When iterating over a block, meta instructions have no effect on wait counts,
but their presence drops the reference to earlier waitcnt instructions before
they are processed. This results in spurious wait counts, which do not affect
correctness, but are also not required in the resulting program. Skipping meta
instructions as soon as they are seen cleans this up.
This patch tracks the register operands of both VMEM (FLAT, MUBUF,
MTBUF) and SMEM load-store operations and inserts a S_WAIT_XCNT
instruction with sufficient wait-count before potentially redefining
them. For VMEM instructions, XNACK is returned in the same order as
they were issued and hence non-zero counter values can be inserted.
However, SMEM execution is out-of-order and so is their XNACK reception.
Thus, only zero counter value can be inserted to capture SMEM dependencies.
try_emplace can default-construct values, so we do not need to do so
on our own. Plus, try_emplace(Key) is much simpler/shorter than
insert({Key, LongValueType()}).
wb/wbinv use storecnt, inv uses loadcnt.
Track them as VMEM_WRITE_ACCESS and VMEM_READ_ACCESS to avoid
InsertWaitCnt incorrectly eliminating the waitcnts after these instructions.
Solves SWDEV-526604
Add target feature for point sample acceleration and enable it for
relevant
targets.
Also add support to insert waitcnts where required when point sample
accel may
have occurred. This has implications for out of order returns, which is
why
extra waitcnts are required.
Add a VMEM_NOSAMPLER bit in the register masks to determine when
waitcnt is required.
Noticed on Windows when running LLVM as part of a graphics driver, with
total stack usage limited to about 128 KB. In some cases this function
would overflow the stack.
On Linux this reduces stack usage in this function from about 32 KB to
about 0.5 KB.
If we cannot find any lds DMA instruction that is aliased by some load
from lds, we will still insert vmcnt(0). This is overly cautious since
handling inter-thread dependences is normally managed by the memory
model instead of the waitcnt pass, so this change updates the behavior
to be more inline with how other types of memory events are handled.
It is an architectural requirement that there must be no outstanding GDS
instructions when an "always GDS" instruction is issued, and also that
an always GDS instruction must be allowed to complete.
Insert waits on DScnt/LGKMcnt prior to (if necessary) and subsequent to
(unconditionally) any always GDS instruction, and an additional S_NOP if
the subsequent wait was followed by S_ENDPGM.
Always GDS instructions are GWS instructions, DS_ORDERED_COUNT,
DS_ADD_GS_REG_RTN, and DS_SUB_GS_REG_RTN (the latter two as considered
always GDS as of this patch).
In dynamic VGPR mode, Waves must deallocate all VGPRs before exiting. If
the shader program does not do this, hardware inserts `S_ALLOC_VGPR 0`
before S_ENDPGM, but this may incur some performance cost. Therefore
it's better if the compiler proactively generates that instruction.
This patch extends `si-insert-waitcnts` to deallocate the VGPRs via a
`S_ALLOC_VGPR 0` before any `S_ENDPGM` when in dynamic VGPR mode.
- Change InstrInfoEmitter to emit OpName as an enum class
instead of an anonymous enum in the OpName namespace.
- This will help clearly distinguish between values that are
OpNames vs just operand indices and should help avoid
bugs due to confusion between the two.
- Rename OpName::OPERAND_LAST to NUM_OPERAND_NAMES.
- Emit declaration of getOperandIdx() along with the OpName
enum so it doesn't have to be repeated in various headers.
- Also updated AMDGPU, RISCV, and WebAssembly backends
to conform to the new definition of OpName (mostly
mechanical changes).
In ceratin situations it is beneficial to wait for all outstanding
loads regardless of specific load's data we need. This may allow
to reduce a number of cache requests.
Fixes: SWDEV-511507
MSG_DEALLOC_VGPRS slows down very small waveslot limited kernels. It's
been identified this message is only really needed for VGPR limited
kernels. A kernel becomes VGPR limited if a total number of VGPRs per
SIMD / number of used VGPRs is more than a number of wave slots.
For setScore, the root function is setScoreByInterval with RegInterval
input
For determineWait, the root function is determineWait with RegInterval
input
When generating waitcounts before a use or def skip VGPRs. We never have
a real implicit VGPR operands on memory instructions, it is only for
super-reg liveness accounting.
Some other instructions (MOVRELS as an example) may have real implicit
VGPR uses though.
This is less then ideal but most of the problems observed with spills.
Implicit defs and uses on spill stores were accounted as real defs and
uses, while only exist for liveness accounting. As a result unneded
waits were generated.
Fixes: SWDEV-484177
When a loop contains a VMEM load whose result is only used outside the
loop, do not bother to flush vmcnt in the loop head on GFX12. A wait for
vmcnt will be required inside the loop anyway, because VMEM instructions
can write their VGPR results out of order.
SLoadAddresses previously held data across different functions and used
these for dominance queries of blocks in different functions. This is
not intended; clear the state at the end of the pass.
An appropriately configured image resource descriptor can trigger
image_sample instructions to store outputs directly to a linked memory
location instead of returning to VGPRs.
This is opaque to the backend as instruction encoding is unchanged;
however, a mechanism is require to allow frontends to communicate that
these instructions do not require destination VGPRs and store to memory.
Flagging these as stores means they will not be optimized away.
