Prathamesh Kulkarni <prathamesh.kulka...@linaro.org> writes: > Hi Richard, > For the following (contrived) test: > > void foo(int32x4_t v) > { > v[3] = 0; > return v; > } > > -O2 code-gen: > foo: > fmov s1, wzr > ins v0.s[3], v1.s[0] > ret > > I suppose we can instead emit the following code-gen ? > foo: > ins v0.s[3], wzr > ret > > combine produces: > Failed to match this instruction: > (set (reg:V4SI 95 [ v ]) > (vec_merge:V4SI (const_vector:V4SI [ > (const_int 0 [0]) repeated x4 > ]) > (reg:V4SI 97) > (const_int 8 [0x8]))) > > So, I wrote the following pattern to match the above insn: > (define_insn "aarch64_simd_vec_set_zero<mode>" > [(set (match_operand:VALL_F16 0 "register_operand" "=w") > (vec_merge:VALL_F16 > (match_operand:VALL_F16 1 "const_dup0_operand" "w") > (match_operand:VALL_F16 3 "register_operand" "0") > (match_operand:SI 2 "immediate_operand" "i")))] > "TARGET_SIMD" > { > int elt = ENDIAN_LANE_N (<nunits>, exact_log2 (INTVAL (operands[2]))); > operands[2] = GEN_INT ((HOST_WIDE_INT) 1 << elt); > return "ins\\t%0.<Vetype>[%p2], wzr"; > } > ) > > which now matches the above insn produced by combine. > However, in reload dump, it creates a new insn for assigning > register to (const_vector (const_int 0)), > which results in: > (insn 19 8 13 2 (set (reg:V4SI 33 v1 [99]) > (const_vector:V4SI [ > (const_int 0 [0]) repeated x4 > ])) "wzr-test.c":8:1 1269 {*aarch64_simd_movv4si} > (nil)) > (insn 13 19 14 2 (set (reg/i:V4SI 32 v0) > (vec_merge:V4SI (reg:V4SI 33 v1 [99]) > (reg:V4SI 32 v0 [97]) > (const_int 8 [0x8]))) "wzr-test.c":8:1 1808 > {aarch64_simd_vec_set_zerov4si} > (nil)) > > and eventually the code-gen: > foo: > movi v1.4s, 0 > ins v0.s[3], wzr > ret > > To get rid of redundant assignment of 0 to v1, I tried to split the > above pattern > as in the attached patch. This works to emit code-gen: > foo: > ins v0.s[3], wzr > ret > > However, I am not sure if this is the right approach. Could you suggest, > if it'd be possible to get rid of UNSPEC_SETZERO in the patch ?
The problem is with the "w" constraint on operand 1, which tells LRA to force the zero into an FPR. It should work if you remove the constraint. Also, I think you'll need to use <vwcore>zr for the zero, so that it uses xzr for 64-bit elements. I think this and the existing patterns ought to test exact_log2 (INTVAL (operands[2])) >= 0 in the insn condition, since there's no guarantee that RTL optimisations won't form vec_merges that have other masks. Thanks, Richard