Is it a bug allowing to copy GIMPLE_ASM with labels?

Is it a bug allowing to copy GIMPLE_ASM with labels?

[Bin.Cheng]

Hi,
Give below test:

volatile int a, b, c;
__attribute__((noinline)) int foo ()
{
  int i;
  for (i = 0; i < 1000; i++)
    {
      if (i % 17)
        a++;
      else
        b++;
      asm volatile(
          "foo_label:\n"
          "pushq %%rbx\n"
          "popq %%rbx\n" :"=m"(c) :"r"(i)
      );
      c++;
    }
  return 0;
}
compiled with:
gcc -O2 -fno-crossjumping -ftracer tracer-1.c -o tracer-1.o -c
will end up with following assembler error message:
tracer-1.c: Assembler messages:
tracer-1.c:16: Error: symbol `foo_label' is already defined

Root cause is in tracer.c which duplicates basic block without
checking if any GIMPLE_ASM defines labels.
Is this a bug or invalid code?

Thanks,
bin

Re: Is it a bug allowing to copy GIMPLE_ASM with labels?

[Alexander Monakov]

On Sat, 29 Dec 2018, Bin.Cheng wrote:
> tracer-1.c: Assembler messages:
> tracer-1.c:16: Error: symbol `foo_label' is already defined
> 
> Root cause is in tracer.c which duplicates basic block without
> checking if any GIMPLE_ASM defines labels.
> Is this a bug or invalid code?

This is invalid code, GCC documentation is clear that the compiler
may duplicate inline asm statements (passes other than tracer can do
that too, loop unswitching just to give one example).

We don't provide a way to write an asm that wouldn't be duplicated.

Alexander

Re: Is it a bug allowing to copy GIMPLE_ASM with labels?

[Bin.Cheng]

On Sat, Dec 29, 2018 at 3:42 PM Alexander Monakov <amonakov@ispras.ru> wrote:
>
> On Sat, 29 Dec 2018, Bin.Cheng wrote:
> > tracer-1.c: Assembler messages:
> > tracer-1.c:16: Error: symbol `foo_label' is already defined
> >
> > Root cause is in tracer.c which duplicates basic block without
> > checking if any GIMPLE_ASM defines labels.
> > Is this a bug or invalid code?
>
> This is invalid code, GCC documentation is clear that the compiler
> may duplicate inline asm statements (passes other than tracer can do
> that too, loop unswitching just to give one example).
>
> We don't provide a way to write an asm that wouldn't be duplicated.
I see, thanks for elaboration.

Thanks,
bin
>
> Alexander

Re: Is it a bug allowing to copy GIMPLE_ASM with labels?

[Segher Boessenkool]

Hi!

On Sat, Dec 29, 2018 at 10:41:54AM +0300, Alexander Monakov wrote:
> On Sat, 29 Dec 2018, Bin.Cheng wrote:
> > tracer-1.c: Assembler messages:
> > tracer-1.c:16: Error: symbol `foo_label' is already defined
> > 
> > Root cause is in tracer.c which duplicates basic block without
> > checking if any GIMPLE_ASM defines labels.
> > Is this a bug or invalid code?
> 
> This is invalid code, GCC documentation is clear that the compiler
> may duplicate inline asm statements (passes other than tracer can do
> that too, loop unswitching just to give one example).
> 
> We don't provide a way to write an asm that wouldn't be duplicated.

But should there be?  Is there (valid!) code for which it would be more
convenient?

We already have a hook targetm.cannot_copy_insn_p with which targets can
say not to copy certain insns.  It will be trivial to do something like
that for "asm restrict" (or whatever is a better name :-) ) (so make some
cannot_copy_insn_p that for asm checks that flag, and for everything else
uses the hook...  something like that).


Segher