* <https://libre-soc.org/openpower/sv/>
* <https://libre-soc.org/openpower/sv/rfc/ls008/>
* <https://bugs.libre-soc.org/show_bug.cgi?id=1040>
-* <https://git.openpower.foundation/isa/PowerISA/issues/87>
+* <https://git.openpower.foundation/isa/PowerISA/issues/123>
**Severity**: Major
# Notation, Section 1.3.2
-When register operands (`RA, RT, BF`) are prefixed by a single underscore
-(`_RT, _RA, _BF`) the variable contains the contents of the instruction field
-not the contents of the Register File referenced *by* that field. Example:
-`_RT` contains the contents of bits 5 thru 10. The relationship
-`RT = GPR(_RT)` is thus always true. Uses include making alternative
-decisions within an instruction based on whether the operand field
-is zero or non-zero.
+When destination register operands (`RT, RS`) are prefixed by a single
+underscore (`_RT, _RS`) the variable also contains the contents of the
+instruction field.
+This avoids confusion in pseudocode when a destination register is
+assigned (`RT <- x`) but earlier it was the operand bits that were
+checked (`if RT = 0`)
----------------
\newpage{}
-# svstep: Vertical-First Stepping and status reporting
-
-SVL-Form
-
-* svstep RT,SVi,vf (Rc=0)
-* svstep. RT,SVi,vf (Rc=1)
-
-| 0-5|6-10|11.15|16..22| 23-25 | 26-30 |31| Form |
-|----|----|-----|------|----------|-------|--|--------- |
-|PO | RT | / | SVi | / / vf | XO |Rc| SVL-Form |
-
-Pseudo-code:
-
-```
- if SVi[3:4] = 0b11 then
- # store pack and unpack in SVSTATE
- SVSTATE[53] <- SVi[5]
- SVSTATE[54] <- SVi[6]
- RT <- [0]*62 || SVSTATE[53:54]
- else
- # Vertical-First explicit stepping.
- step <- SVSTATE_NEXT(SVi, vf)
- RT <- [0]*57 || step
-```
-
-Special Registers Altered:
-
- CR0 (if Rc=1)
-
-**Description**
-
-svstep may be used
-to enquire about the REMAP Schedule and it may be used to alter Vectorisation
-State. When `vf=1` then stepping occurs.
-When `vf=0` the enquiry is performed without altering internal
-state. If `SVi=0, Rc=0, vf=0` the instruction is a `nop`.
-
-The following Modes exist:
-
-* `SVi=0`: appropriately step srcstep, dststep, subsrcstep and subdststep to the next
- element, taking pack and unpack into consideration.
-* When `SVi` is 1-4 the REMAP Schedule for a given SVSHAPE may be
-returned in `RT`. SVi=1 selects SVSHAPE0 current state,
-through to SVi=4 selects SVSHAPE3.
-* When `SVi` is 5, `SVSTATE.srcstep` is returned.
-* When `SVi` is 6, `SVSTATE.dststep` is returned.
-* When `SVi` is 0b1100 pack/unpack in SVSTATE is cleared
-* When `SVi` is 0b1101 pack in SVSTATE is set, unpack is cleared
-* When `SVi` is 0b1110 unpack in SVSTATE is set, pack is cleared
-* When `SVi` is 0b1111 pack/unpack in SVSTATE are set
-
-As this is a Single-Predicated (1P) instruction, predication may be applied
-to skip (or zero) elements.
-
-* Vertical-First Mode will return the requested index
- (and move to the next state if `vf=1`)
-* Horizontal-First Mode can be used to return all indices,
- i.e. walks through all possible states.
-
-**Vectorisation of svstep itself**
-
-As a 32-bit instruction, `svstep` may be itself be Vector-Prefixed, as
-`sv.svstep`. This will work perfectly well in Horizontal-First
-as it will in Vertical-First Mode.
-
-Example: to obtain the full set of possible computed element
-indices use `sv.svstep RT.v,SVI,1` which will store all computed element
-indices, starting from RT. If Rc=1 then a co-result Vector of CR Fields
-will also be returned, comprising the "loop end-points" of each of the inner
-loops when either Matrix Mode or DCT/FFT is set. In other words,
-for example, when the `xdim` inner loop reaches the end and on the next
-iteration it will begin again at zero, the CR Field `EQ` will be set.
-With a maximum of three loops within both Matrix and DCT/FFT Modes,
-the CR Field's EQ bit will be set at the end of the first inner loop,
-the LE bit for the second, the GT bit for the outermost loop and the
-SO bit set on the very last element, when all loops reach their maximum
-extent.
-
-*Programmer's note (1): VL in some situations, particularly larger Matrices,
-may exceed 64,
-meaning that `sv.svshape` returning a considerable number of values. Under
-such circumstances `sv.svshape/ew=8` is recommended.*
-
-*Programmer's note (2): having conveniently obtained a pre-computed
-Schedule with `sv.svstep`,
-it may then be used as the input to Indexed REMAP Mode
-to achieve the exact same Schedule. It is evident however that
-before use some of the Indices may be arbitrarily altered as desired.
-`sv.svstep` helps the programmer avoid having to manually recreate
-Indices for certain
-types of common Loop patterns, and in its simplest form, without REMAP
-(SVi=5 or SVi=6),
-is equivalent to the `iota` instruction found in other Vector ISAs*
-
-**Vertical First Mode**
-
-Vertical First is effectively like an implicit single bit predicate
-applied to every SVP64 instruction. **ONLY** one element in each
-SVP64 Vector instruction is executed; srcstep and dststep do **not**
-increment, and the Program Counter progresses **immediately** to
-the next instruction just as it would for any standard scalar v3.0B
-instruction.
-
-A mode of srcstep (SVi=0) is called which can move srcstep and
-dststep on to the next element, still respecting predicate
-masks.
-
-In other words, where normal SVP64 Vectorisation acts "horizontally"
-by looping first through 0 to VL-1 and only then moving the PC
-to the next instruction, Vertical-First moves the PC onwards
-(vertically) through multiple instructions **with the same
-srcstep and dststep**, then an explict instruction used to
-advance srcstep/dststep. An outer loop is expected to be
-used (branch instruction) which completes a series of
-Vector operations.
-
-Testing any end condition of any loop of any REMAP state allows branches to be
-used to create loops.
-
-Programmer's note: when Predicate Non-Zeroing is used this indicates to
-the underlying hardware that any masked-out element must be skipped.
-*This includes in Vertical-First Mode*, and programmers should be keenly
-aware that srcstep or dststep or both *may* jump by more than one as
-a result, because the actual request under these circumstances was to execute
-on the first available next *non-masked-out* element.
-
-*Programmers should be aware that VL, srcstep and dststep are global in nature.
-Nested looping with different schedules is perfectly possible, as is
-calling of functions, however SVSTATE (and any associated SVSTATE) should
-obviously be stored on the stack in order to achieve this benefit*
-
--------------
-
-\newpage{}
-
+[[!inline pages="openpower/sv/svstep" raw=yes ]]
[[!inline pages="openpower/sv/setvl" raw=yes ]]
# SVSTATE SPR
projects / libreriscv.git / blobdiff