From: lkcl <lkcl@web>
Date: Tue, 14 Jun 2022 19:17:48 +0000 (+0100)
Subject: (no commit message)
X-Git-Tag: opf_rfc_ls005_v1~1782
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=90252acd4f6b2a5d54347a855783a3fe62344571;p=libreriscv.git

---

diff --git a/openpower/sv/mv.swizzle.mdwn b/openpower/sv/mv.swizzle.mdwn
index 8c6e2fc5f..d5b3e4287 100644
--- a/openpower/sv/mv.swizzle.mdwn
+++ b/openpower/sv/mv.swizzle.mdwn
@@ -271,3 +271,28 @@ that swaps to Outer-subvector loops, and when `UNPACK_en` is set
 it is the destination that swaps its loop-order.  Setting both
 `PACK_en` and `UNPACK_en` is neither prohibited nor `UNDEFINED`
 because the behaviour is fully deterministic.
+
+*However*, in
+Vertical-First Mode, when both are enabled,
+with both source and destination being outer loops a **single**
+step of srstep and dststep is performed.  Contrast this when
+one of `PACK_en` is set, it is the *destination* that is an inner
+subvector loop, and therefore Vertical-First runs through the
+entire `dst_subvl` group. Likewise when `UNPACK_en` is set it
+is the source subvector that is run through as a group.
+
+```
+if VERTICAL_FIRST:
+    # must run through SUBVL or dst_subvl elements, to keep
+    # the subvector "together".  weirdness occurs due to
+    # PACK_en/UNPACK_en
+    num_runs = SUBVL # 1-4
+    if PACK_en:
+        num_runs = dst_subvl # destination still an inner loop
+    if PACK_en and UNPACK_en:
+        num_runs = 1 # both are outer loops
+    for substep in num_runs:
+        (src_idx, offs) = yield from index_src()
+        dst_idx = yield from index_dst()
+        move_operation(RT+dst_idx, RA+src_idx+offs)
+```