-# LD/ST-Update-PostIncrement
-
-TODO (key stub notes below)
+# RFC ls011 LD/ST-Update-PostIncrement
+* Funded by NLnet under the Privacy and Enhanced Trust Programme, EU
+ Horizon2020 Grant 825310, and NGI0 Entrust No 101069594
* <https://bugs.libre-soc.org/show_bug.cgi?id=1048>
+* <https://libre-soc.org/openpower/sv/rfc/ls011/>
+* <https://bugs.libre-soc.org/show_bug.cgi?id=1045>
+* <https://git.openpower.foundation/isa/PowerISA/issues/TODO>
+
+**Severity**: Major
+
+**Status**: New
+
+**Date**: 21 Apr 2023.
+
+**Target**: v3.2B
+
+**Source**: v3.0B
+
+**Books and Section affected**:
+
+```
+ Chapter 2 Book I, new Fixed-Point Load / Store Sections 3.3.2 3.3.3
+ Chapter 4 Book I, new Floating-Point Load / Store Sections 4.6.2 4.6.3
+```
+
+**Summary**
+
+```
+ TODO
+```
+
+**Submitter**: Luke Leighton (Libre-SOC)
+
+**Requester**: Libre-SOC
+
+**Impact on processor**:
+
+```
+ Addition of new Load/Store Fixed and Floating Point instructions
+```
+
+**Impact on software**:
+
+```
+ Requires support for new instructions in assembler, debuggers, and related tools.
+ Reduces instructions in hot-loops
+```
+
+**Keywords**:
+
+```
-The following instructions are proposed to be added in EXT2xx,
-duplicating LD/ST-Update functionality but moving the update
-of RA to *after* the Memory operation. These types of
-instructions are already present in x86 (sort-of).
+```
+
+**Motivation**
+
+Moving the update of RA to *after* the Memory operation saves on instruction count
+both outside and inside hot-loops. strncpy may be reduced to 11 Vector instructions,
+3 of which are the zeroing loop, 5 of which are the copy. Percentage-wise LD/ST
+Update Post-Increment represents a massive 20% reduction.
+
+**Notes and Observations**:
+
+These types of instructions are already present in x86 (sort-of).
* x86 chose that store should be pre-indexed and load should be post-indexed
* Power ISA chose everything to be pre-indexed
+* Motorola 68000 (decades old) has pre- and post- indexed
+
+<https://tack.sourceforge.net/olddocs/m68020.html#2.2.2.%20Extra%20MC68020%20addressing%20modes>
<https://azeria-labs.com/memory-instructions-load-and-store-part-4/>
+**Changes**
+
+Add the following entries to:
+
+* New Load/Store Sections
+* Appendices
+
+[[!tag opf_rfc]]
+
+--------
+
+\newpage{}
+
+TODO (key stub notes below)
+
+
+
The LD/ST-Immediate-Post-Increment instructions are all Primary
Opcode: there are 13 of these. LD/ST-Indexed-Post-Increment
are all effectively 9-bit XO and consequently may easily
One alternative idea is that bit 31 could be allocated (retrospectively)
to Post-Increment. Although it may be too late for Scalar Power ISA
-it **may** be possible to consider for SVP64Single and/or SVP64-Vector
+it **may** be possible to consider for SVP64Single and/or SVP64-Vector,
+but this risks creating a non-Orthogonal ISA.
