[v1.x][BUGFIX] Impose a plain format for concat's output when oneDNN would use padding

[PawelGlomski-Intel]

Description

Right now, oneDNN may choose a blocked format for the output of concat, in cases that may require additional padding (thus more memory). In (de)convolution we make sure to only select a primitive_desc which has the expected (from tensor size) memory size requirements, so the same has to be done in this case.

Unlike convolution's, concat's primitive_desc does not support iteration over multiple implementations, so here I manually impose a plain format when oneDNN would choose a blocked one with padding.

Resolves #19586

Checklist

Essentials

• PR's title starts with a category (e.g. [BUGFIX], [MODEL], [TUTORIAL], [FEATURE], [DOC], etc)
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage
• Code is well-documented

Changes

• Impose a plain format for concat's output when mkldnn uses padding
• Fix and add missing comments related to memory planning and padded formats
• Add/Change tests that cover this case

[mxnet-bot]

Hey @PawelGlomski-Intel , Thanks for submitting the PR
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[PawelGlomski-Intel]

Sorry for incidental review requests, I pushed a wrong branch

[PawelGlomski-Intel]

@mxnet-bot run ci [unix-gpu]

[mxnet-bot]

Jenkins CI successfully triggered : [unix-gpu]

[PawelGlomski-Intel]

@mxnet-bot run ci [unix-gpu]

[mxnet-bot]

Jenkins CI successfully triggered : [unix-gpu]

[PawelGlomski-Intel]

@PatricZhao, @szha could you please review this?

[szha]

Thanks for the fix!