[Bug c/66784] New: no symbol emitted for builtin with lto

["guido.hatzsis at yandex dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66784

            Bug ID: 66784
           Summary: no symbol emitted for builtin with lto
           Product: gcc
           Version: lto
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: guido.hatzsis at yandex dot com
  Target Milestone: ---

No symbols are emitted when compiling a built-in with -flto.

eg:
# cat << __EOF > bar.i
_Complex float __mulsc3(float x, float y, float z, float a) { return -1.0; }
__EOF 

# rm bar.o ; gcc  -c bar.i ; gcc-nm bar.o 
0000000000000000 T __mulsc3

# rm bar.o ; gcc -flto  -c bar.i ; gcc-nm bar.o
/usr/lib/gcc/x86_64-pc-linux-gnu/5.1.0/../../../../x86_64-pc-linux-gnu/bin/nm:
bar.o: no symbols

# cat << __EOF > bar.i
void __mulsc3(float x, float y, float z, float a) { }
__EOF

# rm bar.o ; gcc -flto  -c bar.i ; gcc-nm bar.o
bar.i:1:6: warning: conflicting types for built-in function ‘__mulsc3’
 void __mulsc3(float x, float y, float z, float a) { }
      ^
00000000 T __mulsc3
>From gcc-bugs-return-491613-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Tue Jul 07 01:22:37 2015
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From: "kkojima at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/66780] [4.9 Regression] Compiling with -fstack-protector-strong causes binary to segfault
Date: Tue, 07 Jul 2015 01:22:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idf780

--- Comment #1 from Kazumoto Kojima <kkojima at gcc dot gnu.org> ---
I can reproduce the issue with the trunk cross compiler.
It seems that openproc function in proc/readproc.c is miscompiled
with -fstack-protector-strong.  Here is a reduced test case:

--
int t;
struct s {};
int bar (void);
int baz (int, struct s *);

int
foo (int x)
{
  struct s sbuf;
  static int d;
  int val = bar ();

  if (d)
    {
      t = baz (x, &sbuf);
      d = 1;
    }

  return val;
}
--

It turned out that the fix for PR65249 causes this problem.
The codes for stack protect can be inserted after some function
call returning a value.  That return value in R0 register could
be clobbered with the fix for PR65249.
I thought that stack_chk_guard thingy is inserted at the head
of the function.  It's not the case, unfortunately.
I think that the wrong code is worse than the ICE.  I'd like
to revert the patches of PR65249 and reopen that PR.