[Bug inline-asm/28686] New: ebp from clobber list used as operand

["Martin dot vGagern at gmx dot net" <gcc-bugzilla at gcc dot gnu dot org>]

#ifndef __PIC__
# define REG "ebx"
#else
# define REG "ebp"
#endif

#ifndef NBEFORE
void some_function_before(){
}
#endif

void test_function (){
    long var = 42;
    asm volatile(
             "inc %0\n#DEBUG %%0=%0, clobber: %%"REG", ..."
             :"+rm"(var)
             :
             :"%"REG"","%ecx","%esi","%edi","%edx","%eax");
}

========================

This little piece of code did several strange things for different flags:

1. #DEBUG %0=%ebp, clobber: %ebp, ...
   e.g. -fPIC -fomit-frame-pointer -O2, not -DNBEFORE

   This is the core of my bug report. The compiler should never ever use a
   register from the clobber list to store an operand. It doesn't do this
   for ebx, and it doen't do this if there function containing the asm is
   the first in the translation unit.
   But for ebp and with another function before, this strange bug occurs.
   Another function making a difference looks a bit like bug 28635

2. can't find a register in class 'GENERAL_REGS' while reloading 'asm'
   e.g. -O1, not -fomit-frame-pointer

   This seems to be a problem of -O1. Probably the compiler decides to use
   the r alternative and has problems falling back to m when this does not
   work.
   Perhaps the rationale is that gcc only looks at how to get the variables
   into the asm code with the least number of operations, and it's the
   programmer's task to make sure all mentioned operand constraints are
   possible on the target architecture. But this would be strange.
   If it were -O0 instead of -O1 I'd say it's bug 11203

3. #DEBUG %0=-12(%ebp), clobber: %ebp, ...
   e.g. -fPIC -O0, not -fomit-frame-pointer

   Seems like clobber lists get completely ignored for -O0. Perhaps this
   makes sense, as the compiler doen't have to care about registers being
   clobbered if all variables are stored in memory.
   Still this is strange behaviour.
   This is bug 11807


-- 
           Summary: ebp from clobber list used as operand
           Product: gcc
           Version: 4.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: inline-asm
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: Martin dot vGagern at gmx dot net
 GCC build triplet: i686-pc-linux-gnu-gcc
  GCC host triplet: i686-pc-linux-gnu-gcc
GCC target triplet: i686-pc-linux-gnu-gcc


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28686