Hi!
On 2021-09-20T13:46:03+0100, Julian Brown <jul...@codesourcery.com> wrote:
> On Fri, 17 Sep 2021 16:26:50 +0200
> Thomas Schwinge <tho...@codesourcery.com> wrote:
>
>> > @@ -1449,8 +1634,120 @@ oacc_do_neutering (void)
>>
>> > + addr_range ar
>> > + = first_fit_range (conflicts, size, align, &worker_shm_bounds);
>> > +
>> > + splay_tree_delete (conflicts);
>> > +
>> > + if (ar.invalid ())
>> > + {
>> > + unsigned HOST_WIDE_INT base;
>> > + base = bounds_lo + random () % 512;
>> > + base = (base + align - 1) & ~(align - 1);
>> > + if (base + size > bounds_hi)
>> > + error_at (UNKNOWN_LOCATION, "shared-memory region overflow");
>>
>> My dice doesn't have 512 faces -- what am I to read into the
>> expression 'random () % 512' here? (Surely this must offend the
>> folks of <https://reproducible-builds.org/>.) ;-)
Also <https://gcc.gnu.org/PR102408> "[OpenACC]
omp-oacc-neuter-broadcast.cc: random() not available on all platforms"...
> For this one -- the randomness shouldn't be necessary for the
> correctness of the patch (i.e. it could just be "base = bounds_lo", or
> indeed folded into the line after).
>
> The "ar.invalid ()" case happens when we fail to allocate a block of
> memory in LDS space for broadcasting a particular set of variables,
> and trigger a fall-back path in the broadcasting code that adds extra
> barriers around the broadcast in question. I imagine I was thinking
> that adding randomness could mean we can "get lucky" sometimes and
> avoid needing those barriers in some cases, but in fact I don't think
> that was implemented, so the randomness is useless. (Or it could just
> have been leftover debug code... oops).
Pushed to master branch commit e87789f197e47259c94349821d3446f7d959e08f
"Evaluate 'random ()' to '0' in 'pass_omp_oacc_neuter_broadcast'", see
attached.
Grüße
Thomas
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>From e87789f197e47259c94349821d3446f7d959e08f Mon Sep 17 00:00:00 2001
From: Thomas Schwinge <tho...@codesourcery.com>
Date: Tue, 21 Sep 2021 08:54:49 +0200
Subject: [PATCH] Evaluate 'random ()' to '0' in
'pass_omp_oacc_neuter_broadcast'
Julian Brown,
<http://mid.mail-archive.com/20210920134603.16459021@squid.athome>:
| [...] the randomness shouldn't be necessary for the
| correctness of the patch (i.e. it could just be "base = bounds_lo", or
| indeed folded into the line after).
|
| The "ar.invalid ()" case happens when we fail to allocate a block of
| memory in LDS space for broadcasting a particular set of variables,
| and trigger a fall-back path in the broadcasting code that adds extra
| barriers around the broadcast in question. I imagine I was thinking
| that adding randomness could mean we can "get lucky" sometimes and
| avoid needing those barriers in some cases, but in fact I don't think
| that was implemented, so the randomness is useless. (Or it could just
| have been leftover debug code... oops).
gcc/
PR other/102408
* omp-oacc-neuter-broadcast.cc (oacc_do_neutering): Evaluate
'random ()' to '0'.
---
gcc/omp-oacc-neuter-broadcast.cc | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/gcc/omp-oacc-neuter-broadcast.cc b/gcc/omp-oacc-neuter-broadcast.cc
index aa5990ed7a1..e43338f3abf 100644
--- a/gcc/omp-oacc-neuter-broadcast.cc
+++ b/gcc/omp-oacc-neuter-broadcast.cc
@@ -1782,9 +1782,8 @@ oacc_do_neutering (unsigned HOST_WIDE_INT bounds_lo,
if (ar.invalid ())
{
- unsigned HOST_WIDE_INT base;
- base = bounds_lo + random () % 512;
- base = (base + align - 1) & ~(align - 1);
+ unsigned HOST_WIDE_INT base
+ = (bounds_lo + align - 1) & ~(align - 1);
if (base + size > bounds_hi)
error_at (UNKNOWN_LOCATION, "shared-memory region overflow");
std::pair<unsigned HOST_WIDE_INT, bool> base_inrng
--
2.33.0
