags: analyzed finalized only_called_at_startup
  Called by:
  Calls: abort/4 (0.39 per call) pow/3 (1.00 per call) pow/2 (1.00 per call)

but then somehow it's all wrong when reading the call op of the call stmt.
The ltrans object fn decl state stream of main has both a builtin and
a non-builtin.  That's because LTRANS thinks the builtin prevailed.  Bah.
That's because it happens to come "first" and we skip lto_symtab_merge_decls
for LTRANS.  Probably ok, but then we also should skip lto_fixup_decls.

[Bug lto/56168] [4.8 Regression] GCC seems to disregard -fno-builtin when compiling with LTO

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56168

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> 2013-02-01 12:40:18 UTC ---
Created attachment 29329
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29329
alternative patch

Patch which disables fixup_decls in LTRANS mode (fixes the testcase).  Trying
that on LTO bootstrap now ...

[Bug lto/56168] [4.8 Regression] GCC seems to disregard -fno-builtin when compiling with LTO

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56168

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

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

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> 2013-02-04 12:20:06 UTC ---
Fixed.

[Bug lto/56168] [4.8 Regression] GCC seems to disregard -fno-builtin when compiling with LTO

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56168

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> 2013-02-04 12:19:34 UTC ---
Author: rguenth
Date: Mon Feb  4 12:19:25 2013
New Revision: 195709

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=195709
Log:
2013-02-04  Richard Guenther  <rguenther@suse.de>

    PR lto/56168
    * lto-symtab.c (lto_symtab_merge_decls_1): Make non-builtin
    node prevail as last resort.
    (lto_symtab_merge_decls): Remove guard on LTRANS here.
    (lto_symtab_prevailing_decl): Builtins are their own prevailing
    decl.

    lto/
    * lto.c (read_cgraph_and_symbols): Do not call lto_symtab_merge_decls
    or lto_fixup_decls at LTRANS time.

    * gcc.dg/lto/pr56168_0.c: New testcase.
    * gcc.dg/lto/pr56168_1.c: Likewise.

Added:
    trunk/gcc/testsuite/gcc.dg/lto/pr56168_0.c
    trunk/gcc/testsuite/gcc.dg/lto/pr56168_1.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/lto-symtab.c
    trunk/gcc/lto/ChangeLog
    trunk/gcc/lto/lto.c
    trunk/gcc/testsuite/ChangeLog