Fix up DEBUG_INSN handling in regcprop (PR bootstrap/45028)

Hi!

Bootstrap currently fails on sparc*-*-solaris*.  The problem is
that first regcprop changes
mov %o0, %g1
DEBUG this => %g1
DEBUG somethingelse => %g1
...
stx %g1, [%fp + xxx]
# Both %o0 and %g1 dead now

into
mov %o0, %g1
DEBUG this => %g1
DEBUG somethingelse => %g1
...
stx %o0, [%fp + xxx]
# Both %o0 and %g1 dead now

the DEBUG insns weren't adjusted, because there weren't any uses of %o0
found and debug insns are only changed if we know changing them won't
extend the lifetime of the function.  The check is done before actually
propagating into the insn though (because in some cases the code afterwards
kills the chains).

Then DCE sees the mov %o0, %g1 insn is useless and removes it (but doesn't
reset any of the following debug insns that depend on it).  Which means
that the DEBUG insns now effectively refer to whatever the register had
before, and in the Solaris -mcmodel=medmid case that was a setm4 temporary,
and unspec from it leads to ICE in output_operand.

The following patch fixes that by redoing the used regs discovery if a
normal insn has been actually changed.  In the above case it means that it
notices %o0 being used after the DEBUG insns and so adjusts %g1 in them to
%o0.

Arguably, DCE should be probably also fixed to note separately a weak use
between register setter and DEBUG insn consuming that register and if the
setter is being removed as useless, it should also reset the DEBUG insns.
Normally, such resetting or adjusting happens when computing the df note
problem, but apparently DCE doesn't do that.

Bootstrapped/regtested on x86_64-linux and i686-linux.
Ok for trunk?

2010-07-22  Jakub Jelinek  <jakub@redhat.com>

	PR bootstrap/45028
	* recgprop.c (copyprop_hardreg_forward_1): If changed is true,
	call cprop_find_used_regs again via note_uses.



	Jakub

On Thu, 22 Jul 2010, Jakub Jelinek wrote:

> Hi!
> 
> Bootstrap currently fails on sparc*-*-solaris*.  The problem is
> that first regcprop changes
> mov %o0, %g1
> DEBUG this => %g1
> DEBUG somethingelse => %g1
> ...
> stx %g1, [%fp + xxx]
> # Both %o0 and %g1 dead now
> 
> into
> mov %o0, %g1
> DEBUG this => %g1
> DEBUG somethingelse => %g1
> ...
> stx %o0, [%fp + xxx]
> # Both %o0 and %g1 dead now
> 
> the DEBUG insns weren't adjusted, because there weren't any uses of %o0
> found and debug insns are only changed if we know changing them won't
> extend the lifetime of the function.  The check is done before actually
> propagating into the insn though (because in some cases the code afterwards
> kills the chains).
> 
> Then DCE sees the mov %o0, %g1 insn is useless and removes it (but doesn't
> reset any of the following debug insns that depend on it).  Which means
> that the DEBUG insns now effectively refer to whatever the register had
> before, and in the Solaris -mcmodel=medmid case that was a setm4 temporary,
> and unspec from it leads to ICE in output_operand.
> 
> The following patch fixes that by redoing the used regs discovery if a
> normal insn has been actually changed.  In the above case it means that it
> notices %o0 being used after the DEBUG insns and so adjusts %g1 in them to
> %o0.
> 
> Arguably, DCE should be probably also fixed to note separately a weak use
> between register setter and DEBUG insn consuming that register and if the
> setter is being removed as useless, it should also reset the DEBUG insns.
> Normally, such resetting or adjusting happens when computing the df note
> problem, but apparently DCE doesn't do that.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux.
> Ok for trunk?

Ok.

Thanks,
Richard.

> 2010-07-22  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR bootstrap/45028
> 	* recgprop.c (copyprop_hardreg_forward_1): If changed is true,
> 	call cprop_find_used_regs again via note_uses.
> 
> --- gcc/regcprop.c.jj	2010-07-09 13:44:25.000000000 +0200
> +++ gcc/regcprop.c	2010-07-22 17:28:39.000000000 +0200
> @@ -947,7 +947,14 @@ copyprop_hardreg_forward_1 (basic_block 
>  
>      did_replacement:
>        if (changed)
> -	anything_changed = true;
> +	{
> +	  anything_changed = true;
> +
> +	  /* If something changed, perhaps further changes to earlier
> +	     DEBUG_INSNs can be applied.  */
> +	  if (vd->n_debug_insn_changes)
> +	    note_uses (&PATTERN (insn), cprop_find_used_regs, vd);
> +	}
>  
>        /* Clobber call-clobbered registers.  */
>        if (CALL_P (insn))
> 
> 
> 	Jakub
> 
>