On 07/20/2017 06:04 AM, Tom de Vries wrote: > 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.
Is that with or without the patch? >> @@ -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. Yeah, that doesn't seem correct. Would you like to take over this patch? I saw that you started working on this issue (or a similar one to it) in PR81442. Cesar