51 lines
2.4 KiB
Markdown
51 lines
2.4 KiB
Markdown
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---
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name: sass-diff
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description: Use when asked to check for SASS (or PTX) changes between commits, branches, or a local changeset; guides normalization, comparison, and reporting of CUDA disassembly diffs.
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---
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# SASS Diffs
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Use this when asked to check for SASS changes between commits, branches or a local changeset.
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## Goal
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Detect relevant changes in generated CUDA machine code (i.e. SASS) while filtering noise from addresses, symbols, metadata, etc.
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Any non-trivial change must be detected.
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## Inputs to establish
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* Compilation target under test
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* The CUDA SM architectures to compile for. Try to detect this from the code and offer the user a list of suggestions.
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The user must confirm or provide this list.
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* Baseline source (e.g. the previous commit/branch or the current commit without the changes in the working copy).
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* Comparison source (e.g. the current commit/branch or the current commit with the changes in the working copy).
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* Whether a SASS (default) or PTX diff is requested.
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## Disassembly listing generation
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* Compile both, the baseline and comparison source, with the same compiler flags and options.
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When not specified otherwise, lookup the options from `compile_commands.json`
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or the current build system (i.e. CMake files).
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Make sure the CUDA SM architectures (`CMAKE_CUDA_ARCHITECTURES`) are set to the user-provided or approved list.
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* Dump the disassembly from the binaries produced in the previous set using `cuobjdump -sass` or `cuobjdump -ptx`.
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## Comparison rules (what matters)
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Ignore as trivial:
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* Register renaming with identical instruction sequence and operands.
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* Pure label renumbering or reordering of identical basic blocks.
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* Formatting-only differences or reordered symbol tables.
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* Changes to symbol names (global function names)
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## Reporting
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* If any non-trivial change was detected, report the top 5 regions where a non-trivial change was detected,
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including the name of the kernel they appeared in.
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* Provide a short summary of the diff type,
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including opcode changes, memory access size/cache policy changes, control-flow changes, register-count changes,
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spills/local memory, shared memory, and occupancy-relevant resource deltas.
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* Explicitly state if only noise was detected.
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* If you are not sure if the differences are impactful, show it and ask the user for guidance.
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* Keep the disassembly dumps available and tell the user where they can find them.
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