* Reimplement LCS used by spirv-diff
Two improvements are made to the LCS algorithm:
- The LCS algorithm is reimplemented to use a std::stack instead of
being recursive. This prevents stack overflow in the LCSTest.Large
test.
- The LCS algorithm uses an NxM table. Previously, entries of this
table were {size_t, bool, bool}, which is now packed in 32 bits. The
first entry can assume a maximum value of min(N, M), which
realistically for SPIR-V diff will not be larger than 1 billion
instructions. This reduces memory usage of LCS by 75%.
This partially reverts 845f3efb8a and
enables LCS tests.
* Stabilize the output of spirv-diff
std::map is used instead of std::unordered_map to ensure the output of
spirv-diff is identical everywhere.
This partially reverts 845f3efb8a and
enables spirv-diff tests.
spirv-diff is a new tool that produces diff-style output comparing two
SPIR-V modules. The instructions between the src and dst modules are
matched as best as the tool can, and output is produced (in src
id-space) that shows which instructions are removed in src, added in dst
or modified between them. The order of instructions are not retained.
Matching instructions between two SPIR-V modules is not trivial, and
thus a number of heuristics are applied in this tool. In particular,
without debug information, it's hard to match functions as they can be
reordered. As such, this tool is primarily useful to produce the diff
of two SPIR-V modules derived from the same source.
This tool can be useful in a number of scenarios:
- Compare the SPIR-V before and after modifying a shader
- Compare the SPIR-V produced from a shader before and after compiler
codegen changes.
- Compare the SPIR-V produced from a shader before and after some
transformation or optimization.
- Compare the SPIR-V produced from a shader with different compilers.
Shahbaz Youssefi
Diego Novillo