Re: [PATCH, dataflow]: Fix PR55845, 454.calculix miscompares on x86 AVX due to movement of vzeroupper
On 01/07/2013 03:26 PM, Jakub Jelinek wrote: > 2012-01-08 Jakub Jelinek > Uros Bizjak > > PR rtl-optimization/55845 > * df-problems.c (can_move_insns_across): Stop scanning at > volatile_insn_p source instruction or give up if > across_from .. across_to range contains any volatile_insn_p > instructions. Ok. r~
Re: [PATCH, dataflow]: Fix PR55845, 454.calculix miscompares on x86 AVX due to movement of vzeroupper
On Tue, Jan 8, 2013 at 12:26 AM, Jakub Jelinek wrote: > On Mon, Jan 07, 2013 at 05:52:23PM +0100, Uros Bizjak wrote: >> TBH, I'm not that familiar with the RTL infrastructure enough to >> answer these questions. While I can spend some time on this problem, >> and probably waste quite some reviewer's time, the problem is not that >> trivial as I hoped to be, so I would kindly ask someone with better >> understanding of this part of the compiler for the proper solution. > > After discussion with rth on IRC, this modified patch just uses > volatile_insn_p, making all UNSPEC_VOLATILE (wherever in insn) and asm > volatile into a complete scheduling barrier for optimizations that use this > function. Thanks! Just two little nits in the testcase: > +foo (int size, double y[], double x[]) foo (int size, double *y, double *x) > + return (sum); return sum; Uros.
Re: [PATCH, dataflow]: Fix PR55845, 454.calculix miscompares on x86 AVX due to movement of vzeroupper
On Mon, Jan 07, 2013 at 05:52:23PM +0100, Uros Bizjak wrote:
> TBH, I'm not that familiar with the RTL infrastructure enough to
> answer these questions. While I can spend some time on this problem,
> and probably waste quite some reviewer's time, the problem is not that
> trivial as I hoped to be, so I would kindly ask someone with better
> understanding of this part of the compiler for the proper solution.
After discussion with rth on IRC, this modified patch just uses
volatile_insn_p, making all UNSPEC_VOLATILE (wherever in insn) and asm
volatile into a complete scheduling barrier for optimizations that use this
function.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2012-01-08 Jakub Jelinek
Uros Bizjak
PR rtl-optimization/55845
* df-problems.c (can_move_insns_across): Stop scanning at
volatile_insn_p source instruction or give up if
across_from .. across_to range contains any volatile_insn_p
instructions.
2012-01-08 Uros Bizjak
Vladimir Yakovlev
PR rtl-optimization/55845
* gcc.target/i386/pr55845.c: New test.
--- gcc/df-problems.c.jj2012-11-19 14:41:26.181898964 +0100
+++ gcc/df-problems.c 2013-01-07 18:38:33.064974313 +0100
@@ -3858,6 +3858,8 @@ can_move_insns_across (rtx from, rtx to,
}
if (NONDEBUG_INSN_P (insn))
{
+ if (volatile_insn_p (PATTERN (insn)))
+ return false;
memrefs_in_across |= for_each_rtx (&PATTERN (insn), find_memory,
NULL);
note_stores (PATTERN (insn), find_memory_stores,
@@ -3917,7 +3919,9 @@ can_move_insns_across (rtx from, rtx to,
if (NONDEBUG_INSN_P (insn))
{
if (may_trap_or_fault_p (PATTERN (insn))
- && (trapping_insns_in_across || other_branch_live != NULL))
+ && (trapping_insns_in_across
+ || other_branch_live != NULL
+ || volatile_insn_p (PATTERN (insn
break;
/* We cannot move memory stores past each other, or move memory
--- gcc/testsuite/gcc.target/i386/pr55845.c.jj 2013-01-07 18:30:19.168801389
+0100
+++ gcc/testsuite/gcc.target/i386/pr55845.c 2013-01-07 18:30:19.168801389
+0100
@@ -0,0 +1,39 @@
+/* { dg-do run } */
+/* { dg-require-effective-target avx } */
+/* { dg-options "-O3 -ffast-math -fschedule-insns -mavx -mvzeroupper" } */
+
+#include "avx-check.h"
+
+#define N 100
+
+double
+__attribute__((noinline))
+foo (int size, double y[], double x[])
+{
+ double sum = 0.0;
+ int i;
+ for (i = 0, sum = 0.; i < size; i++)
+sum += y[i] * x[i];
+ return (sum);
+}
+
+static void
+__attribute__ ((noinline))
+avx_test ()
+{
+ double x[N];
+ double y[N];
+ double s;
+ int i;
+
+ for (i = 0; i < N; i++)
+{
+ x[i] = i;
+ y[i] = i;
+}
+
+ s = foo (N, y, x);
+
+ if (s != 328350.0)
+abort ();
+}
Jakub
Re: [PATCH, dataflow]: Fix PR55845, 454.calculix miscompares on x86 AVX due to movement of vzeroupper
On Sun, Jan 6, 2013 at 5:22 PM, Jakub Jelinek wrote:
>> --- df-problems.c (revision 194945)
>> +++ df-problems.c (working copy)
>> @@ -3916,6 +3916,10 @@ can_move_insns_across (rtx from, rtx to, rtx acros
>> break;
>>if (NONDEBUG_INSN_P (insn))
>> {
>> + /* Do not move unspec_volatile insns. */
>> + if (GET_CODE (PATTERN (insn)) == UNSPEC_VOLATILE)
>> + break;
>> +
>
> Shouldn't UNSPEC_VOLATILE be handled similarly in the across_from ..
