hexagon: fix CPY fence bug

[yshsharke]

Overview

On Hexagon backend, for normal CPY, op_cpy() treats any non-null src[1] as a synchronization fence and stores the fence sequence into the first four bytes of src[1]. This corrupts the ordinary CPY destination.

This PR adds a condition to limit the atomic fence store to only the explicit fence tensor with HTP_TENSOR_FENCE flag.

Additional information

Test on Hexagon v81 with test-backend-ops shows that the normal CPY case is fixed. The test command is:

test-backend-ops test -b HTP0 -o CPY

	Passed	Failed
Before	0	134
After	134	0

Failed Test Case Example

test-backend-ops test -b HTP0 -o 'CPY(type_src=f32,type_dst=f32,ne_src=[256,4,3,1],permute_src=[0,0,0,0],permute_dst=[0,0,0,0],_src_transpose=1)' -j 1

ggml_opencl: selected platform: 'QUALCOMM Snapdragon(TM)'

ggml_opencl: device: 'QUALCOMM Adreno(TM) 840 (OpenCL 3.0 Adreno(TM) 840)'
ggml_opencl: default device: 'QUALCOMM Adreno(TM) 840 (OpenCL 3.0 Adreno(TM) 840)'
ggml-hex: Loading driver libcdsprpc.so
ggml-hex: FASTRPC_GET_DOMAINS[0]: type 1 id 1000 name 'nsp1000' status 1 instance-id 0
ggml-hex: using CDSP domain: instance-id 0 id 1000 name 'nsp1000'
ggml-hex: Hexagon backend (experimental) : allocating new registry : ndev 1
ggml-hex: Hexagon Arch version v81
ggml-hex: HTP0 allocating new session
ggml-hex: HTP0 hwinfo: threads 8, hvx 8, hmx 1, vtcm 8 MB
ggml-hex: HTP0 new session : session-id 0 domain-id 100000 uri file:///libggml-htp-v81.so?htp_iface_skel_handle_invoke&_modver=1.0&_dom=nsp1000&_session=0 handle 0xb4000070205c1a40
ggml-hex: HTP0 op batching: n-bufs 16 n-tensors 8192 n-ops 1024 vmem 3355443200
Testing 3 devices

Backend 1/3: GPUOpenCL
  Skipping
Backend 2/3: HTP0
  Device description: Hexagon
  Device memory: 0 MB (0 MB free)

[CPY] ERR = 0.000563718 > 0.000000000   CPY(type_src=f32,type_dst=f32,ne_src=[256,4,3,1],permute_src=[0,0,0,0],permute_dst=[0,0,0,0],_src_transpose=1): FAIL
  0/1 tests passed

Failing tests:
  CPY(type_src=f32,type_dst=f32,ne_src=[256,4,3,1],permute_src=[0,0,0,0],permute_dst=[0,0,0,0],_src_transpose=1)
  Backend HTP0: FAIL
Backend 3/3: CPU
  Skipping
2/3 backends passed
FAIL

Requirements

• I have read and agree with the contributing guidelines
• AI usage disclosure: YES, this bug was found and analyzed by AI. I have run the tests, and I am responsible for all submitted changes.

[max-krasnyansky]

Oh. I missed this one in the tests. Looks like the test makes src[1] == dst. Normally that's not the case.

[max-krasnyansky]

@lhez for second ack