On Tue, Dec 6, 2022 at 2:11 PM Sebastian Huber
<[email protected]> wrote:
>
> On 05/12/2022 08:44, Richard Biener wrote:
> > On Mon, Dec 5, 2022 at 8:26 AM Sebastian Huber
> > <[email protected]> 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.
Likely. I'd use the gimple_build () API from gimple-fold.h which
builds the expression(s) to a gimple_seq creating necessary temporaries
on-the-fly and then insert that sequence on the edge.
But even the above should work.
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.
I think that's something for the backend - we're not good
CSEing parts of an "invariant" address and the above might
be the form required when relocations are needed.
Richard.
>
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