tcgen05.cp

tcgen05.cp#

tcgen05.cp copies a descriptor-defined shared image into TMEM. It is issued by a single thread, not collectively by the warps whose TMEM lanes receive the data. Select shape, CTA group, multicast and optional decompression directly in the opcode.

TMEM shape and replicas#

Operands are dst_tmem, src_shared, both with suffix (row,b32_word) and 32-bit storage elements. An earlier axis is an explicit repeat.

Shape / multicast

Atom extents

TMEM lanes

128x256b

(128,8)

Consecutive 128 lanes

128x128b

(128,4)

Consecutive 128 lanes

4x256b

(4,8)

0, 32, 64, 96 relative to the origin

64x128b.warpx2::02_13

(64,4)

64 consecutive lanes, replicated 64 lanes apart

64x128b.warpx2::01_23

(64,4)

Logical row r maps to 64*(r//32)+r%32, replicated 32 lanes apart

32x128b.warpx4

(32,4)

32 consecutive lanes, four replicas 32 lanes apart

The destination layout must state these replicas explicitly; the pattern does not infer multicast. Columns are consecutive b32 cells with a 128-bit aligned origin. The whole footprint, including replicas, must stay inside the 128-lane, 512-column TMEM address space. A CTA-group-2 opcode makes both CTAs copy from their own corresponding shared storage into their own TMEM. The launch, allocation and commit must use the matching CTA-group protocol.

Shared descriptor address walk#

Supply ldo_bytes, sdo_bytes and swizzle=0/1/2/3. Before swizzling, row r starts at (r//8)*sdo_bytes + (r%8)*(16 << swizzle) bytes relative to the descriptor origin. Without swizzling, word w adds (w//4)*ldo_bytes + (w%4)*4. With swizzling, words are contiguous and add 4*w; hardware ignores LDO in that case.

Descriptor strides are nonnegative 16-byte multiples below 2^18; origins are 16-byte aligned. Swizzled bases require 256/512/1024-byte period alignment for modes 1/2/3. The complete physical walk is checked, including the origin’s swizzle phase. A 4-row logical region still needs a backing storage block large enough for the descriptor’s eight-row organization.

Example: one 128x128b copy and readback#

from tvm.script import tirx as T
from tvm.backend.cuda.axis import TLane, TCol
from tvm.tirx.layout import S, TileLayout

tmem_layout = TileLayout(S[(128, 4) : (1 @ TLane, 1 @ TCol)])


@T.function
def copy_to_tmem(A: T.Tensor((128, 4), "uint32"), Out: T.Tensor((128, 4), "uint32")):
    T.device_entry(launch=T.cuda.LaunchConfig(grid=1, block=128))
    tid = T.cuda.thread_idx("x")
    warp = T.cuda.warp_id()
    shared = T.alloc_shared((128, 4), "uint32", layout="default", align=16)
    address = T.alloc_shared((1,), "uint32", layout="default")
    mbar = T.alloc_shared((1,), "uint64", layout="default")
    if warp == 0:
        T.ptx.tcgen05.alloc.cta_group__1.sync.aligned.shared__cta.b32(
            T.address_of(address), T.uint32(32)
        )
    if tid == 0:
        T.ptx.mbarrier.init.shared.b64(mbar.ptr_to([0]), T.uint32(1))
    for j in range(4):
        shared[tid, j] = A[tid, j]
    T.cuda.cta_sync()
    T.ptx.fence.proxy.async_.shared__cta()
    mem = T.cuda.decl_tmem(
        address[0], ty_args=[T.Tensor((128, 4), "uint32", scope="tmem", layout=tmem_layout)]
    )
    if tid == 0:
        T.cuda.tile.apply(
            T.ptx["tcgen05.cp.cta_group::1.128x128b"],
            mem,
            shared,
            ldo_bytes=16,
            sdo_bytes=128,
            swizzle=0,
        )
        T.ptx.tcgen05.commit.cta_group__1.mbarrier__arrive__one.shared__cluster.b64(
            mbar.ptr_to([0])
        )
    T.cuda.mbarrier_wait(mbar.ptr_to([0]), 0)
    T.ptx.tcgen05.fence__after_thread_sync()
    word = T.alloc_local((1,), "uint32", layout="default")
    for j in range(4):
        T.ptx["tcgen05.ld.sync.aligned.32x32b.x1.b32"](word[0], address[0] + T.uint32(j))
        T.ptx.tcgen05.wait__ld.sync.aligned()
        Out[tid, j] = word[0]
    T.cuda.cta_sync()
    if warp == 0:
        T.ptx.tcgen05.relinquish_alloc_permit.cta_group__1.sync.aligned()
        T.ptx.tcgen05.dealloc.cta_group__1.sync.aligned.b32(address[0], T.uint32(32))

One cp instruction copies 2048 bytes. Its commit triggers one barrier arrival, rather than a TMA-style expected-byte transaction. The scalar x1 readback issues are caller code and independently expose each TMEM word.

import numpy as np
import tvm

x = np.arange(512, dtype="uint32").reshape(128, 4)
compiled = tvm.tirx.compile(copy_to_tmem, target="cuda", pipeline="tirx")
out = tvm.runtime.tensor(np.zeros_like(x), tvm.cuda())
compiled(tvm.runtime.tensor(x, tvm.cuda()), out)
np.testing.assert_array_equal(out.numpy(), x)

Native FP4/FP6 decompression#

Append .b8x16.b4x16_p64 or .b8x16.b6x16_p32 to the opcode. The b32 footprint above stays unchanged: each 16-byte shared block contains sixteen packed values followed by eight bytes (FP4) or four bytes (FP6) of padding. The destination contains sixteen expanded bytes. Four-bit values gain two low zero bits; six-bit values gain two high zero bits. A 256-bit row contains two such blocks. The pattern emits one native decompression instruction per repeat, with no software unpacking loop.

For instance, the example’s opcode can be explicitly replaced with tcgen05.cp.cta_group::1.128x128b.b8x16.b4x16_p64 when the source data has been prepared in that packed format. The reference then compares the expanded values, not the original words or padding. A dtype name alone neither prepares the payload nor chooses this qualifier.

Allocation, shared proxy fencing, election, commit, wait and deallocation are caller code. pred gates the cp but does not adjust a surrounding completion protocol. Implementation: patterns/tmem_copy.py and patterns/descriptors.py under python/tvm/backend/cuda/tile.

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