From: lkcl <lkcl@web>
Date: Tue, 4 Oct 2022 05:23:06 +0000 (+0100)
Subject: (no commit message)
X-Git-Tag: opf_rfc_ls005_v1~199
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=4753815656c9094b49d90949fcc7687849494f6b;p=libreriscv.git

---

diff --git a/openpower/sv/svp64/discussion.mdwn b/openpower/sv/svp64/discussion.mdwn
index a5ebcfe86..9da9f5383 100644
--- a/openpower/sv/svp64/discussion.mdwn
+++ b/openpower/sv/svp64/discussion.mdwn
@@ -220,6 +220,13 @@ four aspects:
 3. is the loss of the dynamic meaning "VL=0" nop effect important?
 4. why would "sv.op all-scalar" be inside a loop in the first place?
 
+Summary so far:
+
+* failfirst needs to be an illegal exception if all-scalar
+* non-zeroing predication on all-scalar with VL>1 requires
+  all relevant bits to be set, this changes to the **first**
+  bit for auto-VL=1
+
 ## answers to 2, RM Modes
 
 **Normal Mode:**
@@ -297,7 +304,8 @@ predication-based offsets (and REMAP) (not to be confused with VSPLAT mode).
 
     Answer:
 
-    No, scalar-mode requires RA.isvec=0 RT.isvec=0, but VSPLAT is RA.isvec=0 RT.isvec=1.
+    No, scalar-mode requires RA.isvec=0 RT.isvec=0, but
+    VSPLAT is RA.isvec=0 RT.isvec=1.
 
 VL>1 at the moment, with a scalar source and scalar dest, will
 not undergo any changes to the EA compared to if VL=1.
@@ -315,16 +323,24 @@ interfered with, except that, again, RT may be set as a vector destination.
         EA = ireg[RA] + ireg[RB]*j   # register-strided
 ```
 
-Vector destination is again "VLSPLAT" mode, but if a Scalar
+Vector destination is again "VSPLAT" mode, but if a Scalar
 destination was set with VL>1, then just as with LD-immediate
 it is the entire predicate mask which must be zero to stop
 the scalar element from being loaded, and the same effect may
 be achieved with VL=1 by ORing all predicate mask bits down to
 a single bit as a new predicate.
 
+**CR ops**
+
+TODO
+
+**Branch-Conditional**
+
+TODO
+
 ## answers to 4, loops/uses
 
-### REMAP
+**REMAP**
 
 A REMAP would redirect operations from the first nonmasked
 predicated element to the first **REMAPped** element, and combined
@@ -341,7 +357,7 @@ answer: use at least one vector source.  this solves the predication issue.
 question: does this impact LD/ST which has special overrides
 and mode-selection based on RA.isvec?
 
-### predication
+**predication**
 
 with nonzeroing the application of a predicate mask to an all-scalar
 operation effectively tests **ALL** relevant bits 0..VL-1 as nonzero in the
@@ -350,7 +366,7 @@ decision-making, whereas VL=1 will only test the first.
 a need for merging (ORing) all bits into a single alternative predicate mask
 (single-bit) is the sort of thing we can probably live with.
 
-### fast traditional packed SIMD
+## fast traditional packed SIMD
 
 A major motivation for changing SVP64 with all isvec=0 to temporarily
 override VL to 1 is to allow supporting traditional SIMD that has