On 15.06.2023 07:23, Hongtao Liu wrote: > On Wed, Jun 14, 2023 at 5:03 PM Jan Beulich <jbeul...@suse.com> wrote: >> >> On 14.06.2023 09:41, Hongtao Liu wrote: >>> On Wed, Jun 14, 2023 at 1:58 PM Jan Beulich via Gcc-patches >>> <gcc-patches@gcc.gnu.org> wrote: >>>> >>>> ... in vec_dupv4sf / *vec_dupv4si. The respective broadcast insns are >>>> never longer (yet sometimes shorter) than the corresponding VSHUFPS / >>>> VPSHUFD, due to the immediate operand of the shuffle insns balancing the >>>> need for VEX3 in the broadcast ones. When EVEX encoding is required the >>>> broadcast insns are always shorter. >>>> >>>> Add two new alternatives each, one covering the AVX2 case and one >>>> covering AVX512. >>> I think you can just change assemble output for this first alternative >>> when TARGET_AVX2, use vbroadcastss, else use vshufps since >>> vbroadcastss only accept register operand when TARGET_AVX2. And no >>> need to support 2 extra alternatives which doesn't make sense just >>> make RA more confused about the same meaning of different >>> alternatives. >> >> You mean by switching from "@ ..." to C code using "switch >> (which_alternative)"? I can do that, sure. Yet that'll make for a >> more complicated "length_immediate" attribute then. Would be nice > Yes, you can also do something like > (set (attr "length_immediate") > (cond [(eq_attr "alternative" "0") > (if_then_else (match_test "TARGET_AVX2) > (const_string "") > (const_string "1")) > ...]
Yes, that's along the lines of what I was thinking of. I'm uncertain about one aspect of what you spelled out above, though: What is the meaning of the empty string in (const_string "")? Shouldn't this be "0" or "*"? >> But that'll be for vec_dupv4sf only, as vec_dupv4si is subtly >> different. > Yes, but can we use vpbroadcastd for vec_dupv4si similarly? Well, the use there is similar, but the folding with the shuffle alternative won't be possible, because of the new first alternative also allowing m for the source, when the shuffle one allows for only Yv. The extra m is pointless to have in vec_dupv4sf (because a later alternative with a wider ISA [avx] has it already), while in vec_dupv4si the similar later alternative resolves to vbroadcastss, not vpbroadcastd. I should be able to fold the two vpbroadcastd alternatives, along the lines of what I've done in the vec_dupv2di patch just sent. (As I just realized the m in what are alternatives 1 each in patch v1 is pointless, since already taken care of by other alternatives.) Jan
