According to v-spec, tail agnostic behavior can be either kept as
undisturbed or set elements' bits to all 1s. To distinguish the
difference of tail policies, QEMU should be able to simulate the tail
agnostic behavior as "set tail elements' bits to all 1s". An option
'rvv_ta_all_1s' is added to enable the behavior, it is default as
disabled.
There are multiple possibility for agnostic elements according to
v-spec. The main intent of this patch-set tries to add option that
can distinguish between tail policies. Setting agnostic elements to
all 1s makes things simple and allow QEMU to express this.
We may explore other possibility of agnostic behavior by adding
other options in the future. Please understand that this patch-set
is limited.
v2 updates:
- Addressed comments from Weiwei Li
- Added commit tail agnostic on load / store instructions (which
I forgot to include into the patch-set)
v3 updates:
- Missed the very 1st commit, adding it back
v4 updates:
- Renamed vlmax to total_elems
- Deal with tail element when vl_eq_vlmax == true
v5 updates:
- Let `vext_get_total_elems` take `desc` and `esz`
- Utilize `simd_maxsz(desc)` to get `vlenb`
- Fix alignments to code
v6 updates:
- Fix `vext_get_total_elems`
v7 updates:
- Reuse `max_elems` for vector load / store helper functions. The
translation sets desc's `lmul` to `min(1, lmul)`, making
`vext_max_elems` equivalent to `vext_get_total_elems`.
v8 updates:
- Simplify `vext_set_elems_1s`, don't need `vext_set_elems_1s_fns`
- Fix `vext_get_total_elems`, it should derive upon EMUL instead
of LMUL
v9 updates:
- Let instructions that is tail agnostic regardless of vta respect the
option and not the vta.
v10 updates:
- Correct range to set element to 1s for load instructions
v11 updates:
- Separate addition of option 'rvv_ta_all_1s' as a new (last) commit
- Add description to show intent of the option in first commit for the
optional tail agnostic behavior
- Tag WeiWei as Reviewed-by for all commits
- Tag Alistair as Reviewed-by for commit 01, 02
- Tag Alistair as Acked-by for commit 03
v12 updates:
- Add missing space in WeiWei's "Reviewed-by" tag
v13 updates:
- Fix tail agnostic for vext_ldst_us. The function operates on input
parameter 'evl' rather than 'env->vl'.
- Fix tail elements for vector segment load / store instructions
A vector segment load / store instruction may contain fractional
lmul with nf * lmul > 1. The rest of the elements in the last
register should be treated as tail elements.
- Fix tail agnostic length for instructions with mask destination
register. Instructions with mask destination register should have
'vlen - vl' tail elements.
v14 updates:
- Pass lmul information to into vector helper function.
`vext_get_total_elems` needs it.
v15 updates:
- Rebase to latest `master`
- Tag Alistair as Acked by for commit 04 ~ 14