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