Kewen and Richard, Thanks for your comments. Please let me clarify it. 在 2023/9/27 19:10, Richard Sandiford 写道: > Yeah, I agree there doesn't seem to be a good reason to exclude vectors. > Sorry to dive straight into details, but maybe we should have something > called bitwise_mode_for_size that tries to use integer modes where possible, > but falls back to vector modes otherwise. That mode could then be used > for copying, storing, bitwise ops, and equality comparisons (if there > is appropriate optabs support).
The vector mode is not supported for compare_by_pieces and move_by_pieces. But it is supported for set_by_pieces and clear_by_pieces. The help function widest_fixed_size_mode_for_size returns vector mode when qi_vector is set to true. static fixed_size_mode widest_fixed_size_mode_for_size (unsigned int size, bool qi_vector) I tried to enable qi_vector for compare_by_pieces. It can pick up a vector mode (eg. V16QImode) and works on some cases. But it fails on a constant string case. int compare (const char* s1) { return __builtin_memcmp_eq (s1, "__GCC_HAVE_DWARF2_CFI_ASM", 16); } As the second op is a constant string, it calls builtin_memcpy_read_str to build the string. Unfortunately, the inner function doesn't support vector mode. /* The by-pieces infrastructure does not try to pick a vector mode for memcpy expansion. */ return c_readstr (rep + offset, as_a <scalar_int_mode> (mode), /*nul_terminated=*/false); Seems by-pieces infrastructure itself supports vector mode, but low level functions do not. I think there are two ways enable vector mode for compare_by_pieces. One is to modify the by-pieces infrastructure . Another is to enable it by cmpmem expand. The expand is target specific and be flexible. What's your opinion? Thanks Gui Haochen