Re: [PATCH] postreload: Invalidate reg_state info at barrier/volatile insns

[Eric Botcazou]

> With the patch from http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49452
> the regstate information is resetted at the unspec_volatile instead of
> invalidated!

You're right.  This wouldn't have happened if the code had been properly 
commented.

> 2011-11-14  Andreas Krebbel  
>
>   * postreload.c (reload_combine): Mark reg_state as invalid at a
>   barrier if there has been a use already.

Let's be conservative instead and distinguish the two cases: in the barrier 
case, we don't change anything and just add the missing comment, along the 
lines of "Crossing a barrier resets all the use information".  In the volatile 
case, we unconditionally invalidate with a similar comment.

-- 
Eric Botcazou

[PATCH] postreload: Invalidate reg_state info at barrier/volatile insns

[Andreas Krebbel]

Hi,

a problem in postreload causes a miscompilation of libgomp on s390x.

insn 1: r1 = r1 + r2
insn 2: r3 = r1
insn 3: unspec_volatile
insn 4: use r1

With the patch from http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49452
the regstate information is resetted at the unspec_volatile instead of
invalidated!  So while doing a backward insn scan insn 2 is considered
to be the first use of r1 and postreload does the following
optimization causing r1 to hold an invalid value at insn 4:

insn 1: deleted
insn 2: r3 = r1 + r2
insn 3: unspec_volatile
insn 4: use r1

The attached patch fixes the problem for me.  The patch invalidates
the reg_state if there has been a use already. Otherwise it is left as
is.

I don't have a testcase since the failure can only be seen in
combination with a reload patch I'm currently working on.

Bootstrapped on s390x and x86_64. No regressions.

Ok for mainline?

Bye,

-Andreas-


2011-11-14  Andreas Krebbel  

* postreload.c (reload_combine): Mark reg_state as invalid at a
barrier if there has been a use already.

Index: gcc/postreload.c
===
*** gcc/postreload.c.orig
--- gcc/postreload.c
*** reload_combine (void)
*** 1315,1322 
else if (BARRIER_P (insn)
   || (INSN_P (insn) && volatile_insn_p (PATTERN (insn
for (r = 0; r < FIRST_PSEUDO_REGISTER; r++)
! if (! fixed_regs[r])
! reg_state[r].use_index = RELOAD_COMBINE_MAX_USES;
  
if (! NONDEBUG_INSN_P (insn))
continue;
--- 1315,1323 
else if (BARRIER_P (insn)
   || (INSN_P (insn) && volatile_insn_p (PATTERN (insn
for (r = 0; r < FIRST_PSEUDO_REGISTER; r++)
! if (! fixed_regs[r]
! && reg_state[r].use_index != RELOAD_COMBINE_MAX_USES)
!   reg_state[r].use_index = -1;
  
if (! NONDEBUG_INSN_P (insn))
continue;