> + int scale = 0;
> + if (scalar_p)
> + {
> + if (stmt_info
> + && stmt_info->stmt
> + && gimple_code (stmt_info->stmt) == GIMPLE_ASSIGN)
> + {
> + tree lhs = gimple_assign_lhs (stmt_info->stmt);
> + if (TREE_CODE (lhs) == ARRAY_REF)
> + {
> + tree index = TREE_OPERAND (lhs, 1);
> + /* Two more instructions are needed to access non-zero
> + array element. */
> + if (TREE_CODE (index) != INTEGER_CST
> + || compare_tree_int (index, 0) != 0)
> + scale = 2;
> + }
> + }
> + }
Not fully understand this part, why access non-zero array elements should be
penalized with additional cost, is it testcase specific or it's general?
> + else if (vector_int_conversion_p && !TARGET_SSE4_1)
> + {
> + /* Two instructions are needed to emulate vector integer
> + conversions. One more instruction is needed to emulate
> + 2-element vector conversion of QImode and HImode. */
> + machine_mode rhs_mode = TYPE_MODE (rhs_type);
> + rhs_mode = GET_MODE_INNER (rhs_mode);
> + scale = (rhs_mode == SImode || GET_MODE_NUNITS (mode) != 2
> + ? 2 : 3);
> + }
It's reasonable to increase cost for signed conversion w/o sse4.1, but for
unsigned conversion it's not needed, also I don't think GET_MODE_NUNITS (mode)
== 2 makes difference from 4/8, it looks tricky.
For the original PR, you're trying to prevent vectorization for 2-elemenet
reduction.
Revising per-stmt cost to prevent 2-element integer vectorization may hurt
others.
Maybe we can add a specific heuristic to add additional cost for 2-element
integer vectorization when vector width is less equal WORD, and this should
solve the issue in the PR and don't regress others.
Thanks,
Hongtao
--
H.J.