> across_to loop? Both UNSPEC_VOLATILE and volatile asm are handled there
> just with
> trapping_insns_in_across |= may_trap_p (PATTERN (insn));
> but your new change doesn't prevent moving just trapping insns across
> UNSPEC_VOLATILE, but any insns whatsoever. So supposedly for UNSPEC_VOLATILE
> the first loop should just return false; (or fail = 1; ?).
> For asm volatile I guess the code is fine as is, it must always describe
> what exactly it modifies, so supposedly non-trapping insns can be moved
> across asm volatile.
>
>> if (may_trap_or_fault_p (PATTERN (insn))
>> && (trapping_insns_in_across || other_branch_live != NULL))
>> break;
>
> You could do the check only for may_trap_or_fault_p, all UNSPEC_VOLATILE
> may trap.
>
> BTW, can't UNSPEC_VOLATILE be embedded deeply in the pattern?
> So volatile_insn_p (insn) && asm_noperands (PATTERN (insn)) == -1?
> But perhaps you want to treat that way only UNSPEC_VOLATILE directly in the
> pattern and all other UNSPEC_VOLATILE insns must describe in detail what
> exactly they are changing? This really needs to be better documented.
TBH, I'm not that familiar with the RTL infrastructure enough to
answer these questions. While I can spend some time on this problem,
and probably waste quite some reviewer's time, the problem is not that
trivial as I hoped to be, so I would kindly ask someone with better
understanding of this part of the compiler for the proper solution.
Uros.
Re: [PATCH, dataflow]: Fix PR55845, 454.calculix miscompares on x86 AVX due to movement of vzeroupper
> BTW, can't UNSPEC_VOLATILE be embedded deeply in the pattern? > So volatile_insn_p (insn) && asm_noperands (PATTERN (insn)) == -1? > But perhaps you want to treat that way only UNSPEC_VOLATILE directly in the > pattern and all other UNSPEC_VOLATILE insns must describe in detail what > exactly they are changing? This really needs to be better documented. Yes, I think that we should document that UNSPEC_Vs are full optimization barriers so the existing blockage insn of all ports are really blockage. That's already what is implemented and seems non-controversial (unlike the volatile asms). Something like: Index: rtl.def === --- rtl.def (revision 194946) +++ rtl.def (working copy) @@ -213,7 +213,9 @@ DEF_RTL_EXPR(ASM_OPERANDS, "asm_operands */ DEF_RTL_EXPR(UNSPEC, "unspec", "Ei", RTX_EXTRA) -/* Similar, but a volatile operation and one which may trap. */ +/* Similar, but a volatile operation and one which may trap. Moreover, it's a + full optimization barrier, i.e. no instructions may be moved and no register + (hard or pseudo) or memory equivalences may be used across it. */ DEF_RTL_EXPR(UNSPEC_VOLATILE, "unspec_volatile", "Ei", RTX_EXTRA) /* Vector of addresses, stored as full words. */ I'd also propose that blockage insns always be UNSPEC_Vs (that's already the case in practice, but the manual also lists volatile asms). And I'm somewhat dubious about the distinction between toplevel and embedded UNSPEC_Vs in a pattern; IMO, that shouldn't make any difference. -- Eric Botcazou
Re: [PATCH, dataflow]: Fix PR55845, 454.calculix miscompares on x86 AVX due to movement of vzeroupper
On Sun, Jan 06, 2013 at 04:48:03PM +0100, Uros Bizjak wrote:
> --- df-problems.c (revision 194945)
> +++ df-problems.c (working copy)
> @@ -3916,6 +3916,10 @@ can_move_insns_across (rtx from, rtx to, rtx acros
> break;
>if (NONDEBUG_INSN_P (insn))
> {
> + /* Do not move unspec_volatile insns. */
> + if (GET_CODE (PATTERN (insn)) == UNSPEC_VOLATILE)
> + break;
> +
Shouldn't UNSPEC_VOLATILE be handled similarly in the across_from ..
across_to loop? Both UNSPEC_VOLATILE and volatile asm are handled there
just with
trapping_insns_in_across |= may_trap_p (PATTERN (insn));
but your new change doesn't prevent moving just trapping insns across
UNSPEC_VOLATILE, but any insns whatsoever. So supposedly for UNSPEC_VOLATILE
the first loop should just return false; (or fail = 1; ?).
For asm volatile I guess the code is fine as is, it must always describe
what exactly it modifies, so supposedly non-trapping insns can be moved
across asm volatile.
> if (may_trap_or_fault_p (PATTERN (insn))
> && (trapping_insns_in_across || other_branch_live != NULL))
> break;
You could do the check only for may_trap_or_fault_p, all UNSPEC_VOLATILE
may trap.
BTW, can't UNSPEC_VOLATILE be embedded deeply in the pattern?
So volatile_insn_p (insn) && asm_noperands (PATTERN (insn)) == -1?
But perhaps you want to treat that way only UNSPEC_VOLATILE directly in the
pattern and all other UNSPEC_VOLATILE insns must describe in detail what
exactly they are changing? This really needs to be better documented.
Jakub
