https://libre-soc.org/openpower/sv/vector_ops/discussion/
This is based on the AVX512 conflict detection instruction. Internally the logic is used to detect address conflicts in multi-issue LD/ST operations. Two arrays of values are given: the indices are compared and duplicates reported in a triangular fashion. the instruction may be used for histograms (computed in parallel)
input = [100, 100, 3, 100, 5, 100, 100, 3]
conflict result = [
0b00000000, // Note: first element always zero
0b00000001, // 100 is present on #0
0b00000000,
0b00000011, // 100 is present on #0 and #1
0b00000000,
0b00001011, // 100 is present on #0, #1, #3
0b00011011, // .. and #4
0b00000100 // 3 is present on #2
]
Pseudocode:
for i in range(VL):
for j in range(1, i):
if src1[i] == src2[j]:
result[j] |= 1<<i
Idea 1: implement this as a Triangular Schedule, Vertical-First Mode,
using mfcrweird and cmpi. first triangular schedule on src1,
secpnd on src2.
Idea 2: implement using outer loop on varying setvl Horizontal-First
with 1<<r3 predicate mask for src2 as scalar, creates CR field vector, transfer into INT with mfcrweird then OR into the
result.
li r3, target
li result, 0
for i in range(target):
setvl target
addi r3, r3, -1 # shift 1<<r3 predicate down by one
sv.addi/sm=1<<r3 t0, src1.v, 0 # copy src1[i]
sv.cmpi src2.v, t0 # compare src2 vector to scalar
sv.mfcrweird t1, cr0.v, eq # copy CR eq result bits to t1
or result, result, t1
See cr int predication for full details on the crweird instructions: the primary important aspect here is that a Vector of CR Field's EQ bits is transferred into a single GPR. The secondary important aspect is that VL is being adjusted in each loop, testing successively more of the input vector against a given scalar, each time.
To investigate: