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Date: Sat, 08 Jan 2011 18:58:00 -0000
From: Jan Hubicka <hubicka@ucw.cz>
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Cc: gcc-bugs@gcc.gnu.org
Subject: Re: [Bug lto/47222] [4.6 Regression] Revision 168593 failed many	tests
Message-ID: <20110108185419.GC10740@atrey.karlin.mff.cuni.cz>
References: <bug-47222-4@http.gcc.gnu.org/bugzilla/> <bug-47222-4-EQfi7Tfeil@http.gcc.gnu.org/bugzilla/>
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> I tried
> -int g_edi=INIT_EDI, g_esi=INIT_ESI, g_ebx=INIT_EBX; 
> -int g_ebp, g_ebp_save, g_esp, g_esp_save;
> +int g_edi __attribute__((externally_visible)) =INIT_EDI;
> +int g_esi __attribute__((externally_visible)) =INIT_ESI;
> +int g_ebx __attribute__((externally_visible)) = INIT_EBX; 
> +int g_ebp __attribute__((externally_visible));
> +int g_esp __attribute__((externally_visible));
> +int g_ebp_save __attribute__((externally_visible));
> +int g_esp_save __attribute__((externally_visible));
Weird, for me it seems to work as expected:

evans:/abuild/jh/trunk-3/build-inst2/gcc/:[1]# cat t.c
__attribute__ ((externally_visible))
int a;
main()
{
  asm("movl %eax, a");
}
evans:/abuild/jh/trunk-3/build-inst2/gcc/:[0]# ./xgcc -B ./ -O2 t.c -flto
evans:/abuild/jh/trunk-3/build-inst2/gcc/:[0]# cat t2.c
int a;
main()
{
  asm("movl %eax, a");
}
evans:/abuild/jh/trunk-3/build-inst2/gcc/:[0]# ./xgcc -B ./ -O2 t2.c -flto
/abuild/jh/trunk-install/x86_64-unknown-linux-gnu/bin/ld: /tmp/ccP7Lfjk.ltrans0.ltrans.o: in function main:ccP7Lfjk.ltrans0.o(.text.startup+0x3): error: undefined reference to 'a'
collect2: ld returned 1 exit status

Perhaps some extra var needs annotation?
>  int n_error;
> 
>  int
> 
> and it doesn't make a difference.
> 
> > I think this testcase is "yours", so perhaps you can fix it?
> > Was there some reason to use the ASMNAME hack instead of memory output
> > constraint?
> 
> We want to verify the contents of registers.

Still, I think the cleanest way is:
evans:/abuild/jh/trunk-3/build-inst2/gcc/:[0]# cat t3.c
int a;
main()
{
  asm __volatile__ ("movl %%eax, %0":"=m"(a));
}
evans:/abuild/jh/trunk-3/build-inst2/gcc/:[0]# ./xgcc -B ./ -O2 t3.c -flto
evans:/abuild/jh/trunk-3/build-inst2/gcc/:[0]#

It avoids the ASMNAME hack and makes outputs explicit.