From: Sebastian Huber <sebastian.huber@embedded-brains.de>
To: Richard Biener <richard.guenther@gmail.com>
Cc: GCC Development <gcc@gcc.gnu.org>
Subject: Re: -fprofile-update=atomic vs. 32-bit architectures
Date: Tue, 6 Dec 2022 14:11:54 +0100 [thread overview]
Message-ID: <8dfe2880-783c-d63e-2315-959455988294@embedded-brains.de> (raw)
In-Reply-To: <CAFiYyc2UeNH5q_taibDS7jmzUuPBLf+tWLDOG90pgT1ro5RjXg@mail.gmail.com>
On 05/12/2022 08:44, Richard Biener wrote:
> On Mon, Dec 5, 2022 at 8:26 AM Sebastian Huber
> <sebastian.huber@embedded-brains.de> wrote:
>> On 08/11/2022 11:25, Richard Biener wrote:
>>>> It would be great to have a code example for the construction of the "if
>>>> (f()) f();".
>>> I think for the function above we need to emit __atomic_fetch_add_8,
>>> not the emulated form because we cannot insert the required control
>>> flow (if (f()) f()) on an edge. The __atomic_fetch_add_8 should then be
>>> lowered after the instrumentation took place.
>> Would it help to change the
>>
>> if (__atomic_add_fetch_4 ((unsigned int *) &val, 1, __ATOMIC_RELAXED)
>> == 0)
>> __atomic_fetch_add_4 (((unsigned int *) &val) + 1, 1,
>> __ATOMIC_RELAXED);
>>
>> into
>>
>> unsigned int v = __atomic_add_fetch_4 ((unsigned int *) &val, 1,
>> __ATOMIC_RELAXED)
>> == 0)
>> v = (unsigned int)(v == 0);
>> __atomic_fetch_add_4 (((unsigned int *) &val) + 1, 1,
>> __ATOMIC_RELAXED);
> that's supposed to add 'v' instead of 1? Possibly use uint32_t here
> (aka uint32_type_node).
>
>> to get rid of an inserted control flow?
> That for sure wouldn't require any changes to how the profile
> instrumentation works,
> so yes it would be simpler.
Yes, this seems to work. After a bit of trial and error I ended up with
something in gimple_gen_edge_profiler() like this (endian support is
missing):
else if (flag_profile_update == PROFILE_UPDATE_SPLIT_ATOMIC)
{
tree addr = tree_coverage_counter_addr (GCOV_COUNTER_ARCS, edgeno);
tree f = builtin_decl_explicit (BUILT_IN_ATOMIC_ADD_FETCH_4);
gcall *stmt1 = gimple_build_call (f, 3, addr, one,
build_int_cst (integer_type_node,
MEMMODEL_RELAXED));
tree low = create_tmp_var (uint32_type_node);
gimple_call_set_lhs (stmt1, low);
tree is_zero = create_tmp_var (boolean_type_node);
gassign *stmt2 = gimple_build_assign (is_zero, EQ_EXPR, low,
build_zero_cst (uint32_type_node));
tree high_inc = create_tmp_var (uint32_type_node);
gassign *stmt3 = gimple_build_assign (high_inc, COND_EXPR, is_zero,
build_one_cst (uint32_type_node),
build_zero_cst (uint32_type_node));
tree addr_high = create_tmp_var (TREE_TYPE (addr));
gassign *stmt4 = gimple_build_assign (addr_high, addr);
gassign *stmt5 = gimple_build_assign (addr_high, POINTER_PLUS_EXPR,
addr_high,
build_int_cst (size_type_node, 4));
gcall *stmt6 = gimple_build_call (f, 3, addr_high, high_inc,
build_int_cst (integer_type_node,
MEMMODEL_RELAXED));
gsi_insert_on_edge (e, stmt1);
gsi_insert_on_edge (e, stmt2);
gsi_insert_on_edge (e, stmt3);
gsi_insert_on_edge (e, stmt4);
gsi_insert_on_edge (e, stmt5);
gsi_insert_on_edge (e, stmt6);
}
It can be probably simplified. The generated code:
.type f, @function
f:
lui a4,%hi(__gcov0.f)
li a3,1
addi a4,a4,%lo(__gcov0.f)
amoadd.w a5,a3,0(a4)
lui a4,%hi(__gcov0.f+4)
addi a5,a5,1
seqz a5,a5
addi a4,a4,%lo(__gcov0.f+4)
amoadd.w zero,a5,0(a4)
li a0,3
ret
looks good for this code:
int f(void)
{
return 3;
}
The loading of the high address could be probably optimized from
lui a4,%hi(__gcov0.f+4)
addi a4,a4,%lo(__gcov0.f+4)
to
addi a4,a4,4
I wasn't able to figure out how to do this.
--
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next prev parent reply other threads:[~2022-12-06 13:11 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-04 8:27 Sebastian Huber
2022-11-04 9:53 ` Gabriel Paubert
2022-11-04 10:02 ` Sebastian Huber
2022-11-05 11:18 ` Richard Biener
2022-11-08 6:22 ` Sebastian Huber
2022-11-08 10:25 ` Richard Biener
2022-11-08 12:00 ` Sebastian Huber
2022-11-08 13:52 ` Richard Biener
2022-12-05 7:26 ` Sebastian Huber
2022-12-05 7:44 ` Richard Biener
2022-12-06 13:11 ` Sebastian Huber [this message]
2022-12-06 16:08 ` Richard Biener
2022-12-07 8:51 ` Sebastian Huber
2022-12-07 9:09 ` Richard Biener
2022-12-07 9:24 ` Sebastian Huber
2022-12-07 11:49 ` Richard Biener
2022-12-07 9:55 ` Sebastian Huber
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