Eliminate redundant NCHW↔NHWC permute_copy and NHWC-safe view_copy transposes in ToTosaMemoryFormatPass (#18314)

[3l1]

Summary:

Two optimizations in ToTosaMemoryFormatPass to reduce TOSA TRANSPOSE nodes:

1. NHWC-safe reshape detection: When a 4D→4D view_copy has monotonic
   shape_indices on the raw shapes and preserves both the batch dim (index 0)
   and the last dimension (NHWC channel) alone in their output groups, skip
   inserting input/output transposes. The view_copy can operate directly on
   NHWC data.

2. Redundant permute_copy elimination: Model-level permute_copy ops whose
   permutation matches channels_last_order (NCHW→NHWC) or its inverse
   (NHWC→NCHW) AND whose input already has NHWC tosa_dim_order are redundant
   with the tosa_dim_order annotation. Replace them with view_copy (identity
   reshape) to avoid generating TOSA TRANSPOSE nodes. Standalone permute
   models (NCHW input from placeholder) are not affected.

Differential Revision: D97266678

[pytorch-bot]

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❌ 2 New Failures, 4 Unrelated Failures

As of commit 7ebe074 with merge base fb90480 ():

NEW FAILURES - The following jobs have failed:

• pull / unittest-arm-backend-with-no-deps (test_pytest_models_tosa) / linux-job (gh)
  RuntimeError: Command docker exec -t 451dc4b4d18874b29172f822dbced65610f986e281c29bc48202be5e48697c24 /exec failed with exit code 1
• pull / unittest-arm-backend-with-no-deps (test_pytest_ops_tosa) / linux-job (gh)
  RuntimeError: Command docker exec -t b8d7d78b57cedcfdce6cf36be7688c07300df9d37c345762a4d8bf9d78516ee9 /exec failed with exit code 1

FLAKY - The following jobs failed but were likely due to flakiness present on trunk:

• pull / test-models-linux (add, portable, linux.2xlarge) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• pull / test-models-linux (mv2, xnnpack-quantization-delegation, linux.2xlarge) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / unittest / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest-editable / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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[AdrianLundell]

Hi, thanks for the PR! This is a complex topic to get right in all cases and FYI we are also planning on improving this internally so it is very nice to get some help with that. I see there are some errors in our unittests so looks like there are a few edge-cases to iron out before a proper review. Let us know if you have any questions about the current logic to help with this.

In the meanwhile that I have two comments:

1. The first optimization seems like a slighly more narrow condition of the "is_channel_reshape" function, do you think it could fit into there rather than a separate function?
2. For the second optimization, have you observed performance regressions due to noop transposes? Our working assumption has been that this is optimized away by the compiler.