On Mon, Aug 14, 2017 at 2:48 PM, Richard Sandiford
<richard.sandif...@linaro.org> wrote:
> We weren't checking whether the phi in a conditional reduction was
> used by the condition itself (which isn't a case we handle).
>
> Tested on aarch64-linux-gnu and x86_64-linux-gnu. OK to install?
Ok.
Richard.
> Thanks,
> Richard
>
>
> 2017-08-11 Richard Sandiford <richard.sandif...@linaro.org>
>
> gcc/
> PR tree-optimization/81835
> * tree-vect-loop.c (vect_is_simple_reduction): Simply checks for
> the phi SSA_NAME. Check that the condition in a COND_EXPR does
> not depend on the phi.
>
> gcc/testsuite/
> PR tree-optimization/81835
> * gcc.dg/vect/pr81815.c: New test.
>
> Index: gcc/tree-vect-loop.c
> ===================================================================
> --- gcc/tree-vect-loop.c 2017-08-04 11:41:05.710206063 +0100
> +++ gcc/tree-vect-loop.c 2017-08-14 13:46:28.336459006 +0100
> @@ -2690,15 +2690,15 @@ vect_is_simple_reduction (loop_vec_info
> *double_reduc = false;
> *v_reduc_type = TREE_CODE_REDUCTION;
>
> - name = PHI_RESULT (phi);
> + tree phi_name = PHI_RESULT (phi);
> /* ??? If there are no uses of the PHI result the inner loop reduction
> won't be detected as possibly double-reduction by vectorizable_reduction
> because that tries to walk the PHI arg from the preheader edge which
> can be constant. See PR60382. */
> - if (has_zero_uses (name))
> + if (has_zero_uses (phi_name))
> return NULL;
> nloop_uses = 0;
> - FOR_EACH_IMM_USE_FAST (use_p, imm_iter, name)
> + FOR_EACH_IMM_USE_FAST (use_p, imm_iter, phi_name)
> {
> gimple *use_stmt = USE_STMT (use_p);
> if (is_gimple_debug (use_stmt))
> @@ -2847,10 +2847,7 @@ vect_is_simple_reduction (loop_vec_info
> simply rewriting this into "res += -x[i]". Avoid changing
> gimple instruction for the first simple tests and only do this
> if we're allowed to change code at all. */
> - if (code == MINUS_EXPR
> - && ! ((op1 = gimple_assign_rhs2 (def_stmt))
> - && TREE_CODE (op1) == SSA_NAME
> - && SSA_NAME_DEF_STMT (op1) == phi))
> + if (code == MINUS_EXPR && gimple_assign_rhs2 (def_stmt) != phi_name)
> code = PLUS_EXPR;
>
> if (code == COND_EXPR)
> @@ -2864,6 +2861,14 @@ vect_is_simple_reduction (loop_vec_info
> op4 = TREE_OPERAND (op3, 1);
> op3 = TREE_OPERAND (op3, 0);
> }
> + if (op3 == phi_name || op4 == phi_name)
> + {
> + if (dump_enabled_p ())
> + report_vect_op (MSG_MISSED_OPTIMIZATION, def_stmt,
> + "reduction: condition depends on previous"
> + " iteration: ");
> + return NULL;
> + }
>
> op1 = gimple_assign_rhs2 (def_stmt);
> op2 = gimple_assign_rhs3 (def_stmt);
> Index: gcc/testsuite/gcc.dg/vect/pr81815.c
> ===================================================================
> --- /dev/null 2017-08-14 10:10:17.469973707 +0100
> +++ gcc/testsuite/gcc.dg/vect/pr81815.c 2017-08-14 13:46:28.334496436 +0100
> @@ -0,0 +1,26 @@
> +/* { dg-do run } */
> +
> +int __attribute__ ((noinline, noclone))
> +f (int *x, int n)
> +{
> + int b = 13;
> + for (int i = 0; i < n; ++i)
> + {
> + int next = x[i];
> + b = b < 100 ? next : 200;
> + }
> + return b;
> +}
> +
> +static int res[32];
> +
> +int
> +main (void)
> +{
> + for (int i = 0; i < 32; ++i)
> + res[i] = i;
> + res[15] = 100;
> + if (f (res, 32) != 200)
> + __builtin_abort ();
> + return 0;
> +}
