On 07/13/2017 06:53 PM, Cesar Philippidis wrote:
Similarly, for nvptx vector reductions, when it comes time to initialize
the reduction variable, the nvptx BE constructs a branch so that only
vector lanes 1 to vector_length-1 are initialized the the default value
for a given reduction type, where vector lane 0 retains the original
value of the reduction variable. For similar reason to the gang and
worker reductions, I set the probability of the new edge introduced for
the vector reduction to even.
Hi,
The problem that you describe in abstract term looks like this concretely:
....
(gdb) call debug_bb_n (4)
;; basic block 4, loop depth 0, freq 662, maybe hot
;; prev block 3, next block 16, flags: (VISITED)
;; pred: 3 [always (guessed)] (FALLTHRU,EXECUTABLE)
# VUSE <.MEM_61>
# PT = nonlocal unit-escaped null
_18 = MEM[(const struct .omp_data_t.33D.1518 &).omp_data_i_9(D)
clique 1 base 1].s2D.1519;
# VUSE <.MEMD.1540>
# USE = anything
_72 = GOACC_DIM_POS (2);
if (_72 != 0)
goto <bb 16>; [100.00%] [count: INV]
else
goto <bb 17>; [INV] [count: INV]
;; succ: 16 [always] (TRUE_VALUE)
;; 17 (FALSE_VALUE)
...
The edge to bb16 has probability 100%. The edge to bb17 has no
probability set.
@@ -5211,6 +5213,7 @@ nvptx_goacc_reduction_init (gcall *call)
/* Create false edge from call_bb to dst_bb. */
edge nop_edge = make_edge (call_bb, dst_bb, EDGE_FALSE_VALUE);
+ nop_edge->probability = profile_probability::even ();
/* Create phi node in dst block. */
gphi *phi = create_phi_node (lhs, dst_bb);
Setting the probability of the edge to bb17 to 50% LGTM.
But obviously having an accumulative outgoing edge probability of 150%
is not a good idea.
Thanks,
- Tom
