On 05/12/2022 08:44, Richard Biener wrote:
On Mon, Dec 5, 2022 at 8:26 AM Sebastian Huber
<sebastian.hu...@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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