On Thu, Sep 12, 2013 at 3:16 AM, Cong Hou <co...@google.com> wrote:
> Hi
>
> There is a bug in the function vect_recog_dot_prod_pattern() in
> tree-vect-patterns.c. This function checks if a loop is of dot
> production pattern. Specifically, according to the comment of this
> function:
>
> /*
> Try to find the following pattern:
>
> type x_t, y_t;
> TYPE1 prod;
> TYPE2 sum = init;
> loop:
> sum_0 = phi <init, sum_1>
> S1 x_t = ...
> S2 y_t = ...
> S3 x_T = (TYPE1) x_t;
> S4 y_T = (TYPE1) y_t;
> S5 prod = x_T * y_T;
> [S6 prod = (TYPE2) prod; #optional]
> S7 sum_1 = prod + sum_0;
>
> where 'TYPE1' is exactly double the size of type 'type', and
> 'TYPE2' is the same size of 'TYPE1' or bigger. This is a special case
> of a reduction computation.
> */
>
> This function should check if x_t and y_t have the same type (type)
> which has the half size of TYPE1. The corresponding code is shown
> below:
>
> oprnd0 = gimple_assign_rhs1 (stmt);
> oprnd1 = gimple_assign_rhs2 (stmt);
> if (!types_compatible_p (TREE_TYPE (oprnd0), prod_type) ||
> !types_compatible_p (TREE_TYPE (oprnd1), prod_type))
> return NULL;
> if (!type_conversion_p (oprnd0, stmt, true, &half_type0,
> &def_stmt, &promotion) || !promotion)
> return NULL;
> oprnd00 = gimple_assign_rhs1 (def_stmt);
>
> /*======================V see here! */
> if (!type_conversion_p (oprnd0, stmt, true, &half_type1,
> &def_stmt, &promotion) || !promotion)
> return NULL;
> oprnd01 = gimple_assign_rhs1 (def_stmt);
> if (!types_compatible_p (half_type0, half_type1))
> return NULL;
> if (TYPE_PRECISION (prod_type) != TYPE_PRECISION (half_type0) * 2)
> return NULL;
>
> Here the function uses x_T (oprnd0) to check the type of y_t, which is
> incorrect. The fix is simple: just replace it by oprnd1.
>
> The failed test case for this bug is shown below:
>
> int foo(short *a, int *b, int n) {
> int sum = 0;
> for (int i = 0; i < n; ++i)
> sum += a[i] * b[i];
> return sum;
> }
Bootstrapped and tested on ... ?
Please add a testcase that fails at runtime without the patch and
succeeds with it.
Thanks,
Richard.
>
> thanks,
> Cong
>
>
> Index: gcc/tree-vect-patterns.c
> ===================================================================
> --- gcc/tree-vect-patterns.c (revision 200988)
> +++ gcc/tree-vect-patterns.c (working copy)
> @@ -397,7 +397,7 @@ vect_recog_dot_prod_pattern (vec<gimple>
> || !promotion)
> return NULL;
> oprnd00 = gimple_assign_rhs1 (def_stmt);
> - if (!type_conversion_p (oprnd0, stmt, true, &half_type1, &def_stmt,
> + if (!type_conversion_p (oprnd1, stmt, true, &half_type1, &def_stmt,
> &promotion)
> || !promotion)
> return NULL;