stdupx, ls011, high, 10, yes, EXT2xx, no, isa/pifixedstore, 3R1W
# FP LD/ST-Postincrement
-lfdu, ls011, high, PO, yes, EXT2xx, no, isa/pifixedload, 1R2W
-lfsu, ls011, high, PO, yes, EXT2xx, no, isa/pifixedload, 1R2W
-lfdux, ls011, high, 10, yes, EXT2xx, no, isa/pifixedload, 2R2W
-lsdux, ls011, high, 10, yes, EXT2xx, no, isa/pifixedload, 2R2W
-stfdu, ls011, high, PO, yes, EXT2xx, no, isa/pifixedstore, 2R1W
-stfsu, ls011, high, PO, yes, EXT2xx, no, isa/pifixedstore, 2R1W
-stfdux, ls011, high, 10, yes, EXT2xx, no, isa/pifixedstore, 3R1W
-stfsux, ls011, high, 10, yes, EXT2xx, no, isa/pifixedstore, 3R1W
+lfdup, ls011, high, PO, yes, EXT2xx, no, isa/pifixedload, 1R2W
+lfsup, ls011, high, PO, yes, EXT2xx, no, isa/pifixedload, 1R2W
+lfdupx, ls011, high, 10, yes, EXT2xx, no, isa/pifixedload, 2R2W
+lsdupx, ls011, high, 10, yes, EXT2xx, no, isa/pifixedload, 2R2W
+stfdup, ls011, high, PO, yes, EXT2xx, no, isa/pifixedstore, 2R1W
+stfsup, ls011, high, PO, yes, EXT2xx, no, isa/pifixedstore, 2R1W
+stfdupx, ls011, high, 10, yes, EXT2xx, no, isa/pifixedstore, 3R1W
+stfsupx, ls011, high, 10, yes, EXT2xx, no, isa/pifixedstore, 3R1W
# LD/ST-Shifted-Postincrement
-lbzuspx, ls011, med, 10, yes, EXT2xx, no, ls011, 2R2W
-lhzuspx, ls011, med, 10, yes, EXT2xx, no, ls011, 2R2W
-lhauspx, ls011, med, 10, yes, EXT2xx, no, ls011, 2R2W
-lwzuspx, ls011, med, 10, yes, EXT2xx, no, ls011, 2R2W
-lwauspx, ls011, med, 10, yes, EXT2xx, no, ls011, 2R2W
-lduspx, ls011, med, 10, yes, EXT2xx, no, ls011, 2R2W
-stbuspx, ls011, med, 10, yes, EXT2xx, no, ls011, 3R1W
-sthuspx, ls011, med, 10, yes, EXT2xx, no, ls011, 3R1W
-stwuspx, ls011, med, 10, yes, EXT2xx, no, ls011, 3R1W
-stduspx, ls011, med, 10, yes, EXT2xx, no, ls011, 3R1W
+lbzupsx, ls011, med, 10, yes, EXT2xx, no, ls011, 2R2W
+lhzupsx, ls011, med, 10, yes, EXT2xx, no, ls011, 2R2W
+lhaupsx, ls011, med, 10, yes, EXT2xx, no, ls011, 2R2W
+lwzupsx, ls011, med, 10, yes, EXT2xx, no, ls011, 2R2W
+lwaupsx, ls011, med, 10, yes, EXT2xx, no, ls011, 2R2W
+ldupsx, ls011, med, 10, yes, EXT2xx, no, ls011, 2R2W
+stbupsx, ls011, med, 10, yes, EXT2xx, no, ls011, 3R1W
+sthupsx, ls011, med, 10, yes, EXT2xx, no, ls011, 3R1W
+stwupsx, ls011, med, 10, yes, EXT2xx, no, ls011, 3R1W
+stdupsx, ls011, med, 10, yes, EXT2xx, no, ls011, 3R1W
# FP LD/ST-Shifted-Postincrement
lfdupsx, ls011, med, 10, yes, EXT2xx, no, ls011, 2R2W
# Example
-** Load Byte and Zero with Post-Update**
+Here is an annotated example where the pseudo-code changes to
+just use `RA` as the address, otherwise remaining the same.
+No actual change to the Effective Address computation itself
+occurs, in any of the Post-Update instructions.
+
+**Load Byte and Zero with Post-Update**
D-Form
Pseudo-code:
```
- EA <- (RA)
- RT <- ([0] * (XLEN-8)) || MEM(EA, 1)
- RA <- (RA) + EXTS(D)
+ EA <- (RA) # EA just RA
+ RT <- ([0] * (XLEN-8)) || MEM(EA, 1) # then load
+ RA <- (RA) + EXTS(D) # then update RA after
```
Special Registers Altered:
where the same pseudocode for `lbzu` is:
```
- EA <- (RA) + EXTS(D)
- RT <- ([0] * (XLEN-8)) || MEM(EA, 1)
- RA <- EA
+ EA <- (RA) + EXTS(D) # EA includes D
+ RT <- ([0] * (XLEN-8)) || MEM(EA, 1) # load from RA+D
+ RA <- EA # and update RA
```
+-----
+
+\newpage{}
+
+# Fixed-point Load with Post-Update
+
+Add the following additional Section to Fixed-Point Load: Book I 3.3.2.1
+
+[[!inline pages="openpower/isa/pifixedload" raw=yes ]]
+
+-----
+
+\newpage{}
+
+# Fixed-Point Store Post-Update
+
+Add the following as a new section in Fixed-Point Store, Book I
+
+[[!inline pages="openpower/isa/pifixedstore" raw=yes ]]
+
+\newpage{}
+[[!inline pages="openpower/isa/fixedload" raw=yes ]]
+\newpage{}
+[[!inline pages="openpower/isa/fixedstore" raw=yes ]]
+\newpage{}
+[[!inline pages="openpower/isa/fpload" raw=yes ]]
+\newpage{}
+[[!inline pages="openpower/isa/fpstore" raw=yes ]]
[[!tag opf_rfc]]
projects / libreriscv.git / blobdiff